ECSS Paris 2023: OP-PN03
INTRODUCTION: Exercise-induced hypohydration (EIH) impairs endurance performance, with field data suggesting well-trained runners regularly experience EIH during training and competition. It is unclear if habitual exposure to EIH in such athletes attenuates the hypohydration-induced performance decline. Thus, this study assessed the impact of habitual exposure to EIH on performance and physiology responses whilst hypohydrated in runners habituated (H) and non-habituated (NH) to EIH. METHODS: 11 habituated (H: V̇O2peak 63 ± 9 mL/kg/min) and 10 non-habituated (NH: V̇O2peak 60 ± 7 mL/kg/min) athletes completed familiarisation (ad-libitum water intake) and 2 experimental trials, involving a treadmill preload (PL; 8-11 x 6 min at 70% V̇O2peak, 1 min rest; standardised within participant) and a 3 km time-trial (TT) in 28°C. Water replacement (80% mass loss; EU) or minimal water intake (100 mL; HH) was provided during PL, aiming for ~3% total body water (TBW; via bioelectrical impedance) loss in HH. Venous blood and nude mass measures were made pre-PL, post-PL and post-TT, with gastrointestinal (GI)/skin temperature, heart rate, perceptual responses and oxygen uptake measured throughout. 3 km TT performance was the primary outcome. RESULTS: Post-PL relative TBW loss in EU (H -1.1 ± 0.4%; NH -1.0 ± 0.2%) and HH (H -3.4 ± 0.8%; NH -3.2 ± 0.2%) was not different between groups (P≥0.227). Hypohydration increased heart rate, RPE and thirst (P≤0.046), decreased body mass and plasma volume (P≤0.003), but did not alter GI or skin temperature, oxygen uptake, running economy, GI comfort or thermal sensation (P≥0.129). However, there were no trial*time*group interactions for any physiological or perceptual variables during PL (P≥0.198). There was a trial*group interaction for 3 km TT performance (P=0.041), with NH athletes 4.2% slower in HH (EU 817 ± 43 s; HH 855 ± 60 s; P=0.013), but H athletes not different between trials (EU 703 ± 83 s; HH 708 ± 78 s; P=0.658). During TT, there was a mean effect of group where NH had a 0.4°C greater GI temperature compared to H (P=0.004). During familiarisation, NH drank more water ad-libitum (H 0.50 ± 0.24 L; NH 0.85 ± 0.42 L; P=0.031), meaning hypohydration was greater in H athletes (H -1.6 ± 0.4%; NH -1.1 ± 0.4%; P=0.021). CONCLUSION: These data demonstrate that EIH impairs endurance performance in non-habituated athletes only, but no differences were observed between groups for physiological or perceptual variables. Interestingly, during TT, NH athletes had a greater GI temperature, indicating impaired thermoregulation during running performance, potentially exacerbating the effects of hypohydration. The greater ad-libitum water intake and lower hypohydration in NH runners indicates differences in hydration behaviour that might explain some of the observed performance effects. These results suggest that regular exposure to and familiarisation with EIH may attenuate the expected decline in performance whilst hypohydrated.
Read CV Thomas CableECSS Paris 2023: OP-PN03
INTRODUCTION: Strenuous exercise increases circulating hepcidin levels during post-exercise, potentially contributing to the reduced iron storage in individuals who engage in regular physical activity. While prolonged exposure to hypoxia, lasting days to weeks, suppresses hepcidin levels and enhances iron absorption, interest is growing in short-term exposure to hypoxia that can be integrated into athletes’ training routines. The present study aimed to examine the effects of acute hypoxic exposure at different timings on exercise-induced hepcidin responses. METHODS: Twelve healthy individuals (5 women, 7 men; age: 23 ± 2 years; height: 169.9 ± 8.3 cm; body mass: 62.4 ± 8.1 kg) participated in a single-blind, randomized, cross-over design study. They completed high-intensity interval running under three different conditions on separate days: (1) normoxic control (CON; resting in normoxia before and after exercise), (2) pre-exercise hypoxic exposure (Pre-HYPO; 2-hour exposure to hypoxia before exercise), and (3) post-exercise hypoxic exposure (Post-HYPO; 2-hour exposure to hypoxia after exercise). The fraction of inspired oxygen was 12.5% in the hypoxic environment and 20.9% in the normoxic control environment. The exercise protocol consisted of eight sets of 4-minute running intervals at 85% of maximal oxygen uptake in a normoxic environment. Venous blood samples were collected at 2 hours before exercise (baseline), immediately before, immediately after exercise, and 3 hours post-exercise. Blood analyses included measurements of serum iron, ferritin, erythropoietin (EPO), and hepcidin levels. RESULTS: Serum EPO levels increased significantly immediately after exercise and 3 hours post-exercise in both Pre-HYPO and Post-HYPO trials (p < 0.05 vs. baseline). The immediate post-exercise EPO response was greater in Pre-HYPO trial (45.7 ± 15.9% increase from baseline) than in the CON trial (3.4± 17.5%, p < 0.05). At 3 hours post-exercise, EPO was still higher in both Pre-HYPO trial (53.0 ± 31.5% increase from baseline) and Post-HYPO trial (50.0 ± 24.1%) than in CON trial (11.9 ± 16.8%, p < 0.05). Serum hepcidin elevated at immediately after exercise and 3 hours post-exercise compared to baseline (p < 0.05). However, the serum hepcidin level did not differ significantly among the three trials at any time points (p > 0.05). No significant differences among the trials were observed for serum iron or ferritin (p > 0.05). CONCLUSION: Both “pre-exercise hypoxic exposure” and “post-exercise hypoxic exposure” enhanced EPO secretions in young women and men. However, despite the increased erythropoietic responses, exercise-induced elevations in serum hepcidin were not suppressed with pre-exercise hypoxic exposure or post-exercise hypoxic exposure.
Read CV Chao-an LinECSS Paris 2023: OP-PN03
INTRODUCTION: The ability to adapt to exercise training varies among individuals, raising concerns about the uniformity of health benefits derived from training interventions [1]. Central to this issue is the concept of high- and low-responders to exercise training, which assumes that the ability to adapt to a specific exercise prescription is a fixed trait of individuals [2]. However, when small groups (n=10-19) of young, moderately trained individuals are repeatedly exposed to identical aerobic training programs, individual training responses are not consistent [3-6]. Whether these observations extend to other populations and larger sample sizes are currently unknown. Hence, the present study examined whether individual responses to two identical aerobic training interventions are reproducible in middle-aged, untrained males and females. METHODS: Forty-two untrained but healthy men and women (♀ 21; ♂ 21; age, 54±9 years; maximal oxygen uptake (VO2max), 32±7 mL/min/kg) underwent two identical 8-week aerobic training interventions (ET-1 and ET-2), separated by an 8-week wash-out period. ET-1 and ET-2 included 24 supervised 45-min interval sessions, alternating between high-intensity (4×5 min and 4×8 min) and moderate-intensity (6×6 min) cycling exercise. Participants´ VO2max, maximal 1-min power output during the VO2max test (MPOVO2max), and maximal 15-min mean power output (MMPO15min) were determined before and after each intervention period. The reproducibility of pre-test values and change scores across ET-1 and ET-2 was determined using intraclass correlation coefficients (ICC). Pearson correlation coefficients (r) were used to evaluate the strength and direction of the relationships between scores. 95% confidence intervals (CIs) were calculated to interpret the results. RESULTS: At the onset of ET-1 and ET-2, VO2max, MPOVO2max, and MMPO15min demonstrated excellent reproducibility and very strong associations between training interventions (ICC = 0.96-0.98, r = 0.97-0.98, 95% CIs not including zero). Changes in MPOVO2max and MMPO15min during ET-1 and ET-2 exhibited some level of reproducibility (ICC = 0.35 and 0.29, respectively) and weak associations (r = 0.38 and 0.32, respectively), with 95% CIs not including zero. In contrast, changes in VO2max were neither reproducible nor correlated (95% CIs including zero). CONCLUSION: When exposed to two identical aerobic training interventions, individual changes in MPOVO2max and MMPO15min were partially reproducible in middle-aged, untrained males and females. In contrast, VO2max changes were not. These findings challenge the notion of fixed high- and low-responders to exercise training and question the predictability of individual responses to exercise training prescriptions based on the observed response to a single training period. References [1] Joyner & Lundby 2018. Exerc Sport Sci Rev. [2] Senn 2004. Bmj. [3] Del Giudice et al. 2020. JSAMS. [4] Jacques 2023. EJSS. [5] Islam et al. 2021. JSAMS. [6] Voisin et al. 2019. Exerc Sport Sci Rev.
Read CV Ingvill OddenECSS Paris 2023: OP-PN03