Sex differences in response to maximal exercise stress test in trained adolescents

BACKGROUND Sex comparisons between girls and boys in response to exercise in trained adolescents are missing and we investigated similarities and differences as a basis for clinical interpretation and guidance. METHODS A total of 24 adolescent females and 27 adolescent males aged 13-19 years underwent a maximal bicycle exercise stress test with measurement of cardiovascular variables, cardiac output, lung volumes, metabolic factors/lactate concentrations and breath-by-breath monitoring of ventilation, and determination of peak VO(2). RESULTS Maximum heart rate was similar in females (191 ± 9 bpm) and males (194 ± 7 bpm), cardiac index at maximum exercise was lower in females (7.0 ± 1.0 l/min/m(2)) than in males (8.3 ± 1.4 l/min/m(2), P < 0.05). Metabolic responses and RQ at maximum exercise were similar (females: 1.04 ± 0.06 vs. males: 1.05 ± 0.05). Peak VO(2) was lower in females (2.37 ± 0.34 l/min) than in males (3.38 ± 0.49 l/min, P < 0.05). When peak VO(2) was normalized to leg muscle mass sex differences disappeared (females: 161 ± 21 ml/min/kg vs. males: 170 ± 23 ml/min/kg). The increase in cardiac index during exercise is the key factor responsible for the greater peak VO(2) in adolescent boys compared to girls. CONCLUSIONS Differences in peak VO(2) in adolescent boys and girls disappear when peak VO(2) is normalized to estimated leg muscle mass and therefore provide a tool to conduct individual and intersex comparisons of fitness when evaluating adolescent athletes in aerobic sports.