ECSS Paris 2023: OP-PN03
INTRODUCTION: In hot or humid environments, there is a reduced capacity for dry or evaporative cooling, which can result in uncompensable heat stress and rises in core temperature (Tcore) [1]. Cardiovascular adjustments (e.g. elevated heart rate, cardiac output and peripheral vasodilation) attempt to meet heat loss demands by facilitating greater skin blood flow (SkBF) and occur in parallel to increases in sudomotor function [2]. An individual’s ability to thermoregulate (i.e. enhanced vasodilation and eccrine sweating) and, consequently, tolerate such conditions, can be chronically or acutely modified [3]. Taurine supplementation enhances sweating onset and rate during exercise in the heat [4] and induces greater peripheral arterial vasodilation [5], but its potential role in thermoregulation at rest has not been evaluated. The current study aimed to determine the effect of oral taurine supplementation on sweating, vascular, cardiometabolic and Tcore responses during 90 min passive heat exposure. METHODS: Thirteen, healthy, euhydrated, non-heat acclimated female (n = 2) and male (n = 11) participants (26 ± 5 years, 79.3 ± 9.6 kg) completed a 90 min passive heating protocol (38.4 ± 0.4°C, relative humidity 55.9 ± 1.9%), following eight-days of oral taurine supplementation (50 mg/kg of body mass) or placebo in a double-blind, randomised, cross-over design. Whole-body sweat loss (WBSL), local sweat rate (LSR), SkBF, cutaneous vascular conductance (CVC), brachial artery diameter and blood flow, mean arterial pressure (MAP), parameters of cardiac function, pulmonary gas exchange and Tcore were assessed. Relative % SkBF and brachial artery vasodilation (V%) were analysed during- and post-isometric handgrip exercise, respectively, at three timepoints (20, 50 and 80 min). Plasma taurine concentrations were determined from post-supplementation blood samples. RESULTS: Oral taurine supplementation increased WBSL by 16.2% (p < 0.049), leg LSR by 26.6% (p = 0.011), SkBF by 19.3% (p = 0.016) and CVC by 9.3% (p = 0.027) compared to placebo. Post-isometric handgrip brachial artery (8.0 vs 5.8%; p = 0.002) and SkBF (6.3 vs 4.6%; p = 0.020) V% were greater in the taurine condition; however, no differences in resting brachial artery diameter and blood flow, MAP, cardiometabolic parameters or Tcore were observed (p > 0.05). Plasma taurine bioavailability was increased in taurine vs placebo (258 ± 55 vs 74 ± 26 µM). CONCLUSION: Oral taurine supplementation influenced aspects of thermoregulation during passive heat exposure, with enhanced sweating and cutaneous vasodilatory responses, without affecting other parameters of cardiometabolic function. These findings have potential implications for individuals at risk of heat stress in environmental conditions that permit dry and evaporative heat dissipation. REFERENCES: 1. Cramer & Jay, 2016, Auton Neurosci. 2. Crandall & Wilson, 2015, Compr Physiol. 3. Periard et al., 2021, Physiol Rev. 4. Page et al., 2019, Eur J Sport Sci. 5. Sun et al., 2016, Hypertens.
Read CV Jennifer PeelECSS Paris 2023: OP-PN03
INTRODUCTION: Aging entails a gradual deterioration in physical capabilities and cellular functions, including impaired mitochondrial function and heightened oxidative stress. Resistance training (RT) mitigates a decline in physical function, yet its impact on oxidative stress and mitochondrial function is unknown. Polyphenols (PP) possess antioxidant properties and can bolster mitochondrial biogenesis, but their effects in the elderly are relatively uncharted. This double-blinded RCT examines the individual and combined influences of RT and PP supplementation on muscle performance, oxidative stress, and mitochondrial respiration, with the hypothesis that mitochondrial respiratory capacity and H2O2 emission will increase and decrease, respectively, with an enhanced effect of combined RT and PP supplementation. METHODS: 40 men and women (55-70 yrs) were randomized to ingest a PP supplement (700 mg/day) or placebo daily for one month (loading period). Then a 12-week supervised RT-based program (x3/wk), while continuing either PP or placebo (PLB), was carried out. Anthropometrics, muscle power and strength were measured at the study start, after loading and after RT. Muscle biopsies were obtained before and after RT, and analyzed for mitochondrial respiratory capacity (MRC) and H2O2 emission (Oroboros 2k). Here we report preliminary results of the RT (n=16 as one group regardless of PP or PLB) as unblinding will be done in June when the last subject is finished. Statistical analysis of MRC and H2O2 emission is done by two-way RM ANOVA, and other outcomes by a paired t-test. RESULTS: RT led to increased leg maximal voluntary contraction strength (159±50 vs 178±53 Nm; P < 0.001), handgrip strength (39.1±12.2 vs 42.1±3.5 kg; P < 0.01) and sit-to-stand test reps (14.5±3 vs 16.8±3.4 reps; P = 0.0001), with a tendency towards higher VO2max (2382±429 vs 2464±470 ml O2/min; P = 0.08). Mitochondrial H2O2 emission decreased (main effect; P < 0.05) and MRC increased (main effect; P = 0.02) with RT. Lean mass was only significantly increased with RT in the male (n=9) participants (59.7±4.5 vs 60.9±4.8 kg; P = 0.005) with no significant change for the women (n=7)(P = 0.29). CONCLUSION: These results imply that resistance-based training can improve mitochondrial bioenergetics and attenuate oxidative stress by increasing respiratory capacity and lowering mitochondrial reactive oxygen species production in individuals at the onset of aging. This is of particular importance in this population, as aging is associated with impaired mitochondrial function and increased oxidative stress, which may be linked to the development of several age-related diseases. The effect of PP supplementation awaits the unblinding.
Read CV Mathias Flensted-JensenECSS Paris 2023: OP-PN03
INTRODUCTION: AMP-activated protein kinase (AMPK) is an important regulator of adaptations to endurance exercise. Training with low carbohydrate availability can increase AMPK activation (Bartlett, Hawley and Morton, 2015), but whether increased AMPK activation is due to low carbohydrate availability per se or due to concurrent increases in fatty acid availability/oxidation is unclear. The aim of this study was to assess the independent effects of carbohydrate and fatty acid availability on exercise-induced skeletal muscle AMPK activation. METHODS: Eight active males cycled on three occasions for 1 hour at 95% of lactate threshold 1 with ingestion of either carbohydrate (CARB), niacin (NIACIN), or placebo (FAST) in a crossover design (11±6-day washout). After baseline breath, blood and muscle samples, participants consumed a drink (1.6 g/kg maltodextrin or placebo) and tablets (10 mg/kg niacin or placebo). Following 1 hour of rest participants cycled with further carbohydrate (0.8 g/kg/hr maltodextrin), niacin (10 mg/kg/hr) or placebo and blood and expired breath samples were collected every 15 minutes. Following exercise, a further muscle sample was obtained. Plasma was analysed for NEFA concentrations, and muscle for glycogen concentrations using the hexokinase method. Muscle protein content and phosphorylation status was assessed by semi-quantitative western blotting and expressed as the fold-change from pre- to post-exercise. Normality of data were checked by visual inspection of residuals. Differences between CARB vs FAST and CARB vs NIACIN were analysed by paired t-tests. RESULTS: Fat oxidation was lower in CARB vs. FAST (13±8 g vs. 22±9 g, p=0.003) but there was no significant difference between CARB vs. NIACIN (15±8 g, p=0.59). There was no evidence for differences in glycogen use with CARB (58±56 mmol/kgDM) vs FAST (97±56 mmol/kgDM, p=0.27). However, muscle glycogen use with NIACIN (142±76 mmol/kgDM) was higher than CARB (p=0.01). ACCSer79 phosphorylation status (ratio p-ACC to total-ACC) was decreased with CARB (1.6±1.8 fold) vs. both FAST (2.1±2.1 fold, p=0.04) and NIACIN (2.0±0.8 fold, p = 0.02). AktSer473 phosphorylation (ratio p-Akt to total-Akt) was increased with CARB (1.7±0.6 fold) vs. FAST (1.0±0.4 fold, p<0.01), but the difference between CARB vs. NIACIN (1.7±0.6 fold) was not statistically significant (p=0.08). CONCLUSION: These data suggest that augmented glycogen use during exercise with niacin use increases skeletal muscle AMPK signalling independent from circulating fatty acid concentrations. Therefore, low carbohydrate availability may be more important than fatty acid availability for AMPK induced adaptations to exercise. References: Bartlett JD, Hawley JA, Morton JP. Carbohydrate availability and exercise training adaptation: too much of a good thing? Eur J Sport Sci. 2015;15(1):3-12. doi: 10.1080/17461391.2014.920926.
Read CV Louise BradshawECSS Paris 2023: OP-PN03