ECSS Paris 2023: CP-PN23
INTRODUCTION: Heat acclimation training enhances thermoregulatory adaptation; however, it can be time-consuming and physically demanding for athletes. As an alternative, passive methods such as hot water immersion have gained increasing attention (1). In particular, CO₂ hot water bathing imposes greater thermal stress than tap hot water bathing (our unpublished data), leading us to hypothesize that it may be effective for heat acclimation. Therefore, this study explores the feasibility of CO₂ water bathing as a novel heat acclimation method. METHODS: Participants were 10 male college athletes. The acclimation trial consisted of whole-body CO₂ hot water bathing (40°C, 1000 ppm) for 10 min and resting for 5 min × 3 sessions × 3 days. During the trial, rectal temperature (Tre), skin temperature (Tsk), subjective indicators (thermal sensation (TS), and thermal comfort (TC)), heart rate, whole-body sweat loss (WBSL) and sweating sodium concentrations (Na) were measured. To assess heat acclimation, a heat stress test was conducted before and after the acclimation trial, in which participants cycled at 50% VO₂max until their rectal temperature reached 38.5°C. Heat acclimation effects were evaluated based on the time required to reach 38.5°C. RESULTS: Mean exercise duration increased slightly but not significantly (Pre 38.7 ± 6.1 min, Post 39.6 ± 7.7 min, p = 0.70). WBSL and Na also showed slight improvements, but the changes were not significant (WBSL, Pre 1369.5 ± 387 g, Post 1394.5 ± 483.5 g, p = 0.80; Na, Pre 1619.0 ± 538.6 mmol/L, Post 1379.4 ± 454.8 mmol/L, p = 0.099). There was also no interaction effect for Tre; however, Tsk was significantly lower in the Post condition during exercise (p < 0.05). TS and TC were also significantly lower in the Post condition (p < 0.05). CONCLUSION: A short, three-day acclimatation bath reduced Tsk, TS and TC during exercise. Since a decrease in Tsk is associated with a lower TS (2), this short acclimatation with CO2 baths may have contributed to a reduced subjective indicator during exercise in hot environment. These improvements in subjective indicators are important for athletes competing in sports (3). Reference (1) Heathcote SL, et al. (2018). Front Physiol. 20; 9:1851. (2) Schlader, Z. J. et al. (2011). Eur J Appl Physiol., 111(8), 1631–1639. (3) Schulze, E., D et al., (2015). Int J Sports Physiol Perform. 10, 655–663.
Read CV RISA IWATAECSS Paris 2023: CP-PN23
INTRODUCTION: Cooling the head, face and neck can have strong perceptual effects that contribute to improved performance. The aims of this systematic review were to; i) determine the effect of cooling strategies targeting the head, face and neck on physical and cognitive performance; ii) determine any associated physiological and perceptual responses; iii) synthesize any reported adverse events following the use of these strategies; and iv) provide practical applications for the use of these strategies to improve performance. METHODS: We conducted a systematic review and multi-level meta-analysis, adhering to the PRISMA guidelines. Studies that investigated the effect of cooling strategies targeting the head, face, or neck on a physical or cognitive task using a controlled trial design were included. RESULTS: Sixty-three studies were identified, involving 618 participants (86.6% male). Cooling strategies included water-perfused devices (18.7%); phase change neck collars (17.3%); fanning/cold air (14.7%); phase change headwear (13.3%); ice/gel packs (13.3%); cold towels (5.3%); menthol application (4.0%); water spraying/dousing (4.0%); or a combination of strategies (9.3%). The effect of cooling on both self-paced and fixed-intensity exercise tasks was inconclusive; the 95%CI of the pooled effect was compatible with no effect and medium beneficial effects, but not harmful effects. We were unable to pool cognitive data. Cooling reduced the skin temperature at the target site and improved thermal sensation and thermal comfort. Effects on heart rate, and core and mean skin temperatures were negligible. Adverse events were rare, and no intervention subgroup was superior. CONCLUSION: The effect of cooling the head, face and neck on self-paced and fixed-intensity exercise tests was inconclusive, with both no and medium beneficial effects possible. We found no evidence of harmful performance effects. Cooling the head, face and neck reduced the skin temperature at the target site and improved thermal sensation and thermal comfort. There was no effect on heart rate, and effects on core temperature and mean skin temperature were so small they were considered physiologically negligible. Adverse events associated with the interventions were rare, and there was no report of any cooling strategy making a participant feel cooler and then pushing beyond their thermal limits, causing exertional heat illness. No intervention subgroup was superior, and hence, athletes are recommended to experiment with a range of rule-compatible and available head, face and neck cooling strategies, including different doses and timings, to determine the optimal strategy for their individual and sport context.
Read CV Christopher StevensECSS Paris 2023: CP-PN23
INTRODUCTION: Athletes strive to achieve optimal performance in competitions, with warm-up or passive warming being commonly employed to enhance muscle function. Previous studies indicate that elevated muscle temperature can increase maximal muscle strength (1). This effect is hypothesized to result from increased blood flow to active muscles through vasodilation and enhanced contractility due to reduced muscle viscosity (2). Although this suggests that blood flow and muscle stiffness are related to maximal muscle strength, the direct relationship between muscle temperature-induced changes in blood supply, muscle stiffness, and performance enhancement remains unclear. Therefore, this study aimed to examine whether variations in maximal muscle strength following muscle temperature modulation through cold water immersion (CWI), hot water immersion (HWI), and neutral-warm water immersion (NWI) are attributable to changes in muscle blood flow and muscle elastic modulus. METHODS: 12 healthy males participated in three conditions: CWI (10°C), HWI (40°C), and NWI (34°C). Lateral vastus muscle temperature, muscle shear wave velocity, and femoral artery blood flow were measured pre- and post-immersion. In addition, isokinetic maximal knee extension muscle strength was also measured post-immersion. Repeated-measures correlation analysis was conducted to assess intra-individual relationships between muscle temperature, blood flow, shear wave velocity, and maximal muscle strength in paired measurements collected multiple times across individuals. RESULTS: The muscle temperature and femoral artery blood flow decreased in the CWI and NWI conditions, and increased in the HWI condition (all P < 0.05). The shear wave velocity showed no differences between conditions, as well as no main effects of time or interactions (P > 0.05). The maximal knee extension muscle strength was lower in the CWI condition than in the HWI and NWI conditions (P < 0.05). Additionally, repeated-measures correlation analysis revealed positive associations between muscle temperature and blood flow (r = 0.66, P < 0.05), muscle temperature and muscle strength (r = 0.76, P < 0.05), and blood flow and muscle strength (r = 0.59, P < 0.05), while there was no relation between muscle strength and shear wave velocity (P > 0.05). CONCLUSION: These results suggest that the increase in maximal knee extension muscle strength induced by muscle warming may be attributed to enhanced blood supply to active muscles. In contrast, muscle stiffness remained unchanged with muscle warming and was not associated with maximal knee extension strength. Reference: 1. Bergh U, Ekblom B. Influence of muscle temperature on maximal muscle strength and power output in human skeletal muscles. Acta Physiol Scand. 1979 Sep;107(1):33-7. 2. Bishop D. Warm up I: potential mechanisms and the effects of passive warm up on exercise performance. Sports Med. 2003;33(6):439-54.
Read CV Atsumu KitanoECSS Paris 2023: CP-PN23