Abstract
This study examined acute neuromuscular, biochemical, and subjective fatigue responses to two strength training protocols-back squats with calf raises vs. back squats with plyometric exercises-in elite youth soccer players. The aim was to track the progression and resolution of fatigue over a 72 h recovery period and evaluate the practical feasibility of both protocols within high-performance training schedules. Thirty-two male athletes from a national youth elite training center participated in a crossover-controlled study. Each player completed both interventions, separated by an 8-day washout period. A comprehensive test battery assessed neuromuscular performance via the countermovement jump (CMJ), drop jump, isometric mid-thigh pull, adductor squeeze, and sit-and-reach test; biochemical markers via creatine kinase (CK); and subjective markers using the Hooper Index, visual analog scale (VAS), and session rating of perceived exertion (sRPE). Measurements were taken at baseline and 24, 48, and 72 h post-exercise. No significant interaction effects (training modality × time) were found (p > 0.05), indicating comparable fatigue and recovery trajectories for both protocols, whereas significant main effects of time were observed across all parameters, including CMJ [F(3,26) = 29.373, p < 0.001, η (2) = 0.772] and CK [F(3,26) = 51.504, p < 0.001, η (2) = 0.856]. Fatigue peaked between 24 and 48 h post-exercise and returned to baseline by 72 h. Subjective fatigue (Hooper, VAS) mirrored objective markers. Both traditional and reactive strength training induced short-term fatigue that resolved within 72 h, supporting their safe implementation in elite youth training programs, provided adequate recovery is allowed between sessions.