E. R. Buskirk

Premature ventricular complexes induced by stress testing: Their frequency and response to physical conditioning☆

Abstract Premature ventricular complexes occurred with increasing frequency and in a greater proportion of men according to the work load imposed among 196 middle-aged “high risk” men free of manifest heart disease. The proportion of men with any ventricular ectopic activity increased from less than 3 percent at standing rest to 30 percent at the top work load, and from less than 3 percent at heart rates of 73 to 102 beats/min to over 50 percent at heart rates above 173 beats/min. Between the stress of a submaximal test (to heart rate 150) and a test to maximal oxygen consumption, there was a sizable increase (35 percent) in the yield of premature ventricular complexes and of complex forms and runs. The prognostic importance of ectopic beats during progressive stress tests required systematic study in populations. After an 18 month program of progressive conditioning exercise in these previously sedentary men, several analyses among subjects who adhered well to the program revealed that the work threshold for ectopic activity may have been increased, the proportion of men with ectopic beats diminished, and the frequency of premature ventricular complexes per man diminished. The results are suggestive but not conclusive that exercise favorably affects this aspect of cardiac activity. A more definitive study is indicated, using hygienic efforts to modify multiple influences on ectopic ventricular activity.

EFFECTS OF AN ENDURANCE TRAINING REGIMEN ON ASSESSMENT OF WORK CAPACITY IN PREPUBERTAL CHILDREN

The cardiovascular effects of a 12-week endurance training regimen were studied among normally active and healthy prepubertal children. Twenty-six 8- to 12-year-old children (20 boys and 6 girls) volunteered and 10 acted as control subjects. The training regimen consisted of distance running for progressively longer periods (from 10 to 35 min) 2 to 3 times per week, with 2 additional sessions per week devoted to running games. Those who were trained ran a cumulative average distance of 95.6 km (58.9 miles). Intensity of work was assessed from running pace and heart rate. The target workout intensity was 75% to 80% of aerobic capacity (Vo2 max). Growth and development accounted for increases in height, weight, body circumferences, and diameters, and fat-free body weight. Heart rate (HR) during submaximal workloads, both running and walking, decreased in the trained group (p less than 0.01) and (p less than 0.05). HRmax did not change, but Vo2 max increased significantly (average 7%) in the trained group but not in the controls. No significant change attributable to training was found for submaximal cardiac output, stroke volume, or arteriovenous oxygen difference. The Vo2 max value before conditioning was a relatively poor predictor of the magnitude of improvement in functional capacity, but those with higher initial Vo2 max logged more cumulative training mileage. It was concluded that prepubertal children respond to an endurance training regimen by improving their running capacity, which is, to a limited extent, associated with increased aerobic capacity.

Validity of the ultrasonic technique as a method of measuring subcutaneous adipose tissue.

Subcutaneous adipose tissue measurements, at abdomen, suprailiac, subscapular, and mid-triceps sites, made with the ultrasonic and skinfold caliper techniques were compared using data from 20 women and 17 men from a pool of subjects of 22 women and 20 men. In addition, comparisons were made between ultrasonic, soft-tissue roentgenographic and skinfold caliper techniques at the suprailiac and mid-triceps sites on 6 women and 12 men. Repeat measurements with the ultrasonic technique produced correlation coefficients of 0-87 and above. Correlations between skinfold caliper and ultrasonic measurements were generally higher among women than men over each of the four sites. A highly significant relationship, r = 0-88, was observed between the ultrasonic measurements and soft-tissue roentgenograms over the mid-triceps site. The correlation between the fat-muscle interface measured on the roentgenogram and ultrasonic measurements at the suprailiac site was 0-78. Multiple echoes and interfaces were observed at the suprailiac site on some subjects.

Physiological and perceptual indicators of physical stress in 41-to 60-year-old men who vary in conditioning level and in body fatness

ABSTRACTPerceived exertion during exercise was studied in 51 physically active and in 19 sedentary men, 41–60 years old, by the use of a numerical scale for rating of perceived exertion (RPE). The subjects, who varied in degree of adiposity, each had two or more characteristics associated with the p

A syndrome of periodic hypothalamic discharge

Abstract A fourteen year old boy is described who has had cyclical manifestations of nausea, vomiting, fever, emotional disturbance and marked weight change. Associated findings during the attacks were facial plethora, hypertension, abnormal glucose tolerance, elevated plasma ACTH and adrenal hyperfunction. The results of roentgenologic and physiologic studies are compatible with a lesion of the central nervous system, with periodic release of ACTH resulting in a clinical disease secondary to hyperadrenocorticism. The studies reported reaffirm the role of the hypothalamus in certain homeostatic mechanisms. The disease process was effectively suppressed with exogenous dexamethasone treatment during two periods of administration.

A comparison of methods of assessment of body composition including neutron activation analysis of total body nitrogen.

Fourteen healthy men underwent determinations of total body nitrogen (TBN) by prompt gamma neutron activation analysis and total body potassium (TBK) by whole body counting to estimate the muscle and nonmuscle components of the fat-free body mass (FFBM) and their protein contents. Comparison of FFBM estimated from TBN and TBK (60.6 +/- 6.9 kg, mean +/- SD), densitometry (62.3 +/- 7.1 kg), TBK alone (62.2 +/- 8.0 kg) and TBW (63.9 +/- 7.8 kg) showed no differences among the techniques. Similarly, there were neither differences in fat mass nor percent body fat among the methods. Analysis of the chemical composition of FFBM of this group showed TBK/FFBM = 62.6 +/- 2.3 mEq/kg, TBW/FFBM = 74.6 +/- 0.2%, TBN/FFBM = 32.74 +/- 1.09 g/kg, protein/FFBM = 20.5+/- 0.7%. The calculated mineral content of the FFBM was 6.4%. These values are strikingly similar to the values calculated by direct chemical analysis. It was concluded that the combined TBN-TBK method is a valid technique for estimating body composition in man.

Effects of daily and intermittent exposures on heat acclimation of women

Twelve women, who differed in physical condition and body size, were heat acclimated utilizing either a daily or intermittent (every 3rd day) exposure pattern in an environmental chamber. The women walked for 100 min at 5.2 km/h up a 2.5% grade on a motor-driven treadmill Climatic chamber conditions were 46.5°C Ta, 24.5°C Twb ± 0.5°C. Although individual acclimation varied, significant reduction in heat strain was observed in all subjects, e.g., the ability to complete the assigned task with increasing ease, a decrease in working heart rate, a decrease in rectal temperature rise, a decrease in mean skin temperature, an increase in sweat rate, an increase in evaporative rate, and a decrease in heat storage. The pattern of heat exposures, daily or every third day, had no discernible effect on the rate of heat acclimation. The highly conditioned subjects showed less physiological strain, particularly during the first few heat exposures, and maintained some relative advantage throughout the series of 10 exposures. Body size, in the range studied, appeared to exert little influence on the amount of thermal strain.

HEAT ACCLIMATIZATION PATTERNS IN OBESE AND LEAN INDIVIDUALS

An investigation is presented of artificial heat acclimatization in women and men who varied widely in body composition, particularly body fatness. The subjects were intentionally selected to include individuals who were habitually active physically and those who were not. To date, only limited evidence is available in the literature to suggest that women acclimatize to heat in a manner similar to Women have also been studied in hot environments that simulated industrial situations3 and their physiological responses to moderate heat while resting have been appraised.225 On the average, body fatness tends to be higher in women than men and this factor may play a role in the lower limits of endurance in women exposed to heat as compared to men. It has been reported that obese individuals are more susceptible to heat injury than the This fact coupled with the conclusion that the larger individual because of his smaller surface area per unit of heat producing mass has a lower work capacity in the heat,15 stimulated us to start exploration of the impact of body fatness on ability to tolerate exercise in the heat.

The Effect of Heat Stress on Reaction Time to Centrally and Peripherally Presented Stimuli

The effect of heat stress on reaction time to centrally and to peripherally presented stimuli was determined for lean and obese subjects whose work levels on a treadmill in a heat chamber produced either a 2.5 or 5% loss of body weight in six hours. Peripheral reaction time improved with practice, but central reaction time was not affected. Obesity, eccentricity of the peripheral stimulus, and the level of dehydration did not have significant effects on reaction time. It was concluded that, for short periods of time, the effects of heat stress can be overcome for highly motivated and experienced subjects.

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.