Estimation of joint and muscle forces during exercise in various postures.

An understanding of joint and muscle forces is essential for prescribing appropriate exercises for patients with musculoskeletal disorders. This study aimed to determine the joint and muscle forces during exercises in the sitting or supine posture. Ten healthy males (age: 25.4 ± 2.6 years) performed three standing exercises (gait, squat, and forward lunge) and three exercises in sitting or supine postures (knee extension while sitting, straight leg raise, and bridging). The joint and muscle forces of the lumbar spine and lower extremities were estimated using the musculoskeletal model simulation based on the motion capture data. In the analysis of the exercises in the sitting or supine postures, the external forces acting from the chair or floor on the body were estimated using the optimization algorithm. The hip and tibiofemoral joint force, as well as muscle force such as VL, GMAX, and GAS, exhibited significantly greater magnitudes during standing exercises. However, the L4-L5 joint force during bridging was equivalent to those during gait and squat. Bridging generated significantly larger muscle force in ES and MF than those during gait. Exercises performed in the sitting or supine postures induced a larger load on L4-L5 and hip joint and trunk extensor muscle forces than exercises in the standing posture. While the joint and muscle forces were generally larger during standing rather than sitting or supine exercises, certain notable exceptions were observed, such as bridging exercise. It suggested that physical therapists should use caution when performing supine exercise on patients with low back pain.