Abstract
The efficacy of a 14-day field-based heat acclimatization (HA) training camp in 16 international female soccer players was investigated over three phases: phase 1: 8 days moderate HA (22. 1°C); phase 2: 6 days high HA (34.5°C); and phase 3: 11 days of post-HA (18.2°C), with heart rate (HR), training load, core temp (Tc), and perceptual ratings recorded throughout. The changes from baseline (day−16) in (i) plasma volume (PV), (ii) HR during a submaximal running test (HRex) and HR recovery (HRR), and (iii) pre-to-post phase 2 (days 8–13) in a 4v4 small-sided soccer game (4V4SSG) performance were assessed. Due to high variability, PV non-significantly increased by 7.4% ± 3.6% [standardized effect (SE) = 0.63; p = 0.130] from the start of phase 1 to the end of phase 2. Resting Tc dropped significantly [p < 0.001 by −0.47 ± 0.29°C (SE = −2.45)], from day 1 to day 14. Submaximal running HRR increased over phase 2 (HRR; SE = 0.53) after having decreased significantly from baseline (p = 0.03). While not significant (p > 0.05), the greatest HR improvements from baseline were delayed, occurring 11 days into phase 3 (HRex, SE = −0.42; HRR, SE = 0.37). The 4v4SSG revealed a moderate reduction in HRex (SE = −0.32; p = 0.007) and a large increase in HRR (SE = 1.27; p < 0.001) from pre-to-post phase 2. Field-based HA can induce physiological changes beneficial to soccer performance in temperate and hot conditions in elite females, and the submaximal running test appears to show HRex responses induced by HA up to 2 weeks following heat exposure.
Highlights
Athletes are often required to compete in hot and humid environmental conditions, which, if sufficiently hot and coupled with high exercise intensities, can lead to heat stress and, eventually, hyperthermia
Week 6 was the remote training and Session RPE (sRPE) weekly sum was estimated at 1,760 AUC heat load (AU), which can be considered a de-loading/recovery week
Four field-based heat acclimatization (HA) protocols utilizing team sport players demonstrated a mean plasma volumes (PV) expansion of 5.4% (Buchheit et al, 2011, 2013, 2016; Racinais et al, 2012), similar to the current study’s trend of 7.4 ± 3.6% across phase 1 (LA) and phase 2 (Cancun; Figure 4). This would be a similar PV expansion to what we found during an indoor heat acclimation study in some of the same athletes, where we demonstrated ∼9% PV increase (Pethick et al, 2018)
Summary
Athletes are often required to compete in hot and humid environmental conditions, which, if sufficiently hot and coupled with high exercise intensities, can lead to heat stress and, eventually, hyperthermia. Field-based protocols, such as those utilized by Buchheit et al (2011, 2013, 2016) and Racinais et al (2012) previously in male soccer players, have highlighted the potential of repeated heat training exposures to elicit adaptations and offset the impedance of cardiovascular strain during exercise in the heat. This type of training has the potential to improve sport performance in more temperate conditions (∼14–20◦C) (Lorenzo et al, 2010; Corbett et al, 2014; Buchheit et al, 2016). It is important to understand how to utilize an effective field-based heat acclimatization protocol in order to preserve, or enhance, soccer performance in both extreme temperatures, as well as during more temperate conditions (Corbett et al, 2014)
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