Objectives

American female adolescents are at high risk of a physically inactive lifestyle that likely leads to health problems later in life. We hypothesized that a brief program of endurance exercise training in female adolescents would result in increased energy expenditure and quantifiable structural and functional adaptations.

Study design

Forty-four high school girls (aged 15 to 17 years, none were elite athletes) enrolled in a 5-day per week anatomy class for 5 weeks and were randomly assigned to control (n = 22) and training groups. All subjects participated in a 2-hour daily teaching program. During the remaining time (2 hours), the training group members underwent endurance-type training and control group subjects participated in a computer workshop. The intervention was assessed by (1) comparison of total energy expenditure between groups with the doubly labeled water technique, (2) determination of changes in thigh muscle volume by magnetic resonance imaging, and (3) determination of changes in maximal oxygen uptake by use of respiratory gas exchange responses.

Results

Total energy expenditure was significantly greater (15.3%) in the training group compared with the control subjects (p < 0.003). Five weeks of training led to a 4.3% +/- 1% increase in thigh muscle volume (p < 0.0002) and a 12.1% +/- 3.7% increase in maximal oxygen uptake (p < 0.004); there were no changes in the control group. The training effect was most pronounced in the least fit subjects.

Conclusions

Exercise training programs for female adolescents can be successfully integrated into a high school summer curriculum. Quantifiable, substantial structural and functional responses occur with relatively short periods of training. Approximately 60% of the training response was related to factors independent of muscle size per se. These data may serve to better design physical activity programs for female adolescents.