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 VO2.
Results:
Maximum heart rate was similar in females (191 [PLUS-MINUS SIGN] 9 bpm) and males (194 [PLUS-MINUS SIGN] 7 bpm), cardiac index at maximum exercise was lower in females (7.0 [PLUS-MINUS SIGN] 1.0 l/min/m2) than in males (8.3 [PLUS-MINUS SIGN] 1.4 l/min/m2, P < 0.05). Metabolic responses and RQ at maximum exercise were similar (females: 1.04 [PLUS-MINUS SIGN] 0.06 vs. males: 1.05 [PLUS-MINUS SIGN] 0.05). Peak VO2 was lower in females (2.37 [PLUS-MINUS SIGN] 0.34 l/min) than in males (3.38 [PLUS-MINUS SIGN] 0.49 l/min, P < 0.05). When peak VO2 was normalized to leg muscle mass sex differences disappeared (females: 161 [PLUS-MINUS SIGN] 21 ml/min/kg vs. males: 170 [PLUS-MINUS SIGN] 23 ml/min/kg). The increase in cardiac index during exercise is the key factor responsible for the greater peak VO2 in adolescent boys compared to girls.
Conclusions:
Differences in peak VO2 in adolescent boys and girls disappear when peak VO2 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.