Repercussões da fadiga nos parâmetros fisiomecânicos do salto vertical contínuo com contramovimento

Abstract

Fatigue is defined as a temporary reduction in the capacity to produce maximal force or power, resulting in impaired performance. The execution intensity of vertical jumping dictates the characteristics of fatigue and, consequently, the resulting physiomechanical adaptations. Thus, the aim of this study was to evaluate the effects of fatigue on the physiomechanical parameters (force, total mechanical power: Ptotal, effective contact time: tce, effective flight time: tae, the time during which external negative work: tbrake, the time during which external positive work: tpush, ratios: tce/tae, tpush/tbrake, step frequency: fstep, system frequency: fs, fstep/fs ratio, and center of mass acceleration, velocity, and displacement) of continuous countermovement vertical jumping. This is a retrospective analysis of a database from a randomized, double-blind, crossover, placebo-controlled clinical trial in which 50 participants performed continuous vertical jump tests (Bosco test) on a force platform to collect the vertical component of ground reaction forces (vertical GRF). Based on whether or not the fatigue threshold was crossed on the maximum power curve, 47 participants were allocated into two groups: maximal (MG) and submaximal (SG). A custom Python routine was developed to extract temporal, spatiotemporal, and kinetic variables. Linear mixed-effects models were used to compare the intercepts and slopes between groups. For intragroup comparisons, model decomposition was performed. Both analyses considered the 60-second time period. The results demonstrated that mean relative Ptotal was significantly higher in MG compared to SG (Δβ0 = 6.50 W·kg-1, IC 95% [0.81; 12.11], p = 0.038), with a significant difference between their slopes (Δβ1 = -27.55 W·kg-1·s-1, IC 95% [-31.84; -23.39], p < 0.001). The mean tce/tae ratio showed no significant difference between intercepts (Δβ0 = 0.18 a.u.; IC 95% [-0.03; 0.42], p = 0.120), but presented a significant difference between slopes (Δβ1 = 0.67 a.u./s; IC 95% [0.46; 0.87], p < 0.001). The elastic mechanism was impaired under the fatigue condition (MG), whereas under the non-fatigue condition (SG) the mechanism appeared to be optimized. The mean tpush/tbrake ratio showed no significant difference in intercepts (Δβ0 = -0.04 a.u., IC 95% [-0.10; 0.02], p = 0.204) nor in slopes (Δβ1 = -0.02 a.u.·s-1, IC 95% [-0.08; 0.04], p = 0.492), indicating that this variable does not appear to be affected by fatigue. The mean fstep/fs ratio showed no significant difference in intercepts (Δβ0 = 0.03 a.u., IC 95% [-0.03; 0.08], p = 0.330), but presented a significant difference in slopes (Δβ1 = 0.09 a.u.·s-1, IC 95% [0.03; 0.15], p < 0.001). Relationships and asymmetries were inverted, with effective contact time exceeding effective flight time and braking time exceeding propulsion time. In conclusion, fatigue reduced performance, and the elastic mechanism proved to be intensity-dependent: impaired during maximal execution and optimized during submaximal execution.