Cortes, N., Morrison, S., & Onate, J. (2013). Fatigue increases variability of joint angles and forces during a side-step cutting task. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 463.

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This study assessed the impact that fatigue has on joint kinetics and kinematics during a side-step cutting task in female soccer players (N = 11) performed the cutting task before-and-after a fatiguing intervention. Fatigue was induced using a Slow-Linear Oxidative Fatigue Protocol. This involved a 30-minute run with six intervals (4 minutes at 70% of VO2peak speed followed by 1 minute at 90% of VO2peak speed). The impact of fatigue on specific kinematic/kinetic variables was assessed through changes in signal regularity, mean amplitude, and overall variability.

Significant differences were found for the mean amplitude of the medio-lateral and vertical force directions. Differences were also seen for hip abduction and knee abduction. A significant fatigue effect was found for approximate entropy of the vertical and medio-lateral forces. Post hoc analysis showed that the forces were more irregular, indicating increased variability over the course of the task. Fatigue also resulted in significant increases in approximate entropy values for knee abduction angle and moment.

Implication. Fatigue has a widespread impact on lower extremity kinematics and kinetics during a dynamic task. Specifically, fatigue resulted in an overall decline in signal amplitude while the pattern of variability/complexity over time increased. This pattern of change may reflect a central deficit when fatigue is present, exacerbating the likelihood of injury.

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