Work performance after dehydration: effects of physical conditioning and heat acclimatization. 1958.

Three groups of five men each were dehydrated overnight in the heat (115 degrees F) on two occasions (D1 and D2) to approximately 5.5% of their starting body weight. During the 3-week period between D1 and D2, one group (AC) was acclimatized to heat and physically conditioned, the second group (C) was physically conditioned and the third group (S) remained sedentary. The response to work after dehydration was assessed by the following criteria: pulse rate (P), rectal temperature (Tr) and maximal oxygen intake (Max. VO2). Pulse rates during and after walking and after running were elevated with dehydration. This elevation was reduced in groups AC and C at D2 as compared to D1, but not in group S. An elevation in T1 with walking also occurred with dehydration, but this elevation was not significantly different at D2 as compared with D1 in any group. Physical conditioning elicited an elevation in Max. VO2 (group AC and C), but the elevation was no greater in group AC than in group C. Dehydration was associated with an equal decrement in Max. VO2 at D1 and D2 in all groups, but the conditioned men (AC and C) maintained a relatively higher Max. VO2 than group S. Thus, physical conditioning was associated with enhanced work performance during dehydration (assessed by the above criteria), whereas acclimatization to heat did not appreciably supplement this effect.

Exercise- and methylcholine-induced sweating responses in older and younger men: effect of heat acclimation and aerobic fitness.

The purpose of this investigation was to examine the effects of aging and aerobic fitness on exercise- and methylcholine-induced sweating responses during heat acclimation. Five younger [Y group-age: 23 +/- 1 (SEM) years; maximal oxygen consumption (VO2max): 47 +/- 3 ml.kg-1.min-1], four highly fit older (HO group- 63 +/- 3 years; 48 +/- 4 ml.kg-1.min-1) and five normally fit older men (NO group -67 +/- 3 years; 30 +/- 1 ml.kg-1.min-1) who were matched for height, body mass and percentage fat, were heat acclimated by daily cycle exercise (approximately 35% VO2max for 90 min) in a hot (43 degrees C, 30% RH) environment for 8 days. The heat acclimation regimen increased performance time, lowered final rectal temperature (Tre) and percentage maximal heart rate (%HRmax), improved thermal comfort and decreased sweat sodium concentration similarly in all groups. Although total body sweating rates (Msw) during acclimation were significantly greater in the Y and HO groups than in the NO group (P < 0.01) (because of the lower absolute workload in the NO group), the Msw did not change in all groups with the acclimation sessions. Neither were local sweating rates (msw) on chest, back, forearm and thigh changed in all groups by the acclimation. The HO group presented greater forearm msw (30-90 min) values and the Y group had greater back and thigh msw (early in exercise) values, compared to the other groups (P < 0.001). In a methylcholine injection test on days immediately before and after the acclimation, the order of sweat output per gland (SGO) on chest, back and thigh was Y > HO > NO, and on the forearm Y = HO > NO. No group differences were observed for activated sweat gland density at any site. The SGO at the respective sites increased in the post-acclimation test regardless of group (P < 0.01), but on the thigh the magnitude of the increase was lower in the NO (P < 0.02) and HO (P = 0.07) groups than in the Y group. These findings suggest that heat tolerance and the improvement with acclimation are little impaired not only in highly fit older but also normally fit older men, when the subjects exercised at the same relative exercise intensity. Furthermore, the changes induced by acclimation appear associated with an age-related decrease in VO2max. However methylcholine-activated SGO and the magnitude of improvement of SGO with acclimation are related not only to VO2max but also to aging, suggesting that sensitivity to cholinergic stimulation decreases with aging.

Perspectives on exercise and wasting.

Recommendations for endpoints in clinical trials of wasting that involve exercise should involve selection that clearly identifies the effects of exercise. Broad endpoints such as morbidity and mortality must be corrected for the effects of age, smoking, hypertension, etc. in order to gain adjusted information pertinent to exercise. Selection of variables related to physiological function although more specific i.e., maximal oxygen uptake, must still be viewed from the perspective that other variables may contribute to the values measured. Nevertheless, physiological information obtained from performance tests may well provide useful endpoints. In this regard, V02 max, heartrate and pulmonary ventilation at fixed work loads, muscular strength, reaction time, flexibility, blood gases, cardiac output, stroke volume, serum lactate, and properties of skeletal muscle such as mitochondria concentration and components related to muscle energetics, e.g., adenosine triphosphate. In addition exercise will definitely impact body mass and composition as well as configuration. The latter is assessable through utilization of somatogramography. Analysis of muscle depends on muscle biopsy and magnetic resonance spectroscopy. Neither of these methods has been employed in clinical trials to the best of our knowledge. Thus, one needs evidence that exercise in the clinical trial provides a discrete effect on performance capabilities, body status and biologically important variables.

Functional consequences of sarcopenia: effects on thermoregulation.

The loss of skeletal muscle mass with aging (sarcopenia), and related changes in body size and composition, may impact body temperature and thermoregulation in both hot and cold environmental conditions. Sarcopenia alters the thermal properties of the body as a passive system because of differences in water content, and thus specific heat, of muscle and adipose tissue. With respect to active thermoregulation in warm environments, differences in fat-free weight (FFW) can explain more than 80% of the variance in absolute blood volume (BV) among individuals (Allen et al., 1956) and BV, in turn, profoundly influences the cardiovascular responses to exercise and heat stress. For example, a lower BV for a given body weight may explain more than half of the variability in maximal oxygen uptake (VO2max). Thus, as VO2max declines, any absolute task represents a higher relative VO2max (% VO2max) and proportionately greater cardiovascular strain. Because BV is an important determinant of left-ventricular filling pressure, and because older individuals rely more on the Frank-Starling mechanism to increase cardiac output (Q), a lower BV may also be associated with an inability to increase Q appropriately. These effects are particularly important under conditions of heat stress, where a larger increase in Q is necessary to perfuse both skin and active muscle vascular beds. With exposure to cold, age-related changes in body composition affect the insulation provided by the peripheral tissues, especially in the limbs. This results in an increased reliance on peripheral vasoconstriction to minimize heat loss, yet this vasoconstriction is attenuated in older individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Body composition and the expiratory reserve volume of pre-pubertal lean and obese boys and girls.

Previously, we examined the expiratory reserve volume (ERV) of the lungs as a function of percentage body fat in an adult population (age range 18-58 years). A negative correlation resulted when ERV (expressed as a percentage of vital capacity, (ERV/VC) x 100) was regressed on percentage fat for both sexes. In the present study, similar comparisons were made for 33 pre-pubertal boys and girls (aged 7-12.5 years). The regression equation for the boys ((ERV/VC) x 100 = 44.2 - 0.56%fat, r = -0.77, P = 0.002) was similar to that of the adult men ((ERV/VC) x 100 = 48.7 - 0.80 %fat, r = -78) and women ((ERV/VC) x 100 = 49.5 - 0.63 %fat, r = -0.70). However, the girls studied did not follow the same pattern. In this group of pre-pubertal girls, a significant increase in (ERV/VC) x 100 with increasing body fatness was seen ((ERV/VC) x 100 = 29.3 + 0.19 %fat, r = 0.48, P = 0.03). In all four groups, no correlation was seen with age or height. Whereas there was a significant correlation between weight and (ERV/VC) x 100 in the adults, no such relationship was evident in the younger subjects. In pre-pubertal obese girls limited upper body muscle development, perhaps as a result of limited physical activity, may explain the different relationship between ERV and body fatness.

Energy turnover and heat exchange in mature lean and obese Zucker rats acutely exposed to three environmental temperatures for 24 hours.

Differences between lean (FA/?, n = 6) and obese (fa/fa, n = 6) mature male Zucker rats' energy turnover and heat storage were compared during a 24-h period when the animals were exposed to ambient temperatures of 30, 15 or 5 degrees C. Energy turnover was examined through measurements of heat production rates via indirect calorimetry and heat loss rates via direct calorimetry. Heat storage rates were calculated as the difference between heat production and heat loss rates. Predicted heat storage rates were also calculated as the product of the change in core temperature and the calculated specific heat of the animal based on body composition (carcass) analysis. A minimal heat loss rate was determined for each animal representing a period of least activity. Various comparisons were made: between groups (lean/obese), temperature (30, 15, 5 degrees C), calorimetry method (indirect/direct), period (light/dark), heat storage (experimental/predicted), and minimal heat loss. Immediately before a test, pretest weight and colonic temperature were obtained. Then, the animal was placed into the calorimeter chamber and remained there unrestrained for 24 h. Normal light/dark periods were maintained. On removal from the calorimeter, core temperature and body weight measurements were again obtained. Upon completion of all tests, body composition was analyzed and surface area determined. Energy turnover, i.e. both heat production and heat loss in the lean and obese animals differed among the 30, 15 and 5 degrees C exposures. The obese animals had relatively greater heat production rate and heat loss rate (kcal/day or kcal/kg (FFM)/day than the lean animals at 30, 15 and 5 degrees C. But, on a relative basis, the increments in heat production in the cold environments were greater for the lean animals. Both the lean and obese animals tended to be more active during the dark period when at 30 degrees C, but the difference was less at 15 degrees C and even less at 5 degrees C. Experimental heat storage rates did not differ significantly from predicted values at any of the temperatures with the possible exception of the animals at 5 degrees C. It was concluded that the mature obese Zucker rats had no major discernible defect in thermoregulation as revealed by rates of heat production and loss, although three of the obese rats did elicit a drop in colonic temperature during exposure to 5 degrees C, i.e. their excessive subcutaneous adiposity and thermal insulation did not prevent a fall in colonic temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Fat-free mass in relation to stature: ratios of fat-free mass to height in children, adults, and elderly subjects.

A cross-sectional relationship of fat-free mass to height expressed as a ratio (FFM:ht) is presented for 1103 people aged 6-86 y. Data are presented for 13 specific age groups by gender. By providing information for normal, healthy individuals, these data may be of comparative value for nutritionists and clinicians concerned with body composition of patients with wasting diseases. The data were collected over 20 y in our laboratory by using the same densitometric procedure. A significant increase in FFM:ht occurs during the preadolescent and adolescent years. The adolescent spurt continues for a longer period for boys than for girls, resulting in a significant gender difference beginning at approximately age 16 y and continuing throughout adulthood. A decline in FFM:ht, not statistically significant, appears to occur in men greater than 60 y of age, and a significant decline occurs among women greater than 50 y of age (alpha less than 0.01). Thus, both gender- and age-related trends that have implications for the interpretation of comparative body-composition status are suggested.

Ventilatory response of moderately obese women to submaximal exercise.

To investigate the effect of moderate obesity on ventilatory responses to graded exercise, we compared the ventilatory responses of ten moderately obese (35 +/- 5 percent body fat) and nine leaner women (22 +/- 2 percent body fat) during walking on a treadmill with incremental increases in percent grade. Speed remained constant at 3.0 mph. In the obese women, VO2 in l/min and ml/FFW/min, fb (b/min), VE (l/min), and HR were significantly greater (P less than 0.05) at all four absolute workloads. At 10.0 and 12.5 percent grade, VO2 (ml/kg/min) was smaller and VE/VO2 was greater in the obese women. The difference in VE/VO2 suggests a lower ventilatory threshold for the obese women. Percent VO2 max and R (VCO2/VO2) were significantly different at 12.5 percent grade only. When VO2 was divided by HR (oxygen pulse), the two groups were not significantly different at any of the four workloads tested. The groups were compared further at workloads representing approximately 55, 65, 75, and 85 percent of VO2 max. HR was not significantly different at any of the four relative exercise intensities. VE was significantly greater in the obese at 85 percent of maximum only (P less than 0.05) and fb was significantly greater at 55, 75, and 85 percent of maximum. Whereas cardiorespiratory responses of moderately obese women are increased at absolute workloads when compared to that of leaner women, HR is similar at comparable intensities of exercise. VE is also similar at comparable intensities of exercise below ventilatory threshold but fb is greater. The effect of the higher fb on exercise tolerance is unknown.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise end-expiratory lung volumes in lean and moderately obese women.

End-expiratory lung volumes (EELV) and expiratory flow rates were determined in 10 moderately obese (mean, 35 percent fat) and 10 relatively lean women (22 percent fat) at rest and during exercise on a treadmill at 55 and 85 percent of VO2max. Expiratory reserve volume (ERV) as a percentage of forced vital capacity (FVC) was used as an index of EELV. Differences in body weight, body fatness, and VO2max were significant (P less than 0.05). The resting EELV in the obese women was less than (P less than 0.01) that in the leaner women (32 vs 37 percent). During exercise at the two intensities, the EELV remained near the resting value in the obese women (approximately 30 percent). In contrast, the leaner women experienced an initial decrease in EELV during exercise at 55 percent of VO2max (i.e., from 37 to 32 percent) (P less than 0.01); thereafter, the EELV changed no further during exercise at 85 percent of VO2max. There were no significant differences in relative expiratory flow rates at rest or during exercise between the obese and lean women. In conclusion, moderately obese women fail to decrease their EELV during exercise in contrast to leaner women who do. A non-linear respiratory system pressure-volume curve, plus increased resistance as maximal flow is approached may combine to determine a lower limit of EELV during exercise.

Age and aerobic power: the rate of change in men and women.

The historic studies by Robinson and Astrand as well as more recent studies present a fairly uniform rate of decline in VO2max with age at 0.40-0.50 ml X kg-1 X min-1 X year-1 in men. In women the rate of decline appears to be less--approximately 0.20-0.35 ml X kg-1 X min-1 X year-1, at least in cross-sectional studies. Further, there is no clear distinction in the rate of change in VO2max when comparing active and inactive populations. Longitudinal studies varying from 2.5 to 21 to 56 years present a confounding picture. The rate of decline in VO2max varies from 0.04 to 1.43 ml X kg-1 X min-1 X year-1. There is some indication that active individuals decline at a slower rate than inactive persons but the results are not uniform. A possible explanation is that changes in VO2max over the entire age range may be curvilinear, with active individuals declining slowly as long as they maintain a regular exercise program, and sedentary individuals declining at a rapid rate during their 20's and 30's followed by a slower rate of decline of their VO2max as they age further.

Habitual daily energy expenditure and activity levels of lean and adult-onset and child-onset obese women.

The energy expenditure (EE) of eight lean, eight adult-onset obese (AOO), and eight child-onset obese (COO) women was determined over three 24-h periods by the factorial method, modified by subject-keypunched and mechanically recorded activity diaries. Mean daily EE was significantly higher in the pooled obese women (2472 +/- 488 kcal) than in lean women (1979 +/- 302 kcal) due to higher energy costs of sedentary and light activity in the obese. EE during moderate-to-strenuous activity was similar between groups because lean women performed these activities more vigorously. AOO and COO differed significantly in neither mean EE nor habitual activity. Fat-free mass (FFM) was a better predictor than body weight of both mean daily EE and the energy cost of activity. These data indicate that EE is positively related to obesity. Obese women tend to limit possible EE by reducing the vigorousness of weight-supported activity.

Sports science and body composition analysis: emphasis on cell and muscle mass.

Because we are unsure of many of the constants that we use in the calculation of components of body composition, there is a need for a greater number of postmortem analyses in order to prepare better equations for more accurate utilization of indirect noninvasive measurements. At present, most investigators who study active people (including athletes) use techniques that only provide an approximation of body fatness. Because excess fat serves as a burden to the body during transport in the performance of many physical activities, fatness constitutes a variable of concern. Fat-free body weight is usually calculated by difference and serves as a reference for some physiological functions. Although fat-free weight and lean body mass are not the same, most investigators calculate fat-free weight and many use the terms interchangeably. Some of the assumptions and problems in utilizing hydrodensitometry in the calculation of body fatness remain unresolved, such as the true densities of the different gross components of body composition in the young, aged, physically fit, etc. A variety of body composition profiles of different athletes have been published in recent years, which substantially augment efforts initiated in the 1940s and 1950s. The regular employment of a total body water assessment along with hydrodensitometry would improve the accuracy of calculation of body fatness, but the procedure is somewhat expensive in cost and time of subject involvement. In order to extend our knowledge of body composition and to quantitatively ascertain the mass of skeletal muscle, some of the procedures for calculating cell and muscle mass are reviewed including total body potassium, total body nitrogen, creatinine excretion, and 3-methylhistidine excretion. These procedures reveal important information, but require further investigation before we are confident that we are measuring cell or muscle mass. We have focused on 3-methylhistidine excretion because preliminary investigation suggests that it may reveal differences in muscle mass not detected by densitometry.

Body composition and expiratory reserve volume in female gymnasts and runners.

Previous research in this laboratory demonstrated a reduction in expiratory reserve volume of the lungs (ERV) with increasing body fatness (%F, by densitometry). The present study was done to determine if smaller ERV values could be demonstrated in lean female athletes with greater than normal upper-body muscle development. Expiratory reserve volume, vital capacity (VC), and segmental body volumes by densitometry were measured in members of two collegiate women's teams--gymnastics (G) (N = 10) and track (R) (N = 10). The runners provided a control group by being similar to gymnasts in age, weight, and body fatness, but they did not engage in upper-body weight training or gymnastic exercises. The two groups were not significantly different in body weight (means G +/- SD = 53.0 +/- 6.1 kg; means R = 50.8 +/- 4.6 kg) or %F (means G = 16.8 +/- 3.2%; means R = 14.8 +/- 3.8%), but R subjects were taller (means = 165.4 +/- 5.5 cm vs 158.7 +/- 4.8 cm, P less than 0.01). Expiratory reserve volume, expressed as a percent of VC, (ERV X VC-1) 100, was significantly (P less than 0.001) less in the gymnasts (means +/- SD = 29.7 +/- 7.1) as compared to the runners (43.1 +/- 6.4). All other lung capacities as volumes were comparable in both groups. Arm and thorax volumes indicated greater upper-body size in the G subjects (arm volume, means +/- SD of G = 4.8 +/- 0.6 liters, of R = 4.0 +/- 0.6 liters, P less than 0.01; thorax volume, means +/- SD of G = 7.8 +/- 1.4 liters, or R = 5.6 +/- 1.0 liters, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Fat-free mass as a function of maximal oxygen consumption and 24-hour urinary creatinine, and 3-methylhistidine excretion.

The relationships between maximal oxygen consumption (VO2max) with fat-free mass (FFM), and with 24-h urinary excretion of 3-methylhistidine (3MH) and creatinine (Cr), were studied in 12 active men age 31.4 +/- 9 yr (mean +/- SD). FFM, VO2max and VO2maxWt-1 were 50.9 +/- 9.1 kg, 3.8 +/- 0.9 L X min-1, and 54.8 +/- 9.4 ml X kg-1 X min-1, respectively. Urinary 3MH and Cr after 3 days on a meat-free diet were 213.9 +/- 30.8 mumol X day-1 and 1.60 +/- 0.3 g X day-1, respectively. 3MH X Cr-1 was 135.3 +/- 16.8 mumol X g-1 or 15.3 +/- 1.9 molar ratio X 10(3). The strongest (p less than 0.01) associations found were 3MH versus FFM, FFM versus VO2max, and 3MH versus VO2max. Other significant (p less than 0.05) relationships were Cr versus FFM, Cr versus 3MH, and Cr versus VO2max. Nonsignificant correlations were found for 3MH X Cr-1 versus VO2max X kg-1 X min-1 versus FFM, 3MH X Cr-1 versus VO2max, and FFM versus VO2max X kg-1 X min-1. The best predictor of FFM was 3MH. It was concluded that endogenous urinary 3MH excretion is a valid method to study human body composition and that 3MH is more closely related to FFM (r = 0.93) than VO2max (r = 0.78).