The Effects of Thermal-isolation Pads Placed over Working Muscles
on Endurance Performance
S. Wenger
1,2
, R. Csapo
2
and W. Nachbauer
2
1
Centre of Technology of Ski and Alpine Sport, Fürstenweg 185, 6020 Innsbruck, Tyrol, Austria
2
Department of Sport Science, University of Innsbruck, Fürstenweg 185, 6020 Innsbruck, Tyrol, Austria
1 INTRODUCTION
Human thermoregulation aims at keeping core
temperature constant at around 37 °C, regardless of
exercise intensity or environmental conditions.
Exercise at vigorous intensity typically induces a
rise in core temperature that may negatively affect
performance in endurance tasks (Noakes, 2000).
On the other hand, skeletal muscles are known to
work most efficiently at higher muscle temperatures
(36 °C compared to 32 °C in 18 mm depth) (Inoue et
al., 2016). This imposes a conflict of interest in
designing apparel for winter endurance sports.
Clothing, e.g. for cross country skiing, should
facilitate overall heat dissipation to keep the body´s
core temperature constant while, at the same time,
promoting high muscle temperatures to maximize
muscle performance. Combining a relatively thin
pant with thermal insulation pads placed over the
working muscles may be a useful yet reasonable
approach to reach this goal.
2 OBJECTIVES
The aim of this study was to test the effects of
thermal insulation of working muscles on
parameters reflecting physical stress provoked by a
moderately intense endurance task in a cool
environment.
3 METHODS
Ten male sport students (age: 23.3 ± 3.2 y, height:
182 ± 5.4 cm, BMI: 22.1 ± 1.4) volunteered to
participate in the study. After a treadmill-based step
test to determine their maximum running velocity
(MV), participants were scheduled for two visits to
compare different running pants: Both tested pants
were made of identical material (94% polyester and
6% elastane; 80 g/m
2
) and had the same size and cut.
One pant (P
INSUL
) featured additional insulation pads
(94% polyester, 6% elastane; 380 g/m
2
) positioned
over the knee extensor and plantar flexor muscles;
the other pant (P
COOL
) was made without these pads
to facilitate heat dissipation. During all tests,
subjects wore identical long-sleeve shirts composed
of the same material as the pants.
Subjects were exercising for 45 min at 60% of
their MV on a treadmill (5% inclination) at constant
ambient conditions (7 °C and 40% relative
humidity). Average testing speed was 9.6 ± 0.6
km/h.
Measurements were taken before (t0) and during
the exercise, after 15 min (t1), 30 min (t2) and 45
min (t3) of running, respectively. Heart rate (HR),
blood lactate (BL) and core temperature (CT) were
measured at t0, t1, t2, t3. Weight loss (WL) during
exercise was calculated and thermal images were
taken at t0 and t3 to determine the surface
temperature (ST) of clothes. ANOVAs with repeated
measurements were used to determine the influence
of the factor “pant” on all outcome measures.
4 RESULTS
At time point t3, thermal images showed
significantly lower ST for P
INSUL
compared to P
COOL
at the front- (p = 0.007) and backside (p = 0.005) of
the legs with (P
INSUL
: 20.1 ± 1.1 °C vs. P
COOL
:
21.1 ± 0.9 °C). Descriptive statistics of ST as
measured over the anterior and posterior aspect of
the legs are presented in Figure 1.
During exercise HR increased significantly (p <
0.001) from 99.3 bpm (t0) to 163 bpm (t3) (Figure 2
(a)). After the exercise (t3) HR was lower for P
INSUL
(162.1 ± 10.3 bpm) compared to P
COOL
(164.8 ± 11.5
bpm), with differences tending towards statistical
significance (p = 0.055).
As evident from Figure 2 (b), BL was rising from
t0 to t3 by 0.8 mmol/l but no significant difference
14
Wenger, S., Csapo, R. and Nachbauer, W.
The Effects of Thermal-isolation Pads Placed over Working Muscles on Endurance Performance.
In Extended Abstracts (icSPORTS 2016), pages 14-15
Copyright
c
 2016 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

(p = 0.973) in the rise of lactate was found between
pants (ΔP
INSUL
: 0.8 ± 0.5 mmol/l vs. ΔP
COOL
:
0.8 ± 0.6 mmol/l).
CT dropped slightly during the protocol from
36.6 ± 0.4 °C (t0) to 36.3 ± 0.7 °C (t3), with no
significant differences between pants (p = 0.558).
Average WL from t0 to t3 was 645 ± 120 g without
significant differences between pants (p = 0.961).
Figure 1: Surface Temperature of clothes (°C) as measured
over the anterior and posterior aspect of the legs before
(t0) and after 45 min (t3) of exercise.
Figure 2: Heart rate (a) and blood lactate (b) during
execution of the endurance task with the insulating
(P
INSUL
) and cooling (P
COOL
) pant.
5 DISCUSSION
The goal of this study was to test the effects of
thermal insulation of working muscles on endurance
exercise performance in a cool environment. While
thermal images indicated that usage of running pants
containing insulation pads (P
INSUL
) was associated
with significantly higher internal temperatures in
active muscles (reflected by lower external heat
emission), no significant differences in parameters
reflecting physical stress were found between pants.
This might be due to the relatively moderate climatic
conditions simulated in the current study.
Previous studies have suggested that lower
muscle temperatures may lead to reduced endurance
performance. In contrast to our work, however, these
studies used interventions involving either active
muscle cooling or exercise in substantially colder (<
0 °C) environments (Inoue et al., 2016, Oksa, 2002).
Findings by Sandsund et al. (2012) suggest that
endurance performance is best between -4 °C and
+1 °C when a thin racing suit (Insulation: 1.3 Clo) is
used. Hence, it may be speculated that local
insulation of working muscles would only have
positive effects on endurance performance at
temperatures below 1°C. In conclusion, usage of
insulation pads to increase the temperature of
working muscles had no statistical effect on
measures of physical stress obtained during an
endurance run under cool environmental conditions.
Building up on the preliminary findings obtained in
this study, further experiments will be performed
under colder ambient conditions.
REFERENCES
Inoue, K., Kume, M. & Yoshida, T. 2016. Effects of
Lower Limb Cooling on the Work Performance and
Physiological Responses During Maximal Endurance
Exercise in Humans. In: LEE, R. (ed.) Applied
Computing & Information Technology. Cham:
Springer International Publishing.
Noakes, T. D. 2000. Exercise and the cold. Ergonomics,
43, 1461-1479.
Oksa, J. 2002. Neuromuscular performance limitations in
cold. Int J Circumpolar Health, 61.
Sandsund, M., Saursaunet, V., Wiggen, Ø., Renberg, J.,
Færevik, H. & Van Beekvelt, M. C. 2012. Effect of
ambient temperature on endurance performance while
wearing cross-country skiing clothing. Eur J Appl
Physiol, 112, 3939-3947.
The Effects of Thermal-isolation Pads Placed over Working Muscles on Endurance Performance
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