Author(s): PYNN, J., WEBER, J., HAYWARD, S., LANOVAZ, J., FARTHING, J., Institution: UNIVERSITY OF SASKATCHEWAN, Country: CANADA, Abstract-ID: 2721

INTRODUCTION:
Jump testing is commonly used to monitor neuromuscular fatigue. The countermovement rebound jump (CMRJ), consisting of a countermovement jump (CMJ) followed immediately by a rebound jump (RJ), may be sensitive through eccentric or “braking” metrics. Limited research has assessed CMRJ monitoring across a university volleyball season. This study examined day (pre- vs post-competition), weekend (week-to-week), sex, and match exposure (high vs low sets played) effects on CMRJ force-time output and braking metrics across the season.
METHODS:
Thirty-two university volleyball athletes (15 male: age=20.8±1.8y, height=193.9±8.1cm, mass=90.6±10.5kg; 17 female: age=20.5±1.4y, height=181.5±7.5cm, mass= 70.2±8.6kg) were tested across four competition weekends (two matches/weekend). Athletes completed three CMRJ repetitions on Day 1 (24h pre-competition) and Day 2 (48h post-competition); trials were averaged. Force-time data were collected on dual force plates (Hawkin Dynamics). Extracted metrics were: CMJ-jump height (CMJ-H), modified reactive strength index (CMJ-mRSI), average relative braking force (CMJ-rABF), and average relative braking power (CMJ-rABP); and RJ metrics - jump height (RJ-H), modified reactive strength index (RJ-mRSI), average relative braking force (RJ-rABF), average relative braking power (RJ-rABP), and relative braking net impulse (RJ-rBNI). Match exposure was sets played (high ≥ 5; low <5). Linear mixed-effects models tested fixed effects of day, week, sex, and exposure (including interactions), with participant ID as a random effect.
RESULTS:
Day×exposure interactions were observed for CMJ-rABF, CMJ-rABP and RJ-rABP (all p<.05). CMJ-rABF demonstrated a day×sex×exposure interaction (p<.05); males showed significant Day 1-Day 2 reduction in high exposure (Δ=-12.1%BW, p<.001) but not low exposure (p=.165), females showed reductions in high (Δ=-6.1%BW, p=.003) and low exposure (Δ=-5.1%BW, p=.006). For CMJ-rABP, significant day×sex (p=.025) and day×exposure (p=.002) interactions were observed; Day 1-Day 2 change was greater in males (Δ=-1.19W*kg⁻¹) than females (Δ=-0.53W*kg⁻¹), and greater in high (Δ=-1.31W*kg⁻¹) vs. low exposure (Δ=-0.41W*kg⁻¹). RJ-rBNI showed a significant day×exposure interaction (p<.001), where Day 1-Day 2 differences were significant for high (Δ=-0.028 Ns*kg⁻¹, p=.040) and low (Δ=0.043 Ns*kg⁻¹, p<.001) exposure. Day×week interactions were observed for CMJ-mRSI and RJ-rBNI; Day 1-Day 2 differences occurred in Weeks 1-2 for CMJ-mRSI (all p≤.011) and Week 4 for RJ-rBNI (p=.014). Output metrics showed main effects (CMJ-H: day, week, sex; RJ-H: week; RJ-mRSI: day).
CONCLUSION:
Braking-phase metrics were sensitive to pre- vs post-competition changes and match exposures, where common metrics (e.g., jump height) showed fewer interactions. Higher match exposure may alter neuromuscular function, and given the high eccentric demand in volleyball, monitoring CMRJ braking metrics in-season may better inform recovery and load management decisions.