Author(s): SOUSA, A.1,2, PIALOUX, V.3, VIANA, J.L.1,2, MILHEIRO, J.4, REIS, V.M.1,5, MILLET, G.P.6, Institution: UNIVERSITY OF MAIA, Country: PORTUGAL, Abstract-ID: 793

INTRODUCTION:
High exercise training workloads are linked to immune dysfunction, inflammation, oxidative stress, and muscle damage. Exposure to hypoxia is also known to have an impact on immune function, as tissue-specific oxygen level variations affect immune cells. The overlapping effects of exercise (especially high-intense) performed under hypoxic conditions suggests an impairment of immune function. However, the mechanism underlying this depression has not been elucidated and might be mediated by endocrine factors. This study assessed biomarkers of immune function and hormonal activity after prolonged exposure to high-intensity training performed under hypoxic and normoxic conditions.
METHODS:
Twenty well-trained subjects (mean ± SD: 50.99.6 ml.kg. -1min.-1, 34.9 ± 8.4 yrs and 73.29.4 kg for ( V) ̇O2max, age and weight, respectively) were either assigned to the normoxia (CON: n=10) or hypoxia (HYP: n=10) condition for 4 weeks, performing 3 training sessions (high intensity interval training =2, repeated sprint training =1) each week. In the week before (baseline) and after the 4-weeks period (post-intervention), venous blood samples were collected (in the late afternoon/ early evening period) from the median cubital vein for analysis of immune function - interleukin-10 (IL-10), -4 (IL-4), -6 (IL-6), - 1beta (IL-1β), immunoglobulin A (IgA), C-reactive protein (CRP) and tumor necrosis factor alpha (TNF‑α), and, hormonal activity biomarkers – adrenocorticotropic (ACTH), cortisol and insulin. Comparison between groups and study phase (baseline and intervention) were examined (p<.05).
RESULTS:
At baseline, groups were comparable for all biomarkers except IL‑1β (p=0.025). After the 4 weeks-period, differences between groups were found for IgA (p=0.037, ~15% higher for HYP) and insulin activity (p=0.017, ~50% higher for CON) only. From baseline to post-intervention period, IgA (p=0.036, ~30%) and insulin (p=0.009, ~17%) activity increased for HYP and CON groups, respectively. No other differences were found between groups and time periods.
CONCLUSION:
The results suggest that repeated hypoxic exposure combined with high-intensity training elicited a selective immune modulation, reflected by higher circulating IgA in HYP group, without concomitant increases in CRP or key cytokines (e.g., IL‑6, TNF‑α) at rest, which contrasts with the expected immune depression. In contrast, insulin responses differed by condition, with higher post-intervention insulin in CON and a within-group increase from baseline, indicating a condition-specific metabolic/endocrine adaptation not accompanied by HPA-axis activation (ACTH/cortisol unchanged).
Acknowledgements: This work was funded by National Funds by FCT - Foundation for Science and Technology under the following project UID/04045: Research Center in Sports Sciences, Health Sciences, and Human Development and SFRH/BPD/114670/2016.