Aerobic
and glycolytic
metabolism
D. PENDERGAST, P. CERRETELLI, AND Department of Physiology, School of Medicine, Buffalo, New York 14214
PENDERGAST, D.,P. CERRETELLI,AND D.W. RENNIE. Aerobic and glycolytic metabolism in arm exercise. J. Appl. Whysiol.: Respirat. Environ. Exercise Physiol. 47(4): 754-760,1979.Eight kayakers (K) and 3 sedentary subjects (S) performed arm cranking and pedaling while erect or supine at each of several work loads from submaximal to the highest they could sustain for 2 min and for intervals varying from 10 s to 5 min. From measurements of Vos and blood lactate concentration, the aerobic and glycolytic energy release in arm work was assessed. For steady-state aerobic work all subjects had a mechanical efficiency averaging 0.24 independent of posture or exercise mode. Per unit fat-free limb volume, arm VOW I,,EiXof group K was 1.5-fold that of group S, whereas leg VOW lf,aXwas the same in each group. Compared to group S, glycolytic arm work in group K was characterized by: 1) higher thresholds for release of lactate at the onset of submaximal work, 2) lower blood lactate concentrations during comparable absolute or relative submaximal work, 3) higher conventional anaerobic thresholds for absolute, but not relative work loads, 4) higher maximal rates of lactate release, and 5) the same maximal blood lactate concentrations. Measurement of the early lactate threshold, which occurred at considerably lower arm work loads than did anaerobic threshold, but which was greatly increased by specific muscle training, may provide a simple, sensitive, and nontraumatic evaluation of muscle training. arm exercise; anaerobic threshold and muscle training; blood lactate; body position, exercise mode and maximum 02 uptake; kayaking; glycolytic metabolism in arm work .
STUDIES have reported relatively low arm maximal oxygen consumption (VOW nlax)compared to leg VO 2max(3, 4, 7, 9, 22, 26), relatively high blood lactate concentration in arm work at comparable absolute or relative submaximal loads (2, 4, 11, 19), and relatively low anaerobic thresholds (AT) for arm work as measured either by increased expired ventilation-to-oxygen consumption ratio (TE/~o~) (22, 30) or by an abrupt steady increase in blood lactate concentrations at progressively more severe work loads (9). Further, a number of studies have demonstrated that the effects of training are highly specific to the trained muscle (13, 24) and, for the case of arm training, include increased arm vor n,ax(7) and decreased blood lactate concentrations at comparable arm work loads (19, 21). Although central adjustments of the circulation accompany training (6, 7), the weight of evidence accounting for specific training effects in humans seemsto favor improvement in the oxidative potential of trained muscle caused by changes in oxidative enzyme activities, myoglobin concentration, distribution, and size of fiber types, and capillarization (1, 6, 13, 14, 24, 27). In NUMEROUS
754
in arm exercise
D. W. RENNIE State University
of New
York at Buffalo,
addition to training effects, the position of arms during work plays an important role in modifying blood lactate concentration and the cardiovascular adjustments. Concomitant leg work also appears to decrease arm voz nlax below what could be achieved by arm work alone (3). Less attention has been paid to the early rise in blood lactate whose threshold in submaximal arm work is well below anaerobic threshold. The phenomenon of an early rise of blood lactate, followed by a plateau or a decrease has been commonly observed in submaximal leg exercise and classically ascribed to muscle hypoxia that may occur in the first 1 or 2 min of work (2). More recently, this early transient appearance of blood lactate has been attributed to selective recruitment of glycogenolytic fibers early in muscle work (12, 24) because there is some question whether local muscle hypoxia does occur (10, 15).
We recently observed that arm work in untrained subjects resulted in a considerably larger release of early lactate and OZ deficit than did the same absolute or relative leg work, suggesting that the oxidative metabolism of the untrained arm responded particularly slowly during the early minutes of work (5). With this background, the purposes of the present study were to compare untrained and specifically arm-trained individuals with respect to 1) VOW max for arm work, 2) the early release of lactate over a broad range of work loads from submaximal to maximal, and 3) the classic anaerobic threshold for arm work. MATERIALS
AND METHODS
Measurements of Aerobic MetaboZism The experiments were carried out on 11 volunteers whose physical characteristics are summarized in Table 1: 3 sedentary subjects (S I-3) and 8 white-water kayakers (K 4-11). None of the sedentary subjects engaged in a regular fitness program or had engaged in sports or activity requiring an unusually high degree of endurancetype arm training. The kayakers were either local competitive kayakers (subj K 4-6) or nationally ranked kayakers (K 7-l 1) in active training. Fat-free arm and leg volumes were calculated from measurements of limb circumference and skin-fold thickness as in a previous study (5), and fat-free body mass was determined from measurements of underwater weighing. Most exercises were performed on two identical electrically braked bicycle ergometers arranged in such a manner that both arm cranking and leg pedaling could
0161-7567/79/0000-0000$01.25
Copyright
0 1979 the American
Physiological
Society
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (128.059.222.107) on January 15, 2019.
ARM
755
EXERCISE
be carried out in either the supine or upright position. In the latter case, the seat was adjusted for the subject’s comfort in leg pedaling, whereas for arm cranking the center of the ergometer shaft was positioned at the level of the subject’s shoulders. In supine work the subjects lay on a board with the center of the pedal shaft positioned either 55 cm above the board (arms) or 30 cm above it (legs). In each case the subject was strapped to the board at the hips and shoulders and the feet were attached to the pedals. Steady-state VOW was determined by collecting the subject’s expired gas (\jE) in a bag between the 4th and 6th min from the onset of work. VE was determined by a dry gas meter and its composition assessedby mass spectrometer (Perkin Elmer 1100). Following preliminary practice runs, the work loads were randomized and spaced at long time intervals, usually 24 h, to minimize any change in the fitness of the subjects or the initial glycogen stores of their muscles. Generally two or more runs were performed for each mode of work. The following external power ranges were employed: arm cranking: 25-125 watts (W) for sedentary subjects, 62.5-200 W for kayakers; leg pedaling: 37.5-225 W for both groups; combined arm and leg: 100-300 W for both groups. To evaluate the degree of arm training of each group and to determine the optimal exercise mode for comparison of lactate release, we initially determined J?o?rr,ax while subjects performed maximal exercises scattered throughout the experimental period in the following conditions: upright and supine bicycling, upright and supine arm cranking, and supine arm cranking plus leg pedaling. vo 2maxduring kayaking was measured from continuous collection of expired gas while kayakers paddled at progressively higher velocities around a 20-m-diam annular pool (observers on a tracking platform) or while they paddled at comparable velocities in open water (observers on a tracking motor boat). To measure voz nlaxduring running, subjects ran on a motor-driven treadmill at a velocity of lo-12 km. h-’ as the incline was progressively raised 2.5” every 2 min. Expired gas was collected for 1 or 2 min prior to the exhaustion level, as signaled by the subject.
leg (dorsalis pedis) venous samples drawn repetitively for 30 min following the exercise. As appears in Fig. 1, peak lactate concentration in leg venous blood was reached 56 min after cessation of arm work. This was similar to what was found when sampling from an arm vein after the cessation of leg exercise (20). In contrast, when sampling from the antecubital vein after arm exercise, blood lactate was highest immediately at the offset of work and then declined exponentially (tl,z = 17 min) throughout recovery. When simultaneous samples were taken from arm and leg veins after arm exercise, the time courses of blood lactate concentrations intersected at approximately 6 min (variability: 5-7 min in 6 trials) and decreased at the same rate thereafter. The intersection time, t, was the time when all blood samples for the present study were taken and represents the minimum time required for uniform mixing of lactate throughout the blood compartments of the body. It has been documented by multiple-site muscle biopsy and simultaneous blood sampling (18) that about 5-6 min are also required to minimize tissue-blood gradients of lactate. RESULTS
AND
DISCUSSION
Aerobic Metabolism There were no significant differences in J?oz between groups for any given work load by either arms or legs in different postures. The range of aerobic performance by the arms was considerably wider for the kayakers (62.5200 W) than for sedentary subjects (25-100 W), whereas the range of the performance by the legs only and by the combined arms plus legs was essentially the same for the two groups. The individual regressions of VOW on external work, calculated by the method of least squares, were as follows
I01 9 L0b mm01 - I-’ 0
0 sampling from arm i
0
”
” leg I
Estimates of GZycoZytic Metabolism The three sedentary subjects (S 1-3) and three local kayakers (K 4-6) carried out a separate series of different arm work loads ranging 25-125 W for sedentary subjects and 62.5-200 W for kayakers to ascertain the threshold and amount of lactate released during the time course of a 5-min exercise load. All subjects exercised for either 10 s, 1, 2, or 5 min at each work load investigated. The order of exercise times was randomized and a venous blood sample was taken 6 min after exercise stopped. Blood lactic acid concentration was determined by an enzymatic method (Calbiochem) on samples taken from the antecubital vein. To standardize the sampling, preliminary experiments were carried out in which two kayakers performed equivalent supramaximal work loads by the arms, after which blood lactate concentrations were measured in both arm and
’
and glycolytic
metabolism
D. PENDERGAST, P. CERRETELLI, AND Department of Physiology, School of Medicine, Buffalo, New York 14214
PENDERGAST, D.,P. CERRETELLI,AND D.W. RENNIE. Aerobic and glycolytic metabolism in arm exercise. J. Appl. Whysiol.: Respirat. Environ. Exercise Physiol. 47(4): 754-760,1979.Eight kayakers (K) and 3 sedentary subjects (S) performed arm cranking and pedaling while erect or supine at each of several work loads from submaximal to the highest they could sustain for 2 min and for intervals varying from 10 s to 5 min. From measurements of Vos and blood lactate concentration, the aerobic and glycolytic energy release in arm work was assessed. For steady-state aerobic work all subjects had a mechanical efficiency averaging 0.24 independent of posture or exercise mode. Per unit fat-free limb volume, arm VOW I,,EiXof group K was 1.5-fold that of group S, whereas leg VOW lf,aXwas the same in each group. Compared to group S, glycolytic arm work in group K was characterized by: 1) higher thresholds for release of lactate at the onset of submaximal work, 2) lower blood lactate concentrations during comparable absolute or relative submaximal work, 3) higher conventional anaerobic thresholds for absolute, but not relative work loads, 4) higher maximal rates of lactate release, and 5) the same maximal blood lactate concentrations. Measurement of the early lactate threshold, which occurred at considerably lower arm work loads than did anaerobic threshold, but which was greatly increased by specific muscle training, may provide a simple, sensitive, and nontraumatic evaluation of muscle training. arm exercise; anaerobic threshold and muscle training; blood lactate; body position, exercise mode and maximum 02 uptake; kayaking; glycolytic metabolism in arm work .
STUDIES have reported relatively low arm maximal oxygen consumption (VOW nlax)compared to leg VO 2max(3, 4, 7, 9, 22, 26), relatively high blood lactate concentration in arm work at comparable absolute or relative submaximal loads (2, 4, 11, 19), and relatively low anaerobic thresholds (AT) for arm work as measured either by increased expired ventilation-to-oxygen consumption ratio (TE/~o~) (22, 30) or by an abrupt steady increase in blood lactate concentrations at progressively more severe work loads (9). Further, a number of studies have demonstrated that the effects of training are highly specific to the trained muscle (13, 24) and, for the case of arm training, include increased arm vor n,ax(7) and decreased blood lactate concentrations at comparable arm work loads (19, 21). Although central adjustments of the circulation accompany training (6, 7), the weight of evidence accounting for specific training effects in humans seemsto favor improvement in the oxidative potential of trained muscle caused by changes in oxidative enzyme activities, myoglobin concentration, distribution, and size of fiber types, and capillarization (1, 6, 13, 14, 24, 27). In NUMEROUS
754
in arm exercise
D. W. RENNIE State University
of New
York at Buffalo,
addition to training effects, the position of arms during work plays an important role in modifying blood lactate concentration and the cardiovascular adjustments. Concomitant leg work also appears to decrease arm voz nlax below what could be achieved by arm work alone (3). Less attention has been paid to the early rise in blood lactate whose threshold in submaximal arm work is well below anaerobic threshold. The phenomenon of an early rise of blood lactate, followed by a plateau or a decrease has been commonly observed in submaximal leg exercise and classically ascribed to muscle hypoxia that may occur in the first 1 or 2 min of work (2). More recently, this early transient appearance of blood lactate has been attributed to selective recruitment of glycogenolytic fibers early in muscle work (12, 24) because there is some question whether local muscle hypoxia does occur (10, 15).
We recently observed that arm work in untrained subjects resulted in a considerably larger release of early lactate and OZ deficit than did the same absolute or relative leg work, suggesting that the oxidative metabolism of the untrained arm responded particularly slowly during the early minutes of work (5). With this background, the purposes of the present study were to compare untrained and specifically arm-trained individuals with respect to 1) VOW max for arm work, 2) the early release of lactate over a broad range of work loads from submaximal to maximal, and 3) the classic anaerobic threshold for arm work. MATERIALS
AND METHODS
Measurements of Aerobic MetaboZism The experiments were carried out on 11 volunteers whose physical characteristics are summarized in Table 1: 3 sedentary subjects (S I-3) and 8 white-water kayakers (K 4-11). None of the sedentary subjects engaged in a regular fitness program or had engaged in sports or activity requiring an unusually high degree of endurancetype arm training. The kayakers were either local competitive kayakers (subj K 4-6) or nationally ranked kayakers (K 7-l 1) in active training. Fat-free arm and leg volumes were calculated from measurements of limb circumference and skin-fold thickness as in a previous study (5), and fat-free body mass was determined from measurements of underwater weighing. Most exercises were performed on two identical electrically braked bicycle ergometers arranged in such a manner that both arm cranking and leg pedaling could
0161-7567/79/0000-0000$01.25
Copyright
0 1979 the American
Physiological
Society
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (128.059.222.107) on January 15, 2019.
ARM
755
EXERCISE
be carried out in either the supine or upright position. In the latter case, the seat was adjusted for the subject’s comfort in leg pedaling, whereas for arm cranking the center of the ergometer shaft was positioned at the level of the subject’s shoulders. In supine work the subjects lay on a board with the center of the pedal shaft positioned either 55 cm above the board (arms) or 30 cm above it (legs). In each case the subject was strapped to the board at the hips and shoulders and the feet were attached to the pedals. Steady-state VOW was determined by collecting the subject’s expired gas (\jE) in a bag between the 4th and 6th min from the onset of work. VE was determined by a dry gas meter and its composition assessedby mass spectrometer (Perkin Elmer 1100). Following preliminary practice runs, the work loads were randomized and spaced at long time intervals, usually 24 h, to minimize any change in the fitness of the subjects or the initial glycogen stores of their muscles. Generally two or more runs were performed for each mode of work. The following external power ranges were employed: arm cranking: 25-125 watts (W) for sedentary subjects, 62.5-200 W for kayakers; leg pedaling: 37.5-225 W for both groups; combined arm and leg: 100-300 W for both groups. To evaluate the degree of arm training of each group and to determine the optimal exercise mode for comparison of lactate release, we initially determined J?o?rr,ax while subjects performed maximal exercises scattered throughout the experimental period in the following conditions: upright and supine bicycling, upright and supine arm cranking, and supine arm cranking plus leg pedaling. vo 2maxduring kayaking was measured from continuous collection of expired gas while kayakers paddled at progressively higher velocities around a 20-m-diam annular pool (observers on a tracking platform) or while they paddled at comparable velocities in open water (observers on a tracking motor boat). To measure voz nlaxduring running, subjects ran on a motor-driven treadmill at a velocity of lo-12 km. h-’ as the incline was progressively raised 2.5” every 2 min. Expired gas was collected for 1 or 2 min prior to the exhaustion level, as signaled by the subject.
leg (dorsalis pedis) venous samples drawn repetitively for 30 min following the exercise. As appears in Fig. 1, peak lactate concentration in leg venous blood was reached 56 min after cessation of arm work. This was similar to what was found when sampling from an arm vein after the cessation of leg exercise (20). In contrast, when sampling from the antecubital vein after arm exercise, blood lactate was highest immediately at the offset of work and then declined exponentially (tl,z = 17 min) throughout recovery. When simultaneous samples were taken from arm and leg veins after arm exercise, the time courses of blood lactate concentrations intersected at approximately 6 min (variability: 5-7 min in 6 trials) and decreased at the same rate thereafter. The intersection time, t, was the time when all blood samples for the present study were taken and represents the minimum time required for uniform mixing of lactate throughout the blood compartments of the body. It has been documented by multiple-site muscle biopsy and simultaneous blood sampling (18) that about 5-6 min are also required to minimize tissue-blood gradients of lactate. RESULTS
AND
DISCUSSION
Aerobic Metabolism There were no significant differences in J?oz between groups for any given work load by either arms or legs in different postures. The range of aerobic performance by the arms was considerably wider for the kayakers (62.5200 W) than for sedentary subjects (25-100 W), whereas the range of the performance by the legs only and by the combined arms plus legs was essentially the same for the two groups. The individual regressions of VOW on external work, calculated by the method of least squares, were as follows
I01 9 L0b mm01 - I-’ 0
0 sampling from arm i
0
”
” leg I
Estimates of GZycoZytic Metabolism The three sedentary subjects (S 1-3) and three local kayakers (K 4-6) carried out a separate series of different arm work loads ranging 25-125 W for sedentary subjects and 62.5-200 W for kayakers to ascertain the threshold and amount of lactate released during the time course of a 5-min exercise load. All subjects exercised for either 10 s, 1, 2, or 5 min at each work load investigated. The order of exercise times was randomized and a venous blood sample was taken 6 min after exercise stopped. Blood lactic acid concentration was determined by an enzymatic method (Calbiochem) on samples taken from the antecubital vein. To standardize the sampling, preliminary experiments were carried out in which two kayakers performed equivalent supramaximal work loads by the arms, after which blood lactate concentrations were measured in both arm and
’
