Interactive effects of body posture and exercise training on maximal

Interactive effects of body posture and exercise training on maximal oxygen uptake CHESTER A. RAY AND KIRK J. CURETON Exercise Physiology Laboratory, Department of Physical Education, University of Georgia, Athens, Georgia 30602 RAY, CHESTERA., ANDKIRK J. CURETON.Interactive effects body posture and exercise training on maximal oxygen uptake. J. Appl. Physiol. 71(2): 596-600, 1991.-To determine the effect of posture on maximal 0, uptake (\jo2 ,,,) and other cardiorespiratory adaptations to exercise training, 16 male subjects were trained using high-intensity interval and prolonged continuous cycling in either the supine or upright posture 40 min/day 4 days/wk for 8 wk and 7 male subjects served as nontraining controls. VO, maxmeasured during upright cycling and supine cycling, respectively, increased significantly (P < 0.05) by 16.1 t 3.4 and 22.9 * 3.4% in the supine training group (STG) and by 14.6 * 2.0 and 6.0 k 2.0% in the upright training group (UTG). The increase in VO, maxmeasured during supine cycling was significantly greater (P < 0.05) in the STG than in the UTG. The increase in voZmaxin the UTG was significantly greater (P < 0.05) when measured during upright exercise than during supine exercise. However, there was no significant difference in posture-specific \jozmexadaptations in the STG. A postural specificity was also evident in other maximal cardiorespiratory variables (ventilation, CO, production, and respiratory exchange ratio). In the UTG, maximal heart rate decreased significantly (P < 0.05) only during supine cycling; there was no significant difference in maximal heart rate after training in the STG. We conclude that posture affects maximal cardiorespiratory adaptations to cycle training. Additionally, supine training is more effective than upright training in increasing maximal cardiorespiratory responses measured during supine exercise, and the effects of supine training generalize to the upright posture to a greater extent than the effects of upright training generalize to the supine posture. Therefore, supine cycle training can be used as an alternative to upright cycling to improve or maintain cardiorespiratory capacity in individuals who are unable to perform upright exercise. of

cycling;

metabolism;

training

specificity

PREVIOUSSTUDIES have found that increases in maximal or peak 0, uptake (Vo2) are, at least in part, specific to the muscles trained. For example, after run training, maximal VO, (ire, ,,,) increased significantly more when measured during treadmill running than during swimming (14); likewise, swim training increased VO, m8X when measured during swimming but not during treadmill running (10). A similar specificity has been found for arm and leg cycle training compared with other modes of exercise (4-6,9,11,13,X5,19). A question that has not been studied is whether there is a postural specificity in the vo 2maxadaptation to exercise training. Increases in V0 2maxmay result from peripheral adaptations in the trained muscles that increase vascular con596

0161-7567191

$1.50 Copyright

ductance or 0, extraction or from central circulatory adaptations that increase maximal cardiac output independent of altered vascular conductance. Clausen (4) has argued that central circulatory adaptations should generalize to different modes of exercise and to exercise involving untrained muscles. He summarized considerable evidence that indicates that central circulatory adaptations are dependent on volume overload of the heart (large absolute end-diastolic volume, stroke volume, and cardiac output) during training. Studies utilizing radionuelide ventriculography have established that left ventricular end-diastolic volume and stroke volume are substantially greater during supine than during upright cycling (16). Thus, supine cycle training may cause greater central circulatory adaptations that generalize to other forms of exercise. Therefore, with this background, the purposes of the present study were I) to compare directly the effects of supine and upright cycle training on maximal cardiorespiratory responses and 2) to determine the extent to which adaptations obtained from training in one posture generalize to a different posture. It was hypothesized that, because of the greater central circulatory volume overload (i.e., increased ventricular filling and stroke volume) during supine cycle training, central cardiac adaptations and increases in VO 2maxafter supine training would be greater than after upright training. Furthermore, it was hypothesized that adaptations to supine cycle training would generalize to upright cycling to a greater degree than adaptations to upright cycle training would generalize to supine cycling. Submaximal circulatory and metabolic data from the same study have been presented in a previous paper (17). METHODS Subjects. Twenty-three men, 18-33 yr, volunteered to participate in the study. They had not participated in systematic endurance exercise training for 23 yr before the study. After a detailed explanation of the procedures, risks, and benefits to be derived from participation, they gave written informed consent. Subjects were screened medically by use of a medical history and an examination by a cardiologist. In Table 1, the physical characteristics of the subjects are summarized. Experimental design. Metabolic and cardiorespiratory variables were assessedin all subjects during maximal supine and upright cycling on a stationary ergometer before and after an 8-wk period of exercise training. Six-

CC) 1991 the American

Physiological

Society

EFFECT

TABLE

TRAINING

1. Physical characteristics of the subjects

Group

n

Control Supine Upright

7 8 8

Values

OF

Age, Yr 2x0* 1.5 24.8+_ 1.6 24.4+1 .l

are means

Height, cm 176.0t3.7 t 77.4k2.2 178.2+ 1.2

Pretest Weight, kg

Post test Weight, kg

77.9k5.4 79.3k3.3 78.6k3.6

79.1k5.4 79.623.6 78.5k3.6

+ SE.

teen subjects were randomly assigned to one of two experimental groups participating either in a supine or upright cycle training program. The remaining seven subjects served as nontraining controls and did not participate in any form of exercise training during the experimental period. This design allowed direct comparison of maximal cardiorespiratory adaptations to supine and upright cycle training and determination of the extent to which cardiorespiratory adaptations generalize to the posture not used in training. Exercise training program. The subjects in the experimental groups were trained in the supine or upright posture on a cycle ergometer for a total of 8 wk. Each subject attended four exercise sessions per week. During two sessions, the subject cycled for 3 min at a work rate requiring 50-60% of the posture-specific \jo2max and then cycled for 5 min at a work rate that elicited 90-100% of posture-specific VO, max.This pattern was repeated five times. The intensities of the intervals during supine training,. expressed as a percentage of pretraining uPright v"zmax9 ranged from 42 to 50 and 75 to 83%, respectively. During the other two sessions, the subject cycled for 40 min at a work rate that Vcould be mai ntained throughout the exercise period (-70% of posture-specific VO 2,,,). The work rate was adjusted as the subject’s physical work capacity improved so that a constant heart rate was maintained during the training bouts. The subjects trained under the direct supervision of laboratory personnel. Testing procedures. Before and after the training period, maximal ventilation (vEmax), VO,, Co2 output (Vco 2,,,), and heart rate were assessedduring cycling in both the supine and upright posture. The same protocol was used for both tests. Initially, the subjects cycled for 2 min at -40% of an estimated Vo2 max.Then the subjects cycled for 2 min at a work rate estimated to elicit -70% of Vo, maxand for 2 min at a work rate estimated to elicit 100% of VO, max. After 5 min of recovery, subjects cycled for as long as possible at a work rate 24 W greater than they attained at the final work bout. This was to ensure that a true \jo 2maxwas obtained for each subject. If the increase in \io, was ~150 ml/min above the maximal value obtained on the graded test, an additional work bout was conducted after a 5-min recovery period. A Bosch model 555 electrically braked ergometer with attached couch, specifically designed for supine exercise, was utilized for the supine tests, and a Quinton model 845 electrically braked ergometer was used-for the upright tests. VO, was measured each minute with the use of a computer-automated system, with ventilation measured by a Rayfield dry gas meter and expired 0, and CO, measured by Beckman OM-11 and LB-2 electronic gas analyzers, respectively. Gas analyzers were cali-

POSTIJRE

ON

\jozmllx

597

brated using 100% N, and standard gasespreviously analyzed with the micro-Scholander technique. The highest VO, attained during the test was considered V,Z maxfor cycling in a given posture. Heart rate was measured from electrocardiographic recordings. Statistical analysis. A three-way (group X posture X time) within-subject analysis of variance with repeated measures on the last two factors was used to determine the effects of training and posture on the dependent variables. Tests for simple main effects were used to identify significant differences among means before and after training for each group for each posture. A one-way (group) analysis of variance on pretraining-posttraining . vo 2 max differences was used to determine whether changes in Vo2 max for each exercise posture were significantly different among the three groups. The interaction term from a two-way (posture X time) within-subject analysis of variance with repeated measures on the last factor was used to determine whether changes in Vo2 max between postures for each group were significantly different. An alpha level of 0.05 was used for all significance tests. All values are presented as means t SE. RESULTS . Pretraining vo 2maxy vco

and posttraining mean values for irEmax, maximal respiratory exchange ratio (RER,,,), and maximal heart rate during the upright and supine cycle tests are presented in Table 2 and Fig. 1. Although the mean difference between the upright training group (UTG) and the supine training group (STG) during supine cycling was substantial (-400 ml), there was no significant difference between the experimental groups in V02max before training for either testing posture. Before trainin.g, supine V,Z maxwas significantly lower than upright VO, maxfor all three groups, with supine VO, max averaging 86.3 t 1.4% of upright VO, max. The pretraining supine-to-upright V,Z maxratio was 83.8 t 2.0, 89.7 t 1.6, and 85.3 t 3.3% for the STG, UTG, and control group, respectively. After training, supineto-upright V,Z max ratio was 88.6 t 1.4, 83.0 t 1.4, and 84.6 t 3.2% for the STG, UTG, and control group, respectively. . vo 2maxincreased significantly when measured during upright cycling in both the STG and UTG (16.1 t 3.4 and 14.6 t 2.0%, respectively). When measured during supine cycling, mean Vo2max increased significantly by 22.9 t 3.4 and 6.0 t 2.0% in the STG and UTG, respectively. The increase in Vo2max in the STG was significantly greater than in the UTG. In the UTG, Vo2max increased more (P < 0.05) when measured during upright cycling than during supine cycling (310 ml), whereas there was no significant difference in the changes in the STG (107 ml). Supine and upright VO, maxin the control group did not change significantly after the 8-wk experimental period. Before training, vEmax was significantly higher in both training groups during upright cycling than during supine cycling. In the STG, VE,,, increased significantly by 28.9 t 7.9 and 16.3 t 5.4% when measured during supine and upright cycling, respectively. In the UTG, 2maxy

598

EFFECT

OF

TRAINING

POSTURE

ON

i70zmax

2. Maximal metabolic and cardiorespiratory responsesduring upright and supine cycling before and after cycling training

TABLE

CG Variable

STG

Pretest

Posttest

Pretest

Upright VE, l/min VO,, Vmin vo2, ml kg-’ VCO,, l/min RER HR, beats/min l

l

124.7k8.3 3.14~20 41.6k3.3 3.71~21 1.18+0.05 194+3

min-’

126.0+5.0 3.17+.17 41.2k3.1 3.69&. 19 1.172.03 193&4

l

97.3k7.9 2.69k.21 36.Ok3.3 2.95k.25 1.09k.06 185+5

min-’

107.3k7.0 2.72k.19 35.823.1 3.22~28 1.17+.04 18024

Values are means * SE. CG, control CO, output; RER, respiratory exchange

group; ratio;

Posttest

Pretest

Posttest

exercise 123.826.3 3.35k.16 42.31~ 1.7 3.77k.22 1.12d1.04 186+5

Supine VE, l/min VO,, l/min VO*, ml kg-‘. VCOz, l/min RER HR, beats/min

UTG

142.2?5.2* 3.86~ 14* 49.1?1.8* 4.13+.22* 1.072.04 183+4

134.b4.0 3.56k. 19 45.3H.5 4.42~21 1.25~02 189?4

162.0?6.3* 4.07~ 18* 51.9a.4* 4.83+.28* 1.18~04 187&2

136.9+7.2* 3.42+.14* 43.4+1.8* 3.90+. 16* 1.14504 17925

126.M6.1 3.19k.16 40.7H.l 3.5h.19 l.lO-t.04 187+2

129.2k4.4 3.38&. 19* 43.b1.4” 3.87~27 1.16k.06 177+3*

exercise 107.7k6.5 2.79+. 12 35.3d.5 3.01~20 1.07k.04 17524

STG, supine training group; UTG, upright training HR, heart rate. * Pretest-posttest mean difference

group; VE, ventilation, Vo,, significant at P < 0.05.

O2 uptake;

Vco,,

.

only during upright cycling max increased significantly (21.1 t 4.1%). Before training, VCO, maxwas significantly lower during supine cycling than during upright cycling in all groups. VCO, maxincreased significantly in the STG only during supine cycling and in the UTG only during upright cycling. The increases in VCO, maxwere 32.6 t 8.9 and 11.1 t 5.8% for the STG and 12.4 t 7.0 and 9.1 t 4.1% for the UTG during supine and upright cycling, respectively. No significant changes occurred in RER,,, after training in any group. However, after training RER,,, tended to increase during supine cycling and to decrease during upright cycling in both training groups. After training, maximal heart rate did not change significantly in the STG during either test. Maximal heart rate in the UTG decreased significantly only during supine cycling. No significant changes occurred in any variables in the control group. VE

DISCUSSION

FIG. 1. Posture-specific iTO, max during supine before and after 8 wk of supine or upright exercise group; STG, supine training group; UTG, upright Post difference significant at P < 0.05.

The primary questions to be answered by this study were as follows. 1) Are increases in V,Z maxobtained from cycle training in the supine posture different from those obtained from cycle training in the upright posture? 2) To what extent do adaptations in VO, maxobtained from cycle training in the supine posture generalize to cycling in the upright posture and vice versa? The primary findings were that increases in VO, maxin the STG and UTG, although similar when measured during upright cycling (16.1 vs. 14.6%), were substantially greater in the STG than in the UTG when measured during supine cycling (22.9 vs. 6.0%). This finding indicates that the effects of supine training generalized to the upright posture to a greater extent than the effects of upright training generalized to the supine posture. In the UTG, the increase in . vo 2maxwas significantly greater when measured in the upright posture than when measured in the supine posture, but in the STG the changes measured in the upright and supine postures were not significantly different. Thus there was a postural specificity to VO, maxadaptations to upright training but not to supine training. The average supine 7j02max before training across all groups was 86% of upright iTo, max. This result is consistent with findings of previous studies (2, 19). The lower V0 2maxin supine cycling has been associated with a lower mean blood pressure gradient across the active muscles, a lower peak heart rate, and lower maximal cardiac output. Additionally, a larger muscle mass may be activated during upright exercise, especially during heavy exercise, when upper body movements assist in pedaling. Stenberg et al. (20) showed that, with the addition of arm cycling, supine cycling peak Vo2, peak cardiac output, and heart rate became equivalent to upright cycling values. The present study demonstrates, however, that. supine cycling training decreased the supineupright VO, max difference, whereas upright exercise training accentuated the difference. The supine-to-

n

Pre

0

Post

4.0

3.0 z E s

2.0

1.0

0 CG

Supine

STG

UTG

Exercise

CG

Upright

STG

UTG

Exercise

and upright exercise training. CG, control training group. *Pre-

EFFECT OF TRAINING upright Vo2 max ratio increased from 83.8 to 88.6% in the STG and decreased from 89.7 to 83.0% in the UTG. Significant improvement in V02max after supine cycle training has not been previously documented to our knowledge. We hypothesized that, because of well-established differences in central hemodynamics at rest and during exercise, changes resulting from training supine might be different from those resulting from training upright. In the supine posture, ventricular filling and stroke volume are higher and heart rate and vascular resistance are lower than values in the upright posture at rest and at any given level of vo, (3,16,21). These hemodynamic differences should cause greater volume overload on the central circulation and might improve central circulatory responses and VOW,,, after supine exercise training more than with upright exercise training. This hypothesis was supported for Vo2max measured in the supine posture; VO, max in the STG improved significantly more (22.9%) than in the UTG (6.0%). Thus, for work performed in the supine posture, training performed supine is more effective than training performed upright for improving \io, max. The hypothesis was not supported for VO, max measured in the upright posture. During upright cycling, the increase in \jo2 max after supine training (16.1%) was comparable to the increase observed after upright training (14.6%). The data indicate that supine training is as effective in improving upright cycling V02 maxas upright training and that the effects of supine cycling training on cycling VO, max generalize to a greater extent than those of upright cycle training. Therefore supine exercise training may be a suitable substitute for upright exercise training in situations in which a subject is unable to perform upright exercise as a result of a bodily injury or physiological disorder, e.g., autonomic insufficiency. Our finding that V02max was significantly increased during supine and upright cycling after supine exercise training is in agreement with the findings of Martin et al. (l2), who found increases in both supine and upright cycling peak VO, after swim training. However, these findings are in contrast to an earlier study (10) that did not find an increase in treadmill VO, maxafter swim training. As noted by Martin et al. (l2), the initial fitness level of these subjects was high, which may explain why treadmill VO, max did not increase. The finding that upright exercise training did not increase VO, m8Xto the same extent during both supine and upright cycling agrees with the finding of McArdle et al. (l4), who found a greater increase in treadmill Vo2,,, than in swimming Vo2,,, after a run training program. Previous studies have examined the question of training specifi city by comparing cardiorespiratory respon ses in trained vs. untrained muscles (5, 9-11, 14). Increa ses in V02max after training measured during exercise with untrained muscles have generally been attributed to increases in central circulatory adaptations, i.e., cardiac output and stroke volume, whereas training-induced increases in VO 2maxthat are specific to the exercise-trained muscles have been attributed to peripheral adaptations (4, 5, 11). The present study demonstrates that training of the same muscle mass (legs) in different positions

POSTURE ON 7jozmax

599

elicits differential effects on VO, m8Xwhen tested in different body postures. However, this finding was evident only in the UTG. The increase in posture-specific Vo2 max in the UTG was greater during upright exercise. However, there was no significant difference in VO, maxadaptations in the STG. Thus the present study has identified a postural specificity in the VO, maxadaptation to exercise training that is restricted to training in the upright posture. The present study does not allow us to identify precisely the reasons behind the postural specificity and difference in generalization of training effects between the two exercise training modes because cardiovascular data, with the exception of heart rate, were not obtained during maximal exercise. Although pretraining \jo2 max values in the three groups were not significantly different at the . beginning of the study, a meaningful difference in vo 2max (-400 ml) existed between the UTG and STG during supine exercise. Reanalysis of the data using analysis of covariance, holding constant the effect of differences in pretraining Vo2max values, did not change the results. Therefore the initial differences in Vo2max between the groups did not affect the pattern of adaptations. The greater increases in VO, max during supine exercise after supine training than after upright training and the greater degree of generalization of adaptations resulting from supine training to the upright posture are consistent with our hypothesis that greater cardiac adaptations (increases in peak end-diastolic and stroke volume) may have occurred after supine training because of the greater volume overload during training in the supine posture. Clausen (4) has suggested that central adaptations to training are dependent on the volume overload and, as previously mentioned, generalize to a greater extent to other exercising modes. However, we have found in the same subjects that during submaximal exercise cardiovascular adaptations after training are posture specific. That is, subjects who trained in the supine posture had significant increases in end-diastolic volume and stroke volume and lower heart rate during submaximal supine cycling after training but not during upright cycling, whereas the reverse held true for the UTG (17). It is not clear, however, whether this pattern of cardiovascular adaptations would have been maintained at substantially higher work rates. Peripheral adaptations may have also contributed to the postural specificity and difference in generalization of Vo 2 maxadaptations. One possibility is that there was a different pattern of motor unit recruitment and therefore somewhat different musculature activated during supine training compared with upright training. It was noted by all subjects that supine cycling was more difficult to perform than upright cycling at the same work rate because of a greater feeling of muscle fatigue, i.e., a burning or heavy sensation in the legs, during supine cycling. This probably resulted from the extra effort needed to push the pedals without the assistance of gravity and the body weight. In addition, leg blood flow may have been reduced because the legs were elevated above the torso. The number of motor units activated and the intensity of stimulation also may have been different.

600

EFFECT

OF

TRAINING

Therefore peripheral adaptations related to the pattern and extent of muscle fiber recruitment could have contributed to the posture-specific Voz maxadaptations. Additionally, there may be a more effective blood flow redistribution to the working muscles after training in the STG (1,8). We conclude that posture affects maximal cardiorespiratory adaptation s to cycle t#raining. Additionally, supine training is mor e effective than upright training in increasing maximal cardioresp liratory responses during supine exercise, and the effects of supine training generalize to the upright posture to a greater extent than the effects of upright training generalize to the supine posture. Therefore, supine cycle training can be used as an alternative to upright cycling to improve or maintain cardiorespiratory capacity in individuals who are unable to perform upright exercise. This study was supported by a grant from the American Heart Association, Georgia Affiliate, and by equipment donated by Bosch Medical Electronics. Address for reprint requests: C. A. Ray, 610 MRC, College of Medicine, LJniversity of Iowa, Iowa City, IA 52242. Received

25 June

1990; accepted

in final

form

22 March

1991.

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