Author(s): SUDO, M., NAKAMURA, T., BABA, K., ANDO, S., KANO, Y., Institution: PHYSICAL FITNESS RESEARCH , Country: JAPAN, Abstract-ID: 813

INTRODUCTION:
Exercise-induced skeletal muscle damage is characterized by immediate inflammatory responses followed by myofiber regeneration. This process initiates with ultrastructural disruptions, notably sarcomere hypercontraction, leading to structural fiber degeneration marked by cellular swelling and subsequent leukocyte infiltration. Complete muscle regeneration requires several days to proceed (Sudo et al., 2009). Recent studies suggest that local mechanical vibration accelerates the repair-regeneration cycle in pharmacological models (Seo et al., 2021). However, pharmacological models involve extensive disruption beyond myofibers, limiting translatability to physiological damage where the surrounding environment remains preserved. Therefore, this study investigated the effects of local vibration on the recovery process using an eccentric contraction (ECC)-induced skeletal muscle damage model.
METHODS:
Male Wistar rats were assigned to an ECC group or an ECC with vibration stimulation (ECC+VIB) group (n = 5 per group at each time point). The tibialis anterior (TA) muscle was subjected to ECC loading (40 contractions, 2 sets). In the ECC+VIB group, local vibration (25 Hz) was applied for 5 min at 12-hour intervals, starting one day post-ECC. Muscles were harvested on days 3 (D3), 7 (D7), and 14 (D14) post-ECC. The damage-regeneration process was quantified based on phase-specific morphology: edema (Phase 1) and macrophage infiltration (Phases 2-3) at D3; and the area proportion of Phase 5 regenerating fibers characterized by central nuclei at D7 using the point-counting method. The percentage of mature regenerated fibers with central nuclei was evaluated at D14. Data are expressed as mean +/- SD and analyzed using Welch's t-test or two-way ANOVA.
RESULTS:
There was no significant difference in muscle weight between groups. At D3, the proportions of Phase 2 and Phase 3 were significantly lower in the ECC+VIB group (Phase 2: ECC 22.1 +/- 5.99%, ECC+VIB 15.3 +/- 6.02%, p = 0.05; Phase 3: ECC 21.7 +/- 7.89%, ECC+VIB 12.3 +/- 4.46%, p = 0.008). At D7, the ECC+VIB group exhibited a significantly higher area proportion of Phase 5 regenerating fibers (ECC 19.6 +/- 8.42%, ECC+VIB 40.3 +/- 11.2%, p = 0.006). Furthermore, the percentage of centrally nucleated mature fibers at D14 was significantly higher in the ECC+VIB group (ECC 8.26 +/- 1.79%, ECC+VIB 12.4 +/- 2.25%, p = 0.049).
CONCLUSION:
Local vibration stimulation after ECC loading suppressed early-phase damage (D3) and enhanced the emergence of regenerating fibers in the later stages (D7 and D14). These findings suggest that local vibration stimulation can accelerate the damage-regeneration process following ECC-induced skeletal muscle damage, potentially facilitating functional recovery.
References: Sudo M, Kano Y. (2009). J Physiol Sci 59: 405-412. Seo BR, et al. (2021). Sci Transl Med 13(614): eabe8868.