Maximal oxygen uptake (VO2max) is an important determinant of endurance performance. Heat acclimation/acclimatization (HA/HAz) strategies elicit improvements in endurance performance. When heat exposure is reduced, intermittent heat training (IHT) is potentially beneficial to alleviate HA/HAz adaptation decay, however corresponding VO2max responses are unknown. PURPOSE: To determine the effects of HA/HAz and IHT on VO2max in endurance runners and identify how long VO2max adaptations remain following removal of repeated heat exposure. METHODS: Twenty-seven male endurance runners (mean ± SD; age, 36 ± 12 years; body mass, 73.03 ± 8.97 kg; height, 178.81 ± 6.39 cm; VO2max, 57.48 ± 7.03 ml.kg-1.min-1) completed VO2max and exercise testing at five time points; baseline, pre-HA, post-HA, week 4 of IHT (IHT4), and week 8 of IHT (IHT8). Exercise testing and HA environmental conditions were the same (ambient temperature, 35.42 ± 1.06°C; relative humidity, 46.35 ± 2.48%). Following baseline testing, participants completed HAz, proceeded by 5 days of HA involving exercise to induce hyperthermia (38.50 - 39.50°C) for 60 minutes. Participants were then randomly assigned to one of three IHT groups: once weekly (n = 9), twice weekly (n = 10), or no IHT (n = 8). Differences in VO2max and maximal heart rate at VO2max (HRmax) for baseline, pre-HA, post-HA, IHT4, and IHT8 were analyzed using repeated-measures ANOVAs with Bonferroni corrections post-hoc. RESULTS: No significant VO2max differences were observed between baseline (57.92 ± 6.82 ml.kg-1.min-1), pre-HA (59.65 ± 8.24 ml.kg-1.min-1), and post-HA (59.49 ± 7.18 ml.kg-1.min-1, p = 0.36). No significant group or time effects were identified for VO2max at post-HA, IHT4, and IHT8 (p = 0.67). However, significant HRmax differences were observed between baseline (180 ± 11 beats.min-1), pre-HA (177 ± 10 beats.min-1), and post-HA tests (175 ± 10 beats.min-1, p = 0.01). No significant group or time HRmax differences were shown for post-HA, IHT4, and IHT8 (p = 0.59). CONCLUSION: No changes in VO2max were identified among endurance runners following HA/HAz, potentially due to participants’ high aerobic fitness levels. As IHT maintained VO2max following 8 weeks without repeated heat exposure, it is potentially a beneficial strategy to minimize VO2max adaptation decay in endurance athletes.



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