The oxygen uptake kinetic response to moderate intensity exercise in overweight and non-overweight children

To compare the phase II oxygen uptake time constant (τV'O(2)) and V'O(2) mean response time (V'O(2)MRT) in overweight (OW) and non-OW (NO) children during moderate intensity exercise.

Between subjects where participants completed a maximal ramp exercise test on an electromagnetically braked cycle ergometer to determine peak V'O(2) (V'O(2peak)) and gas exchange threshold (GET). Gas exchange was measured breath-by-breath using a mass spectrometer. On subsequent visits, 6 square-wave transitions (2 per day) from 0 W to 90% GET were completed. Individual phase II τV'O(2) and V'O(2)MRTs were estimated from time aligned average V'O(2) traces.

Eleven OW (11.8±0.4 years) and 12 NO (11.9±0.4 years) children were recruited to the study. The OW group was significantly heavier (62.9±9.7 vs 39.4±5.8 kg, P<0.001), taller (1.58±0.05 vs 1.47±0.07 m, P<0.001) and had a higher body mass index (25.8±3.4 vs 18.3±1.8 kg m(-2), P<0.001).

Both τV'O(2) (30.2±9.6 vs 22.8±7.1 s, P<0.05) and V'O(2)MRT (43.5±10.7 vs 36.3±5.3 s, P<0.05) were significantly slower in OW compared with NO children; absolute V'O(2peak) was higher in the OW compared with NO group (2.23±0.04 vs 1.74±0.04 l min(-1), P<0.05); mass relative V'O(2peak) was lower in OW compared with NO children (35.9±8.3 vs 43.8±6.2 ml kg(-1) min(-1), P<0.05); allometrically scaled V'O(2peak) was similar between OW and NO groups whether relative to body mass(0.67) (139.8±29.1 vs 147.2±23.9 ml kg(-67) min(-1)) or stature(3) (576.0±87.2 vs 544.9±84.9 ml m(-3) min(-1)) (P>0.05); absolute V'O(2) at GET was similar between OW and NO groups (0.94±0.24 vs 0.78±0.27 l min(-1), P>0.05); GET expressed as percentage of V'O(2peak) was similar between the groups (42.0±0.1 vs 44.8±0.1%, P>0.05).

These findings demonstrate impairment in the factors determining V'O(2) kinetics in OW children at a relatively young age. Furthermore, assessment of cardiorespiratory fitness using peak exercise values is likely to be misleading and not useful when designing exercise programmes for OW children.