Effects of Motivational Self-Talk on Endurance and Cognitive Performance in the Heat

Abstract

Purpose: We tested the effectiveness of a two-week motivational self-talk (MST) intervention - specific to heat tolerance - on endurance capacity and cognitive function in the heat.

Methods: Eighteen trained male (n=14) and female (n=4) cyclists randomly received two weeks of MST training (n=9) or a control regimen (CON, n=9). The experimental protocol was a PRE/POST design consisting of 30 min of cycling at 60% peak power output (PPO) in the heat (35°C, 50% relative humidity, ~3.0 m·s-1 airflow), a 30 min rest period, followed by a time to exhaustion (TTE) test at 80% PPO, and an identical rest period. Executive function, reaction time, and working memory were tested at baseline and each rest period. Key measures included TTE, speed and accuracy on the cognitive tests, rectal temperature, heart rate, oxygen consumption, and rating of perceived exertion.

Results: Group (MST vs. CON) × test (PRE vs. POST) × time repeated measures ANOVA revealed that MST significantly increased TTE from PRE (487±173 s) to POST (679±251 s, p = 0.021) concurrent with a higher terminating rectal temperature (PRE: 38.5 ± 0.2°C, POST: 38.8 ± 0.4°C, p=0.023; no TTE (PRE: 531±178 s, POST: 510±216 s, p = 0.28) or rectal temperature (PRE: 38.4 ± 0.3°C, POST 38.4 ± 0.2°C, p=1.000) changes were found in CON. MST significantly improved both speed and accuracy for executive function from PRE/POST, with no PRE/POST differences for CON on any cognitive measure. There were no interactions (all p > 0.05) for other key measures.

Conclusion: Motivational self-talk is effective in altering the internal psychophysiological control of exercise and plays a role in improving endurance capacity and executive function in the heat.

Full text

Effects of Motivational Self-Talk on Endurance
and Cognitive Performance in the Heat
PHILLIP J. WALLACE
1
, BRANDON J. MCKINLAY
2
, NICO A. COLETTA
1
, JANAE I. VLAAR
1
,
MICHAEL J. TABER
1,3
, PHILIP M. WILSON
4
, and STEPHEN S. CHEUNG
1
1
Environmental Ergonomics Laboratory, Department of Kinesiology, Brock University, St. Catharines, Ontario, CANADA;
2
Applied Physiology Lab, Department of Kinesiology, Brock University, St. Catharines, Ontario, CANADA;
3
Falck Safety
Services Canada, Mount Pearl, Newfoundland and Labrador, CANADA; and
4
Behavioural Health Sciences Research Lab,
Department of Kinesiology, Brock University, St. Catharines, Ontario, CANADA
ABSTRACT
WALLACE, P. J., B. J. MCKINLAY, N. A. COLETTA, J. I. VLAAR, M. J. TABER, P. M. WILSON, and S. S. CHEUNG. Effects of
Motivational Self-Talk on Endurance and Cognitive Performance in the Heat. Med. Sci. Sports Exerc., Vol. 49, No. 1, pp. 191–199,
2017. Purpose: We tested the effectiveness of a 2-wk motivational self-talk (MST) intervention—specific to heat tolerance—on en-
durance capacity and cognitive function in the heat. Methods: Eighteen trained male (n= 14) and female (n= 4) cyclists randomly
received 2 wk of MST training (n= 9) or a control regimen (CON, n= 9). The experimental protocol was a PRE/POST design consisting
of 30 min of cycling at 60% peak power output (PPO) in the heat (35-C, 50% relative humidity, ~3.0 mIs
j1
airflow), a 30-min rest
period, followed by a time to exhaustion (TTE) test at 80% PPO, and an identical rest period. Executive function, reaction time, and
working memory were tested at baseline and each rest period. Key measures included TTE, speed and accuracy on the cognitive tests,
rectal temperature, HR, oxygen consumption, and RPE. Results: Group (MST vs CON) test (PRE vs POST) time repeated-measures
ANOVA revealed that MST significantly increased TTE from PRE (487 T173 s) to POST (679 T251 s, P= 0.021) concurrent with a
higher terminating rectal temperature (PRE, 38.5-CT0.2-C; POST, 38.8-CT0.4-C; P= 0.023); no TTE (PRE, 531 T178 s; POST, 510
T216 s; P=0.28) or rectal temperature (PRE, 38.4-CT0.3-C; POST, 38.4-CT0.2-C; P= 1.000) changes were found in CON. MST
significantly improved both speed and accuracy for executive function from PRE/POST, with no PRE/POST differences for CON on any
cognitive measure. There were no interactions (all P90.05) for other key measures. Conclusion: Motivational self-talk is effective in
altering the internal psychophysiological control of exercise and plays a role in improving endurance capacity and executive function in the
heat. Key Words: HEAT TOLERANCE, FATIGUE, PSYCHOLOGICAL SKILLS TRAINING, PSYCHOPHYSIOLOGY
Exercise in the heat is physically demanding, where
endurance capacity is reduced compared with
thermoneutral environments (13) because of an increase
in cardiovascular strain (9), reductions in neuromuscular
function (28), and central fatigue (36). Although physiological
impairment has been clearly implicated, elevated psychological
strain from thermal stress may impair performance via reduced
dopamine levels or motivation (5), arousal (29), and increases
in negative moods (27). A reduction in global and local neural
network efficiency (32), as well as shifts in neural resources in
the attention networks (23), contributes to an increased diffi-
culty in neural processing relative to thermoneutral conditions
(19,30). In addition, task-dependent cognitive changes occur in
the heat (16,31), where higher-order functions such as ex-
ecutive function, vigilance, visual memory, and planning
decreases with a passive rise in core temperature by 1.0-C,
whereas simple tasks such as reaction time and working
memory are less vulnerable (15,19,23). The evidence for
cognitive changes with exercise in the heat is less clear, as
light and moderate exercises have produced improvements
or minimal changes in short-term memory, information
processing, and executive function (7,22,40). However,
potential limitations such as a learning effect of the cogni-
tive batteries used and a lack of thermal clamping during
cognitive tasks hamper full understanding. In addition, psy-
chological perceptions are more vulnerable to thermal stress
(16) and are proposed to alter cognitive function before any
measurable physiological changes in the heat (21). For
example, Gaoua et al. (14) found that, before any changes in
core temperature, sensory displeasure from passive heat ex-
posure significantly reduced working memory but not reac-
tion time.
As there are decrements in performance because of psy-
chological strain, psychological interventions may alter cog-
nitive and endurance capacity in the heat. Simple interventions
such as deception through lower than actual visual and exper-
imenter feedback on ambient and core temperatures—before
Address for correspondence: Stephen S. Cheung, Ph.D., Department of
Kinesiology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines,
Ontario, Canada L2S-3A1; E-mail: scheung@brocku.ca.
Submitted for publication July 2016.
Accepted for publication August 2016.
0195-9131/17/4901-0191/0
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Ò
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DOI: 10.1249/MSS.0000000000001087
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and during exercise in the heat—improves cycling perfor-
mance compared with no deception (8). Furthermore, 4 h of
broad-spectrum mental skills training improved the distance
covered by trained runners for 90 min by 1.15 km (8%) in
30-C (3). Combined, these findings suggest that the plasticity
of psychological perceptions before and during thermal stress
plays an important role in altering exercise capacity. However,
it is unknown if psychological skills training can affect both
exercise and cognitive performance.
Motivational self-talk (MST), which is commonly used in
broad-based psychological skills training (2,3), may be a key
contributor to improved cognitive and endurance capacity
in the heat. MST is a multidimensional top-down regulation
strategy that focuses on an individual_s self-addressed
verbalizations, reappraising negative thought patterns that
arise during tasks with instructional and motivational state-
ments (17). These statements influence an individual_s con-
scious attention and appraisal process, leading to a regulation
of behavioral performance. In thermoneutral environments, a
2-wk MST intervention increased endurance capacity by 18%
during a time to exhaustion (TTE) test (4), and a separate MST
intervention significantly improved 10 km time trials time by
4% (1). MST has been proposed to improve cognitive perfor-
mance, as qualitative analyses have demonstrated improve-
ments in confidence, focus, attention, and a reduction in the
perception of effort (4,17,18). However, the effect of MST on
cognitive function, endurance capacity in the heat, or at an
elevated core temperature (e.g., ~1.0-C) has yet to be system-
atically tested and quantified. Therefore, we tested an MST
intervention that was specific to heat tolerance and cognitive
function. We hypothesized that the MST would 1) increase
endurance capacity by prolonging time to voluntary fatigue
and 2) improve performance in higher-order cognitive tasks as
they are more vulnerable to heat stress and thermal perception.
METHODS
Participants. The experimental protocol and procedures
were approved by the Bioscience Research Ethics Board at
Brock University (REB no. 14-162) and conformed to the latest
revision of the Declaration of Helsinki. All participants were
screened using a modified Physical Activity Readiness Ques-
tionnaire, and a full explanation of procedures, discomforts,
and risks was given before obtaining informed written consent.
Fourteen male and four female trained cyclists and tri-
athletes (18–50 yr) received either a 2-wk MST or a 2-wk
control (CON) regimen (seven males and two females per
group). There were no differences in baseline age, height,
body mass, peak oxygen consumption (V
˙O
2peak
), and peak
power output (PPO) between groups (Table 1). On the basis
of the study of De Pauw et al. (11), participants were clas-
sified as performance level 3 (scale of 1–5).
Experimental design. The experiment implemented a
PRE/POST-test design with four sessions in total. The first
session consisted of collecting anthropometric data, baseline
cognitive function, and determining V
˙O
2peak
. The second
session was a familiarization trial of the experiment protocol
to reduce the learning effect of the cognitive tasks. The third
(PRE) and the fourth (POST) sessions were the experimental
trials, with the same testing protocols as the familiarization
trial. Sessions 1–3 were each separated by a minimum of 1 wk
to ensure recovery and to reduce the potential for heat accli-
mation. Sessions 3–4 were separated by a minimum of 14 d,
during which time either MST or CON was performed. Fe-
male participants completed the experimental sessions during
7–10 d and 21–24 d into their self-reported menstrual cycle.
All sessions were performed at the same time of day to control
for circadian fluctuations in core temperature. Participants
were asked to maintain a similar activity regime throughout
the experiment_s duration, to follow similar meals and hy-
dration practices 24 h before a trial, and to not consume caf-
feine 4 h before a trial.
Preliminary assessment. Upon arrival to the labora-
tory, participants provided informed consent, height (cm) and
mass (kg) were measured, and body fat was determined using
the seven-site skinfold measurement (Harpenden, Baty Inter-
national, West Sussex, UK) technique (20,38). Participants
then completed the Cognitive Failure Questionnaire (CFQ),
which is a 25-item questionnaire that is a self-evaluative
measure of general fluid intelligence and is related to four
factors of absentmindedness (memory, distractibility, blun-
ders, and names) (6,39). Items were scored on a five-point
Likert scale (from 0 = ‘‘never’’ to 4 = ‘‘very often’’). CFQ
scores can range from 0 to 100, where average CFQ scores
are between 19 and 45 (35). Participants were excluded from
the study if the CFQ score is 945, as this score indicates
considerable difficulties in completing tasks that require vig-
ilance. Upon the completion of the CFQ, an incremental test
to exhaustion was performed in a thermoneutral environment
(~22-C, 30% relative humidity [RH]) on a cycle ergometer
(Velotron; RacerMate Inc., Seattle, WA) to determine PPO and
V
˙O
2peak
. The test began with a standardized 5-min warm-up at
100 W, followed by workload increase of 25 W (males) or
20 W (females) each minute until exhaustion. V
˙O
2peak
was
defined as the highest 30-s value measured breath by breath
from expired gases collected through a soft silicone facemask
connected to an online gas collection system, whereas PPO
was the highest power output achieved during the last full
1-min stage.
Experimental protocol. To determine hydration status,
participants voided their bladder to measure urine specific
gravity (USG; PAL-10S, Atago, Tokyo, Japan) upon arrival
for sessions 2–4. Participants were considered euhydrated if
TABLE 1. Physical characteristics of control (CON) and MST groups. There were no differences
between each group (all P90.05) for any of the characteristics.
Variable CON (n=9) MST (n=9)
Height (cm) 175.8 T6.3 176.2 T7.5
Mass (kg) 72.0 T10.3 75.8 T10.3
Age (yr) 39 T10 39 T9
% body fat 14.5 T4.6 13.7 T4.2
V
˙O
2peak
(mLIkg
j1
Imin
j1
) 61.8 T6.0 59.0 T8.4
PPO (W) 338 T40.2 344 T50.0
CFQ score 25.0 T8.0 27.0 T5.0
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USG was e1.020, or else the test was rescheduled. Participants
were dressed in cycling shorts and shoes then performed a
baseline measure of cognitive function using a cognitive test
battery (CTB; described in the CTB section) in a thermoneutral
environment (22.0-C, ~30% RH). Upon the completion of the
CTB, participants entered an environmental chamber set at
35.0-C, ~50% RH, with 3.0 mIs
j1
of airflow, and were fitted
with a soft silicone mask to collect expired gases.
The first exercise period (EX1) consisted of constant-load
cycling with a 5-min warm-up at 100 W followed by 25 min
of cycling at 60% of PPO. Participants were allowed to
freely choose their cadence between 60 and 120 rpm. Upon
the completion of EX1, participants completed a 30-min rest
period (R1) and then performed the CTB. Participants sat in
a chair inside the environmental chamber with airflow
stopped and were fitted with a 100% vinyl poncho to mini-
mize heat loss. To reduce the physical and perceptual strain
of thirst, 250 mL of water was provided ad libitum.
Upon the completion of R1 and the CTB, participants
performed a second constant-load exercise bout (EX2),
consisting of a 5-min warm-up at 125 W followed by 80%
PPO to voluntary exhaustion (4). TTE was determined as
follows: 1) volitional fatigue, 2) cadence dropped less than
60 rpm for five consecutive seconds, or 3) a rectal temperature
(T
re
)of40.0-C for 1 min. No verbal encouragement was
given during the TTE to eliminate the superimposition of any
extraneous verbal statements (4) as well as no external feed-
back (e.g., time, HR, and cadence), and TTE duration was not
provided to any participants to minimize goal setting in future
tests. After the completion of the TTE, participants performed
a second rest period (R2) identical with R1.
MST intervention. Participants were randomly (www.
random.org) selected to receive a 2-wk control (CON) or
MST intervention between the PRE and the POST sessions,
and groups were matched for sex. Participants were not
a priori matched for age, anthropometrics, performance, or
aerobic fitness and were only notified of condition place-
ment at the completion of the PRE trial. CON performed
their normal aerobic training regimen during this period. The
MST intervention was given in two stages by a skills training
workbook (1,4) and was designed to contextualize self-talk
cues through practice to the demands of performing in the heat.
The first stage consisted of two self-talk exercises that fo-
cused on endurance and cognitive performance. In the first
exercise, participants determined a list of negative statements
that occurred during the EX1 and EX2 periods in the PRE trial
then compared their list of negative statements to a list of 12
motivational statements used in previous self-talk literature
(e.g., ‘‘Keep pushing, you_re doing well’’) (4). Participants
then determined their own list of five MST statements, after
which they selected two statements that were deemed helpful
for EX1 and two statements for EX2. In the second exercise,
participants determined a list of negative statements that
occurred during baseline, R1, and R2 during the CTB in the
PRE trial. Participants then compared their list of negative
statements to a list of five motivational statements (e.g., ‘‘I am
focused’’). Participants also generated one statement that they
deemed motivational to use before and during each cognitive
test in the POST trial.
The second stage of the MST was a 2-wk practice phase
designed to rephrase and self-contextualize the use of statements
believed to optimize performance (4). Participants performed
theirnormaltrainingregimenandwererequiredtoperforma
minimum of three sessions in which they practiced their MST
statements. After each exercise session, they completed a
workbook assessing the efficacy, frequency, and their comfort
with the four chosen exercise self-talk statements. Effective
statements were recorded and were used in future exercise
sessions, whereas ineffective statements were recorded and
rephrased or replaced with a more suitable statement chosen
by the participant. An experimenter was available throughout
the practice period if the participant needed assistance with
their workbook. The extent of self-talk usage during practice
periods was assessed using a purpose-built 11-point Likert
scale (from 0 = ‘‘not at all’’ to 10 = ‘‘greatly’’), and the number
of changed statements was recorded.
After the POST trial, each participant completed a group-
specific experiment questionnaire. The MST group was asked
the extent and perceived effectiveness of self-talk usage dur-
ing EX1 and EX2 on a purpose-built 11-point Likert scale
(from 0 = ‘‘not at all’’ to 10 = ‘‘greatly’’). The MST group was
then asked to qualitatively detail the ways self-talk was found
to be beneficial or nonbeneficial. After the POST trial, the
CON group was asked to qualitatively list any psychological
strategies used during the experiment (e.g., self-talk, imagery,
and arousal regulation) and the purpose of their use.
Instrumentation. T
re
and HR were continuously sampled
throughout the trial and converted to 1-min averages. T
re
was
measured (1 Hz) using a flexible thermistor (Mon-A-Therm
Core; Mallinkrodt Medical, St Louis, MO) inserted 15 cm
beyond the anal sphincter. HR was collected (10 Hz) using a
telemetric HR monitor (RS800CX; Polar Electro Oy, Kempele,
Finland). Expired gases were collected through a silicone
facemask with the exhalation port connected to a metabolic
cart (ML206 Gas Analyzer; ADInstruments Inc., Colorado
Springs, CO) and was continuously sampled during EX1 and
EX2 to determine oxygen uptake (V
˙O
2
,LImin
j1
).
RPE was assessed using a 6–20 scale (Borg 1982) and
was recorded at t= 0, 5, 10, 20, and 30 min during EX1 and
taken at t=0 and every 2 min during EX2. Because of the
individual variation of TTE, data (T
re
, HR, V
˙O
2
, and RPE)
were converted into t= 0, iso-50%, iso-75%, and iso-100%
relative time points of EX2 to compare trials.
CTB. To measure progressive changes in cognitive
function, a 15-min CTB (CogState, New Haven, CT) was
performed at baseline, R1, and R2, which consisted of a
Groton Maze Learning Task (GMLT), a detection task, and a
two-back test. A familiarization trial was used to increase
familiarity and to minimize the learning effect of multiple
exposures to tasks.
The GMLT is a touch screen–based cognitive task that
measures executive function through error detection and
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spatial memory. The test consists of a 10 10 grid of
squares that cover a hidden 28-step pathway that includes 11
turns. A blue tile on the top left corner of the screen indicates
the starting position, and a red circle on the bottom right
corner indicates the finish location. The GMLT is performed
six times (initial test sequence and five-block trials) per test.
The GMLT test sequence required approximately 5 to 10 min
to complete. To minimize a learning effect due to repeated
exposure, each maze is randomized and well matched for
difficulty. Performance was measured for the total duration
(s) and total number of errors measured during the five-
block period.
The detection task was used to test psychomotor function
and reaction time. A playing card was presented on the screen
in a face-down position, and participants were tasked with
pressing a key when the card was turned over presenting the
front of the card. This process continues until the task is
completed. There was an interstimulus interval of 2 s between
each presentation of 35 cards and continues until the task is
complete. Performance was measured for speed (mean of the
log
10
transformed reaction times for correct responses) where
a lower score represents a better performance. The detection
task required approximately 2 min to complete.
The two-back test is a measure of attention and visual
working memory. Participants were tasked with determining
if the card presented is identical with the card presented two
cards ago. There were a total of 48 cards presented, and par-
ticipants could either answer ‘‘yes’’ or ‘‘no’’ for the card
presented. Performance for this task was measured for speed
of processing (ms) and total number of errors made. The two-
back test took approximately 2 min to complete.
Data analyses. All continuous variable data are presented
as the mean TSD and were analyzed using separate group
(MST vs CON) trial (PRE vs POST) time mixed-model
repeated-measures ANOVA. A Bonferroni post hoc analysis
was used to test significant main effects. Paired sample t-tests
were used to identify significant main effects at specific time
points within groups.
All ordinal data (RPE and qualitative feedback) are presented
as the median (quartiles 1 and 3). RPE was analyzed using
separate group (MST vs CON) trial (PRE vs POST) time
mixed-model repeated-measures ANOVA, with a Wilcoxon
signed-rank test used to compare within-group effects at spe-
cific time points. A Friedman_sANOVAwasusedtoanalyze
the amount of self-talk usage during the 2-wk practice phase in
MST group. Statistical significance was set at PG0.05. All
analyses were performed using IBM SPSS Statistics for
Windows (version 22.0; IBM Corp., Armonk, NY).
RESULTS
The MST intervention was successful in changing psycho-
logical skill usage. The MST group significantly (P=0.003)
increased their self-talk usage (0–10) in the third practice ses-
sion (10 [9–10] perceived usage) compared with the first
practice session (8 [5–8] perceived usage), with no differences
(P=0.137) compared with the second practice session (8 [7–9]
perceived usage). Overall, the MST group changed approxi-
mately 2 (2–3) statements during the practice period from their
initial first session. There were distinct differences in psy-
chological strategies used in the POST trial between the MST
and the CON. The MST group used two MST statements in
EX1 and two statements in EX2. CON reported using some
forms of self-talk, arousal regulation strategies (e.g., focus on
breathing) and disassociation; however, these strategies were
unstructured and unplanned.
There was no group–trial interaction (P=0.579) at
baseline for USG in between both MST (PRE, 1.012 T
0.001; POST, 1.009 T0.004) and CON (PRE, 1.009 T0.003;
POST, 1.009 T0.005). During EX1, there was a significant
increase (all PG0.05) in T
re
and HR (Fig. 1) and V
˙O
2
and
RPE (Fig. 2), with no trial–time–group (all P90.05) inter-
action between the CON and the MST groups for any of the
variables. T
re
change from baseline increased similarly
and significantly for both MST (PRE, $+1.1-C; POST,
$+1.0-C) and CON (PRE, $+1.1-C; POST, $+1.2-C)
in both trials. T
re
and HR significantly (all PG0.05) decreased
from the start to the end of R1, with no group–trial–time in-
teraction (all P90.05) between CON and MST; T
re
dropped
~0.1-C from the start of R1 to the end of the CTB (~20 min)
in both trials.
FIGURE 1—Rectal temperature (A) and HR (B) responses during the
PRE and the POST trials. EX2 time points are represented as iso–time
points (%) during the TTE task. *Significant difference from PRE to
POST in the MST group only.
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In EX2, there was a significant group–trial interaction (F
1,16
=
14.460, P=0.002) (Fig. 3) for TTE duration. In the CON
group, there was a nonsignificant (P=0.280, A= 0.176) change
in TTE from PRE (531 T178 s) to POST (510 T216 s). The
MST group had a significant (P=0.021, A= 0.886) increase in
TTE from PRE (487 T173 s) to POST (679 T251 s), with all
but one participant improving their TTE. T
re
significantly in-
creased in both groups (F
3,33
= 3.766, P=0.021), with no
differences (all P90.05) for T
re
at any iso–time point
during PRE/POST or at iso-100% (PRE, 38.4-CT0.3-C,
$+1.1-C; POST 38.4-CT0.2-C, $+1.2-C; P=1.000; A=
0.238) for the CON group. The MST group finished with a
significantly higher T
re
by ~0.3-C at iso-100% of the TTE
in POST (38.8-CT0.4-C, $+1.4-C) compared with the
PRE trial (38.5-CT0.2-C, $+1.1-C, P=0.023, A=0.410),
with no differences at iso-0%, iso-50%, and iso-75%. HR and
V
˙O
2
significantly increased (all PG0.05) over the TTE with
no group–time–trial interaction (all P90.05) between CON
and MST conditions.
RPE increased (P90.05) during the TTE with no group–
trial–time interactions (F
3,39
= 1.196, P=0.324) or differences
at any iso–time point. For the eight MST participants that im-
proved TTE, cycling time after an RPE of 19 was assessed as
an indirect indicator of maximal effort. Participants cycled
longer after an RPE rating of 19 in POST (274 T177 s)
compared with PRE (138 T118 s). The MST group rated
the overall usage of self-talk statements (0–10) signifi-
cantly (P=0.046) higher in EX2 (9 [9–10] perceived usage)
compared with EX1 (8 [6–10] perceived usage). In addition,
participants also rated the overall effectiveness of self-talk
statements (0–10) significantly (P=0.026) higher in EX2
(10 [9,10] perceived effectiveness) than in EX1 (8 [6–9]
perceived effectiveness).
Rectal temperature and HR significantly (all PG0.05) de-
creased from the start to the end of R2 (Fig. 1). There was a
significant trial (P=0.002) and group–trial (P=0.013) in-
teraction for T
re
in R2. MST had a significantly (P=0.023)
higher T
re
at the start of POST, which continued throughout
R2. Compared with baseline at the start of each trial, USG
significantly increased (both PG0.05) during trials in both
MST (PRE, 1.016 T0.004; POST, 1.016 T0.004) and CON
(PRE, 1.012 T0.005; POST, 1.013 T0.006), with no group–
trial–time interaction (P=0.337) but remained below the
pretrial dehydration threshold of 1.020.
Performance on the CTB was first analyzed using all par-
ticipants (n= 18) from the familiarization (FAM) trial com-
pared with the PRE trial to test for any potential learning
effect changes because of multiple exposures to the CTB.
There was a significant decrease (all PG0.05) in duration
(Baseline-FAM: 217.9 T65.5 s) and errors (Baseline-FAM:
56.0 T31.6 errors) for the GMLT and a significant im-
provement in speed (Baseline-FAM: 2.55 T0.11) for the
FIGURE 2—Oxygen consu mption (A) and RPE (B) responses during
EX1 and EX2. EX2 time points are represented as iso–time points
(%) during the TTE task. There was no group, group–trial, group–
trial–time differences between control (CON) and motivational skills
training groups from PRE to POST.
FIGURE 3—Individual TTE for control (A) and MST (B) groups. Solid
symbols and lines indicate means. *Significant difference from PRE to
POST in the MST group.
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detection task during FAM (Table 2). There were no changes
in speed or errors for the two-back test during FAM. There
were no differences in performance for any cognitive measure
from R2 in FAM to baseline in PRE (all P90.05), indicating
no further learning effect for the CTB during the PRE and
POST trials.
There were no significant group–time–trial interactions for
both duration (F
2,30
=0.295,P=0.747, A= 0.080) and errors
made (F
2,30
=0.765,P=0.474, A= 0.163) in the GMLT
(Table 2). However, there was a significant trial interaction
for both duration (F
1,16
= 11.798, P=0.005, A=0.421)and
errors made (F
1,16
=5.972,P=0.027, A=0.334).TheMST
group had a significantly faster completion in the POST trial
at baseline (P=0.009)andinR2(P=0.039), but not
during R1 (P=0.164), as well as fewer errors made at
baseline (P=0.019)andR2(P=0.012), but not during R1
(P=0.108), during the GMLT. There were no differences in
duration or errors made at any time point in the CON group
on the GMLT. There were no significant differences in speed
or errors during the detection task or two-back test from PRE
to POST for both MST and CON (Table 2).
DISCUSSION
MST is a top-down regulation strategy requiring participants
to continuously reappraise negative self-talk and bottom-up
feedback with self-contextualized motivational statements. The
MST intervention used in the current study was designed to
address endurance capacity and cognitive function in the heat.
Participants increased usage of MST over the 2-wk practice
period and self-reported significant increases in usage and ef-
fectiveness in the POST trial. CON had a slight but nonsignif-
icant decrement (~4%) in TTE in the POST trial, with no
differences in any physiological or perceptual response. MST
resulted in ~29% improvement in TTE—concurrent with a
longer duration near or at maximal intensity (RPE Q19)—
significantly high use of MST, and higher terminating T
re
.In
addition, MST improved the speed and the accuracy for an
executive function task (GMLT) after the 2-wk MST program
during both baseline testing in thermoneutral temperatures and
after EX2 in the heat. To our knowledge, this is the first study
to quantify the use of a psychological skills training interven-
tion to improve executive function in either a thermoneutral or
a hot environment. Overall, these findings demonstrate that the
internal psychophysiological control of exercise and fatigue
plays an important role in improving endurance capacity and
higher-order cognitive function in the heat. This extends pre-
vious reports that MST is beneficial in improving endurance
capacity (4,26) in thermoneutral environments, as well as the
beneficial use of psychological skills training interventions on
exercise performance in the heat (3).
The improved TTE for MST participants in the POST
compared with PRE trials was concurrent with a higher
terminal T
re
with no differences in HR or V
˙O
2
, suggesting
that a primary response to MST was a greater psychological
tolerance during thermophysiological strain. Psychological
tolerance of thermal discomfort was previously proposed as
a major determinant of exercise-heat capacity across aerobic
fitness groups (9,37). In these studies, despite similar rates
of heat storage, aerobically fit individuals could voluntarily
tolerate exercise-heat stress much longer than nonfit in-
dividuals regardless of hydration or heat adaptation status,
with the primary differences being a reduced perceptual
discomfort at a set T
re
partnered with a much higher terminal
T
re
. Similarly, Morrison et al. (28) observed a reduced tol-
erance to passive hyperthermia in nonaerobically fit in-
dividuals compared with highly fit, yet no differences in
neuromuscular activation in the few nonfit individuals who
could tolerate passive heating to 39.0-C compared with
high-fit. The present data thus extend prior work by
suggesting that even well-trained individuals remain pli-
able and trainable in their psychological tolerance to
thermal or exercise discomfort. Future research is needed
to determine the influence of psychological skills training
on nonaerobically fit individual_s ability to voluntarily
tolerate exercise-heat stress and performance, as a greater
TABLE 2. Performance on the detection test (reaction time), two-back test (working memory), and GMLT (executive function) forcontrol (CON) and motivationalskillstraininginPREandPOSTtrials.
Baseline Rest 1 Rest 2
Variable PRE POST PRE POST PRE POST
Detection task
Speed (ms)
CON 2.52 T0.07 2.50 T0.06 2.52 T0.07 2.52 T0.08 2.51 T0.07 2.52 T0.10
MST 2.48 T0.06 2.50 T0.06 2.51 T0.06 2.51 T0.07 2.52 T0.08 2.49 T0.08
Two-back test
Speed (ms)
CON 2.85 T0.18 2.89 T0.11 2.87 T0.07 2.85 T0.09 2.85 T0.08 2.84 T0.09
MST 2.95 T0.10 2.94 T0.10 2.91 T0.12 2.90 T0.09 2.89 T0.10 2.88 T0.10
Errors (n)
CON 3.0 T4.0 3.0 T3.0 6.0 T5.0 4.0 T6.0 4.0 T4.0 3.0 T3.0
MST 5.0 T5.0 4.0 T6.0 4.0 T4.0 5.0 T5.0 4.0 T2.0 3.0 T4.0
GMLT
Duration (s)
CON 157.0 T33.0 150.0 T36.0 147.0 T19.0 138.0 T20.0 160.0 T58.0 145.0 T50.0
MST 176.0 T51.0 160.0 T40.0* 158.0 T50.0 145.0 T31.0 160.0 T48.0 130.0 T54.0*
Errors (n)
CON 37.0 T13.0 36.0 T19.0 41.0 T10.0 39.0 T19.0 47.0 T25.0 45.0 T27.0
MST 47.0 T18.0 37.0 T12.0* 47.0 T21.0 42.0 T21.0 48.0 T19.0 39.0 T12.0*
*Significant differences from PRE to POST in the MST group.
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potential improvement may be possible due to the rela-
tively lower baseline level of performance.
The conscious perception of exertion and fatigue is the-
orized to be derived from bottom-up afferent input from the
cardiorespiratory, metabolic, and musculoskeletal systems,
as well as the affective appraisal of exercise (12). Endurance
performance is improved by interventions that reduce an
individual_s sense of perceived exertion, whereas perfor-
mance is impaired with increased perception of effort
(24,25). MST has been demonstrated to reduce RPE at 50%
iso–time point during a similar TTE test in thermoneutral
conditions (4), and it has also been shown to have no effect
on RPE during a 10-km time trial despite a significant im-
provement in completion time of ~4% (1). Because of the
constant-load exercise used in the present study, participants
experienced the same level of bottom-up afferent feedback
and difficulty throughout the task, which led to a similar
level of perceived exertion. RPE was similar between trials
during EX1 and during all iso–time points in EX2 for both
groups. However, the duration that the MST group could
tolerate at near-maximal (RPE Q19) exercise was ~100%
greater during POST, suggesting that the MST group likely
improved endurance capacity by continuously reappraising
their desire to voluntarily terminate exercise and perception
of fatigue. Combined with the increased MST usage during
the practice period and high usage and perceived effective-
ness of MST during the TTE, it is unlikely that MST directly
improved performance through a lower perceived exertion
throughout the task, but rather the learned ability to coun-
teract the psychological context-specific demands through-
out the tasks (16) and environmental conditions (1,2).
The MST intervention was used by participants during the
CTB to maintain ‘‘focus’’ or increase ‘‘concentration’’ dur-
ing the tasks, with no reported anxiolytic benefits, whereas
the CON group reported no psychological strategies used in
postexperiment questionnaires. The MST intervention led to
a significant improvement in both the speed and the accu-
racy of the GMLT at baseline before entering the heat, and
in R2 despite the 29% increase in TTE time. There were no
changes in performance for the detection task and two-back
test in either the MST or CON groups, which may reflect these
tests_relative simplicity compared with the GMLT, as simple
tasks are less vulnerable to hyperthermia (T
re
=38.7-C)
compared with complex tasks (16,31,33). These findings
suggest that MST potentially leads to improvements in
executive function but may have minimal to no perfor-
mance changes on simple cognitive task performance in
either thermoneutral or hot environments. Although MST
requires mental effort, it does not appear to add a signif-
icant cognitive load or deplete attentional resources, as
there were no recorded decrements with MST usage in the
POST trial. Future research is needed to determine how
MST specifically affects resource allocation and its role
on cognitive function, as well as its effects at a higher
thermal load (e.g., 939.0-C) than was induced in the cur-
rent study.
The combined improvements in executive function and
endurance capacity may be due to neurobiological changes
that occur with exercise to fatigue and heat stress. Prefrontal
cortex (PFC), lateral PFC, orbitofrontal cortex, anterior in-
sular cortex (AIC), and anterior cingulate cortex (ACC) in-
tegrate afferent feedback and indirectly communicate with
motor output to regulate voluntary exercise performance
(34,35). The AIC and the ACC appraise afferent homeo-
static signals to determine the perception of the bodily state
(including thermal perception and fatigue) and emotions,
predicts future perturbations in homeostasis to determine
behavior, and are part of the executive attention network
(10,30). These neural components become increasingly im-
portant during exercise in the heat, as hyperthermia shifts
neural resources from and reduces activation in the ACC
with a 1.0-C in core temperature (23), reduces dopamine and
motivation (5), and decreases in arousal (through an elevated
>/Aindex) in the PFC that is strongly correlated (r= 0.98) to
exercising T
re
(29). Paulus et al. (30) proposed that in-
terventions working directly on the PFC, ACC, and AIC will
improve performance in adverse environments. MST may
work directly on the ACC (motivational component and task
evaluation) and the AIC (through continuous affective
reappraisal) to prolong the state of voluntary fatigue (34). As
these paralimbic structures are involved in the executive
function network, this may be why cognitive improvements
are primarily seen in executive function tasks. MST appears
to be more beneficial for endurance capacity in hot com-
pared with thermoneutral environments (4) and may be due
to the increased physiological and neurological strain. This
is consistent with research using pharmaceutical manipula-
tions of dopamine, where administration of dopamine re-
uptake inhibitors increased the time to voluntary fatigue (5)
and increased exercise performance in hot but not in
thermoneutral conditions (36). Overall this would indicate
that the brain contributes to exercise tolerance through a top-
down regulation of performance. However, future research
is needed to determine potential mechanisms on how psy-
chological strategies such as MST specifically affect neural
structures/activation during exercise and with various task-
dependent cognitive skills to optimize neural function and
performance in the heat.
An experimental consideration of the study was not using a
sham-control group using an intervention such as neutral self-
talk (1). Experimenters spent more time with participants
(~45 min longer), which may have improved performance
because of social facilitation. Because of the study design, we
cannot fully account for these potential confounding vari-
ables; however, great effort was used to reduce social facili-
tation/external motivation through no verbal feedback or
encouragement during tests, use of same experimenters be-
tween trials, and no knowledge of results given between tri-
als. Barwood et al. (1) found that the use of a sham-control
neutral self-talk and spending the same amount of time with
participants does not influence cycling performance, whereas
the MST intervention had a beneficial effect. No volunteers
MOTIVATIONAL SELF-TALK AND HEAT TOLERANCE Medicine & Science in Sports & Exercise
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197
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were screened out during recruitment because of an overly
high CFQ of 945, but future research should determine
whether MST may have similar effects on individuals with
high levels of absentmindedness. In addition, as improvements
in executive function were not uniform (Baseline, R2 vs R1)
throughout the POST trial, future research is needed to de-
termine whether the extent or perceived effectiveness of
MST usage, core temperature, or exercise task affects ex-
ecutive function.
In summary, a 2-wk MST intervention increased usage
and self-contextualization of MST statements, likely im-
proving voluntary endurance capacity and executive func-
tion in the heat by improving psychological tolerance of
high physiological strain. These findings demonstrate that
the internal psychophysiological control of exercise and fa-
tigue plays an important role in improving endurance ca-
pacity in the heat and that trained athletes can benefit from
psychological skills training interventions. As the MST
intervention also improved executive function in both
neutral and hot environments, future research should test
the specific neural changes and adaptations that occur with
MST and psychological skills training to determine the
underlying mechanisms of the top-down regulation of ex-
ercise and fatigue.
The authors express their gratitude to the participants for their
efforts throughout the study. The study was supported by the Nat-
ural Science and Engineering Research Council (NSERC) of Canada
through a Discovery Grant (no. 227912-12, S. S. Cheung). S. S.
Cheung was supported by a Canada Research Chair, and J. I. Vlaar
was supported by an NSERC Undergraduate Student Research
Award. The authors have no conflicts of interest to declare. The au-
thors declare that the results of the study are presented clearly,
honestly, and without fabrication, falsification, or inappropriate data
manipulation and do not constitute endorsement by the American
College of Sports Medicine.
REFERENCES
1. Barwood MJ, Corbett J, Wagstaff CR, McVeigh D, Thelwell RC.
Improvement of 10-km time-trial cycling with motivational self-
talk compared with neutral self-talk. Int J Sports Physiol Perform.
2015;10(2):166–71.
2. Barwood MJ, Dalzell J, Datta AK, Thelwell RC, Tipton MJ.
Breath-hold performance during cold water immersion: effects of
psychological skills training. Aviat Space Environ Med. 2006;
77(11):1136–42.
3. Barwood MJ, Thelwell RC, Tipton MJ. Psychological skills
training improves exercise performance in the heat. Med Sci Sports
Exerc. 2008;40(2):387–96.
4. Blanchfield AW, Hardy J, De Morree HM, Staiano W, Marcora SM.
Talking yourself out of exhaustion: the effects of self-talk on en-
durance performance. Med Sci Sports Exerc. 2014;46(5):998–1007.
5. Bridge MW, Weller AS, Rayson M, Jones DA. Responses to ex-
ercise in the heat related to measures of hypothalamic serotonergic
and dopaminergic function. Eur J Appl Physiol. 2003;89(5):451–9.
6. Broadbent DE, Cooper PF, FitzGerald P, Parkes KR. The Cogni-
tive Failures Questionnaire (CFQ) and its correlates. Br J Clin
Psychol. 1982;21:1–16.
7. Caldwell JN, Patterson MJ, Taylor NA. Exertional thermal strain,
protective clothing and auxiliary cooling in dry heat: evidence for
physiological but not cognitive impairment. Eur J Appl Physiol.
2012:3597–606.
8. Castle PC, Maxwell N, Allchorn A, Mauger AR, White DK. Decep-
tion of ambient and body core temperature improves self paced cycling
in hot, humid conditions. Eur J Appl Physiol. 2012;112(1):377–85.
9. Cheung SS, McLellan TM. Heat acclimation, aerobic fitness, and
hydration effects on tolerance during uncompensable heat stress.
J Appl Physiol. 1998;84(5):1731–9.
10. Craig AD. How do you feel? Interoception: the sense of the phys-
iological condition of the body. Nat Rev Neur. 2002;3(8):655–66.
11. De Pauw K, Roelands B, Cheung SS, De Geus B, Rietjens G,
Meeusen R. Guidelines to classify subject groups in sport-science
research. Int J Sports Physiol Perform. 2013;8(2):111–22.
12. Ekkekakis P. Pleasure and displeasure from the body: perspectives
from exercise. Cogn Emot. 2003;17(2):213–39.
13. Galloway SD, Maughan RJ. Effects of ambient temperature on the
capacity to perform prolonged cycle exercise in man. Med Sci
Sports Exerc. 1997;29(9):1240–9.
14. Gaoua N, Grantham J, Racinais S, El Massioui F. Sensory displea-
sure reduces complex cognitive performance in the heat. JEnviron
Psychol. 2012;32(2):158–63.
15. Gaoua N, Racinais S, Grantham J, El Massioui F. Alterations in
cognitive performance during passive hyperthermia are task de-
pendent. Int J Hyperther. 2011;27(1):1–9.
16. Hancock PA, Vasmatzidis I. Effects of heat stress on cognitive
performance: the current state of knowledge. Int J Hyperther.
2003;19(3):355–72.
17. Hardy J. Speaking clearly: a critical review of the self-talk litera-
ture. Psychol Sport Exerc. 2006;7(1):81–97.
18. Hatzigeorgiadis A, Zourbanos N, Theodorakis Y. The moderating
effects of self-talk content on self-talk functions. J Appl Sport
Psychol. 2007;19(2):240–51.
19. Hocking C, Silberstein RB, Lau WM, Stough C, Roberts W.
Evaluation of cognitive performance in the heat by functional brain
imaging and psychometric testing. Comp Biochem Physiol A Mol
Integr Physiol. 2001;128(4):719–34.
20. Jackson AS, Pollock ML. Generalized equations for predicting
body density of men. Br J Nutr. 1978;40(3):497–504.
21. Kobrick J, Johnson R. Effects of hot and cold environments on
military performance. In: Gal R, Mangelsdorff AD, editors.
Handbook of Military Psychology. New York: Wiley; 1991.
pp. 215–32.
22. Lee JK, Ang WH, Ng JW, et al. Effects of a carbohydrate-
electrolyte solution on cognitive performance following exercise-
induced hyperthermia in humans. J Int Soc Sports Nutr. 2014;
11(1):51.
23. Liu K, Sun G, Li B, et al. The impact of passive hyperthermia on
human attention networks: an fMRI study. Behav Brain Res.
2013;243:220–30.
24. Marcora S. Perception of effort during exercise is independent of
afferent feedback from skeletal muscles, heart, and lungs. J Appl
Physiol. 2009;106(6):2060–2.
25. Marcora SM, Staiano W, Manning V. Mental fatigue impairs phys-
ical performance in humans. J Appl Physiol. 2009;106(3):857–64.
26. McCormick A, Meijen C, Marcora S. Psychological deter-
minants of whole-body endurance performance. Sports Med.
2015;45(7):997–1015.
27. McMorris T, Swain J, Smith M, et al. Heat stress, plasma concen-
trations of adrenaline, noradrenaline, 5-hydroxytryptamine and cor-
tisol, mood state and cognitive performance. Int J Psychophysiol.
2006;61(2):204–15.
28. Morrison S, Sleivert GG, Cheung SS. Passive hyperthermia re-
duces voluntary activation and isometric force production. Eur J
Appl Physiol. 2004;91(5–6):729–36.
http://www.acsm-msse.org198 Official Journal of the American College of Sports Medicine
APPLIED SCIENCES
Copyright © 2016 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.

29. Nielsen B, Hyldig T, Bidstrup F, Gonzalez-Alonso J, Christoffersen
GR. Brain activity and fatigue during prolonged exercise in the heat.
Pflugers Arch. 2001;442(1):41–8.
30. Paulus MP, Potterat EG, Taylor MK, et al. A neuroscience approach
to optimizing brain resources for human performance in extreme
environments. Neurosci Biobehav Rev. 2009;33(7):1080–8.
31. Pilcher JJ, Nadler E, Busch C. Effects of hot and cold temperature
exposure on performance: a meta-analytic review. Ergonomics.
2002;45(10):682–98.
32. Qian S, Sun G, Jiang Q, et al. Altered topological patterns of large-
scale brain functional networks during passive hyperthermia. Brain
Cogn. 2013;83(1):121–31.
33. Racinais S, Gaoua N, Grantham J. Hyperthermia impairs short-
term memory and peripheral motor drive transmission. J Physiol.
2008;586(19):4751–62.
34. Robertson CV, Marino FE. Prefrontal and motor cortex EEG
responses and their relationship to ventilatory thresholds
during exhaustive incremental exercise. Eur J Appl Physiol.
2015;115(9):1939–48.
35. Robertson CV, Marino FE. A role for the prefrontal cortex in
exercise tolerance and termination. J Appl Physiol. 2016;120(4):
464–6.
36. Roelands B, Meeusen R. Alterations in central fatigue by phar-
macological manipulations of neurotransmitters in normal and
high ambient temperature. Sports Med. 2010;40(3):229–46.
37. Selkirk GA, McLellan TM. Influence of aerobic fitness and body
fatness on tolerance to uncompensable heat stress. J Appl Physiol.
2001;91(5):2055–63.
38. Siri WE. Body composition from fluid spaces and density: analysis
of method. In: Brozek J, Henschel A, editors. Techniques for
Measuring Body Composition. Washington (DC): National Acad-
emy of Science; 1961. pp. 223–4.
39. Wallace JC. Confirmatory factor analysis of the cognitive failures
questionnaire: evidence for dimensionality and construct validity.
Pers Ind Dif. 2004;37(2):307–24.
40. Zhang Y, Balilionis G, Casaru C, et al. Effects of caffeine and
menthol on cognition and mood during simulated firefighting in
the heat. Appl Ergon. 2014;45(3):510–4.
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d
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