Once‐ and twice‐daily heat acclimation confer similar heat adaptations, inflammatory responses and exercise tolerance improvements

• Published in: Physiological reports 2018-12, Vol.6 (24), p.e13936-n/a
• Main Authors: Willmott, Ashley G. B., Hayes, Mark, James, Carl A., Dekerle, Jeanne, Gibson, Oliver R., Maxwell, Neil S.
• Format: Article
• Language: English
• Subjects: Acclimation; Adaptation; Adolescent; Adult; Aerobic capacity; Biomarkers; Body Temperature Regulation; Cortisol; Cytokines - blood; Endurance and Performance; Exercise; Exercise Tolerance; Heart rate; Heat; heat acclimatization; heat adaptation; Humans; Hydrocortisone - blood; immune; Immune response; Immunological tolerance; Immunology; Inflammation; Male; Original Research; Physical Conditioning, Human - methods; Physical fitness; Physical training; Physiology; Plasma Volume; Random Allocation; Studies; Sweat; Thermoregulation; Thermotolerance; training; Tumor necrosis factor; Tumor necrosis factor-TNF
• ISSN: 2051-817X
• DOI: 10.14814/phy2.13936

This experiment aimed to investigate the efficacy of twice‐daily, nonconsecutive heat acclimation (TDHA) in comparison to once‐daily heat acclimation (ODHA) and work matched once‐ or twice‐daily temperate exercise (ODTEMP, TDTEMP) for inducing heat adaptations, improved exercise tolerance, and cytokine (immune) responses. Forty males, matched biophysically and for aerobic capacity, were assigned to ODHA, TDHA, ODTEMP, or TDTEMP. Participants completed a cycling‐graded exercise test, heat acclimation state test, and a time to task failure (TTTF) at 80% peak power output in temperate (TTTFTEMP: 22°C/40% RH) and hot conditions (TTTFHOT: 38°C/20% RH), before and after 10‐sessions (60 min of cycling at ~2 W·kg−1) in 45°C/20% RH (ODHA and TDHA) or 22°C/40% RH (ODTEMP or TDTEMP). Plasma IL‐6, TNF‐α, and cortisol were measured pre‐ and postsessions 1, 5, and 10. ODHA and TDHA induced equivalent heat adaptations (P