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Scientific Programme

Physiology & Nutrition

OP-PN17 - Thermoregulation I

Date: 03.07.2024, Time: 11:00 - 12:15, Lecture room: Carron 2

Description

Chair TBA

Chair

TBA
TBA
TBA

ECSS Paris 2023: OP-PN17

Speaker A Edgar Schwarz

Speaker A

Edgar Schwarz
Saarland University, Institute for Sport and Preventive Medicine
Germany
"Combined effects of pre-cooling and in-play cooling breaks using ice towels and cold drinks during football matches in warm conditions. "

INTRODUCTION: Playing in hot environmental temperatures is a growing concern for sporting and football organisations worldwide. Therefore, to support player health and minimise performance deterioration during football in the heat, strategies, including cooling procedures and breaks in play, have been proposed; however, investigations in field settings remain scarce (Gouttebarge et al., 2023). METHODS: In total, 22 male academy soccer players (age 17 ± 0.8 y) participated in two matches in warm conditions (25.5 ± 2 °C WBGT) and received a cooling intervention (COOL) or a control condition (CON) in a randomised cross-over design. COOL consisted of cold towels (6-9 °C) and cold drinks (5 °C) for 10min of pre-cooling prior to the warmup, 10min before the kick-off, 10min at halftime and for an additional 3min during cooling breaks at 25min into each half. The CON received a placebo drink (17 °C) and no cooling at the same time frames. Core body temperature (Tcore), heart rate (HR), match running performance via gobal positioning system (GPS), sweat loss and fluid intake, rating-of-fatigue (RoF), rating of perceived exertion (RPE), thermal sensation (TS) and perceptions regarding likeability and performance benefits were measured throughout the match-day. RESULTS: Players reached a maximum Tcore of 39.2 ± 0.5 °C in COOL, which did not differ from CON (39.1 °C ± 0.5 °C; p ≥ 0.05). Further, there were no differences between conditions for Tcore, HR, GPS, RoF or RPE (p≥0.05), but TS was lower in COOL during respective breaks (p<0.05). Players sweated significantly less in COOL than in CON (2.5 ± 0.5 L vs 2.9 ± 0.6 L) but made up for that by increasing fluid intake (COOL: 1.2 ± 0.3 L; CON: 1.4 ± 0.3 L). Further, players rated the cold towels and cold drinks better than the placebo drinks (p<0.05) and perceived more benefits from COOL than CON (p<0.05). CONCLUSION: No physiological or performance benefits were observed for the cooling intervention other than the reduced sweat rate. Given the observed warm but not hot environmental conditions, heat strain remained moderate for both groups and may have impacted the effectiveness of the cooling strategy. Nevertheless, the 3min cooling breaks seemed to attenuate the continuous rise in Tcore described in matches without breaks (Mohr et al., 2011). Future observations are needed to investigate the potential benefits of this strategy in hotter temperatures. Gouttebarge V et al. 2023. Protective guidelines and mitigation strategies for hot conditions in professional football: starting 11 Hot Tips for consideration. BMJ Open Sport Exerc, 9, doi:10.1136/bmjsem-2023-001608 Mohr M et al. 2012. Physiological Responses and Physical Performance during Football in the Heat. PLoS ONE, 7(6), doi:10.1371/journal.pone.0039202

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ECSS Paris 2023: OP-PN17

Speaker B Mark Waldron

Speaker B

Mark Waldron
Swansea University , A-STEM
United Kingdom
"Exploring the dependency of informational transfer between core or skin temperatures and sudomotor activity among healthy participants of varying thermoregulatory control "

INTRODUCTION: During hyperthermia, integration of afferent input from central and peripheral thermoreceptors initiates efferent sympathetic signals to activate sweat glands in pulsatile bursts. In this feedback system, core temperature (Tcore) is the primary controlled variable, with skin temperature (Tskin) providing ‘auxiliary’ dynamic feedback [1]. However, the connectivity of efferent signalling between Tcore, Tskin and sweating, as well as the synchrony of sweating between skin sites, across individuals of varying thermoregulatory control has not been investigated. Therefore, we evaluated i) connectivity between Tcore, Tskin and local eccrine sweating of the arm and chest during passive heating and ii) the temporal synchrony of arm and chest sweating. METHODS: Thirteen participants completed 90 min passive heating, twice, across one-week (38±0°C, relative humidity 56±2%). Local sweat rates were continuously measured on the ventral forearm and chest, alongside Tcore (rectal) and mean Tskin (chest, arm and leg). Changes in Tcore across the protocol and thermosensitivity (Tcore change at sweat onset) were measured to determine thermoregulatory control of the sample. Transfer entropy (TE) was used to quantify information flow between Tcore, Tskin and all sweating sites, with higher values demonstrating greater connectivity. Relationships between thermoregulatory control measures and TE were evaluated using repeated measures correlations. Cross-correlation was used to assess sweating synchrony across the two sites. Paired t-tests assessed differences between TE values. Data are means±SD. RESULTS: The TE for Tcore-arm (0.007±0.005 bits) and Tcore-chest (0.009±0.010) was lower (P<0.01 and P <0.01) than Tskin-arm (0.019±0.014 bits) and Tskin-chest (0.022±0.015 bits), respectively, denoting higher information flow from the skin to sweating sites. There were no differences between arm and chest Tskin TE values (P = 0.31). Both Tskin-arm TE and Tskin-chest TE were inversely related to the Tcore increases (r= -0.56 and -0.57, respectively) and thermosensitivity values (r= -0.37 & -0.46, respectively), while Tcore TE values were unrelated (P>0.05). Cross-correlation analysis revealed no time-lag between chest and arm site peak relationships, which were strongly correlated (r=0.98±0.03). CONCLUSION: The notion of Tskin as a dynamic auxiliary feedback mechanism [1] is supported, with reliance upon informational flow between Tskin and sweating of the arm and chest to maintain control of Tcore, which has relatively less TE to sweating sites. Individuals with smaller increases in Tcore and faster sweating onset possessed greater connectivity between Tskin and sweating sites. The temporal correspondence confirms the assumed synchrony between sweating sites, indicating that the pattern of this informational flow is likely to be similar across anatomical locations. These findings may inform future passive assessments of thermoeffector feedback loops. References 1. Romanovsky, 2014, Acta Physiol.

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ECSS Paris 2023: OP-PN17

Speaker C Oliver Gibson

Speaker C

Oliver Gibson
Brunel University London, Department of Life Sciences
United Kingdom
"Unaltered intestinal fatty acid binding protein (iFABP), cytokine and chemokine responses to prolonged passive hyperthermia in healthy humans"

INTRODUCTION: Hyperthermia, whether passive or exertional, can cause small intestine epithelial injury. Epithelial injury can elevate gastrointestinal permeability, facilitate endotoxin translocation and an inflammatory cytokine/chemokine response which are contributory factors in heat illness (Garcia et al., 2022). Exercise-heat stress causes epithelial injury as quantified by changes in intestinal fatty acid binding protein (iFABP) (Walter, et al., 2021a), and a greater inflammatory response relative to normothermic exercise (Garcia et al., 2022). Responses during passive hyperthermia of equivalent magnitudes to exercise-heat stress have yet to be clearly described (Walter et al., 2021b). This experiment aimed to quantify the changes in iFABP, and cytokine/chemokine responses during prolonged passive hyperthermia. It was hypothesised that passive hyperthermia would increase iFABP and cytokine/chemokine concentrations. METHODS: In a counterbalanced order, eight young, healthy males visited the lab on four occasions to undertake 3 h of rest (CON); 3 h of one leg heating (OLH); 3 h of two legs heating (TLH); and 2.5 h of whole-body heating (WBH). Heating was applied via a water perfused garment circulating 50°C water. Core (Tcore) and thigh muscle temperature (Tm) were measured continuously, with the concentration of iFABP and selected cytokines and chemokines (EGF, Eotaxin, FGF-2, FLT-3L, Fractalkine, G-CSF, GM-CSF, GRO, IFN-α2, IFN-γ, IL-6, IL-10, IL-12p40, MCP-3, MDC, sCD40L, TGF-α, TNFα, VEGFα) quantified periodically. Regional (Leg, arm and head) and systemic haemodynamics (cardiac output) were measured by echocardiography and Doppler ultrasound to quantify torso blood flow. RESULTS: Tcore and Tm increased from baseline in OLH (+0.4 ± 0.2°C, +3.4 ± 1.2°C), TLH (+0.7 ± 0.2°C, +3.4 ± 1.3°C) and WBH (+2.3 ± 0.4°C, +6.0 ± 1.7°C) respectively (p < 0.05), but were unchanged in CON. Torso blood flow increased (p < 0.05) from baseline in OLH (+0.26 ± 0.51 L.min-1), TLH (+0.47 ± 0.60 L.min-1) and WBH (+3.24 ± 1.43 L.min-1), but was also unchanged in CON. Cardiac output increased in OLH (+2.1 ± 0.6 L.min-1), TLH (+3.4 ± 0.7 L.min-1), and WBH (+7.3 ± 1.0 L.min-1) vs CON respectively (p < 0.05). Circulating iFABP, and all chemokine/cytokines were unchanged from baseline (p > 0.05) in CON, OLH, TLH or WBH. CONCLUSION: These data identify that iFABP and circulating cytokine and chemokine concentrations do not significantly increase during prolonged local and systemic passive heating. This finding questions the independent effect of hyperthermia on circulating markers of gastrointestinal permeability and subsequent inflammation in healthy humans. References Garcia, C. K., et al., (2022). Exertional heat stroke: pathophysiology and risk factors. BMJ medicine, 1(1):e000239 Walter, E., (2021a). Eur. J. Appl. Physiol., 121(4), 1179-1187 Walter, E., (2021b). Physiol. Rep., 9(16), e14945

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ECSS Paris 2023: OP-PN17