Reduced muscle function, causing greater knee joint load, is a potentially modifiable risk factor of knee osteoarthritis (OA). Exercise is an important treatment of knee OA, but the effect on joint load has not been determined. The aim of this study was to investigate the effect of exercise on knee adduction moment during one-leg rise and gait.Patients below age 65 with early signs of radiographic knee OA, from a population-based cohort on OA development, were invited to participate in the study. They defined their most symptomatic knee as the index knee. Knee adduction moment during one-leg rise from a stool (48cm), and during gait was assessed using a three-dimensional motion analysis system, before and after eight weeks of supervised exercise.Thirteen patients, seven women, mean age 54.5, 12/13 with Kellgren and Lawrence grade I or II, took part in the study. Peak knee adduction moment during one-leg rise was reduced by 0.08 (95% CI 0.01;0.16) Nm/kg, or 14%, for the index knee, and 0.05 (95% CI -0.04;0.14), or 8% for the opposite knee after eight weeks. The reductions in peak adduction moment during gait were smaller and not significant.This study indicates that peak knee adduction moment could be reduced by supervised, individualized exercise in middle-aged patients presenting early signs of knee osteoarthritis, suggesting further investigation of this area. Peak adduction moment during one-leg rise seems to be more sensitive to deviations and change than peak adduction moment during gait in this population.