Variable Degrees of Exercise Capacity Characterized by Comprehensive Cardiopulmonary Exercise Testing among Contemporary Adolescents.

We aimed to characterize underlying physiological mechanisms of variable exercise capacity in normal adolescents. Cardiopulmonary exercise testing (CPET) of disease-free (normal) adolescents was studied retrospectively. The cohort was divided into three groups based on %predicted maximum oxygen consumption (VO2)/kg: < 80% (poor), 80-100% (average), and > 100% (superior) performers. Peak and submaximal CPET parameters were analyzed to correlate with the level of exercise performance. Normal 115 males (29/43/43 in poor/average/superior groups) and 118 females (33/53/32) were studied. Age, peak (p) heart rate (HR), and HR reserve (HRR) were comparable in all groups. There was a positive correlation between pVO2/kg and peak oxygen pulse (OP)/kg (r = 0.93 and 0.95 in males and females, respectively) and between pVO2/kg and a slope of [VO2/kg]/heart rate (HR) (Δ[VO2/kg]/ΔHR) (r = 0.58 and 0.53 in males and females, respectively), whereas pVO2/kg revealed negative correlation with HR/[work rate (WR)/kg] slope (ΔHR/Δ[WR/kg]), HR-dependency (r = -0.33 and -0.27, in males and females, respectively), suggesting peak exercise performance is correlated with stroke volume (SV). Peak WR/kg, ventilatory anaerobic threshold (VAT)/kg, oxygen uptake efficiency slope (OUES)/kg, and submaximal slope of VO2/WR (ΔVO2/ΔWR) showed the same trend as peak VO2/kg. There were stepwise differences among three groups in regression lines of pWR-pVO2, VAT-pVO2, and peak minute ventilation (VE)-pVO2 relationships, suggesting peak exercise capacity was also influenced by aerobic work efficiency (muscle), endurance under an anaerobic condition, and ventilatory oxygenation efficiency (lung), respectively. Submaximal slope of VE/CO2 production (VCO2) (ΔVE/ΔVCO2) was comparable in all groups. Variable levels of exercise capacity in normal adolescents may be influenced by SV, central (lung) and peripheral (muscle) oxygen uptake efficiency, and exercise tolerance beyond anaerobic threshold, but not by chronotropic reserve or ventilatory efficiency of CO2 excretion.