Inter-Individual Variability in Cycling Biomechanics During Experimentally Induced Movement-Evoked Knee Pain

Knee pain can alter lower-limb loading and contribute to inter-limb asymmetry, affecting movement mechanics and rehabilitation. Although cycling is frequently prescribed during rehabilitation, the effects of pain on bilateral cycling biomechanics remain poorly understood. This study investigated experimentally induced movement-evoked knee pain on bilateral torque and power output, inter-limb asymmetry, and inter-individual motor responses during cycling. Twenty-three healthy adults (14M and 9F) completed an incremental cycling test followed by eight randomized constant-load trials under pain and no-pain conditions at two intensities. A custom closed-loop torque-dependent electrical stimulation system induced movement-evoked knee pain during the downstroke while bilateral biomechanics were recorded. At higher intensities, movement-evoked knee pain reduced torque (p=0.026, d=0.566) and power (p=0.010, d=0.657) production in the painful limb and altered the normalized symmetry index (NSI) for power (p=0.005, d=0.659), and torque (p<0.001, d=0.754). At lower intensity, pain-leg power (p=0.154) and torque (p=0.104) did not differ significantly between conditions, although torque NSI indicated greater reliance on the non-pain leg (p=0.017, d=0.538). Despite these group-level responses, substantial inter-individual variability was observed ranging from pronounced unloading to increased pain-leg contribution. These findings demonstrate that movement-evoked knee pain alters cycling mechanical output toward the non-painful limb, with substantial heterogeneity in individual motor responses.