Instantaneous and Cumulative Knee Joint Loading in Cycling With and Without Medial Knee Osteoarthritis.

Medial knee osteoarthritis (KOA) is characterized by altered joint loading that accelerates disease progression. Cycling is often recommended as a low-impact exercise, yet the instantaneous and cumulative determinants of knee joint loading remain unclear. This study examined cyclists with and without KOA to characterize how power, cadence, and crank torque relate to knee load during cycling. Fifty-six recreational cyclists (19 KOA, 19 age-matched controls (CO), 18 younger controls (CY)) performed 3 cadences (60/80/100 rpm) at 3 power outputs (157/210/261W). Three-dimensional kinematics and pedal reaction forces were used to compute knee moments via inverse dynamics. Instantaneous loading was quantified as peak knee adduction (KAMpeak), flexion (KFMpeak), and extension (KEMpeak) moments. Cumulative exposure was assessed using fatigue-weighted cumulative knee load (wCKLKAM, wCKLKFM, wCKLKEM) normalized to 1 h of cycling. Mixed-effects linear models tested the effects of crank torque, power, and cadence on instantaneous and cumulative load. Crank torque best explained all instantaneous moments (all p < 0.001). KOA showed larger positive sensitivity to crank torque in KAMpeak than both control groups, but smaller torque-related increases in KFMpeak (all p ≤ 0.01). For cumulative loading, power best explained wCKLKAM and wCKLKFM, where opposing effects of instantaneous load and cycle count cancel the net effect of cadence. However, higher cadence at a given power was associated with greater wCKLKEM, particularly in KOA (p < 0.001). These results show that crank torque drives instantaneous knee loading, while power output and cadence govern cumulative exposure, highlighting the added value of cumulative metrics for characterizing differences in knee joint loading patterns between cyclists with and without KOA.