Altered multi-muscle coordination patterns in habitual forefoot runners during a prolonged, exhaustive run

Introduction: In response to fatigue during an exhaustive treadmill run, forefoot runner's muscles must adapt to maintain their pace. From a neuromuscular control perspective, certain muscles may not be able to sustain the force to meet the run's demands; thus, there may be alternative muscle coordination in the lower extremity that allows for continued running for an extended period of time. The aim of this study was to quantify the change in muscle coordination during a prolonged run in forefoot runners. Methods: Thirteen forefoot runners performed exhaustive treadmill runs (mean duration: 15.4 ± 2.2 min). The muscle coordination of seven lower extremity muscles was quantified using a high-resolution time-frequency analysis together with a pattern recognition algorithm. Results: The mean EMG intensity for the lateral and medial gastrocnemius muscles decreased with the run (p = 0.02; 0.06). The weight factors of the second principal pattern decrease by 128.01% by the end of run (p = 0.05, Cohen's d = 0.42) representing a relatively greater biceps femoris activation in midstance but smaller midstance rectus femoris, vastus medialis, triceps surae, and tibialis anterior activation. Discussion: These results suggest that forefoot runners cannot sustain plantar flexor activation throughout an exhaustive run and change their muscle coordination strategy as a compensation. Understanding the underlying compensation mechanisms humans use to cope with fatigue will help to inform training modalities to enhance these late stage muscle activation strategies for athletes with the goal of improving performance and reducing injury.