Boys vs men differences in muscular fatigue, muscle and cerebral oxygenation during maximal effort isometric contractions: the effect of muscle blood flow restriction.

PURPOSE: To examine whether the children's superiority, over adults, to resist fatigue during repeated maximal-efforts depends on their often-cited oxidative advantage, attributed to greater muscle blood flow and O2-delivery. We also investigated the mechanisms underlying child-adult differences in muscle-oxygenation (due to O2-supply or O2-utilization) and examined if there are age-differences in cerebral-oxygenation response (a brain-activation index).

METHODS

Eleven men (23.3 ± 1.8yrs) and eleven boys (11.6 ± 1.1 yrs) performed 15 maximal-effort handgrips (3-s contraction/3-s rest) under two conditions: free-flow circulation (FF) and arterial-occlusion (OCC). Force, muscle-oxygenation (TSImuscle) and cerebral-oxygenation (oxyhemoglobin-O2Hbcerebral; total hemoglobin-tHbcerebral; deoxyhemoglobin-HHbcerebral) were assessed.

RESULTS

In boys, force declined less (- 26.3 ± 2.6 vs. - 34.4 ± 2.4%) and at slower rate (- 1.56 ± 0.16 vs. - 2.24 ± 0.17%·rep-1) vs. men in FF (p < 0.01-0.05; d = 0.60-1.24). However, in OCC there were no age-differences in the magnitude (- 38.3 ± 3.0 vs. - 37.8 ± 3.0%) and rate (- 2.44 ± 0.26 vs. - 2.54 ± 0.26%·rep-1) of force decline. Boys compared to men, exhibited less TSImuscle decline in both protocols, and lower muscle VO2 (p < 0.05). Boys, also, presented a smaller O2Hbcerebral and tHbcerebral rise than men in FF; exercising with OCC increased the O2Hbcerebral and tHbcerebral response in boys. Using MVIC as a covariate in FF condition, abolished boys-men differences in force and TSImuscle decline and O2Hbcerebral rise.

CONCLUSION

During repeated maximal-efforts: (i) blood flow is a significant contributor to children's superiority over adults to resist fatigue; (ii) age-difference in muscle hypoxia/deoxygenation is rather attributed to men's greater metabolic demand than to lower muscle-perfusion; and (iii) cerebral oxygenation/blood volume increase more in men than boys under free circulation, implying greater brain activation.