Unbiased Selection Of Countermovement Jump Metrics For Fatigue In Prolonged Heavy Load Rucking

The countermovement jump (CMJ) is a non-invasive, easily administered method to assess neuromuscular fatigue. However, prior studies have analyzed multiple correlated CMJ metrics without a clear rationale. To optimize the utility of the CMJ for fatigue detection and streamline its application, identifying a subset of uncorrelated metrics tailored to the fatigue context is essential. PURPOSE: This study aimed to statistically filter discrete CMJ metrics to optimize the detection of physical fatigue status. METHODS: Sixty-seven healthy, fit adults (Age: 21.9 ± 3.0 y, VO2PEAK: 47.2 ± 6.2 ml·kg-1·min-1, ♂/♀ = 39/28) completed four 30-min treadmill rucking blocks carrying 47% of their lean mass. Each block consisted of two 15-min phases: 1) at a speed equal to 47% VO2PEAK, and 2) to cover the maximum distance possible while self-adjusting speed. Three maximal effort CMJs without arm swing were performed on a calibrated AMTI force plate and averaged at baseline (PRE); between blocks (IB1-3); and at 0, 30, and 60 min of recovery (POST, POST30, POST60). Feature selection via differential analysis (p-value <10E-24, fold change > |1|) alongside correlation-based hierarchical clustering reduced 28 discrete CMJ parameters to a subset of key performance indicators. Linear mixed-effects models with a random subject term determined the influence of time and sex on the selected metrics (α = 0.05). RESULTS: Momentum (MOM), peak concentric velocity (PCV), mean concentric velocity (MCV), mean braking power (MBP), and mean braking force (MBF) were identified as most responsive to the fatigue protocol. Raw metric values and percent changes declined progressively from IB1, with large to extreme effect sizes (0.8 - >2.0) observed at POST, POST30, and POST60. MBP showed the largest percent change across recovery time points (%∆ at POST, POST30, and POST60: -11.53, -11.56, -14.96). MOM, PCV, and MCV were significantly higher in males compared to females based on absolute but not relative change. CONCLUSION: This study provides evidence for an approach to selecting specific CMJ metrics to assess physical fatigue progression. These findings can help practitioners optimize the detection of fatigue by focusing CMJ testing on the most useful indicators, enhancing training and recovery strategies in athletic and military contexts. Supported by: This work was made possible in part by Defense Advanced Research Projects Agency (DARPA) under Grant Number HR0011-22-2-0040. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of DARPA.