Biomechanical Characteristics of Walking and Running during Unloading of the Musculoskeletal System by Vertical Hanging

The article presents the results of a biomechanical analysis of locomotion (walking and running) on a treadmill under normal conditions and when the weight load on the human musculoskeletal system was reduced to 70% of body weight. The study was conducted with the participation of 24 apparently healthy volunteers aged 25.1 ± 5.2 years, body weight from 66 to 90 kg (77.7 ± 6.7 kg), body length from 172 to 192 cm (179.7 ± 6.3 cm). During the study, volunteers performed two treadmill locomotor tests: walking at a speed of 4.5 km/h and running at a speed of 10 km/h with different body weight unloading values: 100 and 70% of body weight. The change in weight load on the musculoskeletal system was performed by vertical hanging. The kinematic, spatiotemporal parameters, ground reaction forces of locomotions, and electromyographic (EMG) activity of leg muscles were recorded and analyzed. The results of the study revealed significant differences in the ground reaction force values of locomotion, as well as kinematic parameters, which was manifested by a decrease in the angular displacements in the knee and ankle joints in the push-off and swing phases. Analysis of the EMG of leg muscles made it possible to determine the contribution of muscles to the performance of walking and running on a treadmill at different weight loads. During walking, when the musculoskeletal system was unloaded up to 30% of the body weight, a significant reduction in the EMG cost was revealed (within 9–23% compared to normal walking). During running, reduction in the EMG cost with a change in the weight load varied from 8 to 37%. Body weight unloading up to 30% decreases the efforts to perform take-off. In addition, the results of the study indicate a change in the contribution of the lower and upper leg muscles when locomotor exercises were performed under conditions of reduced weight load on the musculoskeletal system.