Evaluation of the Combined Application of Neuromuscular Electrical Stimulation and Volitional Contractions on Thigh Muscle Strength, Knee Pain, and Physical Performance in Women at Risk for Knee Osteoarthritis: A Randomized Controlled Trial

Background: Knee osteoarthritis (OA) is a leading cause of disability that is associated with quadriceps weakness. However, strengthening in people with or with risk factors for knee OA can be poorly tolerated. Objective: To assess the efficacy of a 12-week low-load exercise program, using a hybrid training system (HTS) that uses the combination of neuromuscular electrical stimulation and volitional contractions, for improving thigh muscle strength, knee pain relief, and physical performance in women with or with risk factors for knee OA. Design: Randomized, single-blinded, controlled trial. Setting: Exercise training laboratory. Participants: Forty-two women 44-85 years old with risk factors for knee OA. Interventions: Participants randomized to 12 weeks of biweekly low-load resistance training with the HTS or on an isokinetic dynamometer (control). Outcomes: Maximum isokinetic knee extensor torque. Secondary measures included maximum isokinetic knee flexor torque, knee pain (Knee Injury and Osteoarthritis Outcome Score), and timed 20-m walk and chair stand tests. Results: The HTS and control treatments resulted in muscle strengthening, decreased knee pain, and improved physical performance. HTS group quadriceps and hamstring strength increased by 0.06 +/- 0.04 Nm/kg (P > .05) and 0.05 +/- 0.02 Nm/kg (P = .02), respectively. Control group quadriceps and hamstring strength increased by 0.03 +/- 0.04 Nm/kg (P > .05) and 0.06 +/- 0.02 Nm/kg (P = .009), respectively. Knee pain decreased by 11.9 +/- 11.5 points (P < .001) for the HTS group and 14.1 +/- 15.4 points (P = .001) for the control group. The 20-m walk time decreased by 1.60 +/- 2.04 seconds (P = .005) and 0.95 +/- 1.2 seconds (P = .004), and chair stand time decreased by 4.8 +/- 10.0 seconds (P > .05) and 1.9 +/- 4.7 seconds (P > .05) in the HTS and control groups, respectively. These results did not differ statistically between the HTS and control groups. Conclusions: These results suggest the HTS is effective for alleviating pain and improving physical performance in women with risk factors for knee OA. However, the HTS does not appear to be superior to low-load resistance training for improving muscle strength, pain relief, or physical function.