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Body Composition and Physical Performance 1992. Pp. 71-88. Washington, D.C. National Academy Press 5 Effects of Experimental Alterations in Excess Weight on Physiological Responses to Exercise and Physical Performance Kirk l. Cureton INTRODUCTION There is little experimental data describing the effects of altered body composition on physical performance. This is because body composition is difficult and time-consuming to change in human volunteers. In the late 1970s, three studies were conducted that were designed to investigate the effects of experimental alterations in excess weight on physiological re- sponses to exercise and on physical performance capabilities. The research objective was to use an experimental model to simulate the effects of differ- ent levels of body fatness in order to determine whether the cross-sectional data available describing relationships between percent body fat (BF) and physical performance reflected cause and effect. EXCESS WEIGHT, AEROBIC CAPACITY AND RUNNING PERFORMANCE The first study (Cureton et al., 1978) involved investigating the effects of experimental manipulation of excess weight on aerobic capacity and distance running performance. It was known from cross-sectional data that percent BE is inversely related to aerobic capacity (VO2max) expressed rela- tive to body weight (BOO) and to distance running performance (Figure 5-1), but the magnitude of changes in VO2max and distance running performance that result from altered percent BE had not been established. -7 /1
72 % Fat KIRK J. CURETON V02max (ml/kg BW x mint I Distance Run Performance FIGURE 5-1 Diagram of relationships among percent body fat, VO2maX (ml/kg body weight x minute) and distance run performance reported in cross-sectional studies. Six recreational runners, four men and two women, 20 to 30 years of age, were used as subjects. They were relatively lean and had above aver- age VO2max (ml per kg body weight per minute) (Table 5-11. Body compo- sition was estimated from body density, which was determined using hydro- static weighing. A maximal, graded, running treadmill test and the 12-minute run were administered under four added-weight (AW) conditions: 0, 5, 10, and 15 percent AW. Weight was added to the trunk of the subjects using a weight belt and shoulder harness. During submaximal running on the treadmill at 188 meters per minute (7 miles/hour), addition of excess weight significantly and systematically increased ventilation, oxygen uptake in liters per minute, and heart rate but did not significantly alter the oxygen uptake expressed relative to the total weight carried (TW). This latter measure tended to decrease slightly (Table 5-21. During maximal running, addition of excess weight did not signifi- cantly affect ventilation, oxygen uptake in liters per minute, or heart rate but systematically decreased VO2maX (ml/kg TW x minute), treadmill run time, and 12-minute run performance. Under the 15 percent AW condition, these three measures were reduced 6.9 ml/kg/minute (12 percent), 1.5 min- utes (10 percent), and 277 meters (8 percent), respectively, compared to the normal weight condition (Table 5-3~. The changes by individual subjects `_ or Bus vO2max (ml/kg TW x minute) and 12-minute run performance were very consistent (Figure 5-2~. The average reductions in VO2max and 12-minute run distance per 1 percent added weight were 0.5 ml/kg TW x minute and 18 meters, respectively. Comparison of the VO2 (liters per minute) during submaximal and max- imal running clearly indicated that the primary metabolic effects of addition of excess weight were to increase the energy requirement of running at submaximal speeds without affecting the absolute VO2 maX (Figure 5-31. Any submaximal speed of running therefore required a higher percentage of . . VO2 max. and VO2 maX was reached at a lower speed of running, which in turn, resulted in a reduction in treadmill time. The mechanism by which added
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76 KIRK J. CURETON - ~ 3750 - - 3500 Z 3000 :E Cal 3250 2 750 3 64 ,,. 6 0 ~ 56 _ 52 x 48 Cal a> 44 0 5 10 15 % A W no l 0 5 10 15 % A W FIGURE 5-2 Individual values for the 12-minute run performance and VO2max (mllkg total weight x minute) for the four added-weight conditions. SOURCE: Cureton et al. (1978) by permission.
EXCESS WEIGHT, PERFORMANCE AND PHYSIOLOGICAL RESPONSES 3.6 3.2 - . _ _ ~ o _ A. ~ o .> 2.4 2 0 ~ _ Observed \2O2ma~ // I 15%AW ax/ | Hi/ / ~ / 0%AW 1 / ~_~_ I_ I I 1 _ 1 1 4 6 ~ 10 12 14 tM RUN tlME (min) 77 FIGURE 5-3 Treadmill (TM) run time estimated from mean submaximal and max- imal VO2 (liters per minute) values for the 0 percent and 15 percent added-weight (AW) conditions. SOURCE: Cureton et al. (1978) by permission. weight affected the 12-minute run performance should have been the same, assuming an individual ran at the same fraction of the VO2max across AW conditions. A measure of the total excess weight (EW) carried during the treadmill and track runs can be computed by adding the fat weight of each subject to the AW. This increases the dispersion of excess weight compared to that when just AW is considered and substantially strengthens the relationship of EW to VO2maX (ml/kg TW x minute) and 12-minute run performance (Figure 5-4~. The changes in run performance associated with the variation in percent BE closely paralleled the changes that resulted from added weight, which indicates that the relationship of percent BE to these measures was similar to the effects of added weight. Based on the results of this study, it was concluded that (a) excess (fat) weight causally affects VO2max expressed relative to weight and distance running performance and (b) two alternate metabolic explanations can be given for the detrimental effect of excess weight on distance running per- formance. One explanation is that excess (fat) weight increases the energy requirement of submaximal exercise without affecting the absolute VO2 max.
78 3750 _` ~ 3500 as 3250 en 3000 - 1 2750 2500 65: I_ 60 .' 55 E E' SO ~ AS lo > 40 KIRK J. CURETON 0% AW ~ 5%AW 0 10% A ~ · 15%AW 10 15 20 % EW n 0%AW ~ 5 °/0 A W o 10 %AW · 1 5 °/e A W 25 30 I t . I lO 15 20 % E 9/ 25 30 FIGURE 5-4 Relationships of percent excess weight (EW) to 12-minute run per- formance and VO2 (ml/kg total weight x minute). AW = added weight. SOURCE: Cureton et al. (1978) by permission. Therefore, running at any submaximal speed requires a higher percentage of VO2 max. and the pace that can be maintained for a given duration is reduced. An alternate explanation is that excess (fat) weight reduces the VO2max expressed relative to weight without affecting the oxygen requirement of submaximal running per unit weight. Therefore, as for the other explana- tion, the percentage of VO2max used during running at a submaximal speed
EXCESS WEIGHT, PERFORMANCE AND PHYSIOLOGICAL RESPONSES 79 is increased, and the pace that can be sustained for a given duration is reduced. The primary limitation of the AW model is that weight was added to the trunk and not distributed over the limbs and trunk as would be the case for BF. Therefore, the effects of changes in BF might be underestimated by the AW model, because it is known that weight added to the limbs has a bigger effect on the energy requirement of submaximal exercise than weight added to the trunk. Another limitation of the model is that when body weight changes, fat is not the only tissue to change. Gains in BF are typically accompanied by gains in fat-free weight (FFW), and losses in BF are usually accompanied by losses in FEW (Forbes, 19871. Thus, acute changes in the fat-free component of the body that accompany weight loss or gain may have effects not accounted for by the model. The validity of the model is supported by data indicating that the increased oxygen re- quired to walk at a given submaximal speed brought about by adding weight to the trunk using a backpack is the same as that produced by a similar weight gain produced by overeating (Hanson, 1973~. A number of other studies have indicated that the oxygen required per unit weight carried to walk or run at a given speed is not related to whether some of the weight is carried externally using a weighted belt, vest, or backpack (Cureton and 3600 _` _ z 3200 to I1J A 1 2800 cot 2400 - < --Male, % Fat ~ ._ ~--Experimentally | ~~ _ Added Weight Female, % Fat-- ) ~ _ 0 5 10 15 20 25 30 % FAT OR EXCESS WEIGHT FIGURE 5-5 Comparison of regression lines describing the relationship between percent fat and 12-minute run performance in men and women to the regression line describing the effect of added weight on 12-minute run performance.
80 KIRK J. CURETON Sparling, 1980; Goldman and Lampietro, 1962; Hanson, 1973; Miller and Blyth, 19551. To evaluate whether the effects of added weight were the same as the relationship of BF to performance in cross-sectional data, the regression lines relating percent BF to 12-minute run performance in 34 male and 34 female recreational runners (Sparring and Cureton, 1983) were compared to the regression line indicating the average effect of the AW in this study (Figure 5-5~. The slopes of the regression lines were almost identical, which supports the validity of the model and the conclusion that the inverse relationship between BF and distance running performance reported in cross- sectional data is cause and effect. RUNNING PERFORMANCE, METABOLIC RESPONSES AND GENDER DIFFERENCES The second study also used the AW model (Cureton and Sparling, 1980~. The purpose of this study was to investigate the extent to which differences between men and women in distance running performance and metabolic responses during running are due to the gender difference in percent BF. On the average, the percent BF of women is approximately 10 points higher than for men. Women also have lower average VO2 maX (ml/kg BW x minute) and poorer distance running performance (Figure 5-61. Of interest was the determination of the effect of experimentally eliminating the gender differ- ence in percent BF (by adding excess weight to the men) and observing how much the gender differences in VO2maX (ml/l~g TW x minute) and 12-minute run performance were reduced. The subjects for the study were 10 male and 10 female recreational runners who were matched on running mileage and competitive experience. The VO2max expressed relative to fat-free weight (FFW) of the groups was also not significantly different, which indicates that the men and women Female Gender 1+ % Fat _~ V02max (ml/kg BW x mint i_ Distance Run Performance FIGURE 5-6 Diagram of the effects of gender on percent body fat, VO2 maX (ml/kg body weight x minute) and distance run performance based on comparative data in the literature.
EXCESS WEIGHT, PERFORMANCE AND PHYSIOLOGICAL RESPONSES TABLE 5-4 Physical Characteristics of the Subjects in Cureton and Sparling (1980) Study Variable Men (n* = 10) Women (n = 10) mean + standard deviation Age (years) 26.4 + 4.9 25.8 + 4.6 Height (cm) 178.7 + 6.7 160.4 + 6.9 Weight (kg) 70.8 + 8.1 50.6 + 8.1 Fat-free weight (kg) 62.0 + 6.7 40.9 + 6.3 Percent fat 11.4 + 2.3 18.9 + 4.0 *n = number of subjects. SOURCE: Cureton and Sparling (1980) by permission. 81 had similar cardiorespiratory capacity. Both the men and women were relatively lean (Table 5-4~. The measurements and procedures were the same as for the earlier study (Cureton et al., 1978~. Women were measured only once with normal weight. The men were administered the graded treadmill and 12-minute run test twice, once under a normal-weight (NW) condition and once under an AW condition. The objective of the AW condition was to equate the mean percentage EW carried by the men and women. EW was defined as the sum of fat weight and added external weight. Each man was paired with a woman, and weight was added to the man such that his total percent EW was equal to the percent BE of the . . . TABLE 5-5 Means + SD for Physiological Variables Measured During Maximal Treadmill Exercise and 12-Minute Run Performance Men (n = 10) Women (n = 10) Variable Normal Weight Added Weight Normal Weight VE (1 x mind) 123.3 + 14.5 120.5 + 13.4 81.8 + 13.5 VO2(1 x mind) 4.31 + 0.44 4.40 + 0.42 2.82 + 0.49 VO2 (ml x mind x kg FFW-1) 69.8 + 6.0 71.4 + 7.2 68.9 + 5.2 VO2 (ml x mind x kg TOO-1) 61.7 + 5.1 57.8 + 5.9 55.7 + 3.0 Heart rate (b x mind) 187 + 8 185 + 8 185 + 7 R 1.16 + 0.05 1.12 + 0.04 1.13 + 0.06 Treadmill run time (min) 15.6 + 1.4 14.4 + 1.7 11.7 + 0.9 12-Minute run (m) 3362 + 226 3189 + 243 2794 + 156 NOTE: n = number of subjects; FW = fat-free weight; TW = total weight carried; R respiratory exchange ratio: VO2 (1/min) divided by VcO2 (1/min). SOURCE: Cureton and Sparling (1980) by permission. =
82 KIRK J. CURETON Table 5-6 Means + SD for Physiological Variables Measured During Submaximal Treadmill Running (7 mph) Men (n = 10) Women (n = 10) Variable Normal Weight Added Weight Normal Weight VE (1 X min 1) 53.4 + 8.7 54.8 + 12.1 46.3 + 7.6 VO2(1 X min 1) 2.63 + 0.42 2.79 + 0.51 2.05 + 0.35 VO2 (ml x mind x kg FFW-1) 42.4 + 3.7 44.8 + 5.1 50.0 + 3.1 VO2(ml x mind x kg TOO-1) 37.5 + 3.7 36.3 + 4.2 40.4 + 2.1 Heart rate (b x mind) 143 + 6 149 + 7 162 + 9 R 0.91 + .04 0.89 + 0.04 0.93 + 0.04 NOTE: n = number of subjects; FFW = fat-free weight; TW = total weight carried; R = respiratory exchange ratio: vO2(1/min) divided by vcO2(llmin). SOURCE: Cureton and Sparling (1980) by permission. woman. Therefore, different percentages of EW were added to individual men, but the average percent EW added was equal to the mean gender difference in percent BE (7.5 percent). The differences between the men and women during submaximal and maximal running, and on the 12-minute run, were similar to those reported in other studies (Tables 5-5 and 5-61. During running at submaximal speeds, men had higher absolute levels of ventilation and oxygen uptake, but wom- en had higher heart rates and higher oxygen uptake values expressed rela- tive to body weight (BOO) or FFW. The higher VO2 (ml/kg BW x minute) indicated that the women had poorer running economy than the men, which was an unexpected finding. Most studies of trained runners have reported no gender difference in running economy. The mean VO2max expressed in liters per minute and relative to body weight was significantly higher in the men, with the mean gender difference for VO2maX (ml/kg BW x minute) being 6 ml/kg x minute (11 percent). VO2max expressed relative to FFW was not significantly different in the men and women, with the mean gender difference being 1.9 ml/kg x minute (2.8 percent). Mean treadmill run time was 4 minutes (34 percent) longer, and 12-minute run distance was 568 m (20 percent) greater in the men than in the women. As expected, the effects of adding weight to the men were the same as in the first study. The VO2 during running at submaximal speeds expressed in liters per minute or relative to fat-free weight was significantly increased, whereas the VO2 expressed relative to the TW was reduced by a small amount. The mean increase of 2.4 ml in VO2 (ml/kg FFW x minute) elimi
EXCESS WEIGHT, PERFORMANCE AND PHYSIOLOGICAL RESPONSES 70 - ~ 60 '= 50 ._ - t`, 40 o ., 30 70 - 'C 50 ._ ~ 40 o ·> . 30 d NW ~ AW · ~ 4 6 Amp /l 1 1 . . I . . I 1. 8 10 12 14 16 TM RUN TIME (min) . · . · · · ~ 161 188 215 241 268 TM SPEED (m. min~l) · ~ NW ~ AW 295 322 ~I 7~- 4 6 8 10 TM RUN TIME (min) 12 14 16 ~. 161 188 215 241 268 295 322 TM SPEED (m min~l) 83 FIGURE 5-7 Mean submaximal and maximal VO2 (ml/kg fat-free weight x minute) and VO2 (ml/kg total weight x minute) values during running at various speeds during the treadmill test for women and men under the norma~-we~gnt (NW) and added-weight (AW) conditions. Linear regression lines are fitted to the four sub- maximal VO2 values. Open symbols are observed VO2 maX values. Broken vertical lines indicate mean treadmill run times. SOURCE: Cureton and Sparling (1980) by . . permission. . ~. ~· 1 ./% Aft-<. rx 1
84 KIRK J. CURETON nated 32 percent of the gender difference for this variable. VO2max in liters per minute or expressed relative to FEW was not significantly affected by equating excess weight, but VO2max expressed relative to body weight was significantly reduced by an average of 3.9 ml, which reduced the mean gender difference by 65 percent. With excess weight equated in the groups of men and women, there was no significant difference between the men and women in VO2max expressed relative to TW or FEW, with mean differ- ences being 2.1 ml (3.8 percent) and 2.5 ml (3.6 percent), respectively. Addition of weight to the men reduced the mean gender differences in . 210 ~ 190 m 70 5o o ~ 23.0 5 · o 10 ~ . . . . . ·~e'W': . l ~ ~ . 5 20 25 30 15 20 25 30 % FA T % FA T FIGURE 5-8. Scatter diagrams and linear regression lines predicting performances on the standing broad jump (SBJ), 50-yard dash (DASH), agility run (AR), and modified pull-up (MPU) from percent body fat. SOURCE: Johnson (1978) by . . permlsslon.
EXCESS WEIGHT, PERFORMANCE AND PHYSIOLOGICAL RESPONSES 85 treadmill run time and 12-minute run distance by 1.2 minutes (32 percent) and 173 m (30 percent), respectively. Examining the relationships among VO2 expressed relative to FFW and TW during submaximal and maximal running, and treadmill run time (Fig- ure 5-7) revealed that the mechanism through which EW contributed to the gender difference in treadmill run time could be explained in either of two complementary ways. First, the greater EW of women increases the energy required per kg of FFW to run at any given speed without affecting VO2 ma,, (ml/kg FFW x minute). Thus, the percent VO2maX used at different speeds is increased, the pace that can be maintained for a given duration is less, and VO2max is reached at a lower speed of running. Or second, the greater EW of women reduces the VO2max expressed relative to BW without sub- stantially affecting the VO2 (ml/kg BW x minute) required to run at sub- maximal speeds. The percent VO2 maX required to run at submaximal speeds is therefore increased with the same consequences as in the first explana- tion. The conclusions from this experiment were, first, that the greater aver- age gender-specific excess weight (fat) of women causes a portion of the gender differences in VO2maX (ml/kg BW x min) and distance running per- formance. About 65 percent of the gender difference in VO2 maX (ml/kg BW x minute) and about 30 percent of the gender difference in distance running performance in the sample studied were eliminated by removing the gender difference in excess weight (BF). A greater percentage of the gender differ- ences in treadmill time and distance running performance (probably closer to 65 percent) would have been eliminated if there had been no difference in running economy. And second, because the additional gender-specific BF of women is not eliminated by diet or physical training, it provides part of a biological justification for separate distance running performance stan- dards and expectations for men and for women. PHYSICAL PERFORMANCE, BODY FAT AND WOMEN ATHLETES The third study (Johnson, 1978), in which the AW model was used, compared the physical performance changes associated with increased BF based on cross-sectional data with performance changes resulting from add- ed external weight in women athletes. The relationships between percent BF, estimated from body density determined by underwater weighing, to four physical performance tests (50-yd dash, agility run, modified pull-up, and standing long jump) were determined in 44 women varsity athletes at the University of Georgia. A significant negative relationship between per- cent BF and each of the performances was found, although the correlations were not high, ranging from about 0.4 to 0.6 (Figure 5-8~. Six subjects
86 200 180 ID In 60 140 25.0 o 23.0 21.0 KIRK J. CURETON : - ' .. . . . 0 5 10 15 0 5 10 15 %EW 9.0 o - tn 8.0 7.0 _ 25 % E W ~ no_ ~ 0 S 10 15 0 5 %EW ·/.EW 10 15 FIGURE 5-9 Individual values on the standing broad jump (SBJ), 50-yard dash (DASH), agility run (AR), and modified pull-up (MPU) for the four excess-weight conditions. SOURCE: Johnson ~ l 978) by permission. were selected at random from the 44, and the physical performance tests were readministered with 5, 10, and 15 percent AW. Performances on each of the tests decreased consistently and systematically with AW (Figure 5-9~. The slopes of the regression lines relating percent BF to the performance scores based on the cross-sectional data were very similar to the regression lines indicating the average effect of the AW (Figure 5-10~. Therefore, it was concluded that changes in performance associated with increased BF are similar to changes that result from AW. The results support the validity of the AW model for investigating the effects of differences in BF on performance and provide experimental data indicating that relationships be
EXCESS WEIGHT, PERFORMANCE AND PHYSIOLOGICAL RESPONSES 200 . 160 140 - ~ 23.0 A: 21.0 . - _. - ~I I l, 0 5 10 15 , , % EW, , 14 19 24 29 % fAT 9.0 t ~ r ~ 80 C:} 7.0 2S.0 _ 25 ~ _ _ ~'. _ S ~ I I .1 1 0 5 10 _, , %EW , 14 19 24 % fAT 15 _ ._ o - _ . _ 87 5 10 15 ~, ·/. £W , , 14 19 24 29 % FAT Hi. - ~, , 1, . . . 0 5 10 15 I , %EW, , 14 19 24 29 % f AT FIGURE 5-10 Comparison of regression lines predicting the standing broad jump (SBJ), 50-yard dash (DASH), agility run (AR), and modified pull-up (MPU) from percent body fat ~--) and from percent excess weight ~ ). SOURCE: Johnson (1978) by permission. tween percent BE and different types of physical performance that involve movement of the BW are cause and effect relationships. REFERENCES Cureton, K. J., and P. B. Sparling. 1980. Distance running performance and metabolic re- sponses to running in men and women with excess weight experimentally equated. Med. Sci. Sport Exerc. 12:288-294. Cureton, K. J., P. B. Sparling, B. W. Evans, S. M. Johnson, U. D. Kong, and J. W. Purvis.
88 KIRK J. CURETON 1978. Effect of experimental alterations in excess weight on aerobic capacity and distance running performance. Med. and Sci. Sports 10:194-199. Forbes, G. B. 1987. Human Body Composition: Growth, Aging, Nutrition and Activity. New York: Springer-Verlag. Goldman, R. F., and P. F. Lampietro. 1962. Energy cost of load carriage. J. Appl. Physiol. 17:675-676. Hanson, J. S. 1973. Exercise responses following experimental obesity. J. Appl. Physiol. 35 :587-591. Johnson, S. M. 1978. Excess body weight and the physical performance of female college ath- letes. M. A. thesis, Department of Physical Education, University of Georgia. Miller, A. T., and C. S. Blyth. 1955. Influence of body type and body fat content on the metabolic cost of work. J. Appl. Physiol. 8:139-141. Sparling, P. B., and K. J. Cureton. 1983. Biological determinants of the sex difference in 12- min run performance. Med. Sci. Sport Exerc. 15:218-223.
