ECSS Paris 2023: CP-PN06
INTRODUCTION: Isometric wall squat exercise effectively reduces blood pressure and promotes autonomic adaptations, combining minimal equipment requirements with high time efficiency, enabling wide applicability across various settings. (1). Ultraviolet A (UVA) from natural sunlight can enhance skin-derived nitric oxide (NO) release via non-enzymatic mechanisms, increasing its systemic bioavailability, which may influence neuromuscular function due to the role of NO in neurotransmission and synaptic plasticity. (2, 3). This study examined the effects of a four-week isometric wall squat intervention with natural sunlight exposure on muscle strength and NO production. METHODS: Sixty healthy adults (30 men, 30 women; age: 20.92 ± 2.3 years; BMI: 22.24 ± 2.8 kg/m²) were randomly assigned to an outdoor, indoor, or control group. Pre- and post-intervention assessments included body composition, blood NO, an incremental isometric wall squat test, and an isometric mid-thigh pull (IMTP) test for peak force and rate of force development (RFD) at 50 and 200 ms. The wall squat test consisted of five 2-min stages with a 10° reduction in knee angle per stage until task failure, during which peak heart rate (HR_peak) and wall squat duration were recorded. The 4-week training program (three sessions per week) comprised 4 × 2-min isometric wall squats performed at 95% HR_peak. The outdoor group trained outdoors with ~25% of their body surface area exposed to sunlight at one-quarter of the minimal erythema dose (MED) without sunscreen, the indoor group trained indoors without sunlight, and the control group received no intervention. Statistical analysis was conducted using a two-way mixed-design analysis of variance. RESULTS: Significant group × time interactions were observed for IMTP peak force, 200 ms rate of RFD, and blood NO concentration. Following the intervention, the outdoor group demonstrated significant increases in IMTP 200 ms RFD and blood NO concentration (p < .05). IMTP peak force increased significantly in both the outdoor and indoor groups (p < .05), with greater improvements observed in the outdoor group. Heart rate responses during the wall squat test were significantly reduced (p < .01), and wall squat duration was significantly longer in both the outdoor and indoor groups compared with the control group (p < .01). The average daily ultraviolet exposure was 11.25 ± 1.83, 2.70 ± 2.47, and 2.95 ± 3.08 mJ/cm² for the outdoor, indoor, and control groups, respectively. CONCLUSION: Four weeks of isometric wall squat exercises effectively improved lower-limb muscle strength and wall squat endurance performance. When combined with natural sunlight exposure, ultraviolet radiation may promote skin-derived NO release and enhance its systemic bioavailability, thereby modulating neuromuscular adaptations. Moderate sunlight exposure may confer physiological benefits and merits consideration in future exercise and health promotion strategies.
Read CV CHIA-EN CHENECSS Paris 2023: CP-PN06
INTRODUCTION: Progressive overload is widely recommended in resistance training (RT) guidelines (1). However, no randomized controlled trial has directly tested whether the absence of overload progression compromises the time course of muscle hypertrophy. METHODS: Thirty-one untrained participants completed 12 weeks (24 sessions) of RT using a within-subject design. Individuals’ legs were randomized into two training protocols: 1) load progressively adjusted to maintain the target repetition zone over the training sessions (PROG); and 2) no load progression throughout the intervention (N-PROG). Repetitions were maintained within a 10–12 repetition maximum zone for both protocols. Vastus Lateralis (VL) muscle cross-sectional area (mCSA) was assessed via ultrasound at baseline (W0), week 3 (W3), week 6 (W6), week 9 (W9), and week 12 (W12). Volume load (sets × repetitions × load), perceived exertion (OMNI) and repetitions-in-reserve (RIR) were recorded each session and then summarized week-by-week. Repeated-measures analysis was performed to compare the effects of both protocols across the intervention for VL mCSA. Areas under curve (AUCs) (trapezoidal method) for volume load, OMNI, and RIR were compared using paired t-tests. RESULTS: A significant protocol × time interaction was observed for mCSA (p = 0.02). Both protocols increased mCSA over time (p < 0.05). However, only PROG showed a significant increase from W9 to W12 (p = 0.01), whereas N-PROG plateaued during this period (p > 0.05). Additionally, volume load, OMNI and RIR AUCs (across weeks) were greater in PROG than N-PROG (p < 0.001). CONCLUSION: RT without progressive overload promoted meaningful hypertrophy in the early weeks (nine weeks). However, continued hypertrophic gains in later phases occurred only with load progression. These findings suggest that progressive overload may not be essential for early adaptations in untrained individuals, but becomes important for sustaining muscle growth over time.
Read CV Cleiton LibardiECSS Paris 2023: CP-PN06
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.
Read CV Mizuki SudoECSS Paris 2023: CP-PN06