Endurance training of older men: responses to submaximal exercise MARC J. POULIN, DONALD H. PATERSON, DEVIN GOVINDASAMY, AND DAVID A. CUNNINGHAM Faculty of Kinesiology and Department of Physiology, The University of Western Ontario, London, Ontario N6A 3K7, Canada
by a factor of two- to fivefold (depending on POULIN, MARCJ.,DONALD H. PATERSON,DEVINGOVINDA- intensity) the intensity). SAMY, AND DAVID A. CUNNINGHAM. Endurance training of older men: responses to submaximal exercise. J. Appl. Physiol. 73(2): In the present study these concepts of endurance ca452-457,1992.-The purposeof this study wasto quantify the pacity were examined in older men (67 yr). The purposes
exercise responseof older subjectson a time-to-fatigue (TTF) submaximal performance test before and after a training program. Eight older men (67.4 t 4.8 yr) performed two maximal treadmill tests to determine maximum oxygen uptake (vo2 -) and ventilation threshold (TvJ and a constant-load submaximal exercise treadmill test that required an oxygen uptake (vo,) between TvE and vo2,. The submaximal test, performed at the sameabsolute work rate before and after the training program, was performed to volitional fatigue to measureendurancetime. The men trained under supervision at an individualized pace representing -70% of VO, max(80% maximum heart rate) for 1 h, four times per week for 9 wk. Significant increaseswere demonstratedfor VO, max(ml kg-’ min-‘; 10.6%); maximal ventilation (VE, Urnin; 11.6%), and TvE (l/ min; 9.8%). Weight decreased2.1%. Performance time on the TTF test increasedby 180% (7.3 t 3.0 to 20.4 t 13.5 min). The similar end points for TO,, VE, and heart rate during the TTF and maximal treadmill tests establishedthat the TTF test was stopped becauseof physiological limitations. The increase in performance time among the subjectswas significantly correlated with improvements in VO, - and TvE, with the submaximal work rate representing. a voz above TvE by 88% of the difference betweenTvE and VO, maxpretraining and 73% of this difference on posttraining values. l
l
were to determine TTF (endurance time) during a submaximal treadmill test, before and after a 2-mo exercise training program, to describe the changes in physiological responses during submaximal exercise performance, and to examine the relationship of changes in performance TTF in relation to TO, m8xand TvE. An age-related decline in cardiorespiratory capacity is well documented in terms of lower maximal aerobic power, maximal heart rate (HR,,), stroke volume, and cardiac output (3, 19, 28). A loss of muscle strength has also been associated with advancing age (25,28).In older individuals, these losses in maximal performance and a relatively high TvE (4) result in a reduced reserve capacity for vigorous work (4) and may make some daily activities that are crucial for an independent life-style fatiguing and unpleasant to perform (7a). With several months of endurance training of older men and women, Oo, m8xis improved lo-25% (6,18). The impact of tiaining-induced changes, as reflected in maximum measures, on the ability to perform submaximal work tasks is not well known. METHODS
Subjects. A group of 10 older males was recruited. Parmaximum oxygen uptake; ventilation threshold; fatigue; aging ticipants had not taken part in any regular organized
IT WAS DEMONSTRATED by Gleser and Vogel (8) that ex-
ercise endurance time vs. . work intensity [relative to maximum oxygen uptake (VO,,,)] was described by an exponential decay curve and this curve defined an individual’s “endurance capacity.” This relationship between relative work intensity ( %VO, m,) and exercise duration or time-to-fatigue (TTF) has been described for young untrained subjects (8,9) and for well-trained individuals and elite athletes (16). Additionally, McLellan and Skinner (9) found that when exercise intensity was expressed relative to ventilation threshold (Tv,J and 2max, rather than Vo2mar alone, the standard error of the estimate for endurance times was reduced by 30%. Thus, with endurance training, a lo-20% increase in . vo 2max and/or TvE should translate into improvements in endurance time at a given work. rate (relatively lower l
vo
452
physical activity during the previous 3 mo. The study requirements were fully explained to each participant, and each signed an informed consent approved by The University Committee for Research Involving Human Subjects. One subject dropped out of the training program and a second subject was forced to withdraw to undergo elective surgery, which left a sample size of eight completing the study. Testing procedures. The subjects completed a battery of physiological tests over two sessions within a 2-wk period. Subjects were advised not to eat,. smoke, or drink coffee during the 2 h preceding their testing session. All exercise tests were carried out in an air-conditioned laboratory (mean temperature 22.O”C). The first laboratory session included a medical history; 12-lead electrocardiogram; anthropometric measurements including height, weight, and four skinfold thicknesses (triceps, biceps, subscapular, and suprailiac); assessment of leisure activity; and two treadmill (ramp)
0161~Pi67192 $2.00 Copyright 0 1992 the American Physiological
Society
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ENDURANCE TRAINING
453
OF OLDER MEN
point, while the subject straddled the treadmill belt, the
tests to determine Voz,,, and TvE. The two treadmill ramp tests were administered 20-30 min apart with the maximal higher maximum chosen. Two continuous
speed and grade were adjusted (requiring -20 s) to the work rates predicted to elicit the desired 60,. The sub-
treadmill
jects then stepped on the moving treadmill belt, eliciting
tests
allowed
an accurate
assessment
of the
cardiorespiratory after endurance
fitness of elderly males before and training (23). The criteria for stopping the exercise tests were those recommended by the American College of Sports Medicine (1). No tests, however, had to be stopped because of the criteria set forth; rather,
a “square wave” onset of 0, demand. The subjects were verbally encouraged to maintain the work rate as long as possible. The criteria for stopping the test were if 1) the subject signaled he could no longer continue, and the treadmill was then slowed and grade reduced, or 2) the
all tests were to the point of subject volitional
subject grasped the handrails to keep up with the moving
fatigue.
During the maximal treadmill and TTF performance tests, the subjects breathed through a mouthpiece connected to a bidirectional turbine flowmeter (model VMM 110, Alpha Technologies) that measured inspired and expired gas flow rates. The turbine was calibrated daily by
belt or straddled rating perceived
pumping
each participant was based on the 90~ maxachieved on the
IO strokes
of a known
volume
(3.01 liters)
back
the belt. During the test a measure exertion (RPE) using a modified point Borg scale (IO) was obtained every 2 min. Training program. The training program consisted four sessions per week for 9 wk. Training intensity
of lo-
of for
and forth through the turbine. The resultant correction initial exercise tests. The method for determining the factors were used to determine inspired and expired gas training intensity has been described in detail (5). volumes. A mass spectrometer (Perkin Elmer 1100 MediBriefly, the 90, max(in ml kg-l min-‘) achieved during cal Gas Analyzer) was used to continuously analyze in- the ramp test was converted to metabolic equivalents spired and expired gases at a sampling rate of 1 ml/s from and the training intensity in terms of metabolic equivathe sampling port attached distally to the mouthpiece. lents (-70% VOz ,,,) was converted to a walking or jogThe mass spectrometer was calibrated daily, before each ging velocity determined from the formula for the energy testing session, with precision-analyzed gas mixtures. cost of walking or jogging (5). This intensity was mainHR was monitored from a continuous electrocardiogram tained for 4 wk, and then a new prescription was given to with electrodes attached in a modified V-5 configuration. the participants on the basis of a retest during week 4. Data sampling was under the direction of a microcomThis new intensity was held constant for the remaining puter and analog-to-digital converter. The analog signals 5 wk. were sampled and digitized every 10 ms. Changes in gas Exercise leaders provided individual guidance to the concentration signals were aligned with volume meaparticipants. Each training session consisted of a lo- to sures by measuring the time delays for a bolus of gas 15min warm-up that included specific stretching and passing the turbine to result in changes in 0,, CO,, and strength exercises, -30 min of walking or jogging at an N, of the mass spectrometer. Inspired and expired raw individualized pace, an .d a 10-m in warm-down. The men data were converted into breath-by-breath results with were provided with log books In which they recorded disuse of the algorithms of Beaver et al. (2). Two independent viewers, blinded to the subjects’ names and tests, tance covered, time spent at their prescribed pace, and exercis e HR. Organized exercise sessions were held on an analyzed the graphs for Tv, using the detection criteria indoor 200-m track during poor or cold weather condidescribed by Davis et al. (7). The maximal treadmill protocol was initiated with a tions and on an outdoor 400-m track during moderate 2-min warm-up at a walking velocity of 1.07 m/s and 0% and wa rm temperatures. Data analyses. Compa risen s of pre- to posttraining grade. The velocity and grade changes occurred in small were made using paired t tests. Pearson product-moment increments every 15-20 s to elicit a ramplike test. The protocols were designed to elicit 0, demand increases of correlations were used to examine relationships between 3 or 4 ml kg-l mine1 each minute with the protocol se- TTF and changes in VO, maxand TvE. The 0.05 level was lected for each subject to result in a test of 8-12 min in adopted as the minimal level for statistical significance. duration. Subjects were verbally encouraged throughout the test. At the end of the test, the subjects walked for 2 RESULTS min at 0% grade and at 1.07 m/s to properly warm-down. Subject characteristics. Eight men aged 67.4 t 4.8 (SD) During the second laboratory session, a constant-load yr (range 60-75 yr) and of mean height (176.0 * 5.0 cm) submaximal treadmill test was performed to volitional fatigue. The treadmill speed and grade for the test were completed the 9-wk training program. Over this course, by 2.1% (79.6 t 13.5 to determined from the maximal treadmill test such that it weight decreased significantly 78.0 t 14.2 kg), although the sum of four skinfolds was would require a 00, between the TvE and 6ozrnax and unchanged (52.8 k 16.4 to 52.5 t 16.3 mm). The men elicit fatigue in -10 min. The test protocol for different individuals involved a range of speed from 1.24 to 1.57 ranked themselves as “more active than most people they knew” on a five-point activity level questionnaire m/s and grade from 10.5 to 14.3%. The 0, demand during the tests was expressed relative to the TvE and Vo2 maxof that ranged from “I am one of the most active people I l
l
l
each individual [(exercising Vo,(l/min) - T&l/min)] x 1OO . WO 2 max (l/min) - T&/min)] and referred to as the AGO,. The protocol was initiated Avo,(%)
l
=
with a Z-min warm-up at a velocity of 1.07 m/s. At this
know” to “I am one of the least active people I know? Training program. The cardiorespiratory walk/jog component averaged w 30 min/session, with HRs averaging 131 beats/min, corresponding to a training intensity of --80% of HR,,,. The walk or jog velocity averaged 8.1 km/h (2.25 m/s) during Lveehsl-4 and progressed to 8.7
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454
ENDURANCE
TRAINING
1. Responsesduring maximal treadmill exercise before and aft& 9 wk of endurance training of elderly men
TABLE
Variable
V02 max,l/min VOW-, ml 8kg-l. min -1 VCOz ms, llmin klaX9 l/min BTPS beats/min Imlmx~ Rmllax TvE, llmin Tv*, %VO~-, l/min HR at TvE, beats/min RER at Tvp,
Pretraining
2.44t0.28 31.2k5.0 2.78t0.28 94.2d3.9 162.6k14.5
1.15t0.04 1.74t0.20 71.5t7.4 119.Ok9.0 0.88t0.05
Posttraining
2.6320.30" 34.5*6.0* 2.93*0.28* 105.ltl7.1*
158.ltlO.O 1.13_to.o5 1.91t0.18* 72.71k5.7 116.4tB.O 0.89t0.04
Values are means ,t SD for 8 men (age 67.4 t 4.8 yr). VO, -, -, VE,,, HR,,, and RER,,, maximum oxygen uptake, CO, production, ventilation, heart rate, and respiratory exchange ratio, respectively; TvE, ventilation threshold. * Difference is significant at P < ho2
0.05.
km/h (2.42 m/s) during weeks 5-9. The frequency of cardiorespiratory training was four sessions per week (complete compliance). Maximal treadmill test. All treadmill tests were completed to the point of volitional fatigue. There was no significant difference in Vo2,,, on the duplicate tests (pretest 2.36 and 2.42 Urnin; posttest 2.51 and 2.63 11 min). The test-retest correlation coefficients for VO, max were 0.91 between pretraining tests and 0.99 on the posttrainin .g tests. For the pre- and posttests tha ,t showed the higher Vo2, al 1 subjects met the criteria of a plateau in VO, with increasing work rate or an respiratory exchange ratio (RER) A.15. The majority of the tests (75%) resulted in a plateau in VOW. Only four tests showed an increase of VO, by >70 ml with the continued increase in work rate demanding 140 ml over the last 30 s of the tests. RER was >1.15 in six of eight subjects on the pretests and seven of eight subjects on the posttests. The test-retest correlation coefficients for Tv* were 0.94 (Pretest) and 0 .88 (posttes t). Interobserver differences i n determining TvE were small and nonsignificant (l-3%). The interobserver correlation coefficients for pre-TvE and post-TvE were 0.94 and 0.93, respectively. Over the 9-wk training period, VO, m8Xincreased significantly by 7.8 (Urnin) or 10.6% expressed relative to body weight. TvE (Urnin) was increased by 9.8%. TvE as a percent of VO, max(71.5-;72.7%) did not change significantly. HR and RER at TvE were not changed significantly (Table 1). TTF submaximaL test. Performance time on the TTF test increased significantly over the 9-wk training period by 180% (7.3 t 3.0 to 20.4 t 13.5 min). VO, after 3 min of the test at constant grade and speed pre- &d posttraining was not significantly changed. Small but significant increases of vo from a presumed steady state at 3 min into the test toti e values at 5 min were observed, but this “drift” was unchanged over the training period (Table 2). The rel .ative intensities were lower on the posttest such that at 3 min of exercise on the posttest compared with the pretest, the intensity expressed as the AGO,was 72.9 t 26.5 compared with 88.1 t 17.9% and expressed as %h maxwas 92.5 t 6.5 vs. 97.2 t 3.7. The HR and RER at 5 min were significantly lower during the posttest
OF OLDER
MEN
compared with the pretest. The HR was 10 beats/min or 6.6% lower (156 t 16 to 146 t 11 beats/min) and RER was also 6.6% lower (1.13 t 0.06 to 1.06 t 0.08). Compared with the measurements at the time of fatigue during the pretest (average 7.3 min), at the same time during the posttest, RPE was lower (6.3 compared with 9.0) as was HR (147 beats/min compared with 163 beats/min; Table 2). At the point of fatigue, the physiological results (Vo2, VE, HR, and RER) were close to the end points recorded from the maximal treadmill test. On the pretest, TO,, VE, HR, and RER were not significantly different although RER was slightly lower (Fig. 1). During the posttest, voa and VE were the same on the fatigue test as on the maximal treadmill test, whereas HR and RER were significantly lower during the fatigue test (Fig. 1). At fatigue, RPE during the pretest was 9.0 t 1.4 and during the posttest RPE was 8.4 t 2.5. Correlations. The critical r for a significant correlation coefficient was >0.66. The correlation coefficient for increases in performance with increases in Vozrnaxwas not significantly different from zero (Fig. 2A); however, for the changes in relative intensity expressed as the "AVON"there was a higher correlation (r = 0.63; Fig. 2B) and the percent increase in performance showed a significant correlation with the percent decrease in AVo, (r = 0.69). Thus those who increased their performances the most had the largest decreases in relative intensity (corresponding to larger increases in To2 m8xand/or T&. DISCUSSION
The data of the present study are consistent with the concept that adaptations to aerobic training result in substantial increases in endurance capacity during constant-work submaximal exercise. With a short-term endurance training program for older men the performance duration of heavy submaximal exercise was increased by a factor of 2.8 times the pretraining value. The phenomenon that endurance time can increase by a factor of two to four, whereas Vozmaxvaries by only 10 or 20%, has been explained by Gleser and Vogel (8) in terms of data that show endurance time is a function of the relative intensity and increases exponentially with decreasing rel2. Physiological responsesto the same time-to-fatigue performance test before and after 9 wk of endurance training TABLE
Variable
at 3 min, l/min at 5 min, llmin at fatigue, l/min RPE at fatigue RPE (posttest, T2 = Tl)$ HR, beatslmin (posttest, T2 = Tl)$ Time-to-fatigue, min V02 VO, V02
Pretraining
Posttraining
2.38t0.34 2.46k0.35 2.48t0.35 9.0tl.4 9.0t1.4
2.44t0.32 2.55t0.34 2.5620.34 8.4zk2.5 6.3k2.4.f
162.3k12.9 7.3t3.0 (5.0-14.0)
146.6HO.lt 20.4t13.5* (5.3-40.7)
Values are means t SD for 8 men; range in parentheses. RPE, rating of perceived exertion. * Difference is significant at P < 0.05. t Difference between posttest (T2 = Tl) and pretest (fatigue) is significant at P c 0.05. $ Values from posttest (T2) are at the time (same treadmill speed and grade) of the pretest (Tl) end point.
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ENDURANCE
TRAINING
OF OLDER
455
MEN
-OF -O-
post-
Pre-
Post-
Post-
Pre-
PO!+
n iOgax
Test
RI TTF Test
FIG. 1. Comparison of maximum oxygen uptake (vo2 max) and time-to-fatigue (TTF) performance tests on end points for oxygen uptake (VO,), heart rate (HR), resting ventilation (VE), and respiratory exchange ratio (RER). There were no significant differences between end points for pretests. Differences between tests indicated with connecting lines are significant at P < 0.05.
50
1 70
75
80
85
90
Relative Intensity B 50 45-
95
100
105
110
( %\jOamax) +
30
40 50 60 70 80 90 100 110 Relative Intensity (delta v02) FIG. 2. TTF in older men with 9 wk of endurance training. Individual data for pre- (0) and posttraining (0) are shown for endurance time expressed relative to %VO, maxof constant load exercise test (A) and as "AVON" (B). A: curve summarizes data of Gleser and Vogel (8).
n45-5 40535g302 25't- 20e 15.g lo+- 50,
A
::'
70
' 75
' 80
' 85
' 90
' 95
' 100
' 105
110
Relative Intensity ( %V02,,,) FIG. 3. TTF vs. relative intensity ( %voz m,). Curves A and B summarize data of Gleser and Vogel (8) and Saltin (17), respectively, for “endurance capacity” expressed as %VO, -. Mean data in older men are shown for pre- (0) and posttraining (0) TTF.
ative exercise rate. Our data for older men demonstrate a similar relationship between relative work rate and endurance time as that reported for young untrained individuals, and the threefold increase in endurance time during a heavy absolute work rate with a 10% increase in . vo 2 max (and reduction in relative intensity) conforms to that predicted from the graph of Saltin (16) constructed from data in well-trained young individuals (Fig. 3). The “endurance capacity” of these older men after the period of exercise training, when expressed as a relative intensity, closely approximates that of young athletes.
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456
ENDURANCE
TRAINING
Thus, despite losses in cardiorespiratory capacity with age and loss of physical activity, the endurance capacity at levels near maximum are only slightly reduced from those in young unfit men. The increase in this capacity is changed with training to an extent that the performance of the older men during heavy work is remarkably similar to that in young fit or athletic men. The improvement in performance was related to the degree of the reduction in the relative intensity of the constant-load exercise test, with relative intensity expressed in terms of the AVO, between TvE and Vozmax. Thus the largest increases in performance were witnessed in those who showed the greatest increases in both TvE and 60, max.In a study involving young subjects, when intensity was expressed relative to TvE and irO, max, rather than Vo2max alone, the standard error of the estimate for endurance times was reduced by 30% (9). Thus expressing relative intensity in terms of both TvE and 2max appears to provide a reasonable estimate of the expected improvement in performance at submaximal exercise. In the present study, with the AVO, reduced from 88 to 73% consequent to training, the performance duration increased from 7 to 21 min. Furthermore, as described by the exponential relationship of endurance time and relative exercise intensity, and as shown in Fig. 2B, the magnitude of increase in performance is even greater when the test involves a less strenuous relative intensity. In the present study the improvement in performance appears to be related to the domain of exercise intensity (defined as AVO,). Whipp and Ward (26, 27) have defined heavy-intensity exercise as that above the TvE or lactate threshold. During exercise above the TV*, the highest VO, at which steady state can be attained coincides with that at which blood lactate does not continue to rise (15). At higher work rates VO, continues to increase until VO 2m8Xis attained [a delayed slow $70, kinetic component (13)]. For the present data, on the pretest there was a lOO-ml/min increase in $70~ from minutes 3-7 with $70 2 I118X reached at fatigue, whereas on the posttest the slow component increase of Vo, was 120 ml/ min between minutes 3 and 21, but Oo, m8x was not achieved [at this rate of Vo2 increase it would have required an additional 10 min (70 ml/min) to achieve VO, max]. In studying the critical power for long-term work in older men, Overend et al. (12) observed that the critical power occurred at a Vo2 of 92% of Vo2max, and with 24 min of exercise at this intensity the blood lactate showed a slow, progressive increase to 6.5 mmol/l at the end of exercise. In the present study for four of the eight men the constant work on the posttest was below this critical power (92% Vo 2max) and these subjects showed the largest performance improvements. Thus it appears the large performance improvement was achieved by crossing a domain of exercise from that characterized by a continuing rise in lactate and VO, to a relatively lower intensity in which lactate and VO, achieved a relative steady state. In the present study, the similarity of the observed physiological end points served to establish that the TTF test was stopped because of physiological limitations. Thus the fatigue end points occurred at near-maximal l
vo
OF
OLDER
MEN
physiological values (e.g., HR, Vo2). In fact, the postTTF test, if anything, was terminated by volitional fatigue slightly earlier than achievement of maximal responses, with the RPE on the test posttraining lower than on the pretest. Thus the TTF improvement (180%) was at least as large as reported and may represent even greater changes had the subjects been able to achieve the physiological maximum (HR) on the posttest performance that was found on the pretest performance. In light of these findings it is unlikely that the submaximal exercise improvements could be accounted for by habituation to the treadmill (the men had experienced three or more exposures before their first TTF test) or by the “Hawthorne effect” because the fatigue was coincident with physiological end points. A control group was not tested in this study. Previous studies of middle-aged and older men have reported nonsignificant changes in physiological measures for control groups for similar or longer time periods (6, 7). The initial level of VO 2 m8xwas relatively high for men of this age (31 ml kg-l min-l) and the men perceived themselves to be relatively active. Nevertheless, with only 9 wk of training, Vo2max was increased 10.6%. Others (6, 20, 22, 24) have reported v02ma increases ranging from 10 to 20% in older subjects. In the present study significant decreases in HR (7%), RER (7%), and VE (3%) at the same work rate after the training program are similar to changes noted previously with training of older subjects (11,17,18). The submaximal exercise ventilatory equivalent for VO, decreased; an unchanged ventilatory equivalent for CO, production (VCO,) during the submaximal exercise is consistent with the finding of Davis et al. (7) that vE/h02 was unchanged by endurance training and demonstrates that VE changes were more closely related to VCO,than VO,. In regard to submaximal exercise responses with training of the elderly, Cunningham et al. (6) noted that the submaximal exercise improvements were greater than observed for vo 2 max. They reported an increase of 14.7% in VO, at HR of 125 beats/min compared with a 10% increase of vo 2max. In the study of elderly men by Tzankoff et al. (24), a standard walk (5.6 km/h, 9% grade) elicited a VO, requirement before training of 90% of VOGUE, and this was reduced to 79% of V02max after training. Tv, in older individuals has been reported to be higher, as a percentage of V02max, than in younger individuals. Declines in Vo2max over age from the 20’s to 60’s are found to be greater than the declines in TvE (4, 14) and thus explain the relatively high values for TvE as a percentage of V02 max. Daily activities of the elderly that are well below the threshold for improvement or maintenance of VO, maxmay be adequate to maintain TvZ (4). In the present study, regular training did increase Tv, ~10%. In middle-aged men, anaerobic threshold improved 44% after 9 wk of endurance training (7). On the other hand, no changes in TvE were found after endurance training in one study involving older men (21), although training frequency (2.9 sessions/wk) was lower than that of the present study or of previous training studies reporting changes in TvE. Thus, in the present study, short-term endurance training of elderly men elicited typical changes in irO, max l
l
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ENDURANCE
TRAINING
and submaximal exercise responses as well as a significant increase in TvE. The increased TvE and VO, maxwere associated with large improvements in the duration of performance of heavy exercise. These 1.arge improvements in exe Nrcise endu rance capacity are clearly important to daily function of older individuals. This work was supported in part by the Ontario Ministry of Tourism and Recreation, the Natural Sciences and Engineering Research Council of Canada, and The Centre for Activity and Ageing (Affiliated with The University of Western Ontario and The Lawson Research Institute at the St. Joseph’s Health Centre). M. J. Poulin was supported by an Advanced Studies Bursary (Gerontology Research Council of Ontario) and is a Fellow of the Ontario Ministry of Health, Health Research Development Program. Address for reprint requests: D. A. Cunningham, Centre for Activity and Ageing, Faculty of Kinesiology, Thames Hall, The University of Western Ontario, London, Ontario N6A 3K7, Canada. Received 5 September 1991; accepted in final form 26 February 1992.
OF OLDER
11 ORLANDER, J., AND A. ANIANSSON. Effects of physical training on skeletal muscle metabolism and ultrastructure in 70 to 75-year-old men. Acta Physiol. Stand. 109: 149-154, 1980. 12 OVEREND, T. J., D. A. CUNNINGHAM, D. H. PATERSON, AND W. D. F. SMITH. Critical power in young and elderly men. Can. J. Physiol. Pharmacol. 69: AXXlV, 1991. 13. PATERSON, D. H., AND B. J. WHIPP. Asymmetries of oxygen uptake transients at the on- and off-set of heavy exercise in humans. J. Physiol.
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Philadelphia,
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J. S. SKINNER. Submaximal endurance performance related to the ventilation thresholds. Can. J. Appl. T. M.,
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V. BORG, I. JACOBS, R. CECI, AND P. KAISER. A category-ratio perceived exertion scale: relationship to blood and muscle lactates and heart rate. Med. Sci. Sports Exercise 15: 523528,1983.
443: 575-586,
1991.
14. REINHARD, U., P. H. MULLER, AND R. M. SCHMULLING. Determination of anaerobic threshold by the ventilation equivalent in normal individuals. Respiration 38: 36-42, 1979. 15. ROSTON, W. L., B. J. WHIPP, J. A. DAVIS, R. M. EFFROS, AND K. WASSERMAN. Oxygen uptake kinetics and lactate concentration during exercise in man. Am. Rev. Respir. Dis. 135: 1080-1084,1987. 16. SALTIN, B. Oxygen transport during exercise: role of the cardiovascular system. In: Biological Effects of Physical Activity, edited by R. S. Williams and A. G. Wallace. Champaign, IL: Human Kinetics, 1989, p. 3-24. 17. SALTIN, B., L. H. HARTLEY, A. KILBOM, AND I. ASTRAND. Physical training in sedentary middle-aged and older men. Scand. J. Clin. Lab. Invest.
REFERENCES 1. AMERICAN COLLEGE
457
MEN
24: 323-334,
1969.
18. SEALS, D. R., J. M. HAGBERG, B. F. HURLEY, A. A. EHSANI, AND J. 0. HOLLOSZY. Endurance training in older men and women. Cardiovascular response to exercise. J. Appl. Physiol. 57: 1024-1029, 1984. and Aging. Kent, UK: Croom lg. SHEPHARD, R. J. Physical Activity 2. Helm, 1987, p. 167-192. . SUOMINEN, H., E. HEIKKINEN, H. LIESON, D. MICHEL, AND W. HOLLMANN. Effects of 8 weeks’ endurance training on skeletal muscle metabolism in 56-70 year-old sedentary men. Eur. J. Appl.
21. 22. 23. 24
Physiol. Occup. Physiol. 37: 173-180, 1977. THOMAS, S. G., D. A. CUNNINGHAM, J. THOMPSON, AND P. A. RECHNITZER. Exercise training and “ventilation threshold” in elderly. J. Appl. Physiol. 59: 1472-1476, 1985. THOMAS, S. G., D. A. CUNNINGHAM, P. A. RECHNITZER, A. P. DONNER, AND J. H. HOWARD. Determinants of the training response in elderly men. Med. Sci. Sports Exercise 17: 667-672, 1985. THOMAS, S. G., D. A. CUNNINGHAM, P. A. RECHNITZER, A. P. DONNER, AND J. H. HOWARD. Protocols and reliability of maximal oxygen uptake in the elderly. Can. J. Sports Sci. 12: 144-151, 1987. TZANKOFF, S. P., S. ROBINSON, F. S. PYKE, AND C. A. BRAWN.
’ Physiological adjustments to work ical training. J. Appl. Physiol. 33: 25. VANDERVOORT, A. A., K. C. HAYES, and endurance of skeletal muscle
in older men as affected by phys346-350, 1972. AND A. Y. BELANGER. Strength in the elderly. Physiother. Can.
38: 167-173,1986. 26. WHIPP, B. J. Dynamics of pulmonary gas exchange. Circulation 76, Suppl. VI: VI-18-VI-28, 1987. 27. WHIPP, B. J., AND S. A. WARD. Physiological determinants of pulmonary gas exchange kinetics during exercise. Med. Sci. Sports Exercise 22: 62-71, 1990. 28. YOUNG, A. Exercise physiology in geriatric practice. Acta Med. Stand. 711, Suppl.: 227-232, 1985.
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by a factor of two- to fivefold (depending on POULIN, MARCJ.,DONALD H. PATERSON,DEVINGOVINDA- intensity) the intensity). SAMY, AND DAVID A. CUNNINGHAM. Endurance training of older men: responses to submaximal exercise. J. Appl. Physiol. 73(2): In the present study these concepts of endurance ca452-457,1992.-The purposeof this study wasto quantify the pacity were examined in older men (67 yr). The purposes
exercise responseof older subjectson a time-to-fatigue (TTF) submaximal performance test before and after a training program. Eight older men (67.4 t 4.8 yr) performed two maximal treadmill tests to determine maximum oxygen uptake (vo2 -) and ventilation threshold (TvJ and a constant-load submaximal exercise treadmill test that required an oxygen uptake (vo,) between TvE and vo2,. The submaximal test, performed at the sameabsolute work rate before and after the training program, was performed to volitional fatigue to measureendurancetime. The men trained under supervision at an individualized pace representing -70% of VO, max(80% maximum heart rate) for 1 h, four times per week for 9 wk. Significant increaseswere demonstratedfor VO, max(ml kg-’ min-‘; 10.6%); maximal ventilation (VE, Urnin; 11.6%), and TvE (l/ min; 9.8%). Weight decreased2.1%. Performance time on the TTF test increasedby 180% (7.3 t 3.0 to 20.4 t 13.5 min). The similar end points for TO,, VE, and heart rate during the TTF and maximal treadmill tests establishedthat the TTF test was stopped becauseof physiological limitations. The increase in performance time among the subjectswas significantly correlated with improvements in VO, - and TvE, with the submaximal work rate representing. a voz above TvE by 88% of the difference betweenTvE and VO, maxpretraining and 73% of this difference on posttraining values. l
l
were to determine TTF (endurance time) during a submaximal treadmill test, before and after a 2-mo exercise training program, to describe the changes in physiological responses during submaximal exercise performance, and to examine the relationship of changes in performance TTF in relation to TO, m8xand TvE. An age-related decline in cardiorespiratory capacity is well documented in terms of lower maximal aerobic power, maximal heart rate (HR,,), stroke volume, and cardiac output (3, 19, 28). A loss of muscle strength has also been associated with advancing age (25,28).In older individuals, these losses in maximal performance and a relatively high TvE (4) result in a reduced reserve capacity for vigorous work (4) and may make some daily activities that are crucial for an independent life-style fatiguing and unpleasant to perform (7a). With several months of endurance training of older men and women, Oo, m8xis improved lo-25% (6,18). The impact of tiaining-induced changes, as reflected in maximum measures, on the ability to perform submaximal work tasks is not well known. METHODS
Subjects. A group of 10 older males was recruited. Parmaximum oxygen uptake; ventilation threshold; fatigue; aging ticipants had not taken part in any regular organized
IT WAS DEMONSTRATED by Gleser and Vogel (8) that ex-
ercise endurance time vs. . work intensity [relative to maximum oxygen uptake (VO,,,)] was described by an exponential decay curve and this curve defined an individual’s “endurance capacity.” This relationship between relative work intensity ( %VO, m,) and exercise duration or time-to-fatigue (TTF) has been described for young untrained subjects (8,9) and for well-trained individuals and elite athletes (16). Additionally, McLellan and Skinner (9) found that when exercise intensity was expressed relative to ventilation threshold (Tv,J and 2max, rather than Vo2mar alone, the standard error of the estimate for endurance times was reduced by 30%. Thus, with endurance training, a lo-20% increase in . vo 2max and/or TvE should translate into improvements in endurance time at a given work. rate (relatively lower l
vo
452
physical activity during the previous 3 mo. The study requirements were fully explained to each participant, and each signed an informed consent approved by The University Committee for Research Involving Human Subjects. One subject dropped out of the training program and a second subject was forced to withdraw to undergo elective surgery, which left a sample size of eight completing the study. Testing procedures. The subjects completed a battery of physiological tests over two sessions within a 2-wk period. Subjects were advised not to eat,. smoke, or drink coffee during the 2 h preceding their testing session. All exercise tests were carried out in an air-conditioned laboratory (mean temperature 22.O”C). The first laboratory session included a medical history; 12-lead electrocardiogram; anthropometric measurements including height, weight, and four skinfold thicknesses (triceps, biceps, subscapular, and suprailiac); assessment of leisure activity; and two treadmill (ramp)
0161~Pi67192 $2.00 Copyright 0 1992 the American Physiological
Society
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ENDURANCE TRAINING
453
OF OLDER MEN
point, while the subject straddled the treadmill belt, the
tests to determine Voz,,, and TvE. The two treadmill ramp tests were administered 20-30 min apart with the maximal higher maximum chosen. Two continuous
speed and grade were adjusted (requiring -20 s) to the work rates predicted to elicit the desired 60,. The sub-
treadmill
jects then stepped on the moving treadmill belt, eliciting
tests
allowed
an accurate
assessment
of the
cardiorespiratory after endurance
fitness of elderly males before and training (23). The criteria for stopping the exercise tests were those recommended by the American College of Sports Medicine (1). No tests, however, had to be stopped because of the criteria set forth; rather,
a “square wave” onset of 0, demand. The subjects were verbally encouraged to maintain the work rate as long as possible. The criteria for stopping the test were if 1) the subject signaled he could no longer continue, and the treadmill was then slowed and grade reduced, or 2) the
all tests were to the point of subject volitional
subject grasped the handrails to keep up with the moving
fatigue.
During the maximal treadmill and TTF performance tests, the subjects breathed through a mouthpiece connected to a bidirectional turbine flowmeter (model VMM 110, Alpha Technologies) that measured inspired and expired gas flow rates. The turbine was calibrated daily by
belt or straddled rating perceived
pumping
each participant was based on the 90~ maxachieved on the
IO strokes
of a known
volume
(3.01 liters)
back
the belt. During the test a measure exertion (RPE) using a modified point Borg scale (IO) was obtained every 2 min. Training program. The training program consisted four sessions per week for 9 wk. Training intensity
of lo-
of for
and forth through the turbine. The resultant correction initial exercise tests. The method for determining the factors were used to determine inspired and expired gas training intensity has been described in detail (5). volumes. A mass spectrometer (Perkin Elmer 1100 MediBriefly, the 90, max(in ml kg-l min-‘) achieved during cal Gas Analyzer) was used to continuously analyze in- the ramp test was converted to metabolic equivalents spired and expired gases at a sampling rate of 1 ml/s from and the training intensity in terms of metabolic equivathe sampling port attached distally to the mouthpiece. lents (-70% VOz ,,,) was converted to a walking or jogThe mass spectrometer was calibrated daily, before each ging velocity determined from the formula for the energy testing session, with precision-analyzed gas mixtures. cost of walking or jogging (5). This intensity was mainHR was monitored from a continuous electrocardiogram tained for 4 wk, and then a new prescription was given to with electrodes attached in a modified V-5 configuration. the participants on the basis of a retest during week 4. Data sampling was under the direction of a microcomThis new intensity was held constant for the remaining puter and analog-to-digital converter. The analog signals 5 wk. were sampled and digitized every 10 ms. Changes in gas Exercise leaders provided individual guidance to the concentration signals were aligned with volume meaparticipants. Each training session consisted of a lo- to sures by measuring the time delays for a bolus of gas 15min warm-up that included specific stretching and passing the turbine to result in changes in 0,, CO,, and strength exercises, -30 min of walking or jogging at an N, of the mass spectrometer. Inspired and expired raw individualized pace, an .d a 10-m in warm-down. The men data were converted into breath-by-breath results with were provided with log books In which they recorded disuse of the algorithms of Beaver et al. (2). Two independent viewers, blinded to the subjects’ names and tests, tance covered, time spent at their prescribed pace, and exercis e HR. Organized exercise sessions were held on an analyzed the graphs for Tv, using the detection criteria indoor 200-m track during poor or cold weather condidescribed by Davis et al. (7). The maximal treadmill protocol was initiated with a tions and on an outdoor 400-m track during moderate 2-min warm-up at a walking velocity of 1.07 m/s and 0% and wa rm temperatures. Data analyses. Compa risen s of pre- to posttraining grade. The velocity and grade changes occurred in small were made using paired t tests. Pearson product-moment increments every 15-20 s to elicit a ramplike test. The protocols were designed to elicit 0, demand increases of correlations were used to examine relationships between 3 or 4 ml kg-l mine1 each minute with the protocol se- TTF and changes in VO, maxand TvE. The 0.05 level was lected for each subject to result in a test of 8-12 min in adopted as the minimal level for statistical significance. duration. Subjects were verbally encouraged throughout the test. At the end of the test, the subjects walked for 2 RESULTS min at 0% grade and at 1.07 m/s to properly warm-down. Subject characteristics. Eight men aged 67.4 t 4.8 (SD) During the second laboratory session, a constant-load yr (range 60-75 yr) and of mean height (176.0 * 5.0 cm) submaximal treadmill test was performed to volitional fatigue. The treadmill speed and grade for the test were completed the 9-wk training program. Over this course, by 2.1% (79.6 t 13.5 to determined from the maximal treadmill test such that it weight decreased significantly 78.0 t 14.2 kg), although the sum of four skinfolds was would require a 00, between the TvE and 6ozrnax and unchanged (52.8 k 16.4 to 52.5 t 16.3 mm). The men elicit fatigue in -10 min. The test protocol for different individuals involved a range of speed from 1.24 to 1.57 ranked themselves as “more active than most people they knew” on a five-point activity level questionnaire m/s and grade from 10.5 to 14.3%. The 0, demand during the tests was expressed relative to the TvE and Vo2 maxof that ranged from “I am one of the most active people I l
l
l
each individual [(exercising Vo,(l/min) - T&l/min)] x 1OO . WO 2 max (l/min) - T&/min)] and referred to as the AGO,. The protocol was initiated Avo,(%)
l
=
with a Z-min warm-up at a velocity of 1.07 m/s. At this
know” to “I am one of the least active people I know? Training program. The cardiorespiratory walk/jog component averaged w 30 min/session, with HRs averaging 131 beats/min, corresponding to a training intensity of --80% of HR,,,. The walk or jog velocity averaged 8.1 km/h (2.25 m/s) during Lveehsl-4 and progressed to 8.7
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454
ENDURANCE
TRAINING
1. Responsesduring maximal treadmill exercise before and aft& 9 wk of endurance training of elderly men
TABLE
Variable
V02 max,l/min VOW-, ml 8kg-l. min -1 VCOz ms, llmin klaX9 l/min BTPS beats/min Imlmx~ Rmllax TvE, llmin Tv*, %VO~-, l/min HR at TvE, beats/min RER at Tvp,
Pretraining
2.44t0.28 31.2k5.0 2.78t0.28 94.2d3.9 162.6k14.5
1.15t0.04 1.74t0.20 71.5t7.4 119.Ok9.0 0.88t0.05
Posttraining
2.6320.30" 34.5*6.0* 2.93*0.28* 105.ltl7.1*
158.ltlO.O 1.13_to.o5 1.91t0.18* 72.71k5.7 116.4tB.O 0.89t0.04
Values are means ,t SD for 8 men (age 67.4 t 4.8 yr). VO, -, -, VE,,, HR,,, and RER,,, maximum oxygen uptake, CO, production, ventilation, heart rate, and respiratory exchange ratio, respectively; TvE, ventilation threshold. * Difference is significant at P < ho2
0.05.
km/h (2.42 m/s) during weeks 5-9. The frequency of cardiorespiratory training was four sessions per week (complete compliance). Maximal treadmill test. All treadmill tests were completed to the point of volitional fatigue. There was no significant difference in Vo2,,, on the duplicate tests (pretest 2.36 and 2.42 Urnin; posttest 2.51 and 2.63 11 min). The test-retest correlation coefficients for VO, max were 0.91 between pretraining tests and 0.99 on the posttrainin .g tests. For the pre- and posttests tha ,t showed the higher Vo2, al 1 subjects met the criteria of a plateau in VO, with increasing work rate or an respiratory exchange ratio (RER) A.15. The majority of the tests (75%) resulted in a plateau in VOW. Only four tests showed an increase of VO, by >70 ml with the continued increase in work rate demanding 140 ml over the last 30 s of the tests. RER was >1.15 in six of eight subjects on the pretests and seven of eight subjects on the posttests. The test-retest correlation coefficients for Tv* were 0.94 (Pretest) and 0 .88 (posttes t). Interobserver differences i n determining TvE were small and nonsignificant (l-3%). The interobserver correlation coefficients for pre-TvE and post-TvE were 0.94 and 0.93, respectively. Over the 9-wk training period, VO, m8Xincreased significantly by 7.8 (Urnin) or 10.6% expressed relative to body weight. TvE (Urnin) was increased by 9.8%. TvE as a percent of VO, max(71.5-;72.7%) did not change significantly. HR and RER at TvE were not changed significantly (Table 1). TTF submaximaL test. Performance time on the TTF test increased significantly over the 9-wk training period by 180% (7.3 t 3.0 to 20.4 t 13.5 min). VO, after 3 min of the test at constant grade and speed pre- &d posttraining was not significantly changed. Small but significant increases of vo from a presumed steady state at 3 min into the test toti e values at 5 min were observed, but this “drift” was unchanged over the training period (Table 2). The rel .ative intensities were lower on the posttest such that at 3 min of exercise on the posttest compared with the pretest, the intensity expressed as the AGO,was 72.9 t 26.5 compared with 88.1 t 17.9% and expressed as %h maxwas 92.5 t 6.5 vs. 97.2 t 3.7. The HR and RER at 5 min were significantly lower during the posttest
OF OLDER
MEN
compared with the pretest. The HR was 10 beats/min or 6.6% lower (156 t 16 to 146 t 11 beats/min) and RER was also 6.6% lower (1.13 t 0.06 to 1.06 t 0.08). Compared with the measurements at the time of fatigue during the pretest (average 7.3 min), at the same time during the posttest, RPE was lower (6.3 compared with 9.0) as was HR (147 beats/min compared with 163 beats/min; Table 2). At the point of fatigue, the physiological results (Vo2, VE, HR, and RER) were close to the end points recorded from the maximal treadmill test. On the pretest, TO,, VE, HR, and RER were not significantly different although RER was slightly lower (Fig. 1). During the posttest, voa and VE were the same on the fatigue test as on the maximal treadmill test, whereas HR and RER were significantly lower during the fatigue test (Fig. 1). At fatigue, RPE during the pretest was 9.0 t 1.4 and during the posttest RPE was 8.4 t 2.5. Correlations. The critical r for a significant correlation coefficient was >0.66. The correlation coefficient for increases in performance with increases in Vozrnaxwas not significantly different from zero (Fig. 2A); however, for the changes in relative intensity expressed as the "AVON"there was a higher correlation (r = 0.63; Fig. 2B) and the percent increase in performance showed a significant correlation with the percent decrease in AVo, (r = 0.69). Thus those who increased their performances the most had the largest decreases in relative intensity (corresponding to larger increases in To2 m8xand/or T&. DISCUSSION
The data of the present study are consistent with the concept that adaptations to aerobic training result in substantial increases in endurance capacity during constant-work submaximal exercise. With a short-term endurance training program for older men the performance duration of heavy submaximal exercise was increased by a factor of 2.8 times the pretraining value. The phenomenon that endurance time can increase by a factor of two to four, whereas Vozmaxvaries by only 10 or 20%, has been explained by Gleser and Vogel (8) in terms of data that show endurance time is a function of the relative intensity and increases exponentially with decreasing rel2. Physiological responsesto the same time-to-fatigue performance test before and after 9 wk of endurance training TABLE
Variable
at 3 min, l/min at 5 min, llmin at fatigue, l/min RPE at fatigue RPE (posttest, T2 = Tl)$ HR, beatslmin (posttest, T2 = Tl)$ Time-to-fatigue, min V02 VO, V02
Pretraining
Posttraining
2.38t0.34 2.46k0.35 2.48t0.35 9.0tl.4 9.0t1.4
2.44t0.32 2.55t0.34 2.5620.34 8.4zk2.5 6.3k2.4.f
162.3k12.9 7.3t3.0 (5.0-14.0)
146.6HO.lt 20.4t13.5* (5.3-40.7)
Values are means t SD for 8 men; range in parentheses. RPE, rating of perceived exertion. * Difference is significant at P < 0.05. t Difference between posttest (T2 = Tl) and pretest (fatigue) is significant at P c 0.05. $ Values from posttest (T2) are at the time (same treadmill speed and grade) of the pretest (Tl) end point.
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ENDURANCE
TRAINING
OF OLDER
455
MEN
-OF -O-
post-
Pre-
Post-
Post-
Pre-
PO!+
n iOgax
Test
RI TTF Test
FIG. 1. Comparison of maximum oxygen uptake (vo2 max) and time-to-fatigue (TTF) performance tests on end points for oxygen uptake (VO,), heart rate (HR), resting ventilation (VE), and respiratory exchange ratio (RER). There were no significant differences between end points for pretests. Differences between tests indicated with connecting lines are significant at P < 0.05.
50
1 70
75
80
85
90
Relative Intensity B 50 45-
95
100
105
110
( %\jOamax) +
30
40 50 60 70 80 90 100 110 Relative Intensity (delta v02) FIG. 2. TTF in older men with 9 wk of endurance training. Individual data for pre- (0) and posttraining (0) are shown for endurance time expressed relative to %VO, maxof constant load exercise test (A) and as "AVON" (B). A: curve summarizes data of Gleser and Vogel (8).
n45-5 40535g302 25't- 20e 15.g lo+- 50,
A
::'
70
' 75
' 80
' 85
' 90
' 95
' 100
' 105
110
Relative Intensity ( %V02,,,) FIG. 3. TTF vs. relative intensity ( %voz m,). Curves A and B summarize data of Gleser and Vogel (8) and Saltin (17), respectively, for “endurance capacity” expressed as %VO, -. Mean data in older men are shown for pre- (0) and posttraining (0) TTF.
ative exercise rate. Our data for older men demonstrate a similar relationship between relative work rate and endurance time as that reported for young untrained individuals, and the threefold increase in endurance time during a heavy absolute work rate with a 10% increase in . vo 2 max (and reduction in relative intensity) conforms to that predicted from the graph of Saltin (16) constructed from data in well-trained young individuals (Fig. 3). The “endurance capacity” of these older men after the period of exercise training, when expressed as a relative intensity, closely approximates that of young athletes.
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456
ENDURANCE
TRAINING
Thus, despite losses in cardiorespiratory capacity with age and loss of physical activity, the endurance capacity at levels near maximum are only slightly reduced from those in young unfit men. The increase in this capacity is changed with training to an extent that the performance of the older men during heavy work is remarkably similar to that in young fit or athletic men. The improvement in performance was related to the degree of the reduction in the relative intensity of the constant-load exercise test, with relative intensity expressed in terms of the AVO, between TvE and Vozmax. Thus the largest increases in performance were witnessed in those who showed the greatest increases in both TvE and 60, max.In a study involving young subjects, when intensity was expressed relative to TvE and irO, max, rather than Vo2max alone, the standard error of the estimate for endurance times was reduced by 30% (9). Thus expressing relative intensity in terms of both TvE and 2max appears to provide a reasonable estimate of the expected improvement in performance at submaximal exercise. In the present study, with the AVO, reduced from 88 to 73% consequent to training, the performance duration increased from 7 to 21 min. Furthermore, as described by the exponential relationship of endurance time and relative exercise intensity, and as shown in Fig. 2B, the magnitude of increase in performance is even greater when the test involves a less strenuous relative intensity. In the present study the improvement in performance appears to be related to the domain of exercise intensity (defined as AVO,). Whipp and Ward (26, 27) have defined heavy-intensity exercise as that above the TvE or lactate threshold. During exercise above the TV*, the highest VO, at which steady state can be attained coincides with that at which blood lactate does not continue to rise (15). At higher work rates VO, continues to increase until VO 2m8Xis attained [a delayed slow $70, kinetic component (13)]. For the present data, on the pretest there was a lOO-ml/min increase in $70~ from minutes 3-7 with $70 2 I118X reached at fatigue, whereas on the posttest the slow component increase of Vo, was 120 ml/ min between minutes 3 and 21, but Oo, m8x was not achieved [at this rate of Vo2 increase it would have required an additional 10 min (70 ml/min) to achieve VO, max]. In studying the critical power for long-term work in older men, Overend et al. (12) observed that the critical power occurred at a Vo2 of 92% of Vo2max, and with 24 min of exercise at this intensity the blood lactate showed a slow, progressive increase to 6.5 mmol/l at the end of exercise. In the present study for four of the eight men the constant work on the posttest was below this critical power (92% Vo 2max) and these subjects showed the largest performance improvements. Thus it appears the large performance improvement was achieved by crossing a domain of exercise from that characterized by a continuing rise in lactate and VO, to a relatively lower intensity in which lactate and VO, achieved a relative steady state. In the present study, the similarity of the observed physiological end points served to establish that the TTF test was stopped because of physiological limitations. Thus the fatigue end points occurred at near-maximal l
vo
OF
OLDER
MEN
physiological values (e.g., HR, Vo2). In fact, the postTTF test, if anything, was terminated by volitional fatigue slightly earlier than achievement of maximal responses, with the RPE on the test posttraining lower than on the pretest. Thus the TTF improvement (180%) was at least as large as reported and may represent even greater changes had the subjects been able to achieve the physiological maximum (HR) on the posttest performance that was found on the pretest performance. In light of these findings it is unlikely that the submaximal exercise improvements could be accounted for by habituation to the treadmill (the men had experienced three or more exposures before their first TTF test) or by the “Hawthorne effect” because the fatigue was coincident with physiological end points. A control group was not tested in this study. Previous studies of middle-aged and older men have reported nonsignificant changes in physiological measures for control groups for similar or longer time periods (6, 7). The initial level of VO 2 m8xwas relatively high for men of this age (31 ml kg-l min-l) and the men perceived themselves to be relatively active. Nevertheless, with only 9 wk of training, Vo2max was increased 10.6%. Others (6, 20, 22, 24) have reported v02ma increases ranging from 10 to 20% in older subjects. In the present study significant decreases in HR (7%), RER (7%), and VE (3%) at the same work rate after the training program are similar to changes noted previously with training of older subjects (11,17,18). The submaximal exercise ventilatory equivalent for VO, decreased; an unchanged ventilatory equivalent for CO, production (VCO,) during the submaximal exercise is consistent with the finding of Davis et al. (7) that vE/h02 was unchanged by endurance training and demonstrates that VE changes were more closely related to VCO,than VO,. In regard to submaximal exercise responses with training of the elderly, Cunningham et al. (6) noted that the submaximal exercise improvements were greater than observed for vo 2 max. They reported an increase of 14.7% in VO, at HR of 125 beats/min compared with a 10% increase of vo 2max. In the study of elderly men by Tzankoff et al. (24), a standard walk (5.6 km/h, 9% grade) elicited a VO, requirement before training of 90% of VOGUE, and this was reduced to 79% of V02max after training. Tv, in older individuals has been reported to be higher, as a percentage of V02max, than in younger individuals. Declines in Vo2max over age from the 20’s to 60’s are found to be greater than the declines in TvE (4, 14) and thus explain the relatively high values for TvE as a percentage of V02 max. Daily activities of the elderly that are well below the threshold for improvement or maintenance of VO, maxmay be adequate to maintain TvZ (4). In the present study, regular training did increase Tv, ~10%. In middle-aged men, anaerobic threshold improved 44% after 9 wk of endurance training (7). On the other hand, no changes in TvE were found after endurance training in one study involving older men (21), although training frequency (2.9 sessions/wk) was lower than that of the present study or of previous training studies reporting changes in TvE. Thus, in the present study, short-term endurance training of elderly men elicited typical changes in irO, max l
l
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ENDURANCE
TRAINING
and submaximal exercise responses as well as a significant increase in TvE. The increased TvE and VO, maxwere associated with large improvements in the duration of performance of heavy exercise. These 1.arge improvements in exe Nrcise endu rance capacity are clearly important to daily function of older individuals. This work was supported in part by the Ontario Ministry of Tourism and Recreation, the Natural Sciences and Engineering Research Council of Canada, and The Centre for Activity and Ageing (Affiliated with The University of Western Ontario and The Lawson Research Institute at the St. Joseph’s Health Centre). M. J. Poulin was supported by an Advanced Studies Bursary (Gerontology Research Council of Ontario) and is a Fellow of the Ontario Ministry of Health, Health Research Development Program. Address for reprint requests: D. A. Cunningham, Centre for Activity and Ageing, Faculty of Kinesiology, Thames Hall, The University of Western Ontario, London, Ontario N6A 3K7, Canada. Received 5 September 1991; accepted in final form 26 February 1992.
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