This symposium was organized to highlight new information regarding the mechanisms through which physical activity and exercise may affect the process of growth. Exercise associated anabolic effects (i.e., constructive or biosynthetic metabolic processes involved in tissue adaptation to physical activity) are varied and modulated by maturational and nutritional factors. Nonetheless, identifying common processes responsible for the many anabolic effects of physical activity may improve the ways exercise can be used in rehabilitation programs and to promote health. Thus, the overall aim of this symposium is to explore the diverse mechanisms that link physical activity with growth at both the cellular and somatic level. A conceptual model is presented that includes the interaction of central and local components of exercise modulation of growth. Central components encompass the mechanisms through which exercise of skeletal muscle groups can seemingly affect cellular growth and function throughout the body. Local components encompass those mechanisms that stimulate growth, hypertrophy, and the appearance of new mitochondria and capillaries in the muscle, bone, vascular and connective tissues involved in the specific exercise. The physiology of these putative mechanisms and their clinical applications are developed from six different perspectives.

PURPOSE: Cardiopulmonary exercise testing (CPET) is increasingly used as a biomarker of fitness in children. Maximal or peak values remain the most common variables obtained in CPET, but these physiologically challenging high-intensity work rates (WR) are often not achieved. We hypothesized that interactions of gas exchange, heart rate (HR), and WR CPET variables (slopes) could yield useful mechanistic and clinical insights that might enhance the clinical utility of CPET in children. We further hypothesized that the dependence of the slope on body mass could be predicted by the first-principle analysis of body size and physiological response. METHODS: One hundred and sixty-nine healthy participants (8-18 yr old, body mass index <95th percentile, 82 females) underwent dual x-ray absorptiometry scan to estimate lean body mass (LBM) and performed a ramp-type progressive cycle ergometry exercise protocol with a breath-by-breath measurement of gas exchange. Linear regression was used to calculate the slopes among VO2, VCO2, VE, HR, and WR. RESULTS: ΔWR/ΔHR (r = 0.87) and ΔVO2/ΔHR (r = 0.96) were strongly correlated with VO2peak, whereas ΔVO2/ΔWR (r = 0.42) and ΔVE/ΔVCO2 (r = -0.51) were mildly correlated with peak values. LBM was more highly correlated with those slopes predicted to be body size dependent (P < 0.0001) compared with total body mass. CONCLUSIONS: The data largely supported our original hypotheses. Unlike peak or maximal values, which are derived from no more than a few data points at the end of a progressive exercise test, the CPET slopes were calculated from a much larger data set obtained throughout the test. An analysis of these slopes might ultimately prove useful clinically and in research studies when peak values are not achieved.

The relation between fitness and adiposity is particularly relevant to adolescent females in whom fitness is known to decrease and fatness to increase. However, little is known about the interaction of these variables in normally active, nonobese subjects. Our major hypotheses were that adiposity would be inversely correlated with physical fitness and that even a relatively brief intervention would lead to measurable, site-specific changes in body fat. We used a cross-sectional protocol to correlate body adiposity with indexes of fitness and a prospective study design to examine body adiposity before and after a 5-wk period of endurance training in 44 nonobese females aged 15-17 y (control group, n = 22; training group, n = 22). Adiposity was assessed by magnetic resonance imaging of the abdomen and thigh as well as by standard skinfold-thickness measuring techniques. Fitness was assessed by using cycle ergometer measurements of maximal oxygen uptake (VO2max). There were significant negative correlations between VO2max normalized to body weight and subcutaneous abdominal, thigh, and skinfold estimates of fat. However, when VO2 max was normalized to muscle volume these correlations were not significant. Abdominal fat increased in direct proportion to body weight (scaling factor = 1.14 +/- 0.16) but thigh fat increased proportionately less (scaling factor = 0.38 +/- 0.12, P < 0.05). Training increased thigh muscle mass significantly only in the midmuscle region and prevented the observed fat increase in the distal thigh of the control subjects. Body fat distribution in adolescent females appeared to be affected by many factors, including overall body weight and the level of physical activity.

To test the hypothesis that ventilatory responses to exercise mature during growth in healthy children, we examined CO2 production (VCO2) and minute ventilation (VE) before, during, and for 10 min after 1-min bursts of cycle ergometry exercise. Ten children (range: 7-11 y old) and 13 adults (26-42 y old) exercised at work rates corresponding to 50 and 80% of the anaerobic or lactate threshold, 50% of the difference between anaerobic threshold and maximum O2 consumption, 100% of maximum O2 consumption, and 125% of maximum O2 consumption (125% max). Gas exchange was measured breath by breath. Children recovered faster from high-intensity (above anaerobic threshold) exercise as judged by the time constant of single exponential curve-fits to postexercise VCO2 [55 +/- 10 s (1 SD) at 125%. max in children compared with 92 +/- 17 s at 125% max in adults; p less than 0.001] and VE (58 +/- 10 s at 125% max in children compared with 125 +/- 37 s in adults, p less than 0.001). Although we found no significant difference between VCO2 and VE recovery times in children, VE was significantly slower than VCO2 in adults for high-intensity exercise. Moreover, recovery times in adults increased with work intensity but were independent of them in children. Whereas the CO2 costs [calculated as total CO2 produced above baseline per unit work done (mL.J-1)] increased with work intensity in adults, no similar significant relationship was observed in children.(ABSTRACT TRUNCATED AT 250 WORDS)