Fatigue related changes to lower limb muscle activation in female soccer players

Abstract

The objective of this study was to review fatigue-related changes in lower limb muscle mechanics in the female soccer player after 45 minutes of soccer simulated exercise, to provide insight to the high risk of ACL injury. Eight female university players volunteered for the study (± SD) (age 20.8+0.9 years, body mass 163.2+3.6kg and stature 163.2+3.6cm). The players completed identical testing before and after a 45 minute soccer specific fatiguing protocol (modified LIST - agility and sprint performance documented throughout). Testing comprised of EMG analysis during MVC in knee flexion and extension, and DJ performance. Reactive strength index, contact time, jump height, and flight time were also recorded from the DJ via a contact mat in parallel to the EMG recordings. There was no significant change in sprint performance; equally little alteration in agility performance. However fatigue greatly altered muscle mechanics, EMG evaluation illustrated that the ability to perform MVC is significantly impaired (Pre-post difference, VL (P < 0.05), BF (P < 0.05). In terms of dynamic movement all jump performance parameters declined post-LIST, although only statistically significantly different for CT (P< 0.05), and RSI (P< 0.05). EMG analysis was to used to determine pre-activation, activation through GC, and peak activation during the DJ, these scores reflected that muscle activity in the BF was significantly less post-LIST during pre activation, (P < 0.05). Activity during GC also decreased VL (P< 0.05) BF (P < 0.05), additionally peak activation was reduced. Correlation analysis illustrated that muscle stiffness formed in the pre contact phase was related to peak activation as well as activation through GC. Overall co contraction during the DJ was reduced as consequence of the diminished activity in the BF. The results of the study demonstrate that muscle performance is greatly altered with the onset of soccer specific fatigue in the female soccer player, reducing ability to form muscle stiffness through symmetrical recruitment of the knee flexors and extensors on ground contact through. Findings indicate the need for conditioning to help offset the fatigue as a result of soccer exercise, preventing change in technique through altered patterns of recruitment, and particularly the need for muscle imbalances to be addressed by increasing attention to the conditioning of the posterior chain.