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.

Electrical stimulation-induced muscle contraction (ESMC) has demonstrated various physiological benefits, but its effects on the secretion of undercarboxylated osteocalcin (ucOC), a bone-derived cytokine, remain unclear. This study explored the relationship between ESMC, bone strain, and ucOC secretion through two experiments. In the first, young male Fischer 344 rats were divided into three groups: low-frequency ES (LF, 10 Hz), high-frequency ES (HF, 100 Hz), and control (CON). Acute 30-min transcutaneous ES was applied, and both bone strain and ucOC levels were measured. In the second experiment, rats underwent LF or HF long-term ES (two sessions per week for 4 weeks), with ucOC and insulin levels monitored. Results revealed a significant peak in ucOC at 6 h post-acute LF-ESMC. Despite HF-ESMC generating greater bone strain, LF-ESMC, with smaller but repetitive bone strain, proved more effective in stimulating ucOC secretion. In the long-term study, both ESMC groups exhibited early increases in ucOC, with a positive correlation to insulin levels. In conclusion, bone strain induced by ES-mediated muscle contraction promotes ucOC secretion, with both the magnitude and frequency of strain playing critical roles.

Transient receptor potential ankyrin 1 (TRPA1) is a non-selective cation channel expressed in primary sensory neurons and has been proposed as a therapeutic target for pain management. However, the effects of repeated administration of a TRPA1 antagonist on peripheral tissue morphology remain unclear. This study examined whether repeated HC-030031 administration affected the histomorphology of skeletal muscle fibers and muscle spindles in rats. Male Fischer 344 rats were assigned to a control group (Con, n = 10, 12.6 ± 3.3 weeks) or an HC-030031-treated group (HC, n = 10, 13.2 ± 3.7 weeks). HC-030031 was administered subcutaneously once weekly for four weeks. Tibialis anterior muscles were harvested and analyzed using histochemical and morphometric methods. Morphometric analyses included muscle mass, myofiber cross-sectional area (FCSA), roundness of extrafusal muscle fibers, NADH-TR staining intensity-based assessment, and structural parameters of muscle spindles and intrafusal fibers. No significant differences were observed between the groups in body weight, muscle mass, extrafusal FCSA, or fiber roundness. NADH-TR staining was used to distinguish fibers with darker or lighter staining intensity, and FCSA was compared between the Con and HC groups within each staining-based fiber subset. No group differences were detected in the FCSA of either subset. Similarly, no significant differences were observed in intrafusal FCSA, intrafusal fiber roundness, the number of intrafusal fibers per muscle spindle, or muscle spindle density. These findings indicate that repeated HC-030031 administration was not associated with detectable histomorphological alterations in skeletal muscle fibers or muscle spindles under resting conditions in young adult male rats.

Purpose : The critical power (CP) model is widely used to evaluate high-intensity exercise tolerance; however, the performance characteristics reflected by its parameters may differ across athletes with diverse physiological and neuromuscular profiles. This study examined how CP-model parameters relate to aerobic power, indices of anaerobic performance, and nonoxidative energy contribution in male track-and-field athletes. Methods : Twenty male track-and-field athletes completed assessments of maximal oxygen uptake ( ), CP and the curvature constant (W′), maximal accumulated oxygen deficit, maximal anaerobic power, and a 30-second Wingate test. Body composition variables were assessed using high-frequency bioelectrical impedance analysis. Associations between CP-model parameters and performance indices were examined using correlation analysis. Results : CP was significantly and positively correlated with ( r = .64, P = .002) and negatively correlated with several mechanical indices of anaerobic performance. In contrast, W′ was positively associated with mechanically expressed anaerobic performance, including maximal anaerobic power and Wingate-derived peak and mean power ( r = .73–.75, P < .001), as well as body composition variables. No statistically significant association was observed between W′ and maximal accumulated oxygen deficit. Conclusions : These findings indicate that CP and W′ reflect distinct aerobic and mechanical performance characteristics, with CP primarily reflecting aerobic power and W′ representing a mechanically expressed work reserve rather than a purely metabolic index of nonoxidative energy contribution. This distinction highlights the complementary roles of CP-model parameters in performance evaluation.