Efeito da fadiga neuromuscular sobre a regularidade do movimento durante a corrida

Abstract

The entropy analysis quantifies the level of regularity of a movement time-series representative of a given motor behavior. This measure has the potential to identify deficits in the action capacities of the neuromusculoskeletal system in relation to the demands of the task. The presence of neuromuscular fatigue (NMF) reduces the system's capacity to generate muscle force and is frequently identified as a risk factor for musculoskeletal injuries. This study aimed to investigate whether the induced lower limbs’ NMF alters running movement regularity and whether the possible effects remain for up to 20 minutes. A crossover study was carried out with two randomized conditions: NMF (based on the 8RM test in the Leg press) and control (without NMF), with an interval of 5-13 days between them. Twelve young and healthy men, active, asymptomatic, and without a history of lower limb injuries in the last 12 months participated in the study. Angular kinematics of the hip, knee, and ankle (sagittal plane) and pelvic linear acceleration (anterior-posterior, mediolateral, vertical) were assessed with a three-dimensional system (Codamotion, 100Hz) during treadmill running at a self-selected speed. The assessments were done at four different times in both conditions: I) Run_0: pre-NMF assessment (or pre-rest, when it was the control condition); II) Run_1: in the 1st minute, III) Run_2: in the 10th minute, IV) Run_3: in the 20th minute after exhaustion with the NMF exercise (or post-rest). The sample entropy (SampEn) was calculated using Matlab® code. Repeated measures ANOVAs were performed, and pre-planned contrasts were used when the ANOVA effects were significant. The level of significance was set at 0.05. The results showed an interaction effect between conditions and moments (Assessments in time) in the hip (p=0.018), knee (p=0.012), and ankle (p=0.041). In the fatigue condition, in the hip, the entropy increased in Run_1 (p=0.013) and Run_2 (p=0.045), compared to Run_0, and decreased in Run_2 compared to Run_1 (p=0.015). In the knee, the entropy increased in Run_1 (p=0.016), Run_2 (p=0.010) and Run_3 (p<0.001), compared to Run_0. As for the knee, in the ankle, the entropy increased in Run_1 (p=0.002), Run_2 (p=0.026) and Run_3 (p=0.028), compared to Run_0. There were no significant effects on the control condition (p≥0.124) or pelvic acceleration (p≥0.114). These results showed that the NMF reduced the regularity of the movements of the lower limbs joints during running. This regularity reduction may reflect the smaller system’s capacity to resist to mechanical perturbations during the task in the fatigue presence. However, considering that the running continued to be performed successfully and without reduced performance (standardized running speed), the reducing of the regularity could be also an adaptive strategy to maintain the task. In this case, the motor system became more flexible, allowing the exploration of more efficient movement solutions. The recovery of the movement regularity of the hip, which was not observed in the ankle and knee, may be due to the greater mechanical demands generated by the ground reaction force in the distal joints. Entropy measurements of lower limb joints movement have the potential to identify during running the reductions in muscle capacity caused by NMF.