The efficacy of protein supplementation during recovery from muscle-damaging concurrent exercise

This study investigated the effect of protein supplementation on recovery following muscle-damaging exercise, which was induced with a concurrent exercise design. Twenty-four well-trained male cyclists were randomised to 3 independent groups receiving 20 g protein hydrolysate, iso-caloric carbohydrate, or low-calorific placebo supplementation, per serve. Supplement serves were provided twice daily, from the onset of the muscle-damaging exercise, for a total of 4 days and in addition to a controlled diet (6 g·kg^-1·day^-1 carbohydrate, 1.2 g·kg^-1·day^-1 protein, remainder from fat). Following the concurrent exercise session at time-point 0 h, comprising a simulated high-intensity road cycling trial and 100 drop-jumps, recovery of outcome measures was assessed at 24, 48, and 72 h. The concurrent exercise protocol was deemed to have caused exercise-induced muscle damage (EIMD), owing to time effects (p < 0.001), confirming decrements in maximal voluntary contraction (peaking at 15% ± 10%) and countermovement jump performance (peaking at 8% ± 7%), along with increased muscle soreness, creatine kinase, and C-reactive protein concentrations. No group or interaction effects (p > 0.05) were observed for any of the outcome measures. The present results indicate that protein supplementation does not attenuate any of the indirect indices of EIMD imposed by concurrent exercise, when employing great rigour around the provision of a quality habitual diet and the provision of appropriate supplemental controls.