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THE IMPACT OF INTERMITTENT PAIN ON LEG MUSCLE ACTIVATION PATTERNS IN WOMEN WITH KNEE OSTEOARTHRITIS

Abstract

PURPOSE: The purpose of this study was to evaluate the impact of self-reported intermittent pain on muscle activity and co-activation above and below the knee, during a 6-meter walk and 20-centimeter stepdown, in women with knee osteoarthritis (KOA), compared to controls. METHODS: The experimental group (n = 7; Age = 62 ± 8.71 years; BMI = 34.51 ± 5.99 kg/m2) included women that had a clinical diagnosis of KOA, and self-reported intermittent pain. The control group had neither KOA nor pain (n = 10; Age = 59 ± 9.17 years; BMI = 24.47 kg/m2). Participants were excluded from either group if they were unable to walk distances, while unassisted, greater than 200 ft., navigated stairs, had a history of ligament injury to the knees, had undergone total knee arthroplasty, or had any neurological disease(s) that impacted ambulation. Given complex sex differences related to these outcomes, males were excluded. Leg muscle activity was assessed during 5 trials of a 6-meter walk and 5 trials of the 20-centimeter step down, via surface electromyography (sEMG), on the vastus lateralis (VL), semitendinosus (ST), tibialis anterior (TA), and medial gastrocnemius (MG). RESULTS: During the 6-meter walk in the experimental group, regarding impact of Age while controlling for intermittent pain and BMI, there was higher mean ST activity (F (1,13) = 5.79, p = .032, ɳp2 = .308), mean peak ST activity, (F (1,13) = 5.10, p = .042, ɳp2 = .282), and co-activation compared to VL, (F (1,13) = 5.94, p = .030, ɳp2 = .314). During the 20-centimeter step-down in the experimental group, regarding impact of intermittent pain, and while controlling for Age and BMI, there was higher mean ST (F (3,13) = 10.54, p = .006, ɳp2 = .448), and mean peak ST activity (F(3,13) = 17.42, p = .001, ɳp2 = .572). Furthermore, regarding impact of Age, while controlling for the impact of BMI and intermittent pain, there was higher mean peak ST, (F (1,13) = 9.94, p = .008, ɳp2 = .433) in the experimental group. CONCLUSION: The experimental group produced elevated mean and mean peak muscle activity patterns revealing muscle activation abnormality during dynamic tasks. This overactivity possibly due to intermittent pain, which has never been revealed, could lead to abnormal joint load. This abnormal joint load could degrade knee joint cartilage, increase pain, and degrade function.

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