The efficacy of a field-based heat acclimatization training camp to improve performance in elite female soccer players. Authors: Kimberly Bowman, UBC MSc Candidate; Cesar Meylan, Ph.D., Sport Physiologist Women’s National Soccer

Trent Stellingwerff, Ph.D., CSIP Sport Science, Innovation & Research; Wendy Pethick, CSIP Sport Physiologist, Lab Technician;

Michael Koehle, Ph.D., M.D., Associate Professor of Kinesiology Purpose: Heat acclimation training (HA) protocols in laboratory and field settings have been shown to

enhance aerobic capacity in hot and mild conditions and therefore, potentially beneficial to soccer. The

purpose of this study was to undertake a field-based HA protocol using players from the Canadian

Women’s National Soccer Team (WNT) during an ambient environment heat training camp and to

determine the physiological (e.g. core temp (CT)) and performance adaptations during and following the

training camp.

Methods: Seventeen outfield WNT soccer players were involved and the CT monitoring took place during

6 days of training in a mild ambient condition (Phase 1 - Los Angeles, Pre-Acclimatization, 22.1±3.3˚C)

and 5 days of training in a hot ambient condition (Phase 2 - Cancun; Heat Acclimatization, 34.5±1.2˚C) via

the VitalSense® telemetric monitoring system. A baseline plasma volume (PV) laboratory procedure was

determined using the Carbon Monoxide Rebreathe protocol prior to Phase 1. The Dill and Costill

equation was used to calculate the percent change in PV at the start and end of Phase 1 and at the end

of phase 2. HRexercise (HRex) and HRrecovery (HRR) were measured using a Modified 5’-1’ submaximal

running test (12km/h) on the first day of Phase 1, the first and last day of Phase 2 and two more times (a

week apart) at the start of post acclimatization training (mild; 23.2˚C). A 4x2 min, four-aside soccer

game, was played with a 2-min rest period between games at the start and end of Phase 2. Magnitude-

based inference statistics were used to quantify effects.

Results: Average ∆CT from baseline in Phase 1 and 2 was 1.27±0.47˚C and 1.37±0.26˚C, respectively. A

decrease in absolute PV was observed from baseline to the start of Phase 1 (ES: -0.40±0.21). Phase 1 was

effective in returning absolute PV slightly above baseline measures (ES: 0.21±0.27). There was a

7.0±3.5% mean increase in relative PV from the start of phase 1 to the end of phase 2, however, this shift

was less robust in phase 2. Submaximal test variables were initially affected by running in the heat

(HRex: ES: 0.45±0.12; HRR: ES:-1.02±0.35) but 4 days of heat training resulted in a return to baseline. No

changes in these metrics were observed in the first test two days post-phase 2 (mild temperature;

23.2˚C). However, 1-week post-Phase 2 (mild temperature; 23.2˚C), all submaximal variables improved

from baseline (HRex ES: -0.42±0.10; HRR ES: 0.37±0.54). HRex (ES:-0.32±0.18) and HRR (ES:-1.0±0.25)

also improved from Day 1 to Day 5 in Phase 2, while game intensity was lower in terms of metres/min

(ES: -0.46±0.53) but higher in terms of explosiveness (ES: 0.48±0.31).

Conclusions: Training in ambient temperature allowed players to reach a CT threshold to drive PV

expansion but this may be difficult to measure in non-controlled laboratory conditions. However, the use

of simple field metrics demonstrated that adaptations were visible both in hot and mild temperature

after a two-phase camp. HA appears to be an effective strategy to enhance aerobic capacity in both

submaximal and game-like situations.