Comparative efficacy of eccentric and concentric-focused resistance exercise on pain, leg strength and walking endurance in knee osteoarthritis

Abstract

Purpose: Evidence from the Osteoarthritis Initiative shows that as knee osteoarthritis (OA) progresses and pain increases over time, knee flexor and extensor muscle strength decline linearly in both men and women. Strength improvements from various exercises are related to pain reduction and reduction of pain impact on physical function. What remains unclear is which strength training type may be more effective for knee OA pain symptoms and reversing the OA-related strength decline. The primary purpose of this study was to compare the effectiveness of eccentrically-focused resistance exercise (ECC RT) and concentrically-focused resistance exercise (CNC RT) on knee OA symptoms and leg muscle strength over four months. The secondary purpose was to determine whether reduction in knee pain severity was related to knee extensor or flexor strength gain. Methods: 90 participants (60–85 yr, 61% women) were randomized to CNC RT, ECC RT or a wait-list no-exercise control group (CON). All participants completed a graded, Naughton treadmill walking test to exhaustion. Four months of supervised exercise training were completed using traditional weight machines (CNC RT), or modified matched machines that overloaded the eccentric action (ECC RT). Main outcomes included one-repetition maximal strength (1RM; leg extension, leg flexion and leg press), weekly rate of strength gain, Western Ontario McMaster University Osteoarthritis Index (WOMAC) total score and pain, stiffness and function subscores. General linear models with intervention group (ECC RT, CNC RT, CON) and baseline (pre) measures as independent variables, and post-invention measures as the dependent variables were run to assess group differences in change in strength and WOMAC score and to assess which gains in strength best explained improvements in WOMAC scores. Linear regression was used to determine the contribution of the variance in change in walking exercise time to changes in leg strength. Results: Treadmill walking endurance time increased by 6.7%, 10% and 8.3% in the CON, CNC RT and ECC R, respectively. Both CNC RT and ECC RT groups showed an average of 16%–28% improvement relative to CON group (P = 0.003–0.005) for all leg strength measures. The rate of weekly strength gain was greater for CNC RT than ECC RT for leg press and leg curl (by 2.9%–4.8%; both P < 0.05), but not for leg extension (0.7%; P = 0.38). There were no significant differences in WOMAC total and subscores across groups over time. Of the three leg exercises, leg press strength change was the most significant contributor to change in WOMAC Total scores (R2 = 0.223). The change in leg curl strength from baseline to month four was a significant predictor of the change in WOMAC pain subscore (P = .032). Variability existed in the pain responsiveness to training, such that some patients achieved clinically meaningful improvements to pain whereas others did not. Participants with WOMAC pain reduction of ≥30% from baseline to month four showed greater 13.8%–24.7% higher strength gains in all three exercises compared to participants with pain reduction <30%. The four-month changes in leg curl and leg press strength contributed 7.6%–16.7% to the model for walking exercise time (P < 0.05). Conclusions: Both resistance training types were effective in increasing leg muscle strength and contributing to improvement in walking exercise endurance time. The degree of strength gain was associated with pain relief not resistance exercise type. The choice of which strengthening mode to use may be dependent on individual OA treatment goals and tolerance to the exercise.