Impact of Daily Physical Fatigue on Inter-Limb Load Asymmetry and Joint Loading Rates During Daily Living Tasks in Unilateral Knee Osteoarthritis

Background: Knee osteoarthritis (OA) is characterized by progressive joint degradation and altered gait biomechanics. Inter-limb load asymmetry during daily living tasks may accelerate joint deterioration, particularly when combined with physical fatigue. This study investigates the relationship between daily physical fatigue and inter-limb load asymmetry patterns during functional activities in individuals with unilateral knee OA. Objective: To evaluate the impact of fatigue on inter-limb load asymmetry and joint loading rates during daily living tasks in patients with unilateral knee osteoarthritis, and to identify biomechanical and clinical factors associated with load distribution patterns. Methods: One hundred eighteen participants with unilateral knee OA (mean age 62.6 (SD 7.4) years, BMI 29.9 (SD 4.2) kg/m2) completed biomechanical assessments during non-fatigued and fatigued conditions. Ground reaction force measurements were obtained during functional tasks including stair climbing, sit-to-stand transitions, and level walking. Load asymmetry was quantified as the inter-limb difference in peak vertical ground reaction forces. Statistical analysis was conducted using Python (v3.9), including paired t-tests, analysis of variance, and linear regression modeling. Results: Participants demonstrated significantly increased load asymmetry under fatigue conditions (mean difference 8.7% (SD 12.3) %, p < 0.001). Fatigue-induced asymmetry was task-dependent, with stair negotiation showing the greatest increase (11.2% (SD 14.1) %). Peak loading rates on the affected knee were inversely correlated with time-to-peak load during fatigued conditions (r = -0.68, p < 0.001). Disease severity (WOMAC score) and age significantly predicted asymmetry changes (R2 = 0.52, p < 0.001). Conclusions: Physical fatigue exacerbates inter-limb load asymmetry in unilateral knee OA, potentially accelerating joint degeneration. Task-specific interventions targeting fatigue management and load redistribution may improve long-term outcomes. Future longitudinal studies should examine the temporal relationship between acute biomechanical changes and progressive structural joint damage. Keywords: Knee osteoarthritis, load asymmetry, fatigue, biomechanics, ground reaction forces, functional tasks.