Interaction between concurrent and endurance training
strength
D. G. SALE, J. D. MA~DOUGALL, I. JACOBS, AND S. GARNER Departments of Physical Education and Medicine, McMaster University, Hamilton L8S 4Kl; and Defence and Civil Institute of Environmental Medicine, Downsview, Ontario M3M 3B9, Canada
SALE, D. G., J. D. MACDOUGALL, I. JACOBS, AND S. GARNER. Interaction between concurrent strength and endurance truining. J. Appl. Physiol. 68(l): 260470, 1990.-To assessthe
effects of concurrent strength (S) and endurance (E) training on S and E development, one group (4 young men and 4 young women) trained one leg for S and the other leg for S and E (S+E). A secondgroup (4 men, 4 women) trained one leg for E and the other leg for E and S (E+S). E training consistedof five 3-min bouts on a cycle ergometer at a power output corresponding to that requiring 90400% of oxygen uptake during maximal exercise (VO 2&. S training consistedof six setsof 15-20 repetitions with the heaviest possibleweight on a leg press(combined hip and knee extension) weight machine. Training wasdone3 days/wk for 22 wk. Needlebiopsy samples from vastus lateralis were taken before and after training and were examined for histochemical,biochemical, and ultrastructural adaptations.The nominal S and E training programswere “hybrids,” having more similarities as training stimuli than differences; thus S madeincreases(P < 0.05) similar to those of S+E in E-related measuresof VOW max(S, S+E: 8%, 8%), repetitions with the pretraining maximal singleleg presslift [l repetition maximum (RM)] (27%, 24%), and percent of slowtwitch fibers (15%, 8%); and S made significant, although smaller, increasesin repetitions with 80% 1 RM (81%, 152%) and citrate synthase (CS) activity (22%, 51%). Similarly, E increased knee extensor area [computed tomography (CT) scans] as much as E+S (14%, 21%) and made significant, although smaller, increasesin leg press1 RM (20%, 34%) and thigh girth (3.4%, 4.8%). When a presumablystronger stimulus for an adaptation was added to a weaker one, someadditive effects occurred (i.e., increasesin 1 RM and thigh girth that were greater in E+S than E; increasesin CS activity and repetitions with 80% 1 RM that were greater in S+E than S). When a weaker, although effective, stimulus was added to a stronger one, addition generally did not occur. Concurrent S and E training did not interfere with S or E development in comparisonto S or E training alone. skeletal muscle;adaptation; aerobic power; enzyme activity
AND ENDURANCE training represent,intheir extremes, opposite forms of training. Strength training
STRENGTH
consists of a relatively small number of contractions of maximal or near-maximal force. Endurance training con-
sists of a large number of submaximal contractions. Accordingly, the adaptive responses in skeletal muscle to strength and endurance training are different and sometimes opposite. Strength training causes muscle fiber hypertrophy (26) associated with an increase in contractile protein (28), which contributes to an increase 260
in maximal contraction force. In contrast, endurance training usually causes little or no muscle fiber hypertrophy (2,7,12,20,23), but it does cause an increase in the following adaptations expected to enhance endurance performance: capillary density (2, 7, 20, 37, 39), mitochondrial volume density (17), and oxidative enzyme activity (12, 37). Strength and endurance training are often done concurrently by fitness enthusiasts and athletes. However, since the adaptive responses to strength and endurance training are different and some may even be opposite, it is conceivable that skeletal muscle cannot adapt optimally to the two contradictory training stimuli when they are simultaneously imposed. For example, strength training may cause a decrease in capillary density (36, 41) and mitochondrial volume density (29), which would undermine the increase in these measures induced by endurance training. Endurance training has been associated with a loss of strength (5, 31, 33) and decreased muscle fiber size (Z&39), changes obviously antagonistic to strength development. On the other hand, concurrent strength and endurance training may interact to enhance rather than hinder strength and endurance development. Some forms of endurance training have increased strength (31, 34) and muscle fiber size (2, 12). Strength training has increased short- (4-6 min) and long- (60-90 min) term endurance (14.16), maximal aerobic power (14), and oxidative enzyme activity (6). Whether the interaction between concurrent strength and endurance training results in “antagonism” or mutual enhancement of the training response probably depends on several factors, including the initial state of training of the trainees; the training modes; the intensity, volume, and frequency of training; and the way the two forms of training are integrated. In previously untrained subjects, a combination of moderate-to-high intensity and volume endurance and strength training impeded strength development but not increases in maximal aerobic power or short-term endurance (9, 14, 19). In previously endurance-trained subjects, the addition of strength training does not cause the impaired strength development seen in untrained subjects (19), and it improves endurance without increasing aerobic power (15). In the present study, the interaction between concurrent high intensity, moderate volume strength and endurance training was examined in previously untrained subjects. A unique aspect of the study was that several
O161-7567/90 $1.50 Copyright 0 1990 the American Physiological Society
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STRENGTH
AND
ENDURANCE
measures related to skeletal muscle adaptation were made to help explain any evidence of antagonism or mutual enhancement that might be found. METHODS
Subjects
The subjects were eight young women and eight young men without previous experience in intense strength or endurance training. In accordance with the Ethical Guidelines for Research on Human Subjects at McMaster University, we clearly apprised the subjects of the purpose of the study and the physical, psychological, and/or social risks involved in the research, and the students signed an informed consent form. The project carried the approval of McMaster University’s Ethics Committee. Design
Half (4 women, 4 men) of the subjects (group A) were randomly assigned to train both lower limbs for strength and one limb for endurance. The other half of the subjects (group B) trained both limbs for endurance and one limb for strength. Thus group A assessed the interaction between strength and endurance training (S+E) compared with strength training alone (S), while group B assessed the interaction between endurance and strength training (E+S) compared with endurance training alone (E). The characteristics of the subjects in the two groups are presented in Table 1. Training
Training consisted of two ll-wk periods divided by a 3-wk break period, the latter to accommodate a Christmas recess. There were three training sessions per week during the training periods. For each subject a training session lasted -1 h, i.e., the time taken to train both strength and endurance in one leg and strength (group A) or endurance (group B) in the other leg. In legs that did combine strength and endurance training, endurance training preceded strength training in each training session. Strength training. Strength training was done on a “Universal”-type leg press weight training machine (Global Gym, Downsview, Ontario). The training movement (concentric contraction phase) included simultaneous hip and knee extension and ankle plantar flexion. Each repetition of the exercise included a concentric and eccentric contraction phase. Subjects in group A performed six sets of E-20 repetitions maximum (RM); i.e., TABLE 1. Age, height, and body muss Group
A B
Experiment
S vs. S + E E vs. E + S
Age, Yr
20.9zkO.5 20.6t0.3
of subjects Mass,
Height, cm
169.2k4.7 168.1k2.4
Values are means k SE; each group males. S, strength training; E, endurance effect in body mass, pre-post training.
Pre
65.7+5.1 62.2t3.3
consisted training.
kg Post
66.9k4.8 63.8&3.3*
of 4 females and 4 * P < 0.05 for main
TRAINING
INTERACTION
261
the heaviest possible weight was used for the designated number of repetitions of the leg press movement with each leg. Sets were alternated between legs, with 1-min rest periods, until each leg completed the six sets. Subjects in group B performed six sets of 15-20 RM with the randomly designated leg. There were 2-min rest periods between successive sets. Endurance training. Endurance training was performed on a cycle ergometer (Monark). The training consisted of five 3-m+ bouts at a power output corresponding to 90-100% VOWmax.In group A, which trained only one randomly assigned leg for endurance, 3-min rest periods intervened between successive bouts. Group B performed the 3-min bouts alternately with both legs, with l-min rest periods between successive bouts. The training program is summarized in Table 2. Measurements
All measurements were made before and after the 22 wk of training. Aerobic power. Aerobic power (VOWmax)defined here as the peak 02 consumption attained during the single leg test) was measured for each leg separately. The test was performed on an electrically braked cycle ergometer (Jaeger) using a standard continuous progressive loading protocol. The test began at a power output of 30 or 45 W, and the load was increased by 15 W every 2 min until volitional exhaustion. Electrocardiogram monitoring and an open-circuit computerized gas analysis system provided a display of heart rate, expired flow, O2 consumption, COa production, and respiratory exchange ratio every 20 s during the test. Voluntary strength. Voluntary strength of each leg was measured as the maximum weight that could be lifted for one repetition (1 RM) on the weight training apparatus. Measurements were made to the nearest 0.5 kg by means of adapter plates that could be placed on the apparatus weight stacks. Subjects used the same apparatus and body positioning (apparatus seat position) for all tests and training. The test was done twice on separate days before training, and the highest value attained was taken as the pretraining measure. Relative endurance. Relative endurance was measured for each leg on the weight training apparatus as the number of repetitions that could be done with 80% of the 1 RM. Absolute endurance. At the conclusion of the training program, absolute endurance, the number of repetitions done with the pretraining 1 RM, was measured for each leg on the weight lifting apparatus. For both endurance tests, a metronome controlled the rate of repetitions at lO/min. Muscle cross-sectional urea. We measured the crosssectional area of the right and left knee extensors and flexors with a computerized digitizer from photographs of computed tomography (CT) scans obtained with a CT scanner (model 20-30, Ohio-Nuclear). CT scans were made at the mid-thigh level (between the greater trochanter and lateral epicondyle of the femur). Thigh girth and skinfolds. The thigh girth of the right and left legs was measured with a steel tape at the
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262 TABLE
STRENGTH
2. Training
ENDURANCE
TRAINING
INTERACTION
program Group
Leg I
Five 3-min bouts at 90-100% VO
AND
Group
A Leg
Jk!?2
1
kf2
Endurance Five 3-min bouts at 90-100% VO
2 max
B
Five 3-min bouts at 90-100% VO
2 max
2 max
Strength 6 sets, 15-20 RM 6 sets, 15-20 RM 6 sets, 15-20 RM Each group consisted of four females and four males. Endurance training was on a cycle ergometer at a power output corresponding to that requiring 90-100% maximum oxygen output (ii0 2max).Strength training required 6 sets of 15-20 repetitions with heaviest possible weight on a leg press weight machine (RM). Each training session lasted 1 h; 3 training sessions were conducted each week on nonconsecutive days; and two 11-wk training periods were divided by a 3-wk rest period.
midthigh level. At this same level, anterior, posterior, lateral, and medial skinfold measurements were made with Harpenden-type skinfold calipers. Muscle fiber areas, composition, and cupillurizution. Needle biopsy samples were taken from the vastus lateralis of right and left legs. Part of one sample was mounted in an embedding medium and frozen in isopentane cooled with liquid nitrogen for subsequent histochemicaf analyses, and the remaining portion was used for electron microscopy. Muscle fibers were classified as slow twitch (ST or type I) or fast twitch (FT or type II) after staining for myofibrillar adenosine triphosphatase (ATPase) activity at a pH of 9.4, after preincubation at pH 10.3 (13). Muscle fiber composition (%ST) was determined from fields containing a minimum of 218 (max = 1,392) fibers. Photographs of serial sections stained for NADH-tetrazolium reductase (32) were used to determine the mean cross-sectional area of each fiber type using computerized planimetry. The means t SD number of fibers per sample used to calculate fiber area ranged from 50 t 23 to 83 t 25 for ST and from 49 t 21 to 96 t 60 for FT fibers. Capillaries were visualized with an amylaseperiodic acid-Schiff stain (1). Capillaries per fiber and capillaries per square millimeter were determined from fields of 50 fibers. Muscle enzyme activities. A second biopsy sample was frozen directly in liquid nitrogen and stored at -70°C until analyzed. At analysis, the tissue was freeze-dried, and then visible impurities, connective tissue, and blood
test system (42) according to the method described by Hoppeler et al. (18). Volume densities were calculated for myofibrils (V vmYOf),interior mitochondria (Vvmit) 3lipid (vvlip) 9 and cytoplasm (L,). Statistical
Analysis
Data were analyzed with a two-factor (pre-post-training, training condition) analysis of variance with repeated measures on one factor (pre-post-training). The analysis would indicate antagonism or “addition” in concurrent strength and endurance training as a significant interaction between the two factors (pre-post-training x training condition). When a significant interaction was found, a post hoc test (Tukey A) was done to identify significant differences among mean values. Statistical significance was accepted at P 5 0.05. Descriptive statistics included means t SE. RESULTS
The same pattern of results was found in the small number of males and females in each group; therefore, the results from both males and females were pooled for analysis. Effect of Concurrent Strength and Endurance on Strength Development (Group A)
Training
Voluntary strength. Leg press 1 RM increased (P = 0.006) in both the strength-trained leg (S) and the clots were dissected out before the tissue was weighed on strength- and endurance-trained leg (S+E) (Fig. 1). Alan electrobalance (Cahn). The tissue was then homogethough the S leg made a greater increase (30.5 kg, 30.2%) nized by sonication in an ice-cooled medium of 0.1 M than the S+E leg (21.2 kg, 20.4%), the interaction bephosphate buffer, pH 7.7, and supernatant extracts were tween pre-post-training and training condition was not assayed for the activities of phosphofructokinase (PFK), significant (P = 0.18). lactate dehydrogenase (LDH), and citrate synthase (CS) MwxZe cross-sectional urea. Extensor cross-sectional with NADH-coupled enzymatic methods (11, 25). area increased (P c 0.001) similarly in S (12.9%) and Morphometric analysis. Tissue for electron microscopy S+E (11.2%) legs (Fig. 2). Flexor cross-sectional area was immediately fixed in glutarafdehyde, dried in and the ratio of extensor to flexor area did not change ethanol, and embedded in Epon, using standard tech- after training. niques. Slightly oblique sections were then photographed Thigh girth, skinfolds, and body muss. Thigh girth at -~50,000 magnification under a Phillips EM200. An increased slightly but significantly (P = 0.008) overall average of 52 fibers (range, 37-60) were randomly se- (Fig. 3). The S+E leg did not make a significantly greater lected per biopsy, and for each biopsy a photographic increase than the S leg (interaction P = 0.171). The sum of four skinfolds did not change significantly after trainfield for the interior of each fiber was randomly selected and photographed. Stereological analysis was performed on each micrograph by means of a 1680point short-line
ing (Fig. 3). Body mass did not change significantly after training (Table 1).
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STRENGTH
AND ENDURANCE
TRAINING
E+S
S
S+E
E
263
INTERACTION
FIG. 1. Leg press results for one repetition on the weight training apparatus (1 RM) in group A (top left), which strengbh trained one leg (S) and strength and endurance trained the other leg (S+E), and group B (top right), which endurance trained one leg (E) and endurance and strength trained the other leg (E+S). Top: before (open bars) and after (stippled bars) training values. Bottom: increases after training. Values are means & SE. Main effect before vs. after training: * P = 0.006, ** P < 0.001; interaction (E+S > E): T P < 0.001.
E+S
lMuscZe fiber area. There were no significant changes in ST (S, 3,946 & 538 to 4,675 A 537; S+E, 4,481 t 491 to 5,412 $- 1,196) or FT (S, 4,693 t 619 to 5,378 t 783; S+E, 4,884 t 685 to 5,738 & 1,209) fiber area (means t SE, pm2). The FT-to-ST area ratio did not change (S, 1.22 $- 0.12 to 1.15 t 0.10; S+E, 1.09 $- 0.09 to 1.08 t 0.08). Maximal aerobic power (VU~ maw).S (7.9%) and S+E (8.3%) legs made similar increases in VOWmax(P = 0.006, Fig. 4). Weight lifting endurance. Relative endurance (repetitions with 80% 1 RM) increased after training (P = 0.013, Fig. 5). There was a significant interaction (P = 0.013), indicating that the S+E leg (152%) improved moreonthismeasureaftertrainingthantheSleg (81%). S (26.8) and S+E (24.4) were similar in the number of repetitions that could be done with the pretraining 1 RM after training (absolute endurance, Fig. 6). %ST and cupillarization. There was a significant (P = 0.007) increase in %ST fibers in both S (31.8-46.5) and S+E (39.2-47.0) legs (Fig. 7). Capillaries per fiber (S, 1.92 t 0.27 to 1.76 z!z 0.26; S+E, 2.15 + 0.32 to 2.26 & 0.39) and capillaries per square millimeter muscle area
(S, 260 t 15 to 247 t 37; S+E, 256 t 32 to 245 t 39) did not change significantly after training. Muscle enzyme activities. PFK (S, 0.095 t 0.015 to 0.098 t 0.014; S+E, 0.087 t 0.013 to 0.091 t 0.012) and LDH (S, 5.03 t 0.46 to 5.12 t 0.61; S+E, 4.54 $- 0.41 to 4.59 t 0.33) activities (mkatal/kg dry wt) did not change significantly after training. In contrast, CS activity increased significantly (P < 0.001, Fig. 8). There was also a significant (P = 0.005) interaction for this enzyme. The S+E leg (51.2%) showed a larger increase than the S leg (22.1%). lk&chondrial and lipid volume density. Mitochondrial volume density appeared slightly higher in the S+E leg after training, but the change was not statistically sign&ant (Fig. 9), In addition, there were large increases 6, 194%; S+E, 70%) in lipid volume density; these increases also failed to reach statistical significance (P = 0.085~ Fig. 9). Effect of Concurrent Endurance and Strength on Endurance Development (Group B)
Training
Maximal aerobic power (Voz W). E (6.9%) and E+S (7.2%) legs made similar increases in VOW maxafter training (P C 0.001, Fig. 4).
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STRENGTH
AND ENDURANCE
TRAINING
INTERACTION
**
**
I S+E
E+S
FIG. 2. Knee extensor (top) and flexor (bottom) muscle cross-sectional area in group A (left) for S and S+E and group B (right) for E and E+S. Values are means t SE for before (open bars) and after (stippled bars) training. Main effect before vs. after training: * P = 0.012, ** P c 0.001.
9
1
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I
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l .# *:*:a3 l .:.;.: l .*.*. .*~‘~~~ A‘.‘.
.“*.*. . . . =,:o:.: .~~~.=~ .*.*.“ .*“.** a“‘.*. +.*.*. 1. . .
S
S+E
r
t+3
Weight lifting endurance. Relative endurance (repetitions with 80% 1 RM) increased after training (P = 0.022, Fig. 5). There was a significant interaction (P = 0.030). The E+S leg (157%), but not the E leg (60%), increased relative endurance significantly. After training, the E+S leg (51) could do more (P = 0,032) repetitions with the pretraining 1 RM (absolute endurance) than the E leg (16) (Fig. 6). %ST and capillarization. There was a significant (P c 0.001) increase in %ST fibers in both E (49.9-56.3) and E+S (41.6-58.8) legs (Fig. 7). Capillaries per fiber (E, 2.38 z!z 0.22 to 2.19 t 0.22; E+S, 2.48 t 0.26 to 2.49 -I0.26) and capillaries per square millimeter muscle area (E, 308 k 16 to 267 t 13; E+S, 309 t 22 to 265 t 24) did not change significantly after training. Muscle enzyme actiuities. PFK (E, 0.096 t 0.011 to 0.101 t 0,012; E-G, 0.093 t 0.005 to 0.098 t 0.007) and LDH (E, 4.46 t 0.77 to 5.09 t 0.77; E+S, 5.28 t 0.77 to 5.28 k 0.63) activity did not change significantly after training. In contrast, CS activity increased significantly (P = 0.003) and similarly in E (38.1%) and E+S (36.3%) legs (Fig. 8).
.
m
Mituchondrial and lipid volume density. After training, mitochondrial volume density was -9% higher in the E leg and 15% higher in the E+S leg, but the changes were not statistically significant (Fig. 9). The large increases (E, 120%; E+S, 169%) in lipid volume density also failed to reach statistical significance (P = 0.063) (Fig. 9). Voluntary strength. Leg press 1 RM increased significantly (P < 0.001) after training (Fig. 1). There was a significant interaction (P < 0.001). Although both E (20.3%) and E+S (34.1%) legs increased the 1 RM significantly, the increase in the E+S leg was significantly greater. Muscle cross-sectional area. Extensor cross-sectional area increased (P < 0.001) in both E (14.3%) and E+S (20.9%) legs (Fig. 2). The greater increase in the E+S leg was not significant (interaction P = 0.13). Flexor cross-sectional area increased (P = 0.012) in both E (8.8%) and E+S legs (12.4%). The greater increase in the E+S leg was not significant (interaction P = 0.126). The ratio of extensor to flexor cross-sectional area did not change significantly after training. Thigh girth, skinfolds, and body mass. Thigh girth
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STRENGTH
AND ENDURANCE
TRAINING
INTERACTION
265
,.C. .+.*.*. .‘A’. .*.*.+* .. . >x.: .‘*‘.‘. .v.*. .Vb4. .*.=.‘. .*.v. l ‘.‘.‘. A’.‘. .*~*4*. A’.% .*C.‘~ .=A‘. .v.*. .=**4*. .V.*. .*A+* .‘A84 .8.m.mm A+.*. A’.‘. A’*+. . . . >>x . . . ‘.‘.‘.’ . . . . .‘.V. l mmmmmm l . . y*.;*; mm. ~.:m: l *.
-l
_
S
S+E
E+S
80
1
FIG. 3. Thigh girth (tr>p) and sum of 4 (anterior, posterior, medial, lateral) thigh skinfolds (bottom) in group A (left) for S and S+E and group B (right) for E and E+S. Values are means -t SE for before (open bars) and after (stippled bars) training. Main effect before vs. after training: * P C 0.01,** P < 0.001; interaction (E+S > E): t P c 0.05.
f f . 2
70
iz 7 iii CA w 60 z 3 co
50
mm.. .‘A’. .*2.5 .V.‘. .‘.‘.‘. t.V. .+*‘.‘4 .‘.‘.‘. .‘.%‘.
‘_n
S
-
. ..‘A .*mm.*. .‘A’. .m.m.m. .‘.‘.4. .m.8*‘. .v.+* n .*.-mm. A*.‘. .‘.‘.*. ~ mm.
.V.‘. .‘.*.*. my*.> >ya.: 4*.*.*. .V.f .***.‘. 2.=mm.
44’.‘.
2.44..
l rn))> 1
t*‘...
‘....
E 6
S+E
increased slightly but significantly (P < 0.001) after training. The increase in the E+S leg (4.8%) was significantly (interaction P = 0.037) greater than the increase in the E leg (3.4%) (Fig. 3). -The sum of four thigh 3.2
skinfolds did not change significantly after training (Fig. 3). There was a small (2.6%) but significant (P < 0.05) increase in body mass after training (Table 1). Muscle fiber area. There were no significant changes 1
.‘.‘**. .‘.***m .+.m.m. .‘.‘.‘. l mmm.‘. .‘.*.*. n .
.
‘.‘.*m*
l. .4.m.m . . . .‘..I’. mm. mm.. .‘...‘m
FIG. 4. Maximum (left) for S and S+E
_
m... mm.+.*. .*.=.*C ..4
aerobic power in group A and group B (right) for E and E+S. Values are means k SE for before (open bars) and after (stippled bars) training. Main effect before vs, after training: * P = 0.006, ** P < 0,001.
l mmm.*. .m.m.=. mm. l .4.
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266
STRENGTH
AND ENDURANCE
TRAINING
*
50
T4
+
E a 7 8 0
T
40
O”
30
k co 2
20
0
i= i= UJ CL W a
T T
10
0
E a 7 8 0 co Q cn /
INTERACTION
S+E
E
E+S FIG. 5. Repetitions with 80% 1 RM in group A (left) for S and S+E andgroup B (right) for E and E+S. Top: before (open bars) and after (stippled bars) training values. Bottom: increase in repetitions after training. Values are means k SE. Main effect before vs. after training: * P < 0.05; interaction: t P = 0.013 (S+E > S), tJ- P < 0.001 (E+S > E).
30
t
20
0 F
E CL w a
10
d 0
S
S+E
E
in ST (E, 4,864 t 1,318 to 4,786 t 375; E+S, 5,274 t 695 to 5,347 t 367) or FT (E, 5,590 t 687 to 5,543 t 291; E+S, 5,690 $- 555 to 6,299 & 457) fiber area. The FT-to-ST area ratio did not change (E, 1.14 t 0.08 to 1.17 k 0.07; E+S, 1.12 t 0.06 to 1.18 -t 0.05). DISCUSSION
The nominally designated strength (S) and endurance (E) training used in the present study had more in common as training stimuli than differences; thus in group A, the S leg made increases similar to the S+E leg in endurance-related measures of VOW max, repetitions with the pretraining leg press 1 RM, and %ST fibers; and S made significant, although smaller (vs. S+E), increases in repetitions with 80% -1RM, and CS activity. Similarly, in g?vup B, the E leg increased knee extensor CSA as much as the EN leg and made significant,
E+S
although smaller, increases in leg press 1 RM and thigh girth. Therefore the S and E training used in the present study might be considered hybrids rather than extreme or “pure” forms of S and E training. The hybrid nature of the E training was probably due in. part to the high intensity bouts (3 min at 90.100% vo 2 max) employed; such bouts might ensure endurance adaptations in fast- and slow-twitch motor units (8, 27), but they also induced increases in muscle size and strength. In addition, E training by cycling (necessitated in the present study because of the one leg training model) may be more likely to increase strength (31, 34) and muscle size (2, 12; see, however, 39) than, for example, by running. The S training consisted of sets of 15-20 repetitions with a weight ranging from 75-80% 1 RM at the start of training to 85-90% 1 RM by the end of training [by comparison only -5-10 repetitions can be done with 75-90% 1 RM in upper body exercises such
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STRENGTH
AND ENDURANCE
TRAINING
267
INTERACTION
60 -
> u l--
N=5
3o
W u a. Q
3 CT
50-
&j
40-
m LL
20
cJ3 z
0
o\o
i= 6
lo
30 -
Q k!
20 -
0
c 60 -
> a: 7 W
N=4
6o cJ2
E k
40
co z
0
I%
m LL
5o
)co
40-
T
8
F i= W CL
20 30 -
ii? 0
20 -
E
E+S
1
E
E+S
6. Repetitions done, after training, with the heaviest weight that could be lifted for 1 repetition before training in group A (top) for S and S+E and group B (bottom) for E and E+S. Values are means k SE. Interaction (E+S > E): 7 P < 0.05,
7. Percent slow-twitch (ST) of vastus lateralis in group A (top) for S and S+E and group B (bottom) for E and E+S. Values are means + SE for before (open bars) and after (stippled bars) training. Main effect before vs. after training: * P = 0.007, ** P < 0.001.
as the bench press (35) and arm curl (30)]. Although the intensity (%l RM) was appropriate for effective strength training, the number of repetitions per set (15-20) and per training session (90-120) might be considered high (there were -900 contractions in each endurance training session). The S program was successful in inc:easing strength and muscle size, but it also increased Voz max (perhaps due in part to a “central” effect from endurance training of the other leg), weight lifting endurance, and CS activity. When S and E training are done concurrently they may not interact at all; i.e., the concurrent training would cause the same strength and endurance adaptations as S and E training done alone. They may interact to cause antagonism; i.e., strength and/or endurance adaptations would be less than in response to S or E training alone. Or they may interact to cause “addition”; i.e., strength and endurance adaptations would be greater than in response to S and E training alone. Whether interaction occurs and the form it takes probably depend on several factors: the intensity, volume, and frequency of the two types of training; the training modes; the training status
of the subjects; and the way the two forms of training are integrated. Furthermore, the results and conclusions drawn will be affected by the selected criterion measures of strength and endurance development. These factors must be considered in the interpretation of the present and previous studies (3, 9, 10, 14, 15, 19). Antagonism did not occur in the present study, probably because of the hybrid nature of the S and E training involved and the moderate total volume of training. However, previous studies have shown antagonism in the form of impaired strength development (9, 14, 19). Antagonism may have occurred in these studies because of the greater volume of training used (14) or the criterion measure of adaptation used [e.g., impaired high- but not low-velocity isokinetic strength development (9)]. Generally, antagonism may be more likely to occur when large volume extreme forms of S and E training are done concurrently (e.g., marathon run training and competitive weight lifting). In regard to a possible additive effect of combined strength and endurance training, an interesting pattern was found. When a presumably stronger stimulus for a
FIG.
FIG.
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STRENGTH
AND ENDURANCE
TRAINING
INTERACTION
FIG. 8. Citrate synthase (CS) activity in group A (left) for S and S+E and group B (right) for E and E+S. Top: before (open bars) and after (stippled bars) -training-values. Bottom: increases after training. Values are means k SE. Main effect before vs. after training: * P = 0.003, ** P c 0.001; interaction (S+E
1 >S):tP=0.005.
t **
S
S+E
E
given adaptation was added to a weaker stimulus, addition sometimes occurred, but when a weaker stimulus was added to a stronger one, addition did not occur. Thus in group A (S vs. S+E) the addition of E training was additive for increases in endurance (repetitions at 80% 1 RM) and CS activity, although S training alone caused significant increases in these measures. Similarly, in group B (E vs. E+S) the addition of S training was additive for increases in strength and one measure of muscle size (thigh girth), although E training alone caused significant increases in these measures. On the other hand, E training was not additive for increases in strength and muscle size (S vs. S+E), although E training alone caused increases in these measures, nor was S training additive for increases in VOW maxand CS (E vs. E+S), although S training alone caused increases in these measures. An exception was that S training was additive for short-term endurance. The endurance tests were done on the S training device; therefore, the increased endurance was probably partly related to improved strength, skill, and efficiency in the exercise movement in the course of S training.
E+S The training status of the subjects may determine whether antagonism or addition occurs in concurrent strength and endurance training. In previously untrained subjects, endurance development is not impaired (9, 14, 19, present study) and may be enhanced (present study); strength development may (9,14,19) or may not (present study) be impaired. In previously endurance-trained subjects who continue endurance training but add strength training, strength (19) and endurance (15) development may be enhanced. We chose for the present study a training model that provided a within-subject control and evaluation of interaction between concurrent strength and endurance training. Thus group A trained for both strength and endurance in one leg and strength only in the other leg, whereas group B trained for both strength and endurance in one leg and endurance only in the other leg. This model avoided the variability in training response between separate groups containing a small number of subjects. For example, a particular group, despite random assignment of subjects, might by chance contain more trainable subjects. This group would make a greater
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STRENGTH
AND ENDURANCE
- T
S
E
S+E
E+S
-
T
l-
T
T
E E+S S SE 9. Mitochondrial (V, *it) (top) and lipid (V, lip) (bottom) volume density of vastus lateralis in group A &jQ for S and S+E and group B (right) for E and E+S. Values are means +: SE for before (open bars) and after (stippled bars) training. FIG.
response to training, regardless of the method of training. This problem would be minimized with larger groups. The within-subject model used in the present study had at least one limitation. The model was chosen on the assumption that a major part of any interaction (antagonism or addition) caused by concurrent strength and endurance training would be expressed at the peripheral muscle level in measures such as muscle cross-sectional area and enzyme activity. If antagonism or addition occurred but were expressed entirely as a “central” phenomenon, then in our subjects even the legs that did only strength or endurance training would have been affected in the same way as the legs that did combined strength and endurance training. Antagonism or addition would not have been revealed. In the study by Hickson (14), there was evidence that antagonism may in some instances be entirely central (e.g., central nervous system fatigue); voluntary strength development was impaired by concurrent strength and endurance training, but increases in muscle size (indicated by thigh girth measurements) were not impaired. In comparison we found no impairment of strength or muscle size development, but we cannot exclude the possibility that some entirely centrally mediated antagonism occurred in our study. It can be concluded, however, that no peripherally (muscle) mediated antagonism occurred.
TRAINING
INTERACTION
269
In conclusion, one finding of the present study that does not bear directly on the main purpose nevertheless deserves comment. The percent of ST fibers in vastus lateralis increased after -5 mo of training. An increase or any change in %ST fibers after strength or endurance training in humans is unusual but not unprecedented (21, 38, 40). Detraining has been associated with a decrease in %ST fibers (23). Any observed change in fiber type composition raises the issue of the methodological errors associated with determining %ST fibers from single biopsy samples from a large muscle. These errors (e.g., Ref. 4, 24) and their bearing on the interpretation of findings of changes in %ST fibers have been discussed recently elsewhere (23,38). In the present study the preand posttraining biopsy samples were not analyzed in a single batch but rather 5 mo apart, raising the possibility that a difference in the pH or temperature of the preincubation medium in the two analyses caused a systematic error in the staining and subsequent determination of %ST fibers. However, this possibility is diminished by the consideration that a difference of at least several tenths of a pH unit would be necessary to affect the differentiation of the main fiber types (ST vs. FT). Nevertheless, our observed change in %ST fibers should be viewed with caution. The authors thank J. Moroz for general assistance; J. Laufer, T. Brown, and D. Kerrigan-Brown for technical assistance; A. Brown and D. Moroz for coordinating the study; and L. Diskin for secretarial assistance. This study was supported by the Dept. of National Defence, Canada (DCIEM Contract 8SE85-00082) and the Natural Sciences and Engineering Research Council of Canada. Address for reprint requests: D. G. Sale, Dept. of Physical Education, McMaster University, Hamilton, Ontario L8S 4Kl, Canada. Received 14 September 1988; accepted in final form 28 August 1989. REFERENCES 1. ANDERSEN, P. Capillary density in skeletal muscle of man. Acta Physiol. Stand. 95: 203-205, 19’75. 2. ANDERSEN, P., AND J. HENRIKSSON. Capillarysupplytothequadriceps femoris muscle of man: adaptive response to exercise. J. Physiol. Land. 270: 677, 1977. 3. BELL, G. J,, S. R. PETERSEN, H. A. QUINNEY, AND H. A. WENGER. Sequencing of endurance and high-velocity strength training. Can. J. Sport Sci. 13: 214-219, 1988. 4. BLOMSTRAND, E., AND B. EKBLOM. The needle biopsy technique for fiber type determination in human skeletal muscle-a methodological study. Actu Physiol. Scund. 116: 437-442, 1982. 5. COSTILL, D. L. The relationship between selected physiological variables and distance running performance. J. Sports Med. Phys. Fitness 7: 61-66, 1967. 6. COSTILL, D. L., E. F. COYLE, W. F. FINK, G. R. LESMES, AND F. A. WITZMANN. Adaptations in skeletal muscle following strength training. J. Appl. Physiol. 46: 96-99, 1979. 7. DENIS, C., J.-C. CHATARD, D. DORMOIS, M.-T. LINOSSIER, A. GEYSSANT, AND J.-R. LACOUR. Effects of endurance training on capillary supply of human skeletal muscle on two age groups (20 and 60 years). J. Physiol. Puris 81: 379-383, 1986. 8. DUDLEY, G. A., W. M. ABRAHAM, AND R. L. TERJUNG. Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle. J. Appl. Physiol. 53: 844-850, 1982. 9. DUDLEY, G. A., AND R. DJAMIL. Incompatibility of endurance- and strength-training modes of exercise. J. Appl. Physiol. 59: 14461451,1985. 10. DUDLEY, G. A., AND S. J. FLECK. Strength and endurance training. Are they mutually exclusive? Sports Med. 4: 79-85, 1987. 11. ESSEN, B., A. LINDHOLM, AND G. THORTON. Histochemical prop-
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270
STRENGTH
AND
ENDURANCE
TRAINING
D., AND D. SALE. Continuous vs. interval training: a review for the coach and athlete. Can. J. AppZ. Sport Sci. 6: 93-
erties of muscle fibre types and enzyme activities in skeletal muscle of standard-bred trotters of different ages. Equine Vet. J. 12: 1751&0,19&0. 12. GOLLNICK, P. D., R. B. ARMSTRONG, B, SALTIN, C. W. SAUBERT IV, W. L. SEMBROWICH, AND R. E. SHEPHERD. Effect of training on enzyme activity and fiber composition of human skeletal muscle. J. AppZ. Physiol. 34: 107-111, 1973. 13. GUTH, L., AND F. J. SAMAHA. Qualitative differences between actomyosin ATPase of slow and fast mammalian muscle. Ex~.
27. MACDOUGALL,
NeuroZ. 25: 138-152, 1969. 14. HICKSON, R. C. Interference
Sci. Sports 30. MAUGHAN, DELMAN.
of strength development by simultaneously training for strength and endurance. Eur. J. Appl. Physiol. Occ~p. Physiol. 45: 255-263, 1980. 15. HICKSON, R, C., B. A. DVORAK, E. M. GOROSTIAGA, T. T. KuROWSKI, AND C. FOSTER. Potential for strength and endurance training to amplify endurance performance. J. AppZ. Physiol. 65: 22&5-2290,19&&. 16. HICKSON, R. C., M.
A. ROSENKOETTER, AND M. M. BROWN. Strength training effects on aerobic power and short term endurance. 1Med. Sci. Sports Exercise 12: 336-339, 1980. 17. HOPPELER, H. Exercise-induced ultrastructural changes in skeletal muscle. ht. J. Sports Med. 7: 187-204, 1986. 18, HOPPELER, H., P. LUTHI, H. CLASSEN, E. R. WEIBEL, AND H. HOWALD. The ultrastructure of the normal skeletal muscle; a morphometric analysis of untrained men, women and well-trained orienteers. Pfluegers Arch. 344: 217-232, 1973. 19. HUNTER, G., R. DEMMENT, AND D. MILLER. Development of strength and maximum oxygen uptake during simultaneous training for strength and endurance. J. Sports Med. Phys. Fitness 27: 269-275,19&7, 20. INGJER, F.
Effects of endurance training on muscle fibre ATP-ase activity, capillary supply and mitochondrial content in man. J.
Physiol. Land. 294: 419-432, 1979. 21. JANSSON, E., B. &ODIN, AND P. TESCH.
Changes in muscle fibre after physical training. A sign of fibre type
type distribution transformation? Actu Physiol. Scund. 104: 235-237, 1978. 22. KLAUSEN, K., L. B. ANDERSON, AND I. PELLE. Adaptive changes in work capacity, skeletal muscle capillarization and enzyme levels during training and detraining. Actu Physiol. Scund. 113: 9-16, 1981. 23. LARSSON,
L., AND T. ANSVED. Effects of long-term physical training and detraining on enzyme histochemical and functional skeletal muscle characteristics in man. MuscZe Nerve 8: 714-722, 1985. 24. LEXELL, J., K. HENRIKSON~ARSEN, AND M. SJOSTROM. Distribution of different fibre types in human skeletal muscles. A study of cross-sections of whole m. vastus lateralis. Actu Physiol. Stand.
117: 115-122,1983. 25. LOWRY, 0. H., AND J. V. PASSONNEAU. A Flexible System of Enzymatic Analysis. New York: Academic, 1972. 26. MACDOUGALL, J. D., G. C. B. ELDER, D. G. SALE, J. R. MOROZ, AND J. R. SUTTON. Effects of strength training and immobilization on human muscle fibres. Eur. J. AppZ. Physiol. Qccup. Physiol. 43: 25-34,19&O.
INTERACTION
97, 1981. 28. MACDOUGALL,
J. D., D. G. SALE, G. C. ELDER, AND J. R. SUTTON. Muscle ultrastructural characteristics of elite powerlifters and bodybuilders. Eur. J. AppZ. Physiol. Occup. Physiol. 48: 117-126, 1982. 29. MACDOUGALL, J. D., D. G. SALE, J. R. MOROZ, G. C. B. ELDER, J. R. SUTTON, AND H. HOWALD. Mitochondrial volume density in human skeletal muscle following heavy resistance training. Med.
31. 32.
33.
34.
35.
36.
11: 164-166,
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R. J., M. HARMON, S. B. LEIPER, D. SALE, AND A. Endurance capacity of untrained males and females in isometric and dynamic muscular contractions. Eur. J. Appl. Physiol. Occup. Physiol. 55: 395-400, 1986. MOROZ, D. E., AND M. E. HOUSTON. The effects of replacing endurance running training with cycling in female runners. Can. J. Sport Sci. 12: 131-135, 1987. NOVIKOFF, A. B., W. Y. SHIN, AND J. DRUCKER. Mitochondrial localization of oxidation enzymes: staining results with two tetrazolium salts. J. Biophys. Biochem. CytoZ. 9: 47-61, 1961. ONO, M., M. MIYASHITA, AND T. ASAMI. Inhibitory effect of long distance running training on the vertical jump and other performances among aged males. In: Biomechunics V-B, edited by P. V. Komi. Baltimore, MD: University Park, 1976, p. 94-100. ROSLER, K., K. E. CONLEY, H. HOWALD, C. GERBER, AND H. HOPPELER. Specificity of leg power changes to velocities used in bicycle endurance training. J. AppZ. Physiol. 61: 30-36, 1986. SALE, D., AND D. MACDOUGALL. Specificity in strength training: a review for the coach and athlete. Can. J, AppZ. Sport Sci. 6: &792, 1981. SCHANTZ, P. Capillary supply in heavy-resistance trained nonpostural human skeletal muscle. Actu Physiol. Scund. 117: 153-
155,19&3. 37. SCHANTZ,
P. G. Plasticity of human skeletal muscle with special reference to effects of physical training on enzyme levels of the NADH shuttles and phenotypic expression of slow and fast isoforms of myofibrillar proteins (Abstract). Actu Physiol. Scund. Suppl. 128: 55&,19&6. 38. SIMONEAU, J.-A., G. LORTIE, M. R. BOWLAY, M. MARCOTTE, M.C. THIBAULT, AND C. BOUCHARD. Human skeletal muscle fiber type alteration with high-intensity intermittent training. Eur. J. AppZ. Physiol. Occup. Physiol. 54: 250-253, 1985. 39. TERRADOS, N., J. MELICHNA, C. SYLVEN, AND E. JANSSON. Decrease in skeletal muscle myoglobin with intensive training in man. Actu Physiol. 40. TESCH, P.
Stand.
128: 651-652,
1986.
A., AND J. KARLSSON. Muscle fiber types and size in trained and untrained muscles of elite athletes. J. AppZ. Physiol. 59: 1716-1720,19&5. 41. TESCH, P. A., A. THORSSON, AND P. KAISER. Muscle capillary supply and fiber type characteristics in weight and power lifters. J. AppZ. Physiol. 56: 35-38, 1984. 42. WEIBEL, E. B. Stereological methods. In: Practical Biological Morphomettcy. London: Academic, 1979,
Methods
for
vol. 1.
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strength
D. G. SALE, J. D. MA~DOUGALL, I. JACOBS, AND S. GARNER Departments of Physical Education and Medicine, McMaster University, Hamilton L8S 4Kl; and Defence and Civil Institute of Environmental Medicine, Downsview, Ontario M3M 3B9, Canada
SALE, D. G., J. D. MACDOUGALL, I. JACOBS, AND S. GARNER. Interaction between concurrent strength and endurance truining. J. Appl. Physiol. 68(l): 260470, 1990.-To assessthe
effects of concurrent strength (S) and endurance (E) training on S and E development, one group (4 young men and 4 young women) trained one leg for S and the other leg for S and E (S+E). A secondgroup (4 men, 4 women) trained one leg for E and the other leg for E and S (E+S). E training consistedof five 3-min bouts on a cycle ergometer at a power output corresponding to that requiring 90400% of oxygen uptake during maximal exercise (VO 2&. S training consistedof six setsof 15-20 repetitions with the heaviest possibleweight on a leg press(combined hip and knee extension) weight machine. Training wasdone3 days/wk for 22 wk. Needlebiopsy samples from vastus lateralis were taken before and after training and were examined for histochemical,biochemical, and ultrastructural adaptations.The nominal S and E training programswere “hybrids,” having more similarities as training stimuli than differences; thus S madeincreases(P < 0.05) similar to those of S+E in E-related measuresof VOW max(S, S+E: 8%, 8%), repetitions with the pretraining maximal singleleg presslift [l repetition maximum (RM)] (27%, 24%), and percent of slowtwitch fibers (15%, 8%); and S made significant, although smaller, increasesin repetitions with 80% 1 RM (81%, 152%) and citrate synthase (CS) activity (22%, 51%). Similarly, E increased knee extensor area [computed tomography (CT) scans] as much as E+S (14%, 21%) and made significant, although smaller, increasesin leg press1 RM (20%, 34%) and thigh girth (3.4%, 4.8%). When a presumablystronger stimulus for an adaptation was added to a weaker one, someadditive effects occurred (i.e., increasesin 1 RM and thigh girth that were greater in E+S than E; increasesin CS activity and repetitions with 80% 1 RM that were greater in S+E than S). When a weaker, although effective, stimulus was added to a stronger one, addition generally did not occur. Concurrent S and E training did not interfere with S or E development in comparisonto S or E training alone. skeletal muscle;adaptation; aerobic power; enzyme activity
AND ENDURANCE training represent,intheir extremes, opposite forms of training. Strength training
STRENGTH
consists of a relatively small number of contractions of maximal or near-maximal force. Endurance training con-
sists of a large number of submaximal contractions. Accordingly, the adaptive responses in skeletal muscle to strength and endurance training are different and sometimes opposite. Strength training causes muscle fiber hypertrophy (26) associated with an increase in contractile protein (28), which contributes to an increase 260
in maximal contraction force. In contrast, endurance training usually causes little or no muscle fiber hypertrophy (2,7,12,20,23), but it does cause an increase in the following adaptations expected to enhance endurance performance: capillary density (2, 7, 20, 37, 39), mitochondrial volume density (17), and oxidative enzyme activity (12, 37). Strength and endurance training are often done concurrently by fitness enthusiasts and athletes. However, since the adaptive responses to strength and endurance training are different and some may even be opposite, it is conceivable that skeletal muscle cannot adapt optimally to the two contradictory training stimuli when they are simultaneously imposed. For example, strength training may cause a decrease in capillary density (36, 41) and mitochondrial volume density (29), which would undermine the increase in these measures induced by endurance training. Endurance training has been associated with a loss of strength (5, 31, 33) and decreased muscle fiber size (Z&39), changes obviously antagonistic to strength development. On the other hand, concurrent strength and endurance training may interact to enhance rather than hinder strength and endurance development. Some forms of endurance training have increased strength (31, 34) and muscle fiber size (2, 12). Strength training has increased short- (4-6 min) and long- (60-90 min) term endurance (14.16), maximal aerobic power (14), and oxidative enzyme activity (6). Whether the interaction between concurrent strength and endurance training results in “antagonism” or mutual enhancement of the training response probably depends on several factors, including the initial state of training of the trainees; the training modes; the intensity, volume, and frequency of training; and the way the two forms of training are integrated. In previously untrained subjects, a combination of moderate-to-high intensity and volume endurance and strength training impeded strength development but not increases in maximal aerobic power or short-term endurance (9, 14, 19). In previously endurance-trained subjects, the addition of strength training does not cause the impaired strength development seen in untrained subjects (19), and it improves endurance without increasing aerobic power (15). In the present study, the interaction between concurrent high intensity, moderate volume strength and endurance training was examined in previously untrained subjects. A unique aspect of the study was that several
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STRENGTH
AND
ENDURANCE
measures related to skeletal muscle adaptation were made to help explain any evidence of antagonism or mutual enhancement that might be found. METHODS
Subjects
The subjects were eight young women and eight young men without previous experience in intense strength or endurance training. In accordance with the Ethical Guidelines for Research on Human Subjects at McMaster University, we clearly apprised the subjects of the purpose of the study and the physical, psychological, and/or social risks involved in the research, and the students signed an informed consent form. The project carried the approval of McMaster University’s Ethics Committee. Design
Half (4 women, 4 men) of the subjects (group A) were randomly assigned to train both lower limbs for strength and one limb for endurance. The other half of the subjects (group B) trained both limbs for endurance and one limb for strength. Thus group A assessed the interaction between strength and endurance training (S+E) compared with strength training alone (S), while group B assessed the interaction between endurance and strength training (E+S) compared with endurance training alone (E). The characteristics of the subjects in the two groups are presented in Table 1. Training
Training consisted of two ll-wk periods divided by a 3-wk break period, the latter to accommodate a Christmas recess. There were three training sessions per week during the training periods. For each subject a training session lasted -1 h, i.e., the time taken to train both strength and endurance in one leg and strength (group A) or endurance (group B) in the other leg. In legs that did combine strength and endurance training, endurance training preceded strength training in each training session. Strength training. Strength training was done on a “Universal”-type leg press weight training machine (Global Gym, Downsview, Ontario). The training movement (concentric contraction phase) included simultaneous hip and knee extension and ankle plantar flexion. Each repetition of the exercise included a concentric and eccentric contraction phase. Subjects in group A performed six sets of E-20 repetitions maximum (RM); i.e., TABLE 1. Age, height, and body muss Group
A B
Experiment
S vs. S + E E vs. E + S
Age, Yr
20.9zkO.5 20.6t0.3
of subjects Mass,
Height, cm
169.2k4.7 168.1k2.4
Values are means k SE; each group males. S, strength training; E, endurance effect in body mass, pre-post training.
Pre
65.7+5.1 62.2t3.3
consisted training.
kg Post
66.9k4.8 63.8&3.3*
of 4 females and 4 * P < 0.05 for main
TRAINING
INTERACTION
261
the heaviest possible weight was used for the designated number of repetitions of the leg press movement with each leg. Sets were alternated between legs, with 1-min rest periods, until each leg completed the six sets. Subjects in group B performed six sets of 15-20 RM with the randomly designated leg. There were 2-min rest periods between successive sets. Endurance training. Endurance training was performed on a cycle ergometer (Monark). The training consisted of five 3-m+ bouts at a power output corresponding to 90-100% VOWmax.In group A, which trained only one randomly assigned leg for endurance, 3-min rest periods intervened between successive bouts. Group B performed the 3-min bouts alternately with both legs, with l-min rest periods between successive bouts. The training program is summarized in Table 2. Measurements
All measurements were made before and after the 22 wk of training. Aerobic power. Aerobic power (VOWmax)defined here as the peak 02 consumption attained during the single leg test) was measured for each leg separately. The test was performed on an electrically braked cycle ergometer (Jaeger) using a standard continuous progressive loading protocol. The test began at a power output of 30 or 45 W, and the load was increased by 15 W every 2 min until volitional exhaustion. Electrocardiogram monitoring and an open-circuit computerized gas analysis system provided a display of heart rate, expired flow, O2 consumption, COa production, and respiratory exchange ratio every 20 s during the test. Voluntary strength. Voluntary strength of each leg was measured as the maximum weight that could be lifted for one repetition (1 RM) on the weight training apparatus. Measurements were made to the nearest 0.5 kg by means of adapter plates that could be placed on the apparatus weight stacks. Subjects used the same apparatus and body positioning (apparatus seat position) for all tests and training. The test was done twice on separate days before training, and the highest value attained was taken as the pretraining measure. Relative endurance. Relative endurance was measured for each leg on the weight training apparatus as the number of repetitions that could be done with 80% of the 1 RM. Absolute endurance. At the conclusion of the training program, absolute endurance, the number of repetitions done with the pretraining 1 RM, was measured for each leg on the weight lifting apparatus. For both endurance tests, a metronome controlled the rate of repetitions at lO/min. Muscle cross-sectional urea. We measured the crosssectional area of the right and left knee extensors and flexors with a computerized digitizer from photographs of computed tomography (CT) scans obtained with a CT scanner (model 20-30, Ohio-Nuclear). CT scans were made at the mid-thigh level (between the greater trochanter and lateral epicondyle of the femur). Thigh girth and skinfolds. The thigh girth of the right and left legs was measured with a steel tape at the
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262 TABLE
STRENGTH
2. Training
ENDURANCE
TRAINING
INTERACTION
program Group
Leg I
Five 3-min bouts at 90-100% VO
AND
Group
A Leg
Jk!?2
1
kf2
Endurance Five 3-min bouts at 90-100% VO
2 max
B
Five 3-min bouts at 90-100% VO
2 max
2 max
Strength 6 sets, 15-20 RM 6 sets, 15-20 RM 6 sets, 15-20 RM Each group consisted of four females and four males. Endurance training was on a cycle ergometer at a power output corresponding to that requiring 90-100% maximum oxygen output (ii0 2max).Strength training required 6 sets of 15-20 repetitions with heaviest possible weight on a leg press weight machine (RM). Each training session lasted 1 h; 3 training sessions were conducted each week on nonconsecutive days; and two 11-wk training periods were divided by a 3-wk rest period.
midthigh level. At this same level, anterior, posterior, lateral, and medial skinfold measurements were made with Harpenden-type skinfold calipers. Muscle fiber areas, composition, and cupillurizution. Needle biopsy samples were taken from the vastus lateralis of right and left legs. Part of one sample was mounted in an embedding medium and frozen in isopentane cooled with liquid nitrogen for subsequent histochemicaf analyses, and the remaining portion was used for electron microscopy. Muscle fibers were classified as slow twitch (ST or type I) or fast twitch (FT or type II) after staining for myofibrillar adenosine triphosphatase (ATPase) activity at a pH of 9.4, after preincubation at pH 10.3 (13). Muscle fiber composition (%ST) was determined from fields containing a minimum of 218 (max = 1,392) fibers. Photographs of serial sections stained for NADH-tetrazolium reductase (32) were used to determine the mean cross-sectional area of each fiber type using computerized planimetry. The means t SD number of fibers per sample used to calculate fiber area ranged from 50 t 23 to 83 t 25 for ST and from 49 t 21 to 96 t 60 for FT fibers. Capillaries were visualized with an amylaseperiodic acid-Schiff stain (1). Capillaries per fiber and capillaries per square millimeter were determined from fields of 50 fibers. Muscle enzyme activities. A second biopsy sample was frozen directly in liquid nitrogen and stored at -70°C until analyzed. At analysis, the tissue was freeze-dried, and then visible impurities, connective tissue, and blood
test system (42) according to the method described by Hoppeler et al. (18). Volume densities were calculated for myofibrils (V vmYOf),interior mitochondria (Vvmit) 3lipid (vvlip) 9 and cytoplasm (L,). Statistical
Analysis
Data were analyzed with a two-factor (pre-post-training, training condition) analysis of variance with repeated measures on one factor (pre-post-training). The analysis would indicate antagonism or “addition” in concurrent strength and endurance training as a significant interaction between the two factors (pre-post-training x training condition). When a significant interaction was found, a post hoc test (Tukey A) was done to identify significant differences among mean values. Statistical significance was accepted at P 5 0.05. Descriptive statistics included means t SE. RESULTS
The same pattern of results was found in the small number of males and females in each group; therefore, the results from both males and females were pooled for analysis. Effect of Concurrent Strength and Endurance on Strength Development (Group A)
Training
Voluntary strength. Leg press 1 RM increased (P = 0.006) in both the strength-trained leg (S) and the clots were dissected out before the tissue was weighed on strength- and endurance-trained leg (S+E) (Fig. 1). Alan electrobalance (Cahn). The tissue was then homogethough the S leg made a greater increase (30.5 kg, 30.2%) nized by sonication in an ice-cooled medium of 0.1 M than the S+E leg (21.2 kg, 20.4%), the interaction bephosphate buffer, pH 7.7, and supernatant extracts were tween pre-post-training and training condition was not assayed for the activities of phosphofructokinase (PFK), significant (P = 0.18). lactate dehydrogenase (LDH), and citrate synthase (CS) MwxZe cross-sectional urea. Extensor cross-sectional with NADH-coupled enzymatic methods (11, 25). area increased (P c 0.001) similarly in S (12.9%) and Morphometric analysis. Tissue for electron microscopy S+E (11.2%) legs (Fig. 2). Flexor cross-sectional area was immediately fixed in glutarafdehyde, dried in and the ratio of extensor to flexor area did not change ethanol, and embedded in Epon, using standard tech- after training. niques. Slightly oblique sections were then photographed Thigh girth, skinfolds, and body muss. Thigh girth at -~50,000 magnification under a Phillips EM200. An increased slightly but significantly (P = 0.008) overall average of 52 fibers (range, 37-60) were randomly se- (Fig. 3). The S+E leg did not make a significantly greater lected per biopsy, and for each biopsy a photographic increase than the S leg (interaction P = 0.171). The sum of four skinfolds did not change significantly after trainfield for the interior of each fiber was randomly selected and photographed. Stereological analysis was performed on each micrograph by means of a 1680point short-line
ing (Fig. 3). Body mass did not change significantly after training (Table 1).
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E+S
S
S+E
E
263
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FIG. 1. Leg press results for one repetition on the weight training apparatus (1 RM) in group A (top left), which strengbh trained one leg (S) and strength and endurance trained the other leg (S+E), and group B (top right), which endurance trained one leg (E) and endurance and strength trained the other leg (E+S). Top: before (open bars) and after (stippled bars) training values. Bottom: increases after training. Values are means & SE. Main effect before vs. after training: * P = 0.006, ** P < 0.001; interaction (E+S > E): T P < 0.001.
E+S
lMuscZe fiber area. There were no significant changes in ST (S, 3,946 & 538 to 4,675 A 537; S+E, 4,481 t 491 to 5,412 $- 1,196) or FT (S, 4,693 t 619 to 5,378 t 783; S+E, 4,884 t 685 to 5,738 & 1,209) fiber area (means t SE, pm2). The FT-to-ST area ratio did not change (S, 1.22 $- 0.12 to 1.15 t 0.10; S+E, 1.09 $- 0.09 to 1.08 t 0.08). Maximal aerobic power (VU~ maw).S (7.9%) and S+E (8.3%) legs made similar increases in VOWmax(P = 0.006, Fig. 4). Weight lifting endurance. Relative endurance (repetitions with 80% 1 RM) increased after training (P = 0.013, Fig. 5). There was a significant interaction (P = 0.013), indicating that the S+E leg (152%) improved moreonthismeasureaftertrainingthantheSleg (81%). S (26.8) and S+E (24.4) were similar in the number of repetitions that could be done with the pretraining 1 RM after training (absolute endurance, Fig. 6). %ST and cupillarization. There was a significant (P = 0.007) increase in %ST fibers in both S (31.8-46.5) and S+E (39.2-47.0) legs (Fig. 7). Capillaries per fiber (S, 1.92 t 0.27 to 1.76 z!z 0.26; S+E, 2.15 + 0.32 to 2.26 & 0.39) and capillaries per square millimeter muscle area
(S, 260 t 15 to 247 t 37; S+E, 256 t 32 to 245 t 39) did not change significantly after training. Muscle enzyme activities. PFK (S, 0.095 t 0.015 to 0.098 t 0.014; S+E, 0.087 t 0.013 to 0.091 t 0.012) and LDH (S, 5.03 t 0.46 to 5.12 t 0.61; S+E, 4.54 $- 0.41 to 4.59 t 0.33) activities (mkatal/kg dry wt) did not change significantly after training. In contrast, CS activity increased significantly (P < 0.001, Fig. 8). There was also a significant (P = 0.005) interaction for this enzyme. The S+E leg (51.2%) showed a larger increase than the S leg (22.1%). lk&chondrial and lipid volume density. Mitochondrial volume density appeared slightly higher in the S+E leg after training, but the change was not statistically sign&ant (Fig. 9), In addition, there were large increases 6, 194%; S+E, 70%) in lipid volume density; these increases also failed to reach statistical significance (P = 0.085~ Fig. 9). Effect of Concurrent Endurance and Strength on Endurance Development (Group B)
Training
Maximal aerobic power (Voz W). E (6.9%) and E+S (7.2%) legs made similar increases in VOW maxafter training (P C 0.001, Fig. 4).
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**
**
I S+E
E+S
FIG. 2. Knee extensor (top) and flexor (bottom) muscle cross-sectional area in group A (left) for S and S+E and group B (right) for E and E+S. Values are means t SE for before (open bars) and after (stippled bars) training. Main effect before vs. after training: * P = 0.012, ** P c 0.001.
9
1
I
>)X .*.*.*. .*.*.*. ‘A’. ‘*.“‘. ‘.. x.;*: .‘bb.‘. A‘.‘. .~.~~~. .. . b‘b.*.b •~~.~.~ #:.; l ‘*‘*. A‘.‘.
I
.“‘.*a .*.*A 2.‘.‘. ‘*.“*‘ .*. l ..*.*
l .# *:*:a3 l .:.;.: l .*.*. .*~‘~~~ A‘.‘.
.“*.*. . . . =,:o:.: .~~~.=~ .*.*.“ .*“.** a“‘.*. +.*.*. 1. . .
S
S+E
r
t+3
Weight lifting endurance. Relative endurance (repetitions with 80% 1 RM) increased after training (P = 0.022, Fig. 5). There was a significant interaction (P = 0.030). The E+S leg (157%), but not the E leg (60%), increased relative endurance significantly. After training, the E+S leg (51) could do more (P = 0,032) repetitions with the pretraining 1 RM (absolute endurance) than the E leg (16) (Fig. 6). %ST and capillarization. There was a significant (P c 0.001) increase in %ST fibers in both E (49.9-56.3) and E+S (41.6-58.8) legs (Fig. 7). Capillaries per fiber (E, 2.38 z!z 0.22 to 2.19 t 0.22; E+S, 2.48 t 0.26 to 2.49 -I0.26) and capillaries per square millimeter muscle area (E, 308 k 16 to 267 t 13; E+S, 309 t 22 to 265 t 24) did not change significantly after training. Muscle enzyme actiuities. PFK (E, 0.096 t 0.011 to 0.101 t 0,012; E-G, 0.093 t 0.005 to 0.098 t 0.007) and LDH (E, 4.46 t 0.77 to 5.09 t 0.77; E+S, 5.28 t 0.77 to 5.28 k 0.63) activity did not change significantly after training. In contrast, CS activity increased significantly (P = 0.003) and similarly in E (38.1%) and E+S (36.3%) legs (Fig. 8).
.
m
Mituchondrial and lipid volume density. After training, mitochondrial volume density was -9% higher in the E leg and 15% higher in the E+S leg, but the changes were not statistically significant (Fig. 9). The large increases (E, 120%; E+S, 169%) in lipid volume density also failed to reach statistical significance (P = 0.063) (Fig. 9). Voluntary strength. Leg press 1 RM increased significantly (P < 0.001) after training (Fig. 1). There was a significant interaction (P < 0.001). Although both E (20.3%) and E+S (34.1%) legs increased the 1 RM significantly, the increase in the E+S leg was significantly greater. Muscle cross-sectional area. Extensor cross-sectional area increased (P < 0.001) in both E (14.3%) and E+S (20.9%) legs (Fig. 2). The greater increase in the E+S leg was not significant (interaction P = 0.13). Flexor cross-sectional area increased (P = 0.012) in both E (8.8%) and E+S legs (12.4%). The greater increase in the E+S leg was not significant (interaction P = 0.126). The ratio of extensor to flexor cross-sectional area did not change significantly after training. Thigh girth, skinfolds, and body mass. Thigh girth
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,.C. .+.*.*. .‘A’. .*.*.+* .. . >x.: .‘*‘.‘. .v.*. .Vb4. .*.=.‘. .*.v. l ‘.‘.‘. A’.‘. .*~*4*. A’.% .*C.‘~ .=A‘. .v.*. .=**4*. .V.*. .*A+* .‘A84 .8.m.mm A+.*. A’.‘. A’*+. . . . >>x . . . ‘.‘.‘.’ . . . . .‘.V. l mmmmmm l . . y*.;*; mm. ~.:m: l *.
-l
_
S
S+E
E+S
80
1
FIG. 3. Thigh girth (tr>p) and sum of 4 (anterior, posterior, medial, lateral) thigh skinfolds (bottom) in group A (left) for S and S+E and group B (right) for E and E+S. Values are means -t SE for before (open bars) and after (stippled bars) training. Main effect before vs. after training: * P C 0.01,** P < 0.001; interaction (E+S > E): t P c 0.05.
f f . 2
70
iz 7 iii CA w 60 z 3 co
50
mm.. .‘A’. .*2.5 .V.‘. .‘.‘.‘. t.V. .+*‘.‘4 .‘.‘.‘. .‘.%‘.
‘_n
S
-
. ..‘A .*mm.*. .‘A’. .m.m.m. .‘.‘.4. .m.8*‘. .v.+* n .*.-mm. A*.‘. .‘.‘.*. ~ mm.
.V.‘. .‘.*.*. my*.> >ya.: 4*.*.*. .V.f .***.‘. 2.=mm.
44’.‘.
2.44..
l rn))> 1
t*‘...
‘....
E 6
S+E
increased slightly but significantly (P < 0.001) after training. The increase in the E+S leg (4.8%) was significantly (interaction P = 0.037) greater than the increase in the E leg (3.4%) (Fig. 3). -The sum of four thigh 3.2
skinfolds did not change significantly after training (Fig. 3). There was a small (2.6%) but significant (P < 0.05) increase in body mass after training (Table 1). Muscle fiber area. There were no significant changes 1
.‘.‘**. .‘.***m .+.m.m. .‘.‘.‘. l mmm.‘. .‘.*.*. n .
.
‘.‘.*m*
l. .4.m.m . . . .‘..I’. mm. mm.. .‘...‘m
FIG. 4. Maximum (left) for S and S+E
_
m... mm.+.*. .*.=.*C ..4
aerobic power in group A and group B (right) for E and E+S. Values are means k SE for before (open bars) and after (stippled bars) training. Main effect before vs, after training: * P = 0.006, ** P < 0,001.
l mmm.*. .m.m.=. mm. l .4.
.+.‘.‘. .. ...*.*. ... .. . . . l ‘.*.*I* **4...
l .m.m.m lmm.. .‘.*.+ .*.**+m l .*2.* 44.
4.m.
mm.=.*. .. . . . . . 4.444.’
~‘I
i
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266
STRENGTH
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TRAINING
*
50
T4
+
E a 7 8 0
T
40
O”
30
k co 2
20
0
i= i= UJ CL W a
T T
10
0
E a 7 8 0 co Q cn /
INTERACTION
S+E
E
E+S FIG. 5. Repetitions with 80% 1 RM in group A (left) for S and S+E andgroup B (right) for E and E+S. Top: before (open bars) and after (stippled bars) training values. Bottom: increase in repetitions after training. Values are means k SE. Main effect before vs. after training: * P < 0.05; interaction: t P = 0.013 (S+E > S), tJ- P < 0.001 (E+S > E).
30
t
20
0 F
E CL w a
10
d 0
S
S+E
E
in ST (E, 4,864 t 1,318 to 4,786 t 375; E+S, 5,274 t 695 to 5,347 t 367) or FT (E, 5,590 t 687 to 5,543 t 291; E+S, 5,690 $- 555 to 6,299 & 457) fiber area. The FT-to-ST area ratio did not change (E, 1.14 t 0.08 to 1.17 k 0.07; E+S, 1.12 t 0.06 to 1.18 -t 0.05). DISCUSSION
The nominally designated strength (S) and endurance (E) training used in the present study had more in common as training stimuli than differences; thus in group A, the S leg made increases similar to the S+E leg in endurance-related measures of VOW max, repetitions with the pretraining leg press 1 RM, and %ST fibers; and S made significant, although smaller (vs. S+E), increases in repetitions with 80% -1RM, and CS activity. Similarly, in g?vup B, the E leg increased knee extensor CSA as much as the EN leg and made significant,
E+S
although smaller, increases in leg press 1 RM and thigh girth. Therefore the S and E training used in the present study might be considered hybrids rather than extreme or “pure” forms of S and E training. The hybrid nature of the E training was probably due in. part to the high intensity bouts (3 min at 90.100% vo 2 max) employed; such bouts might ensure endurance adaptations in fast- and slow-twitch motor units (8, 27), but they also induced increases in muscle size and strength. In addition, E training by cycling (necessitated in the present study because of the one leg training model) may be more likely to increase strength (31, 34) and muscle size (2, 12; see, however, 39) than, for example, by running. The S training consisted of sets of 15-20 repetitions with a weight ranging from 75-80% 1 RM at the start of training to 85-90% 1 RM by the end of training [by comparison only -5-10 repetitions can be done with 75-90% 1 RM in upper body exercises such
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INTERACTION
60 -
> u l--
N=5
3o
W u a. Q
3 CT
50-
&j
40-
m LL
20
cJ3 z
0
o\o
i= 6
lo
30 -
Q k!
20 -
0
c 60 -
> a: 7 W
N=4
6o cJ2
E k
40
co z
0
I%
m LL
5o
)co
40-
T
8
F i= W CL
20 30 -
ii? 0
20 -
E
E+S
1
E
E+S
6. Repetitions done, after training, with the heaviest weight that could be lifted for 1 repetition before training in group A (top) for S and S+E and group B (bottom) for E and E+S. Values are means k SE. Interaction (E+S > E): 7 P < 0.05,
7. Percent slow-twitch (ST) of vastus lateralis in group A (top) for S and S+E and group B (bottom) for E and E+S. Values are means + SE for before (open bars) and after (stippled bars) training. Main effect before vs. after training: * P = 0.007, ** P < 0.001.
as the bench press (35) and arm curl (30)]. Although the intensity (%l RM) was appropriate for effective strength training, the number of repetitions per set (15-20) and per training session (90-120) might be considered high (there were -900 contractions in each endurance training session). The S program was successful in inc:easing strength and muscle size, but it also increased Voz max (perhaps due in part to a “central” effect from endurance training of the other leg), weight lifting endurance, and CS activity. When S and E training are done concurrently they may not interact at all; i.e., the concurrent training would cause the same strength and endurance adaptations as S and E training done alone. They may interact to cause antagonism; i.e., strength and/or endurance adaptations would be less than in response to S or E training alone. Or they may interact to cause “addition”; i.e., strength and endurance adaptations would be greater than in response to S and E training alone. Whether interaction occurs and the form it takes probably depend on several factors: the intensity, volume, and frequency of the two types of training; the training modes; the training status
of the subjects; and the way the two forms of training are integrated. Furthermore, the results and conclusions drawn will be affected by the selected criterion measures of strength and endurance development. These factors must be considered in the interpretation of the present and previous studies (3, 9, 10, 14, 15, 19). Antagonism did not occur in the present study, probably because of the hybrid nature of the S and E training involved and the moderate total volume of training. However, previous studies have shown antagonism in the form of impaired strength development (9, 14, 19). Antagonism may have occurred in these studies because of the greater volume of training used (14) or the criterion measure of adaptation used [e.g., impaired high- but not low-velocity isokinetic strength development (9)]. Generally, antagonism may be more likely to occur when large volume extreme forms of S and E training are done concurrently (e.g., marathon run training and competitive weight lifting). In regard to a possible additive effect of combined strength and endurance training, an interesting pattern was found. When a presumably stronger stimulus for a
FIG.
FIG.
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FIG. 8. Citrate synthase (CS) activity in group A (left) for S and S+E and group B (right) for E and E+S. Top: before (open bars) and after (stippled bars) -training-values. Bottom: increases after training. Values are means k SE. Main effect before vs. after training: * P = 0.003, ** P c 0.001; interaction (S+E
1 >S):tP=0.005.
t **
S
S+E
E
given adaptation was added to a weaker stimulus, addition sometimes occurred, but when a weaker stimulus was added to a stronger one, addition did not occur. Thus in group A (S vs. S+E) the addition of E training was additive for increases in endurance (repetitions at 80% 1 RM) and CS activity, although S training alone caused significant increases in these measures. Similarly, in group B (E vs. E+S) the addition of S training was additive for increases in strength and one measure of muscle size (thigh girth), although E training alone caused significant increases in these measures. On the other hand, E training was not additive for increases in strength and muscle size (S vs. S+E), although E training alone caused increases in these measures, nor was S training additive for increases in VOW maxand CS (E vs. E+S), although S training alone caused increases in these measures. An exception was that S training was additive for short-term endurance. The endurance tests were done on the S training device; therefore, the increased endurance was probably partly related to improved strength, skill, and efficiency in the exercise movement in the course of S training.
E+S The training status of the subjects may determine whether antagonism or addition occurs in concurrent strength and endurance training. In previously untrained subjects, endurance development is not impaired (9, 14, 19, present study) and may be enhanced (present study); strength development may (9,14,19) or may not (present study) be impaired. In previously endurance-trained subjects who continue endurance training but add strength training, strength (19) and endurance (15) development may be enhanced. We chose for the present study a training model that provided a within-subject control and evaluation of interaction between concurrent strength and endurance training. Thus group A trained for both strength and endurance in one leg and strength only in the other leg, whereas group B trained for both strength and endurance in one leg and endurance only in the other leg. This model avoided the variability in training response between separate groups containing a small number of subjects. For example, a particular group, despite random assignment of subjects, might by chance contain more trainable subjects. This group would make a greater
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STRENGTH
AND ENDURANCE
- T
S
E
S+E
E+S
-
T
l-
T
T
E E+S S SE 9. Mitochondrial (V, *it) (top) and lipid (V, lip) (bottom) volume density of vastus lateralis in group A &jQ for S and S+E and group B (right) for E and E+S. Values are means +: SE for before (open bars) and after (stippled bars) training. FIG.
response to training, regardless of the method of training. This problem would be minimized with larger groups. The within-subject model used in the present study had at least one limitation. The model was chosen on the assumption that a major part of any interaction (antagonism or addition) caused by concurrent strength and endurance training would be expressed at the peripheral muscle level in measures such as muscle cross-sectional area and enzyme activity. If antagonism or addition occurred but were expressed entirely as a “central” phenomenon, then in our subjects even the legs that did only strength or endurance training would have been affected in the same way as the legs that did combined strength and endurance training. Antagonism or addition would not have been revealed. In the study by Hickson (14), there was evidence that antagonism may in some instances be entirely central (e.g., central nervous system fatigue); voluntary strength development was impaired by concurrent strength and endurance training, but increases in muscle size (indicated by thigh girth measurements) were not impaired. In comparison we found no impairment of strength or muscle size development, but we cannot exclude the possibility that some entirely centrally mediated antagonism occurred in our study. It can be concluded, however, that no peripherally (muscle) mediated antagonism occurred.
TRAINING
INTERACTION
269
In conclusion, one finding of the present study that does not bear directly on the main purpose nevertheless deserves comment. The percent of ST fibers in vastus lateralis increased after -5 mo of training. An increase or any change in %ST fibers after strength or endurance training in humans is unusual but not unprecedented (21, 38, 40). Detraining has been associated with a decrease in %ST fibers (23). Any observed change in fiber type composition raises the issue of the methodological errors associated with determining %ST fibers from single biopsy samples from a large muscle. These errors (e.g., Ref. 4, 24) and their bearing on the interpretation of findings of changes in %ST fibers have been discussed recently elsewhere (23,38). In the present study the preand posttraining biopsy samples were not analyzed in a single batch but rather 5 mo apart, raising the possibility that a difference in the pH or temperature of the preincubation medium in the two analyses caused a systematic error in the staining and subsequent determination of %ST fibers. However, this possibility is diminished by the consideration that a difference of at least several tenths of a pH unit would be necessary to affect the differentiation of the main fiber types (ST vs. FT). Nevertheless, our observed change in %ST fibers should be viewed with caution. The authors thank J. Moroz for general assistance; J. Laufer, T. Brown, and D. Kerrigan-Brown for technical assistance; A. Brown and D. Moroz for coordinating the study; and L. Diskin for secretarial assistance. This study was supported by the Dept. of National Defence, Canada (DCIEM Contract 8SE85-00082) and the Natural Sciences and Engineering Research Council of Canada. Address for reprint requests: D. G. Sale, Dept. of Physical Education, McMaster University, Hamilton, Ontario L8S 4Kl, Canada. Received 14 September 1988; accepted in final form 28 August 1989. REFERENCES 1. ANDERSEN, P. Capillary density in skeletal muscle of man. Acta Physiol. Stand. 95: 203-205, 19’75. 2. ANDERSEN, P., AND J. HENRIKSSON. Capillarysupplytothequadriceps femoris muscle of man: adaptive response to exercise. J. Physiol. Land. 270: 677, 1977. 3. BELL, G. J,, S. R. PETERSEN, H. A. QUINNEY, AND H. A. WENGER. Sequencing of endurance and high-velocity strength training. Can. J. Sport Sci. 13: 214-219, 1988. 4. BLOMSTRAND, E., AND B. EKBLOM. The needle biopsy technique for fiber type determination in human skeletal muscle-a methodological study. Actu Physiol. Scund. 116: 437-442, 1982. 5. COSTILL, D. L. The relationship between selected physiological variables and distance running performance. J. Sports Med. Phys. Fitness 7: 61-66, 1967. 6. COSTILL, D. L., E. F. COYLE, W. F. FINK, G. R. LESMES, AND F. A. WITZMANN. Adaptations in skeletal muscle following strength training. J. Appl. Physiol. 46: 96-99, 1979. 7. DENIS, C., J.-C. CHATARD, D. DORMOIS, M.-T. LINOSSIER, A. GEYSSANT, AND J.-R. LACOUR. Effects of endurance training on capillary supply of human skeletal muscle on two age groups (20 and 60 years). J. Physiol. Puris 81: 379-383, 1986. 8. DUDLEY, G. A., W. M. ABRAHAM, AND R. L. TERJUNG. Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle. J. Appl. Physiol. 53: 844-850, 1982. 9. DUDLEY, G. A., AND R. DJAMIL. Incompatibility of endurance- and strength-training modes of exercise. J. Appl. Physiol. 59: 14461451,1985. 10. DUDLEY, G. A., AND S. J. FLECK. Strength and endurance training. Are they mutually exclusive? Sports Med. 4: 79-85, 1987. 11. ESSEN, B., A. LINDHOLM, AND G. THORTON. Histochemical prop-
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D., AND D. SALE. Continuous vs. interval training: a review for the coach and athlete. Can. J. AppZ. Sport Sci. 6: 93-
erties of muscle fibre types and enzyme activities in skeletal muscle of standard-bred trotters of different ages. Equine Vet. J. 12: 1751&0,19&0. 12. GOLLNICK, P. D., R. B. ARMSTRONG, B, SALTIN, C. W. SAUBERT IV, W. L. SEMBROWICH, AND R. E. SHEPHERD. Effect of training on enzyme activity and fiber composition of human skeletal muscle. J. AppZ. Physiol. 34: 107-111, 1973. 13. GUTH, L., AND F. J. SAMAHA. Qualitative differences between actomyosin ATPase of slow and fast mammalian muscle. Ex~.
27. MACDOUGALL,
NeuroZ. 25: 138-152, 1969. 14. HICKSON, R. C. Interference
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