Adaptation to a standardized training program and changes in fitness in a large, heterogeneous population: the HERITAGE Family Study.

PURPOSE: This paper describes the variations in response to a standardized, computer-controlled training program. METHODS: Steady-state heart rate (HR) and oxygen intake (VO2) of 614 healthy, sedentary men and women aged 16-65 yr were measured during three cycle ergometer exercise tests. The HR associated with 55, 65, 70, and 75% of each subject's pretraining VO2max was used to prescribe exercise intensity. Subjects exercised three times a week, beginning at a HR associated with 55% VO2max for 30 min. Duration and intensity was gradually increased over 20 wk of training. The duration and HR of each training session were controlled by a computer. RESULTS: Using the linear relationship between HR, VO2 and power output (PO), PO were predicted for each of 60 training sessions at the respective programmed HR. The average ratio of the actual training HR to programmed HR was 0.99. It was hypothesized that participants whose actual training PO exceeded their predicted PO would improve VO2max more than those whose actual PO was less than their predicted PO. Using the ratio of actual/predicted PO determined after the training was over, participants were arbitrarily assigned to three groups: 128 participants had low (LO) ratios (0.65-0.84), 408 had average (AV) ratios (0.85-1.14), and 78 had high (HI) ratios (1.15-1.34). Secondary analysis showed that the training program significantly increased mean VO2max of all three groups. Those who had a smaller increase in training PO (LO) had significantly less increase in VO2max than those with larger increases in PO (HI). CONCLUSION: People who exercise at a HR associated with the same %VO2max can vary substantially in their training PO, in their rate of increase in PO over a 20-wk training program, and in improvement of their VO2max.

Reproducibility of maximal exercise test data in the HERITAGE family study.

PURPOSE: The reproducibility of responses to maximal cycle ergometer testing was determined using data from the HERITAGE Family study at four Clinical Centers in the United States and Canada. METHODS: Reproducibility was determined from maximal exercise test data obtained a) on 2 d in a sample of 390 subjects (198 men and 192 women), b) across 4 d in an Intracenter Quality Control (ICQC) substudy with 55 subjects who were not part of the main study, and c) across 2 wk in a Traveling Crew Quality Control (TCQC) substudy with the same eight subjects who were tested at each of the four centers. Reproducibility was evaluated using technical errors, coefficients of variation (CV) for repeated measures, and intraclass correlation coefficients (ICC) for selected variables obtained on the main cohort, as well as on the ICQC and TCQC substudies. RESULTS: With the exception of systolic and diastolic blood pressures and respiratory exchange ratio, all the other variables (heart rate, ventilation, VO2, and VCO2) were highly reproducible, with CV below 10% and ICC over 0.86. These results were similar to those previously reported on the same subjects at a submaximal power output associated with 60% VO2max. Results were consistent for the main cohort, the ICQC sample, the TCQC sample, and across all four Clinical Centers. CONCLUSIONS: Day-to-day variations are small and reproducibility is high for maximal values of heart rate, ventilation, VO2 and VCO2 at each of the four Clinical Centers of the HERITAGE Family Study.

Comparison of bioelectric impedance and near-infrared interactance for body composition assessment in a population of self-perceived overweight adults.

This study was conducted to determine the reliability and validity of bioelectric impedance (BIA) and near-infrared interactance (NIR) for body composition assessment in a population that considered themselves to be overweight, using hydrostatic weighing (HW) as the criterion method. Skinfold measurements were also taken for comparison, and the Jackson and Pollock (J-P) and Durnin and Womersley (D-W) equations were used to determine relative body fat. One hundred men and women, ages 18-61, with 15.5-43.3% body fat participated in the study. Reliability correlations for relative body fat (n = 19) were high for the skinfold equations (r = 0.99) and BIA (r = 0.95) and lower for NIR (r = 0.88). Analysis of variance showed that BIA, NIR, and J-P all significantly underestimated relative body fat in this population, while D-W significantly overestimated relative body fat. BIA, relative to HW, had correlations of r = 0.80-0.86 and SEEs of 3.4-3.6% body fat, while correlations for NIR were lower (r = 0.66-0.77) and SEEs were higher (3.8-4.3%) than for BIA. Correlations between D-W and HW ranged from r = 0.72 to 0.84 (SEE = 3.4-4.1%), while similar results were found for the J-P equations (r = 0.72 to 0.86, SEE = 3.0-4.1). BIA predicted 72% of the subjects within 4% of HW values while NIR, D-W, and J-P predicted only 61, 59 and 58%, respectively, within this same range.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate metabolism during exercise in hot and thermoneutral environments.

This study compared the effects of moderately intense exercise in hot and thermoneutral environments on muscle glycogen and carbohydrate utilization. Well-trained, heat acclimatized cyclists (n = 7) rode at 73.6 +/- 1.1% maximal oxygen consumption for 60 min in a thermoneutral room (23.5 +/- 0.6 degrees C, 52.7 +/- 2.9 relative humidity) or an environmental chamber (33.7 +/- 0.1 degrees C, 49.1 +/- 1.8% relative humidity). During each exercise bout, the subjects received 125 ml of water every 15 min. Muscle biopsies from the vastus lateralis were obtained prior to and following each exercise bout. Exercise in the heat significantly elevated rectal temperature and heart rate above and reduced body weight and plasma volume below that produced by exercise in a thermoneutral environment. Plasma glucose and blood lactate concentrations were similar between treatments prior to exercise, but increased to a greater concentration (p < 0.05) when exercise was performed in the heat. No differences between treatments were found for blood glycerol or free fatty acid concentrations, carbohydrate oxidation or muscle glycogen utilization. These results suggest that moderately intense exercise in the heat, as opposed to a thermoneutral environment, does not increase the rate of muscle glycogenolysis or carbohydrate oxidation in well conditioned, heat acclimatized subjects.

Use of skinfolds and bioelectrical impedance for body composition assessment after weight reduction.

The purpose of this study was to determine the accuracy of standard methods for estimating body composition in individuals who have undergone substantial and rapid weight loss. Subjects included 14 participants in a rapid weight reduction program using a very low-calorie diet, and 14 individuals of normal body composition matched with the obese group on the basis of gender, age, and height. Bioelectrical impedance (BI) and skinfold-derived estimates of relative body fat were compared with hydrostatic weighing in both groups. On the basis of mean values, standard errors of estimate (SEE) and simple correlations, none of the skinfold equations or the BI procedure were very accurate in the prediction of body fat in the group of weight-reduced obese patients. The Durnin-Rahaman (D-R) and Durnin-Womersley (D-W) equations were not significantly different from the hydrostatically determined values; however, correlations were low (r = 0.69 and 0.60). The Jackson-Pollock (J-P) equations and BI technique had high correlations (r = 0.78 and 0.89), but were significantly different from hydrostatic weighing. SEE for all equations and BI were high (greater than 4.5%). The control group was best predicted by the J-P equation (r = 0.88, SEE 3.5%, mean value of 21.2 +/- 4.3 vs 22.4 +/- 6.2%). BI and the D-R equation were also reasonably accurate. We conclude that additional research will be necessary to identify a predictive equation using skinfolds or BI that will provide more accurate estimates of relative body fat in individuals who have undergone substantial weight reduction in a relatively short period of time.

Is there energy conservation in amenorrheic compared with eumenorrheic distance runners?

The female distance runner is considered at high risk for secondary amenorrhea and reduced spinal bone mineral, and recent studies have suggested that these disturbances might be nutritionally or metabolically linked. The present study investigated 1) whether there is a physiological basis by which the amenorrheic runner might maintain weight at a lower than expected caloric intake, i.e., conservation of energy, and 2) the potential interactions of reduced energy intake, secondary amenorrhea, and reductions in bone density. Subjects included 13 elite female distance runners, 8 amenorrheic and 5 eumenorrheic, and 5 untrained female controls. Body composition by hydrostatic weighing, bone density and mineral content by dual-photon absorptiometry, and blood samples for hormonal analyses (once per week for 4 wk) were obtained, as were duplicate measures for resting metabolic rate, thermic effect of a meal, and the energy cost of specific (treadmill) and nonspecific (cycle ergometer) physical activity. Energy intake and energy expenditure were estimated by 3-day logs. Energy intakes did not differ (1,781, 1,690, and 1,763 kcal), nor did energy expenditures (2,480, 2,314, and 2,268 kcal), for the amenorrheic and eumenorrheic runner and control groups, respectively. The difference between reported energy intake and estimated energy expenditure of 500-700 kcal was likely due to underreporting or restricting intake, inasmuch as there was no evidence of energy conservation. A possible link was suggested between disordered eating, secondary amenorrhea, and bone mineral loss.