INTRODUCTION: To compare the efficacy of eccentrically-focused resistance exercise (ECC RT) to concentrically-focused resistance exercise (CNC RT) on knee osteoarthritis (OA) symptoms and strength. METHODS: 90 participants consented. Participants were randomized to CNC RT, ECC RT or a wait-list no-exercise control group (CON). 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; knee extension, leg flexion and leg press), weekly rate of strength gain, Western Ontario McMaster University Osteoarthritis Index (WOMAC) total score and sub-scores. RESULTS: 54 participants (60 to 85yr, 61% women) completed the study. Both CNC RT and ECC RT groups showed 16% to 28% improvement relative to CON group (p = 0.003 to 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 knee flexion (by 2.9% to 4.8%; both p < 0.05), but not knee extension (0.7%; p = 0.38). There were no significant differences in WOMAC total and sub-scores across groups over time. Leg press strength change was the greatest contributor to change in WOMAC Total scores (R = 0.223). The change in knee flexion strength from baseline to month four was a significant predictor of the change in WOMAC pain sub-score (F ratio = 4.84, df = 45, p = 0.032). Both modes of strength training were well-tolerated. CONCLUSIONS: Both resistance training types effectively increased leg strength. Knee flexion and knee extension muscle strength can modify function and pain symptoms irrespective of muscle contraction type. Which mode to pick could be determined by preference, goals, tolerance to the contraction type, and equipment availability.

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