Resting ECG in athletic and non-athletic adolescent boys: correlations with heart volume and cardiorespiratory fitness.

Resting ECG was recorded in 59 endurance trained athletic and 81 non-athletic boys aged 10-17 years and the findings were correlated with heart volume and cardiorespiratory fitness. The two groups were physically similar, but the athletes had significantly higher maximal oxygen uptake and the 15-17-year-old athletes had larger heart volumes. ECG findings were rather similar in both groups, the major differences being a lower heart rate in the athletes than in the controls (71 vs 82 beats/min) and a longer PQ interval (0.151 vs. 0.140 s) and a greater sum of SV2 and RV4 (59 vs. 50 mm) in the 15-17-year-old athletes. In the controls no correlation existed between precordial voltage criteria for ventricular hypertrophy and heart volume or between heart volume and cardiorespiratory fitness. Contrary to this, in the athletes both SV2 + RV5 and SV2 + RV4 correlated significantly (r about 0.40) with relative heart volume, and relative heart volume with both maximal oxygen uptake per kg (r = 0.41) and calculated work at heart rate 170 beats/min expressed per kg (r = 0.61). Our findings seem to indicate that as a consequence of endurance training the high level of cardiorespiratory fitness becomes related to a large heart volume. It is obvious that ECG changes due to relative vagal dominance develop earlier in the adolescent athletes than those attributable to anatomical changes.