Salvadego et al.36 studied the pulmonary oxygen uptake kinetic response to constant load exercise of varying intensities (40%, 60%, and 80% of estimated peak VO2) in 14 obese (BMI >97th percentile) and 13 non-obese adolescent boys. They found a slower primary component during low intensity (40% peak VO2) exercise in the obese boys, suggesting a greater oxygen

deficit and therefore increased metabolic contribution from anaerobic glycolysis, lowering exercise tolerance. check details What are the implications of this for daily PA patterns? Essentially, making rapid and frequent transitions between sedentary activities and low to moderate intensity PA will be more fatiguing in the obese children. Therefore one would expect longer rest periods and fewer activity bouts, which corresponds to the findings of McManus and colleagues.23 In Selleckchem PD0332991 the same study, a slow component was apparent during heavy intensity (80% peak VO2) exercise in both the lean and obese boys.36 Although the relative amplitude of the

slow component was similar between the two groups, the best fit for the pulmonary oxygen uptake kinetic response during the slow component was a linear function in the obese, and exponential function in the normal weight boys. A significant inverse relationship was reported for the slope of the linear increase in oxygen uptake and time to exhaustion during the slow component and lends supports to the proposition that during high-intensity PA obese children will

experience greater levels of fatigue because they will attain maximum quicker. This may well account for the lower levels of moderate to vigorous PA noted in studies of free-living PA in obese youngsters.16 and 17 Caution in making such conclusions from the findings of this study are warranted however, given that the intensity of the constant load exercise bouts utilized corresponded to a percentage of peak oxygen uptake, rather than to individual gas exchange threshold values. This may have resulted in the obese children working at a higher relative workload, which appears to be the case at 60% of maximal oxygen uptake and where nine of the 14 obese adolescents displayed a slow component, not apparent in any of the non obese adolescents. In human muscles there is substantial variability in fiber type proportions. Muscle fiber typing usually categorizes the many differing skeletal muscle fibers into three main groups (Type I, Type IIa, and Type IIb) according to their relative speed of contraction and metabolic properties. Type I or slow twitch fibers are smaller, slower to contract, and not capable of generating as much force as Type II fibers. Type I fibers are fatigue resistant; that is, they can continue to contract repeatedly without undue fatigue.