Influence of painful overloading using stair ascending in quadriceps neuromuscular function of women with patellofemoral pain syndrome

Purpose Patellofemoral pain (PFP) is a common knee disorder, exacerbated by activities that load the patellofemoral joint (PFJ), such as climbing stairs. Neuromuscular imbalance control with coactivation between vastus medialis (VM) and vastus lateralis (VL) activation has been investigated in PFP. However, it remains unclear whether knee pain influences these neuromuscular parameters.Objective Investigate the influence of pain at the onset of VM activation relative to VL and at the VM/VL activation ratio.Methods Thirty-eight women aged 18 to 30 years with PFP were recruited. Pain at a visual analog scale and surface electromyography (EMG) of VM and VL was acquired before and after PFJ loading protocol (stair ascending) designed to exacerbate knee pain of people with PFP.Results After performing the PFJ loading protocol, the pain of the participants increased significantly (Mean difference (95%CI) = - 2.37 ( - 2.98; - 1.76); p < 0.001). The VM/VL ratio decreased (p = 0.04) after pain exacerbation. No difference on the onset activation of the VM in relation to the VL was found (p = 0.88).Conclusion The onset of activation of the VM in relation to the VL does not change in the presence of pain. However, the VM/VL activation ratio is altered in the presence of pain in women with PFP. Therefore, interventions that target anticipation of VM onset activation should be discouraged for women with PFP.