Multiscale analysis of mechanical stress in muscle under static and dynamic loading.

Deep tissue injury (DTI) is a serious condition primarily triggered by prolonged mechanical loading rather than short-term excessive force. Cyclic force stimulation has been shown to enhance cellular protection; however, the biomechanical mechanisms underlying tissue and cellular responses to such stimulation remain poorly understood. This study investigates the biomechanical effects of cyclic force transmission from viscoelastic muscle tissue to muscle fibers using a multiscale finite element model with varying cyclic force parameters. Finite element analysis was used to examine the impact of different frequencies and amplitudes of force stimulation, considering the viscoelastic properties of tissues and cells. Results indicated that, on each one of the three model scales, the average maximal Von Mises stress during stress relaxation increased with cyclic force amplitude at a constant frequency. At a fixed amplitude, frequency variations did not influence the average maximal Von Mises stress in the macroscopic and mesoscopic models. However, in the microscopic model, higher frequencies resulted in lower average maximal Von Mises stress at low amplitudes and higher average maximal Von Mises stress at high amplitudes. Notably, a high-frequency, low-amplitude cyclic force mode reduced the average maximal minimum principal stress by 3.6% in the first four seconds and 5.8% in the last 16 seconds of the 20-second stress relaxation period. These findings suggested that such a cyclic force mode may mitigate or delay mechanical damage caused by prolonged mechanical loading, offering insights into potential strategies for preventing DTI.