The Effect of a Silicone Swim Cap on Swimming Performance in Tropical Conditions in Pre-Adolescents

Abstract

We tested whether the silicone swim caps (SC) worn by young swimmers in a tropical climate negatively influence aerobic performance. Nine trained pre- adolescents [11.8 (± 0.8) years] swam randomized 800-m trials (water: 32.9°C, outdoors: shade, 29.2 ± 0.2 °C, 74 ± 0.3 % rh) with a SC or a nude head (NH). Performance times and heart rate (HR) were monitored continuously. Rectal temperature (Trec) was measured before and after trials. The rating of perceived exertion (RPE) was assessed. Stroke frequency (SF), stroke length (SL) and stroke index (SI) were measured every 50-m. The SC trial was significantly longer than NH (799 ± 16 and 781 ± 16 seconds, respectively). Mean delta Trec was significantly greater in SC (0.2 ± 0.1°C vs. -0.1 ± 0.1°C in SC vs. NH), mean SI was significantly different in SC versus NH (1.83 ± 0.07 vs 1.73 ± 0.06); but RPE and mean HR, SF and SL showed no change. We conclude that a silicone swim cap worn in tropical environment significantly decreased 800-m crawl performance without affecting HR or RPE. Silicone swim caps worn by young swimmers in a tropical environment may also have negative effects on training capacity. Key pointsSwimming in tropical climate represents a physiological stressSwimming with swim cap in warm water could induce thermal stressThermoregulation processes have to be used in order to make training in tropical climate safer.

Full text

©Journal of Sports Science and Medicine (2012) 11, 156-161
http://www.jssm.org
Received: 01 June 2011 / Accepted: 30 January 2012 / Published (online): 01 March 2012
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The effect of a silicone swim cap on swimming performance in tropical
conditions in pre-adolescents
Olivier Hue 1 and Olivier Galy 1,2
1 Laboraire ACTES, UFR-STAPS, Université des Antilles et de la Guyane, Campus de Fouillole, France
2 IUFC de Nouvelle-Calédonie, 125 av James Cook, BPX4, 98852 Nouméa Cédex, Nouvelle-Calédonie, France
Abstract
We tested whether the silicone swim caps (SC) worn by young
swimmers in a tropical climate negatively influence aerobic
performance. Nine trained pre-adolescents [11.8 (± 0.8) years]
swam randomized 800-m trials (water: 32.9°C, outdoors: shade,
29.2 ± 0.2 °C, 74 ± 0.3 % rh) with a SC or a nude head (NH).
Performance times and heart rate (HR) were monitored continu-
ously. Rectal temperature (Trec) was measured before and after
trials. The rating of perceived exertion (RPE) was assessed.
Stroke frequency (SF), stroke length (SL) and stroke index (SI)
were measured every 50-m. The SC trial was significantly long-
er than NH (799 ± 16 and 781 ± 16 seconds, respectively). Mean
delta Trec was significantly greater in SC (0.2 ± 0.1°C vs. -0.1 ±
0.1°C in SC vs. NH), mean SI was significantly different in SC
versus NH (1.83 ± 0.07 vs 1.73 ± 0.06); but RPE and mean HR,
SF and SL showed no change. We conclude that a silicone swim
cap worn in tropical environment significantly decreased 800-m
crawl performance without affecting HR or RPE. Silicone swim
caps worn by young swimmers in a tropical environment may
also have negative effects on training capacity.
Key words: Swimming, hot/wet environment, pre-adolescents,
aerobic exercise, performance
Introduction
Performance, fatigue and exhaustion during exercise in
the heat, especially during exercise performed in field
conditions, have recently been presented as a hot topic
(Schlader et al., 2011).
When confronted by heat stress, one of the guide-
lines is to limit, stop or cancel all athletic activities at a
wet bulb globe temperature (WBGT) of 26-29°C (Ameri-
can Academy of Pediatrics, 2000). This is fairly simple to
do in regions that have the four-season pattern of tem-
perature change with only occasional temperature spikes,
but it is much more problematic in tropical climates,
where temperatures often exceed 25°C and humidity
exceeds evapotranspiration for at least 270 days per year
(Salati et al., 1983). For people living in these climates,
one of the most important guidelines for sports activities
is to limit the amount of clothing worn in order to en-
hance thermoregulatory processes. Guadeloupe, with a
mean temperature of 25-26°C and a mean relative humid-
ity of 80-82%, has a tropical climate that has been dem-
onstrated to act as a passive warm-up all day and night
long (Racinais et al., 2004).
It has long been acknowledged that children and
adolescents do not adapt as effectively as adults do to
temperature extremes, such as high climatic heat stress
(Bar-Or, 1998). Several recent reviews and articles reas-
sessed children’s thermoregulation during exercise in the
heat (Falk and Dotan, 2008; Inbar et al., 2004; Rowland,
2008) and reported discrepant findings. Some found no
maturational differences in thermal balance or endurance
performance during exercise in the heat (Rowland, 2008),
whereas others noted that children are more likely to be
susceptible to heat-related injury in extreme environments
(Falk and Dotan, 2008). Still others observed that prepu-
bertal boys are better thermoregulators than both young
adults and the elderly (Inbar et al., 2004). There is con-
sensus today on three points: characterizing children’s
physiological responses and performance outcomes dur-
ing exercise in the heat is far from complete (Rowland et
al., 2008), children and adults employ different thermo-
regulatory strategies (Falk and Dotan, 2008), and children
and young adults exposed to hot climates need to follow
proper guidelines to prevent heat injury or performance
decrement (American Academy of Pediatric, 2000).
Swimming in Guadeloupe can be a distinct chal-
lenge, as the annual mean ocean temperature is 26°C and,
for almost 6 months of the year, the water in Olympic
swimming pools is over 30°C, whereas the recommended
pool temperature for competitive swimming is 27-28°C
(Aquatic Exercise Association, 2008). Nevertheless, ath-
letes who swim competitively train every day. A particu-
larly interesting question thus concerns the extent to
which swimming is affected by a tropical climate. The
thermal balance of swimmers is well known to be regu-
larly challenged because of the high heat transfer coeffi-
cient of water (Wade and Veghte, 1977). Most studies
have reported the effect of cold water on thermoregulation
(Costill et al., 1967; Sloan and Keatinge, 1973), but one
study found that swimming in high water temperature
increased heart rate in relation to hyperthermia and in-
creased skin circulation and esophageal temperature to the
same extent as running in a hot environment (Holmér and
Bergh, 1974). These authors noted an increase of 8
beats·min-1 in heart rate during a 20-min submaximal
swimming exercise (approximately 50% of VO2max) in
34°C water as opposed to 26°C water. Swimming is thus
a sport that induces high thermoregulatory stress in a
tropical climate, as recently confirmed (Hue et al., 2007).
One easy way to enhance thermoregulation in
competitive swimmers in Guadeloupe is to remove the
silicone swim cap that is usually used for gliding as well
as hygienic reasons. Targeted active cooling of the head
during exercise has been recognized as efficacious in
Research article

Hue and Galy
157
improving subjective tolerance and/or the physiological
response to heat stress (Nunneley et al., 1971). Compris-
ing only 8-10% of the body surface area (Brown and
Williams, 1982), it can account for the dissipation of 30%
of the resting heat load and almost 20% during moderate-
intensity exercise (Nunneley et al., 1971). Similarly, the
dorsal head (i.e., the part of the head covered by the
swimming cap) is only a very small part of the body sur-
face but its immersion in cold water (i.e., 12°C) has been
demonstrated to substantially increase core cooling (Gies-
brecht et al., 2005) because of the great amount of blood
flow in the scalp and the lack of vasoconstriction in scalp
blood vessels in response to cold water as opposed to the
surface vessels in other body areas (Froese and Burton,
1957). Very recently, Simmons et al. (2008) demonstrated
the major subjective importance of the head in the percep-
tion of temperature sensation.
The aim of this study was thus to test aerobic
swimming performance during an 800-m event in pre-
adolescents with and without a silicone swim cap. We
hypothesized that removing the cap in a hot/wet environ-
ment would permit better thermoregulation, which in turn
would increase performance.
Methods
Subjects
Seven male [11.7 (± 0.9) years] and two female [11.9 (±
0.2) years] competitive swimmers participated in this
study. All were regionally and inter-regionally ranked
swimmers, native to Guadeloupe, and currently living and
training there [training in swimming for 3.6 (± 0.3) years].
The group belonged to the same club affiliated with the
Guadeloupe Swimming League and regularly trained five
times a week for a total of 7 hours of swimming, or 13 to
15 km per week. The training camp was based at an out-
door 25-m swimming pool. The swimmers were in the
competitive season at the time of the study. Pubertal stage
[1.3 (± 0.1) of the Tanner classification as assessed by a
physician] was determined according to pubic hair and
gonadal development (Tanner and Whitehouse, 1976).
Anthropometric and physiological measurements were
made one week before testing and are presented in Table
1. Informed written consent was given by all pre-
adolescents and their parents. The protocol was approved
by the ethics committee of Guadeloupe University.
Anthropometry
Body mass loss (kg) was measured on a scale by changes
in nude body mass (± 0.1 kg) (Planax Automatic, Terail-
lon, Chatoux, France). The subjects were weighed in the
same conditions before and after exercise. Body fat con-
tent was estimated from the skinfold thickness, expressed
in millimeters, representing the sum of four different skin
areas (biceps, triceps, subscapula, and supra-iliac) meas-
ured on the right side of the body with the Harpenden
skinfold caliper following the method described by
Durnin and Rahaman (1967). The equation of Durnin and
Rahaman (1967) was used to determine the percentage of
fat body mass (FBM). Lean body mass (LBM) was de-
termined from body mass and FBM. Buoyancy was eval-
uated by the measurement of hydrostatic lift (HL) as de-
scribed by Chatard et al. (1990).
Experimental protocol
Swimmers came to the pool one week before the two 800-
m events to perform two 15-m sprints, without diving, to
measure their maximal swim speed. The best performance
in the 400-m event (MAS400) of the current competitive
season was recorded for each swimmer and taken as the
maximal aerobic test (Chatard et al., 1995; Chollet et al.,
2000). The event was held in a 27°C swimming pool in
conditions detailed elsewhere (Hue et al., 2007;
Rodríguez, 2000).
The 800-m event
Each subject performed two trials at approximately the
same time of day to minimize the influence of circadian
variation on internal body temperature (Wenger et al.,
1976). For the duration of the study, the subjects were
asked to maintain similar daily activity and adequate
dietary and fluid intake. The trials began at 5 PM to min-
imize the effects of the sun and to take into account the
daily training rhythms of the swimmers. All subjects
performed two randomized 800-m crawl trials in the trop-
ical environment (water: 32.9 ± 0.1 °C, outdoors: shade,
29.2 ± 0.2 °C, 74 ± 0.3 % rh) on two separate days. In one
trial they wore a silicone swim cap (SC) for the 800-m
event and in the other they swam with nude heads (NH).
The warm-up distances and intensities were standardized;
in both conditions (SC and NH), the warm-ups were per-
formed wearing a swimming cap, as required in Guade-
loupian swimming pools for hygienic reasons.
Table 1. General characteristics and swim profiles of the 9 trained swimmers.
Subject
#
Gender Age
(yr)
Height
(m)
Weight
(kg)
Tanner Stage
(a.v.)
FBM
(%)
LBM
(kg)
HL
(kg)
15m Sprint
(s)
Time of the MAS400 test
(s)
1 ♀ 11 1.57 41.2 2.0 24.0 31.9 .9 11.60 410
2 ♀ 12 1.56 44.1 2.0 23.9 34.2 1.5 11.10 396
3 ♂ 12 1.53 30.9 1.6 11.0 28.9 .4 10.23 360
4 ♂ 11 1.63 42.7 1.4 12.1 37.2 .5 10.80 364
5 ♂ 13 1.58 36.8 1.0 12.5 32.4 .7 10.40 375
6 ♂ 12 1.55 49.2 1.8 19.0 40.0 1.8 10.40 339
7 ♂ 10 1.48 33.9 1.0 14.0 29.6 .5 10.30 342
8 ♂ 11 1.43 34.8 1.0 18.4 26.8 .9 10.20 385
9 ♂ 11 1.49 33.4 1.0 13.5 29.8 1.5 10.60 366
Mean
SEM
11.4
.3
1.53
.02
38.6
2.0
1.4
.1
16.5
1.7
32.3
1.4
1.0
.2
10.80
.20
371
8
Tanner stage: pubertal stage; a.v.: Arbitrary value; FBM: fat body mass; LBM: lean body mass; HL: hydrostatic lift; 15-m sprint: maximal swim
speed; MAS400: maximal aerobic speed at the end of a 400-m test.

Swimming in tropical conditions
158
Heart rate (HR) was monitored continuously using
a portable telemetry unit (Polar Sport-tester PE 4000,
Polar OY, Kempele, Finland) with recording every 5
seconds. The data were analyzed with Polar software
(Polar Electro OY, Professorintie 5, Kempele, Finland).
Rectal temperature (Trec) was measured by the medical
doctor before and immediately after the trials with a rectal
thermometer (Microlife Corporation, Taipei, Japan). After
each trial, the subjects were asked to rate their perceived
exertion (RPE) using the Borg scale (Borg, 1973).
Stroke frequency, stroke length and stroke index
The stroke frequency (SF), expressed as the number of
complete arm cycles·min-1, was measured for each 12.5-m
with a frequency meter (Stopwatch Stroke base 3 time,
Seiko, Japan) over three complete stroke cycles. The
stroke length (SL) was calculated by dividing the speed,
expressed as the distance per second, by the stroke fre-
quency in a 12.5-m segment. The stroke index (SI) was
calculated by multiplying the velocity by the stroke length
(Costill et al., 1985). This index has been demonstrated to
be reliable for assessing swimming skill (Costill et al.,
1985).
Statistical analysis
After a normal distribution was verified using the
Shapiro-Wilk test, the effects of wearing a swim cap on
performance (time, speed and %MAS400), heart rate, and
SF, SL and SI were analyzed using a two-way ANOVA
for repeated measures (condition x distance). When dif-
ferences were observed, Scheffe’s post-hoc test was used
with the contrast method. Temperature and body mass
were analyzed using a two-way ANOVA for repeated
measures (condition x time). The rate of perceived exer-
tion was analyzed using a Student’s t test for paired com-
parisons. Significance was defined as p < 0.05. Data are
presented separately as mean ± SEM.
Results
Performance was influenced by the swim cap condition,
with a significant gain of 18.6 ± 5.0 seconds in NH com-
pared with SC (p < 0.01). The 800-m kinetics showed a
significantly longer time and lower speed for the SC con-
dition compared with the NH condition at 550-m, 650-m,
700-m and 800-m (time x conditions p < 0.04, Figure 1).
The intensity of the NH condition, expressed in
%MAS400m, was significantly higher when compared with
that of the SC condition (95.2 ± 2.0 vs 92.8 ± 1.8
%MAS400m; p < 0.05); however, HR was similar between
tests (189 ± 2 vs 186 ± 3 bpm, in NH vs SC, respectively).
SI was significantly different in SC versus NH (1.83 ±
0.07 vs 1.73 ± 0.06; p < 0.05). In contrast, mean SF and
SL showed no significant differences. Within the trials,
significantly higher values of SF and SI were noted at
550-m and 800-m for the SC condition compared with the
NH condition, whereas SL showed significantly lower
values (p < 0.05, Figure 1). Although rectal temperature
did not differ after the warm-up (i.e., 37.6 ± 0.1 vs 37.7 ±
0.3 in NH and SC, respectively), the post-exercise delta
Trec was significantly higher (p < 0.05) in the SC condi-
tion (0.2 ± 0.1 °C vs -0.1 ± 0.1 °C in SC vs NH). Body
mass was not significantly decreased (0.1 ± 0.1 and 0.2 ±
0.1 kg in NH and SC, respectively) after each trial com-
pared with before the trial. There was no difference in
RPE (13.6 ± 0.9 vs 13.0 ± 0.6, in NH and SC, respec-
tively).
Figure 1. Heart rate, HR; time kinetics: seconds; stroke
frequency (down) and stroke length (up) during SC and NH
800-m events. * SC Significantly different (p < 0.05) from NH.
Discussion
The most important finding of this study was that remov-
ing the silicone cap usually used by competitive swim-
mers increased the pre-adolescents’ swimming perform-
ance in warm water.
To the best of our knowledge, this study is the first
to investigate the response of acclimatized pre-
adolescents to a tropical environment and clothing con-
straints. Most studies of children’s or pre-adolescents’
responses to heat exposure have investigated briefly ex-
posed non-acclimatized children/pre-adolescents or those
acclimated for only a short time to a hot climate (Row-
land, 2008). The subjects of the present study were young
competitive swimmers, native to and living and training
in Guadeloupe, which has a tropical climate that has been
demonstrated to be deleterious to endurance performance.
This has been demonstrated in athletes even when they

Hue and Galy
159
are natives of and living in the hot and wet climate (Vol-
taire et al., 2003). We can therefore assume that the results
of the present study would have been even more pro-
nounced in non-acclimatized pre-adolescents.
Because we did not measure skin temperature or
core temperature during the exercise, we have no data on
the kinetics of total body temperature changes. However,
the warm-ups were performed in the exact same condi-
tions for the two randomized tests and the rectal tempera-
tures were not different after the warm-ups. We can there-
fore assume that the changes in rectal temperature were
due to the 800-m exercise bouts and not to the warm-ups.
Although we did not use a specific test to measure ther-
mal sensation or thermal comfort, the RPE scale has been
demonstrated to be valid for measuring the conscious
perception of effort in hot conditions (Crewe et al., 2008;
Tucker et al., 2004).
One might assume that the mean difference of 18.6
sec in the performance times of these swimmers reflected
diminished motivation and/or an inability to maintain the
same exercise intensity between the 800-m events. Yet a
drop in intensity for the second trial (SC or NH) can be
easily rejected, whether objectively or subjectively evalu-
ated, since the trials were randomized and HR, which is
frequently used as a reliable indicator of objective exer-
cise intensity (Hue et al., 2006; Léger and Thivière,
1988), did not differ between tests. Moreover, the high
values of HR and the %MAS400m suggested that the pre-
adolescents did their best in both trials and were able to
maintain the high intensity currently reported in the litera-
ture for highly-trained young athletes (Billat, 2001) and
swimmers (Bentley et al. 2005). The subjective assess-
ment of intensity could have influenced performance,
particularly since the 800-m event is the longest trial of
the Federation International de Natation Amateur program
for young swimmers. However, this subjective intensity,
evaluated by the Borg scale at the end of each trial, did
not show significant differences within or between the SC
and NH trials. The plausible explanation for the differ-
ence in performance times is that the swimmers were
unable to maintain the same speed during the SC trial for
objective or subjective reasons. As recently demonstrated
for the use of oral adjuvant during exercise in the heat
(Mundel and Jones, 2010), swimming without a silicone
cap may be a more pleasant and rewarding/motivating
experience within the brain, therefore extending the exer-
cise performance. Another explanation could be that NH
produces bradycardia relative to SC. As far as we know,
this phenomenon, which is well known during cold water
face immersion at rest (Finley et al., 1979) or after exer-
cise (Al Haddad et al., 2010), has never been noted during
warm water immersion. Moreover, no study to our
knowledge has been conducted showing that bradycardia
is greater during head immersion than during face immer-
sion.
It might be surprising that the silicone swim cap
could cause heat stress sufficient to decrease thermal
comfort and thus performance, because the difference in
rectal temperature (both between trials but also after ver-
sus before exercise) was very slight. However, a water
temperature of 33°C was shown to be a potential thermal
stress inducing a significantly higher Trec than a tempera-
ture of 28°C during a long but slow swimming test (Fu-
jishima et al., 2001). Moreover, although the dorsal head
(i.e., the part of the head covered by the swimming cap)
represents only a very small part of the body surface, it is
hypothesized that it permits substantial heat loss because
of the great amount of surface blood flow in the scalp and
the lack of vasoconstriction in scalp blood vessels, as
opposed to surface vessels in other body areas (Froese
and Burton, 1957). Furthermore, cooling the head and
face during exercise has been demonstrated to reverse the
hyperthermia-induced increase in RPE during both pas-
sive heating (Armada-da-Silva et al., 2004) and exercise
(Mündel et al., 2007) and the thermal strain and discom-
fort during passive heating without affecting the core
temperature (Mündel et al., 2006; Nunneley and Maldo-
nado, 1983). Very recently head cooling has been demon-
strated to attenuate the increase in core temperature dur-
ing passive heating (Simmons et al., 2008). As stated by
Cheung (2007), “the efficacy of either face fanning or
head cooling to influence either brain temperature or
physiological responses and performance is not univer-
sally evident in the literature and the possible mechanisms
selectively used during this phenomenon are unclear but
results issued from head cooling or head fanning would
tend to support the idea that afferent feedback from cool-
ing the head, irrespective of actual brain temperature, may
play an important role in regulating exercise intensity and
pacing by promoting an improved subjective perception
of heat stress.”
Such a phenomenon (i.e., a decrease in perform-
ance or power output without marked hyperthermia or
increase in Trec) has been demonstrated in cycling by
Tatterson et al. (2000), Hue et al. (2010) and very recently
Schlader et al. (2011), who reported lower work output
during thermal warming versus thermal and non-thermal
cooling despite similar HR, mean skin and rectal tempera-
ture. Schlader et al. (2011) noted that changes in tempera-
ture are not a requirement for the initiation of thermoregu-
latory behaviour in humans and that thermal sensation and
thermal discomfort are capable behavioral controllers. It
is possible that despite the very low change in core tem-
perature, the greater sensitivity to heat changes and the
heightened subjective sensitivity to increases in core tem-
perature in children (Anderson and Mekjavic, 1996) could
have prevented them from performing as well with the
swim cap as without it.
It was interesting to note that the time losses in the
SC 800-m (a mean of 18.6 sec) began at about 550-m and
continued up to 800-m. The biomechanical parameters
indicated that SI was significantly greater in NH condi-
tion, whatever the swim speed. The significantly higher
values of SF and SI and lower SL between 550-m and
800-m in the SC 800-m confirmed this observation. This
demonstrates that the swim cap globally altered swim
performance. The SI is based on the assumption that, at a
given speed, the swimmer with the greatest stroke length
has the most effective swimming technique and skill
(Costill et al., 1985). In the present study, the increase in
SI without a swim cap thus indicated greater swimming
skill in NH condition. This greater efficiency was most
likely related to the lower thermal stress in NH, which
made it easier to recruit more motor units for each arm

Swimming in tropical conditions
160
stroke cycle, thereby resulting in the higher efficiency.
Our data indicate two important points about
swimming performance in tropical conditions: 1) wearing
a silicone swim cap affects performance during a single
continuous exercise in young swimmers, and 2) wearing a
silicone swim cap during long-distance training sessions
accentuates thermal stress and may thus lead to reduced
training intensity, which in turn could affect competitive
performance. We suggest the need for innovation in the
textiles used for caps and for studies to develop technical
means to optimize performance in hot/wet conditions.
Conclusion
In conclusion, this study showed that removing a silicone
swim cap in tropical conditions increased the 800-m per-
formance in young swimmers, probably in relation with
thermoregulation processes and/or subjective perception.
Competitive swimmers spend considerable time in the
water. In order to prevent illness, preserve wellness, and
make swimming training in a tropical climate safer and
more enjoyable, we recommend that young competitive
swimmers and their coaches envisage removing the sili-
cone swim cap during training sessions and competitions
of 800-m or more in tropical environmental conditions.
However, further research is needed in the area of thermo-
regulation in relation with swimming performance.
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Key points
• Swimming in tropical climate represents a physio-
logical stress
• Swimming with swim cap in warm water could in-
duce thermal stress
• Thermoregulation processes have to be used in order
to make training in tropical climate safer
AUTHORS BIOGRAPHY
Olivier HUE
Employment
Université des Antilles et de la Guyane
Degree
PhD, Professor
Research interest
exercise physiology, thermoregulation, heat
acclimation, aerobic exercise
E-mail: ohue@univ-ag.fr
Olivier GALY
Employment
Rectorat de Nouvelle-Calédonie
Degree
PhD
Research interest
triathlon training, health pacific populations,
thermoregulation
E-mail: Olivier.Galy@ac-noumea.nc
 Olivier Hue
Laboraire ACTES, UPRES EA 35-96, UFR-STAPS, Université
des Antilles et de la Guyane, Campus de Fouillole, 97159 Pointe
à Pitre Cédex, France.