Repetitive eccentric biceps contractions may help explain the high incidence of anterior shoulder pain clinically observed in elite windmill pitchers. Injury prevention and treatment mechanisms should focus on the phases with the highest muscle activity.
Background
Although satisfactory outcomes have been reported following total knee replacement (TKR), full recovery of muscle strength and physical function is rare. We developed a relative activation index (RAI) to compare leg muscle activity from unnormalized surface electromyography (sEMG) between TKR and control subjects.
Methods
Nineteen TKR and 19 control subjects underwent gait analysis and sEMG. RAIs were calculated by dividing the average sEMG for two consecutive subphases of stance defined by the direction of the external sagittal plane moment (flexion or extension).
Results
RAIs and external moments indicate TKR subjects have less initial stance antagonist rectus femoris activity (p=0.004), greater middle stance antagonist biceps femoris activity (p<0.001), and less late stance agonist biceps femoris activity (p<0.001) than control subjects. Individuals with TKR demonstrate increased flexor muscle activation during weight bearing, potentially contributing to altered gait patterns found during stance phase of gait.
Conclusion
The RAI helps detail whether decreased external moments correspond to less agonist or more antagonist muscle activity to determine true muscle activity differences between subject groups. Identifying the mechanisms underlying altered muscle function both pre and post-TKR is critical for developing rehabilitation strategies to address functional deficits and disability found in this patient population.
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