Retraining Gastrocnemius Muscle Coordination Reduces Late-Stance Knee Contact Force in Individuals With Knee Osteoarthritis.

Thirteen of eighteen participants with knee osteoarthritis successfully reduced gastrocnemius EMG by at least 10% during an initial 30-minute biofeedback training session.

• Participants walked on a treadmill with adaptive haptic biofeedback instructing them to reduce gastrocnemius EMG.
• The qualification threshold for the second session was a minimum 10% reduction in average gastrocnemius EMG.
• 13 out of 18 participants (72%) met this threshold during the initial session.
• The study focused on individuals with tibiofemoral osteoarthritis.

With haptic biofeedback during the second session, participants reduced gastrocnemius EMG by 25% on average.

• Gastrocnemius EMG was reduced by '25 ± 15%' with feedback (p<0.001).
• The biofeedback paradigm was adaptive, meaning it adjusted to participant performance.
• The same biofeedback protocol used in session one was repeated in session two.
• EMG reduction was measured relative to a no-feedback baseline condition.

Haptic biofeedback-driven gastrocnemius EMG reduction led to a 12% reduction in the late-stance peak knee contact force.

• The late-stance peak of knee contact force was reduced by '12%, or 0.38 ± 0.47 times body weight' (p=0.01).
• Knee contact force was estimated using musculoskeletal models and static optimization.
• The reduction was specifically in the late-stance peak, not overall knee contact force.
• 10 out of 13 participants reduced their knee contact force impulse with the feedback.

Vasti muscle EMG increased significantly during biofeedback training, contributing to increased early-stance knee contact force in some participants.

• Average vasti EMG increased by '38 ± 34%' with feedback (p=0.004).
• The increase in vasti activity contributed to an increase in early-stance knee contact force in some participants.
• This compensatory vasti increase was an unintended consequence of the gastrocnemius reduction strategy.
• The authors identified mitigating increases in vasti EMG as a target for additional work.

Musculoskeletal simulations and prior experiments in young adults without knee pain have demonstrated that reducing gastrocnemius muscle activity can reduce knee contact force.

• This prior evidence formed the mechanistic basis for the intervention tested in the current study.
• The prior work was conducted in young adults without knee pain, making translation to osteoarthritis populations an open question.
• Reduced knee contact force is hypothesized to reduce pain and slow progression of knee osteoarthritis.
• The current study was designed to test whether this strategy could be applied to individuals with tibiofemoral osteoarthritis.