title: Physiological and performance adaptations to an in-season soccer camp in the heat: associations with heart rate and heart rate variability.
abstract: The aim of the present study was to examine the associations between adaptive responses to an in-season soccer training camp in the heat and changes in submaximal exercising heart rate (HRex, 5-min run at 9  km/h), postexercise HR recovery (HRR) and HR variability (HRV). Fifteen well-trained but non-heat-acclimatized male adult players performed a training week in Qatar (34.6 ± 1.9°C wet bulb globe temperature). HRex, HRR, HRV (i.e. the standard deviation of instantaneous beat-to-beat R-R interval variability measured from Poincaré plots SD1, a vagal-related index), creatine kinase (CK) activity, plasma volume (PV) changes, and post-5-min run rate of perceived exertion (RPE) were collected at six occasions in temperate environmental conditions (22°C). Players also performed the yo-yo intermittent recovery test level 1 (Yo-Yo IR1) in the same environmental conditions (22°C), both at the beginning and at the end of the training week. Throughout the intervention, HRex and HRV showed decreasing (P < 0.001) and increasing (P < 0.001) trends, respectively, while HRR remained unaffected (P = 0.84). Changes in HRex [-0.52, 90% confidence limits (-0.64; -0.38), P < 0.001] and SD1 [0.35 (0.19; 0.49), P < 0.001] were correlated with those in PV. There was no change in RPE (P = 0.92), while CK varied according to training contents (P < 0.001), without association with HR-derived measures. Yo-Yo IR1 performance increased by 7 ± 9% (P = 0.009), which was correlated with changes in HRex [-0.64 (-0.84; -0.28), P = 0.01]. In conclusion, we found that an in-season soccer training camp in the heat can significantly improve PV and soccer-specific physical performance; both of which are associated with changes in HRex during a 5-min submaximal run.
authors.affiliation: Sport Science Department, ASPIRE, Academy for Sports Excellence, Doha, Qatar. martin.buchheit@aspire.qa
authors.forename: M
authors.initials: M
authors.lastname: Buchheit
authors.forename: S C
authors.initials: SC
authors.lastname: Voss
authors.forename: L
authors.initials: L
authors.lastname: Nybo
authors.forename: M
authors.initials: M
authors.lastname: Mohr
authors.forename: S
authors.initials: S
authors.lastname: Racinais
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000222:Adaptation, Physiological; D000328:Adult; D054874:Athletic Performance / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D006339:Heart Rate / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D011780:Qatar; D012916:Soccer; D055815:Young Adult