Abstract
CONTEXT: Women with patellofemoral pain (PFP) commonly have hip muscle weakness in comparison with women without PFP. One underlying mechanism for this muscle weakness is inhibition. Although the presence of muscle weakness is well documented in women with PFP, few authors have investigated gluteus medius inhibition in this population. Women are twice as likely to suffer from PFP when compared with men; therefore, we focused on the female population. OBJECTIVE: To compare voluntary activation of the gluteus medius between women with and without PFP. DESIGN: Case-control study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-eight female participants: 13 pain-free control participants (age = 21.6 ± 3.6 years, height = 1.66 ± 0.06 m, mass = 65.4 ± 11.3 kg) and 15 participants with PFP (age = 22.3 ± 3.2 years, height = 1.66 ± 0.07 m, mass = 75.3 ± 22.6 kg, duration of pain = 3.5-96 months). MAIN OUTCOME MEASURES: Standing hip-abduction normalized strength (N·m/kg), superimposed-burst force, and gluteus medius central activation ratio (CAR). Linear modeling was used to compare forces and the CAR between groups while controlling for age, mass, and hip-abduction force. RESULTS: Women with PFP had lower gluteus medius CAR than controls. Overall, after controlling for participant age, mass, and gluteus medius maximal voluntary isometric contraction, the PFP group had an average gluteus medius CAR 2.5% lower than the pain-free control group (control = 98.4% ± 0.01%, PFP = 95.9% ± 0.65%, P = .004). CONCLUSIONS: Women with PFP had reduced voluntary activation of the gluteus medius when assessed with a superimposed burst. Due to the wide range of CAR values found (74%-99%), inhibition was present in some of the participants. This provides evidence that assessment of gluteal voluntary activation could assist with targeted treatment programs for individuals presenting with PFP.