Effect of whey vs. soy protein supplementation on recovery kinetics following speed endurance training in competitive male soccer players: a randomized controlled trial

Background: Soccer-specific speed-endurance training induces short-term neuromuscular fatigue and performance
deterioration over a 72-h recovery period, associated with elevated markers of exercise-induced muscle damage.
We compared the effects of whey vs. soy protein supplementation on field activity, performance, muscle damage
and redox responses following speed-endurance training in soccer players.
Methods: Ten well-trained, male soccer players completed three speed-endurance training trials, receiving whey
protein (WP), soy protein (SP) or an isoenergetic placebo (PL; maltodextrin) according to a randomized, doubleblind, crossover, repeated-measures design. A pre-loading period was applied in each trial during which protein
supplementation was individually adjusted to reach a total protein intake of 1.5 g/kg/day, whereas in PL protein
intake was adjusted at 0.8–1 g/kg/day. Following pre-loading, two speed-endurance training sessions (1 and 2) were
performed 1 day apart, over a 3-day experimental period. During each session, field activity and heart rate were
continuously monitored using global positioning system and heart rate monitors, respectively. Performance
(isokinetic strength of knee extensors and flexors, maximal voluntary isometric contraction, speed, repeated sprint
ability, countermovement jump), muscle damage (delayed-onset of muscle soreness, creatine kinase activity) and
redox status (glutathione, total antioxidant capacity, protein carbonyls) were evaluated at baseline (pre), following
pre-loading (post-load), and during recovery from speed-endurance training