Trend analysis and evaluation of musculoskeletal modeling for the study of military operational movements with load carriage.

The purpose of this study is to analyze and evaluate the trends of estimated muscle forces within the back and lower limbs during five representative operational movements: walking, running, cutting, jumping, and obstacle crossing. Three loading conditions were considered to represent infantry operational equipment. Evaluation was performed by comparing these estimations with experimental electromyography (EMG) measurements via cross-correlation and trend analysis. The results demonstrate good agreement with experimental data. For most muscles, the results were consistent with EMG timings and variation trends between the unloaded and initial loading conditions. Specifically, good agreement with experimental measurements was identified for the gastrocnemius medialis, gluteus maximus, rectus abdominis, and vastus medialis. However, discrepancies were noted for the biceps femoris across all conditions and for the spinal erectors between specific loading conditions. These differences are explained by the inherent assumptions of the musculoskeletal framework and were evaluated alongside load-dependent changes in spatiotemporal parameters. The findings suggest that the model is a suitable tool for estimating the timing and trends of muscle forces in the military population, although caution is advised during complex stabilization phases. Significant increases (p<0.05) in estimated muscle forces were identified for the trunk and lower limbs across most investigated movements. Consequently, practical recommendations such as targeted physical conditioning and load redistribution to the chest are provided to mitigate the risk of overuse injuries.