RESUMO
PURPOSE: To examine the effect of normobaric hypoxia on pulmonary oxygen uptake (VËO2) and muscle oxygenation kinetics during incremental and moderate-intensity exercise in children. METHODS: Eight prepubertal boys (9-11 y) performed incremental cycle tests to exhaustion in both normoxia and hypoxia (fraction of inspired O2 of 15%) followed by repeat 6-minute transitions of moderate-intensity exercise in each condition over subsequent visits. RESULTS: Maximal oxygen uptake (VËO2max) was reduced in hypoxia compared with normoxia (1.69 [0.20] vs 1.87 [0.26] L·min-1, P = .028), although the gas exchange threshold was not altered in absolute terms (P = .33) or relative to VËO2max (P = .78). During moderate-intensity exercise, the phase II VËO2 time constant (τ) was increased in hypoxia (18 [9] vs 24 [8] s, P = .025), with deoxyhemoglobin τ unchanged (17 [8] vs 16 [6], P ≥ .28). CONCLUSIONS: In prepubertal boys, hypoxia reduced VËO2max and slowed VËO2 phase II kinetics during moderate-intensity exercise, despite unchanged deoxyhemoglobin kinetics. These data suggest an oxygen delivery dependence of VËO2max and moderate-intensity VËO2 kinetics under conditions of reduced oxygen availability in prepubertal boys.
RESUMO
Excess adipose tissue may promote chronic systemic inflammation and oxidative stress, causing endothelial damage. Early evidence indicates that obesity may be associated with poorer cerebral perfusion. The purpose of this study was to examine the relationship between body composition and cerebral hemodynamics. A total of 248 middle-aged adults (50-58 years old; 55% women) underwent a ramp test on a cycle-ergometer until volitional exhaustion. Gas exchange was assessed on a breath-by-breath basis. Mean middle cerebral artery velocity (MCAv) was measured using transcranial Doppler, and pulsatility index (PI) calculated. Body composition was assessed by dual X-ray absorptiometry. Statistical analyses were performed using a compositional data approach including a three-compartment model for body composition (trunk fat mass, extremities fat mass, and fat-free mass). The unadjusted models for the whole sample showed that trunk fat mass relative to other compartments was negatively associated with MCAvrest, MCAvmax, and gain, and positively associated with PImax; extremities fat mass relative to other compartments was positively associated with MCAvrest and MCAvmax, and negatively associated with PImax; and fat-free mass relative to other compartments was positively associated with PImax. These associations were sex-dependent, remaining in the women's subgroup. However, after adjusting for confounders, these associations became non-significant, except for PImax in the whole sample and women's subgroup. These findings suggest a possible association between cerebral hemodynamics and body composition in middle-aged adults, highlighting sex-specific differences. Moreover, our results indicate that higher trunk fat mass relative to other compartments may negatively impact cerebral hemodynamics, reducing MCAv and increasing PImax.