Impact of Eccentric Exercise Interventions with Small and Large Ranges of Motion on Rat Skeletal Muscle Tissue and...

Eccentric training induces greater hypertrophy while causing more muscle damage than concentric training. This study examined the effects of small-range eccentric contractions (SR-ECCs) and large-range eccentric contractions (LR-ECCs) on muscle morphology, contractility, and damage in rats. Thirty male Fischer 344 rats were divided into five groups: small-range ECC single-bout (SR-ECC_SB, n = 4), large-range ECC single-bout (LR-ECC_SB, n = 4), SR-ECC intervention (SR-ECC_Intv, n = 7), LR-ECC intervention (LR-ECC_Intv, n = 8), and control (Cont, n = 7). These groups underwent transcutaneous electrical stimulation involving 80 ECCs twice a week for four weeks. The results indicated that the LR-ECC_SB group had more Evans blue dye-positive fibers than other groups. The SR-ECC_Intv group showed no increase in the mean myofiber cross-sectional area. However, Pax7+ and Ki67+ cells significantly increased in both ECC_Intv groups compared to the Cont group, and the connective tissue area was significantly greater in the LR-ECC_Intv than in others. Muscle force was lower in both ECC_Intv groups compared to the Cont group. These findings suggest that SR-ECC intervention may induce a smaller increase in the number of fibers with a large myofiber cross-sectional area and satellite cell proliferation with less muscle damage and myofibrosis compared to LR-ECCs.