Statistical Parametric Mapping Of Force-time Waveforms Of The Countermovement Jump During Prolonged Heavy Rucking

Countermovement jumps (CMJ) performed on force plates have become widely used to detect fatigue, especially in military contexts. While force plates measure many discrete variables, few studies have analyzed the continuous waveforms to identify changes in jump strategy resulting from fatigue. Application of statistical parametric mapping (SPM) to continuous CMJ waveforms allows measurement of spatiotemporal changes that may not be detected by traditional analysis of discrete CMJ variables. PURPOSE: Utilize SPM analysis of CMJ waveforms to identify neuromuscular changes associated with fatigue throughout a prolonged heavy rucking protocol. METHODS: Fit, young adults (Age: 21.9 ± 3.0 y, VO2PEAK: 47.2 ± 6.2 ml·kg-1·min-1, ♂/♀ = 39/28) completed four consecutive 30-min (15 min steady-state at 47% VO2PEAK + 15 min time trial for distance) treadmill rucking blocks carrying 47% of their lean mass. Three maximal effort CMJs without arm swing were performed on a calibrated AMTI force plate and averaged at baseline (PRE) and at 0, 30, and 60 min of recovery (POST, POST30, POST60). The three normalized waveforms were averaged for each subject at every study time point. An SPM two-way (sex x time) repeated measures analysis of variance (ANOVA) was performed to compare changes in force-, velocity-, power-, and displacement-time curves across the physical fatigue protocol. RESULTS: The SPM detected differences between force-, velocity -, and power-time data with main effects for time (p < 0.001 for all) and sex (p < 0.001, p = 0.002, and p < 0.001, respectively). Changes in force, velocity, and power waveforms were observed at all time points in response to the ruck protocol. Pairwise comparisons of PRE to POST, POST30, and POST60 showed differences in force, velocity, and power primarily in the braking and concentric phases. Following the ruck, lower force, greater velocity, and greater power were produced during the braking phase, while lower force, velocity, and power were produced during the concentric phase of the jumps at all recovery time points. CONCLUSION: SPM analysis was able to detect phase-based differences in force, velocity, and power of CMJ waveforms in fit, young adults who performed a high-intensity rucking protocol, demonstrating its utility for assessing fatigue and readiness by considering the whole movement. Supported by: Defense Advanced Research Projects Agency