BACK SQUAT AND DEADLIFT FATIGUING PROTOCOLS ELICIT DISTINCT COUNTERMOVEMENT JUMP PROFILES: PHASE-SPECIFIC PREDICTORS AND SORENESS RESPONSES

INTRODUCTION: Residual fatigue following resistance exercise can compromise neuromuscular performance and modu late recovery kinetics. The back squat (BSQ) and deadlift (DL) are primary lower-limb multi-joint exercises, yet their fatigue and recovery profiles may differ substantially. Phase-specific countermovement jump (CMJ) metrics may provide greater sensitivity for detecting neuromuscular impairment beyond traditional jump height assessment. This study investigated the acute and 24-hour effects of BSQ and DL on CMJ through force-time curve analysis. METHODS: Fifty-four resistance trained adults (>=1 year experience) were randomly allocated to BSQ, DL, or control (CON). Following one-repetition maxi mum (1RM) estimation, BSQ and DL performed 3 x 12 repetitions at 70% 1RM. CMJ testing using a force platform was con ducted at baseline (T0), immediately post-exercise (T1), 30 minutes post-exercise (T30min), and 24 hours after exercise (T24h). Phase-specific CMJ variables, RSImod, and delayed onset muscle soreness (DOMS; 24-48 h) were analyzed. Per centage changes within conditions and differences versus CON (d) were calculated. RESULTS: Both BSQ and DL induced significant decrements in CMJ performance and greater DOMS compared with CON. BSQ reduced jump height at T30min (-7.45%; d=7.32%; p=0.04) and T24h (-1.12%; d=8.13%; p=0.05), whereas DL decreased jump height at T24h (-2.26%; d=9.27%; p=0.01). DL elicited marked reductions in eccentric braking rate of force development at T30min (-17.89%; d=16.61%; p=0.03) and T24h (-13.04%; d=13.41%; p=0.02). Time-related alterations were prominent following BSQ: total jump time decreased at T30min (-4.61%; d=8.42%; p=0.02) and T24h (-2.88%; d=10.01%; p=0.02). Unloading duration decreased in BSQ at T1 (-9.47%; d=13.53%; p=0.01), T30min (-13.10%; d=21.46%; p=0.02), and T24h (-13.61%; d=30.21%; p=0.002), while DL showed reductions only at T24h (-2.75%; d=19.36%; p=0.03). Concentric work declined after BSQ at T1 (-7.07%; d=6.71%; p=0.009), T30min (-8.36%; d=9.70%; p<0.001), and T24h (-0.85%; d=8.92%; p=0.007). RSImod de creased significantly in DL at T24h (-7.14%; d=9.22%; p=0.03). CONCLUSION: A single 3 x 12 session of BSQ or DL at 70% 1RM significantly impairs explosive neuromuscular performance; however, the magnitude and temporal pattern of im pairment differ between exercises. BSQ induced greater immediate mechanical perturbations, with partial recovery of jump height by 24 h. Conversely, DL produced smaller acute decrements but persistent deficits in force development. Notably, phase-specific CMJ metrics and RSImod showed substantial hidden fatigue that was not detectable through jump height alone. These findings emphasize that traditional performance measures can underestimate residual neuro muscular decline, highlighting the importance of analyzing the CMJ force-time curve profile for guiding recovery strategies and optimizing training load prescription.