Muscle force cannot be directly inferred via muscle activity
Assessing neural drive using electromyography (EMG) does not infer the level of muscle force produced in a contraction. Despite the fact that such limitations are widely acknowledged, this issue has received minimal attention within the clinical literature. The following commentary exposes these limitations within the context of patellofemoral pain (PFP); more specifically, the proposed aetiology consisting of an imbalance in force production between the vastus medialis (VM) and vastus lateralis (VL) muscles.
Two approaches are commonly utilised to measure the balance of neural drive between VM and VL – the onset of muscle EMG activation between VM and VL; and the difference in EMG amplitude. Confounders such as altered electromechanical delay (time between EMG signal and patella motion) in PFP, along with the fact that muscle force is dictated by several other biomechanical factors, may lead to a reconsideration of the current interpretation of VM:VL activation onset.
A reconsideration of methods used to assess the imbalance in force production between the VM and VL is required.
> From: Hug et al., J Orthop Sports Phys Ther (2015) (Epub ahead of print). All rights reserved to Journal of Orthopaedic & Sports Physical Therapy. Click here for the Pubmed summary.