Comparison of Antagonist Muscle Activity During Walking Between Total Knee Replacement and Control Subjects Using Unnormalized Electromyography.

BACKGROUND: Although satisfactory outcomes have been reported after 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 2 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 = .004), greater middle stance antagonist biceps femoris activity (P < .001), and less late stance agonist biceps femoris activity (P < .001) than control subjects. Individuals with TKR demonstrate increased flexor muscle activation during weight bearing, potentially contributing to altered gait patterns found during the 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 before and after TKR is critical for developing rehabilitation strategies to address functional deficits and disability found in this patient population.

Biceps activity during windmill softball pitching: injury implications and comparison with overhand throwing.

BACKGROUND: Windmill pitching produces high forces and torques at the shoulder and elbow, making the biceps labrum complex susceptible to overuse injury. Little is known about the muscle firing patterns during a windmill pitch. HYPOTHESIS: Biceps muscle activity is greater during a windmill pitch than during an overhand throw. STUDY DESIGN: Descriptive laboratory study. METHODS: Seven female windmill pitchers underwent motion analysis and surface electromyography evaluation of their biceps muscles during windmill and overhand throwing. Marker motion analysis, muscle activity, and ball release were captured simultaneously. Surface electromyography trials were collected and related to the athletes' phases of pitching and throwing, identified based on predefined softball and baseball pitching mechanics. RESULTS: Throws were of similar velocity (24 m/s, 53 mph, P = .71), but peak biceps brachii muscle activation during the windmill pitch was significantly greater than during the overhand throw when normalized (38% vs 19% manual muscle test, P = .02). The highest muscle activity occurred at the 9-o'clock phase of the windmill pitch, during which the biceps brachii undergoes eccentric contraction. In the overhand throw, the highest level of biceps activity occurred during arm cocking. CONCLUSION: In female athletes, biceps brachii activity during the windmill pitch is higher than during an overhand throw and is most active during the 9-o'clock and follow-through phases of the pitch. CLINICAL RELEVANCE: 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.