Objectives
Electromyography (EMG) is a common technique used in clinical settings, which utilizes visual biofeedback to correct muscle activation during exercise. However, it is unclear whether the correction of muscle activation by the EMG biofeedback training restores proprioception, dynamic stability, and pain. In addition, to our knowledge, no study has investigated acute EMG biofeedback training on proprioception in adults with patellofemoral pain.

Methods
The participants were twenty-nine adults (23 males and 6 females) aged ≥ 20 years with patellofemoral pain. We randomly assigned participants to either the EMG biofeedback training (EBT) group (n=15, mean age: 20.13±1.55 years) or the control group (n=14, mean age: 20.93±2.43 years). Proprioception of the knee joint was measured using joint position sense (30°, 45°, and 60°) tests. A numerical rating scale (NRS) was used to confirm the level of knee pain. The intervention group received EMG biofeedback training to increase the muscle activation of the vastus medialis oblique muscle, providing visual biofeedback using EMG.

Results
The positional error evaluated in the 45° joint position was significantly decreased after the intervention (EBT: pre= 3.76±2.33°, post= 2.11±1.85°, P=0.020), with an interaction between time and group (P=0.028), but not other joint positions (30° and 60°). The NRS score reduced (EBT: pre= 3.87±2.20, post=2.00±1.46, P=0.001), with a significant interaction between time and group (P=0.001).

Conclusions
The findings suggest that acute EMG biofeedback training reduced knee pain in adults with patellofemoral pain. The improvement of positional error was observed in the 45° joint position but not in the other joint positions. Further research is needed to evaluate whether short- and long-term biofeedback training with EMG used in the treatment of patellofemoral pain is associated with outcomes of proprioception.