Fatigue response of rat medial longissimus muscles induced with electrical stimulation at various work/rest ratios

Muscle fatigue may be a precursor to workplace musculoskeletal disorders, with the low back resulting in the most frequently injured body part. Work/rest ratios have an effect on fatigue due to the amount of rest allowance provided following muscle contraction. This study explored various work/rest ratios by electrically stimulating rat medial longissimus muscles. A 3 V stimulus with 0.2 ms pulse duration was applied at a frequency of 30 Hz. There were four stimulation groups consisting of the following duty cycles (DC) and cycle times (CT): DC25%:CT20s, DC25%:CT280s, DC75%:CT20s, and DC75%:CT180s. Muscle fatigue was measured as a decrease in M-wave amplitude and area, and an increase in M-wave duration. The results indicated that fatigue occurred immediately in each of the groups. The higher duty cycle and shorter cycle time group resulted in significantly greater fatigue than the lower duty cycle and longer cycle time group, as measured by increased M-wave amplitude and area. A longer M-wave duration was observed in the high duty cycle long cycle time group. This suggests that the combination of low duty cycle and long cycle times leads to less fatigue. In high duty cycle scenarios, short cycle times result in less fatigue.