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  1. CK Chan,
  2. SH Yung,
  3. MW Liu,
  4. KM Chan
  1. Department of Orthopaedic and Traumatology, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, Hong Kong


Background Hamstring strain during sprinting is one of the dominant injuries among soccer players, which constitutes 12–16% of all injury. Fatigue is claimed to alter the lower limb mechanism during sprinting, which trigger hamstring strain injury.

Objective The purpose of this study was to find out the changes in electromyography and kinematic profile of the lower limb muscles during sprinting after fatigue among female soccer players, hence, to suggest injury prevention strategies. It is hypothesized that the EMG activity of BF and ST decrease after fatigue.

Design Prospective observational study.

Setting Kinematic and electromyographic analysis of sprinting before and after soccer-specific fatigue intervention were measured in an indoor setting.

Participants 9 semi-professional female soccer players were recruited from 1st division club teams.

Risk factor assessment Each subject completed the SAFT90 soccer-specific fatigue protocol that simulates the movement pattern of soccer game.

Main outcome measurements 20 metres sprint test were done on each subject before and after the SAFT90. EMG activity of biceps femoris (BF), semitendinosus (ST), rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) and lower limb kinematic in sagittal plane were measured between 10 m–20 m during the sprints.

Results The sprint time across the pre-test and post-test increased. Significant reduction in stride length and maximum combined hip flexion and knee extension angle were observed in the post-test. The EMG amplitude of BF decreased by 14.3%, and the EMG amplitude of ST increased by 10% in late swing phase across pre-test and post-test.

Conclusions The reduction in maximum combined hip flexion and knee extension angle indicated that the length of hamstring muscle is shortened after fatigue. The alternation in muscle activation of ST and BF could be a mechanism to reduce the risk of muscle strain of BF during the late swing phase of sprinting after fatigue.

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