Muscle Co‐Activation Across Activities of Daily Living in Individuals With Knee Osteoarthritis

OBJECTIVE: Muscle co-activation has been shown to be elevated in individuals with knee osteoarthritis (OA) during gait. Comparisons of muscle co-activation across different activities of daily living such as stair negotiation have yet to be explored. The aim of this study was to explore muscle co-activation across different activities of daily living in patients with knee OA. EMG was recorded from 7 sites, mediolateral gastrocnemius, biceps femoris, semitendinosus, vastus lateralis/medialis, and rectus femoris, and normalized to maximal voluntary isometric contraction. Correlation was used to assess the consistency of co-activation across activities. Repeated-measures analysis of variance assessed the muscle combination by activity differences. RESULTS: Muscle co-activation was highest during stair ascent. When comparing muscle combinations within the same activity, we found that correlations ranged from r = 0.003 to r = 0.897, of which 80% of the combinations were significant. Between activities, muscle co-activation was significantly different (P < 0.05). Mediolateral muscle co-activation was higher than hamstrings/quadriceps across activities. CONCLUSION: Two muscle co-activation strategies were observed during activities of daily living in patients with knee OA to maintain stability. Muscle co-activation was higher during more challenging activities, particularly when the joint was accepting load. Mediolateral muscle co-activation was higher than hamstrings/quadriceps, so that mediolateral co-activation was thought to be a stabilization mechanism, while hamstrings/quadriceps co-activation responds to knee flexion moments, suggesting that different muscle combinations may have different roles in responding to joint demand.