This is the Accepted Version of a paper published in the
Journal: European Journal of Applied Physiology
Stanley, Jamie, Halliday, Aaron, D'Auria, Shaun, Buchheit, Martin, and Leicht,
Anthony S. (2015) Effect of sauna-based heat acclimation on plasma volume
and heart rate variability. European Journal of Applied Physiology, 115 (4). pp.
785-794.
http://dx.doi.org/10.1007/s00421-014-3060-1
© 2015. This manuscript version is made available under
the CC-BY-NC-ND 4.0 license
http://creativecommons.org/licenses/by-nc-nd/4.0/
ResearchOnline@JCU
1
Effect of sauna-based heat acclimation on plasma volume and heart rate variability
Jamie Stanley
1,2
, Aaron Halliday
3
, Shaun D’Auria
4
, Martin Buchheit
5
, Anthony S. Leicht
3
1
Centre of Excellence for Applied Sport Science Research, Queensland Academy of Sport, Brisbane, Australia
2
School of Human Movement Studies, University of Queensland, Brisbane, Australia
3
College of Healthcare Sciences, James Cook University, Townsville, Australia
4
Triathlon Program, Queensland Academy of Sport, Brisbane, Australia
5
Sport Science Unit, Myorobie Association, Montvalezan, France
Corresponding author:
Jamie Stanley, School of Human Movement Studies, The University of Queensland, Brisbane, Queensland
4072, Australia; E-mail: j.stanley@uq.edu.au.
Total word count: 5285 words (excluding abstract, references, tables, figures, acknowledgements, etc)
Abstract word count: 248 words
Number of references: 39
Number of tables: 1
Number of figures: 4
2
Abstract
Purpose: We investigated the effect of post-exercise sauna bathing on plasma volume (PV) expansion and
whether such responses can be tracked by changes in heart rate (HR) based measures.
Methods: Seven, well-trained, male cyclists were monitored for 35 consecutive days (17 d baseline training,
10d training plus sauna, 8d training). Sauna exposure consisted of 30 min (87°C, 11% relative humidity)
immediately following normal training. Capillary blood samples were collected to assess PV changes while
resting seated. HR (HR
wake
) and vagal-related HR variability (natural logarithm of square-root mean squared
differences of successive R−R intervals, ln rMSSD
wake
) were assessed daily upon waking. A sub-maximal cycle
test (5 min at 125 W) was performed on days 1, 8, 15, 22, 25, 29, and 35 and HR recovery (HRR
60s
) and ln
rMSSD
postex
were assessed post-exercise. Effects were examined using magnitude-based inferences.
Results: Compared with baseline, sauna resulted in: 1) peak PV expansion after 4 exposures with a likely large
increase [+17.8% (90% confidence limits, 7.4;29.2)]; 2) reduction of HR
wake
by a trivial-to-moderate amount
[−10.2% (−15.9;−4.0)]; 3) trivial-to-small changes for ln rMSSD
wake
[4.3% (1.9;6.8)] and ln rMSSD
postex
[−2.4%
(−9.1;4.9)]; and 4) a likely moderate decrease in HRR
60s
[−15.6% (−30.9;3.0)]. Correlations between individual
changes in PV and HR measures were all unclear.
Conclusions: Sauna-bathing following normal training largely expanded PV in well-trained cyclists after just 4
exposures. The utility of HR and HRV indices for tracking changes in PV was however uncertain. Future studies
will clarify mechanisms and performance benefits of post-training sauna bathing.
Keywords: heat exposure; blood volume; cardiac parasympathetic activity; post-exercise; cyclists
3
Abbreviations
CV
ES
Coefficient of variation
Effect size
Hb
Haemoglobin
Hct
HR
HR
ex
Haematocrit
Heart rate
Heart rate during the 5-min submaximal (125 W) exercise test
HRR
Heart rate recovery
HRR
60s
Heart rate recovery at 60 seconds post-exercise
HRV
Heart rate variability
HR
wake
Heart rate upon waking
ln rMSSD
postex
Natural logarithm of the rMSSD following submaximal exercise
ln rMSSD
wake
Natural logarithm of the rMSSD upon waking
PV
Plasma volume
rMSSD
Square root mean of the sum of the squared differences between adjacent normal
R−R intervals
SWC
Smallest worthwhile change
YoYoIR2
Yo-Yo Intermittent recovery level 2 test
4
Introduction
In an increasingly competitive elite sporting environment, identifying methods to extract additional marginal
performance gains from already demanding training schedules is of importance to athletes and coaches.
Recently, supplementing training with heat acclimation has garnered increasing interest (Garrett et al. 2012;
Garrett et al. 2009; Garrett et al. 2011; Lorenzo et al. 2010) primarily because the physiological adaptations
including expansion of blood plasma volume (PV) may contribute to improved myocardial efficiency (Horowitz
et al. 1986b), increased ventricular compliance (Horowitz et al. 1986a), and improved maximal cardiac output
(Lorenzo et al. 2010)—all of which translate into improved physical performance in all (i.e., cool, temperate,
and hot) environmental conditions (Racinais et al. 2014).
Traditionally, heat acclimation has involved exercising in 35−45
o
C, 10−90% relative humidity for up to 90 min
for 8−22 consecutive days (Garrett et al. 2011). In highly-trained athletes, heat acclimation elicited increased PV
(6.5%; effect size [ES] = 2.0) (Lorenzo et al. 2010), increased maximal aerobic power in cool (4.9%; ES = 1.5)
and hot (8.1%; ES = 2.0) conditions (Lorenzo et al. 2010), increased lactate threshold in cool (5.1%, ES = 0.3)
and hot (2.9%; ES = 0.1) conditions (Lorenzo et al. 2010), improved time-trial performance in cool (6.2%; ES =
1.1) and hot (8.0%; ES = 1.2) conditions (Lorenzo et al. 2010), and increased the distance covered (42%, ES =
2.0) during intermittent exercise performance in hot conditions (Racinais et al. 2014). Similar physiological and
performance adaptations have been demonstrated following shorter durations of heat acclimation. For example,
5 days of exercising in the heat (total heat exposure of 3 h 45 min) induced a 4.5% (ES = 0.8) increase in PV
accompanied with a 1% (ES = 0.3) improvement time-trial performance in highly-trained rowers (Garrett et al.
2012). Similarly, non-heat-acclimatised semi-professional soccer players demonstrated a 5.7% (ES = 1.2)
increase in PV accompanied with a 7% (ES = 0.5) increase in intermittent exercise performance in cool
conditions following 6 days (total heat exposure of 7 h 30 min) of training in the heat (Buchheit et al. 2011).
Heat acclimation is not without limitations. For athletes living in temperate climates, heat
acclimatization/acclimation necessitates traveling to a location with the appropriate conditions for a specific
training block (Buchheit et al. 2011; Racinais et al. 2014), or alternatively training in a climate chamber (Garrett
et al. 2012; Lorenzo et al. 2010). Both options are expensive, unfeasible in certain situations (e.g., training with
the ball in a climate chamber would be impossible for team sport athletes), and may compromise the quality of
training (Garrett et al. 2011). One study has demonstrated that the acute physiological responses to heat were
