Lower limb joint Loading during high-impact activities: implication for bone health

Osteoporosis, a significant concern among the elderly, results in low-trauma fractures affecting millions globally. Despite the inclusion of physical activities in strategies to mitigate osteoporosis-related fractures, the optimal exercises for bone health remain uncertain. Determining exercises that enhance bone mass requires an understanding of loading on lower limb joints. This study investigates hip, knee, and ankle joint loading during walking, running, jumping, and hopping exercises, assessing impacts at various intensities (maximal, medium, and minimum efforts). A total of 37 healthy, active participants were recruited, with a mean (SD) age of 40.3 (13.1) years, height of 1.7 (0.08) m, and mass of 68.4 (11.7) kg. Motion capture data were collected for each participant while performing six different exercises: a self-selected level of walking, running, counter-movement jump, squat jump, unilateral hopping, and bilateral hopping. A lower body musculoskeletal model was developed for each participant in OpenSim. The static optimization method was used to calculate muscle forces and hip joint contact forces. The study reveals that running and hopping induce increased joint contact forces compared to walking, with increments of 83% and 21%, respectively, at the hip; 134% and 94%, respectively, at the knee; and 94% and 77%, respectively, at the ankle. Jump exercises exhibit less hip and ankle loading compared to walking, with reductions of 36% and 19%, respectively. Joint loading varies across exercises and intensities, running faster increases forces on all joints, especially the hip. Sprinting raises hip forces but lowers forces on the knee and ankle. Higher jumps intensify forces on the hip, knee, and ankle, whereas hopping faster reduces forces on all joints. The study emphasizes the site-specific impact of exercises on lower limb joint loadings, highlighting the potential of running and hopping for bone formation compared to jumping alone. These findings offer insights for optimizing exercise routines to improve bone health, with potential implications for risk prevention, rehabilitation, and prosthetic development.