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Mechanical Properties of Treadmill Surfaces and Their Effects
on Endurance Running
Enrique Colino, Jorge Garcia-Unanue, Leonor Gallardo, Carl Foster,
Alejandro Lucia, and Jose Luis Felipe
Purpose:To characterize, for the first time, the mechanical properties of treadmill surfaces along with a practical interpretation of
their influence on physiological and perceived demands during endurance running compared with other widely used surfaces
such as asphalt and tartan tracks. Methods:Ten experienced male endurance runners performed a 40-minute running bout at
a preferred constant speed on 3 different surfaces (after a randomized, counterbalanced order with a 7-d interval between trials):
asphalt, tartan, or treadmill. Shock absorption, vertical deformation, and energy restitution were measured for the 3 surfaces.
Intensity (based on heart rate data) and rating of perceived exertion were monitored. Results:The values of shock absorption
averaged 0.0% (asphalt), 37.4% (tartan), and 71.3% (treadmill), while those of vertical deformation and energy restitution
averaged 0.3, 2.2, and 6.5 mm and 90.8%, 62.6%, and 37.0%, respectively. Running intensity (as determined by heart rate data)
was higher overall on the treadmill than tartan but not asphalt running. Except for the first 10 minutes, all mean rating of perceived
exertion values were significantly higher in asphalt and treadmill than in tartan. No significant differences were identified
between treadmill and asphalt. Conclusions:The considerably higher shock absorption of the treadmill than the tartan surface
leads to a reduction in the amount of energy returned to the athlete, which in turn increases physiological stress and rating of
perceived exertion during endurance running.
Keywords:sport surfaces, shock absorption, vertical deformation, physical demands
Surface properties can influence endurance running perfor-
mance.
1–3
Indeed, athletes adjust their leg stiffness when running
on surfaces of differing mechanical properties,
4,5
resulting in subtle
changes in lower-limb kinematic patterns, landing style, stride
length, ground reaction force dynamics, and peak impact accel-
erations.
6–10
Thus, surface properties have been reported to affect
physiological responses during endurance running.
11–14
Data from
epidemiological studies suggest that the type of surface is also an
important factor in the etiology of injuries,
15
with increased and
decreased surface stiffness being potentially associated with bone
and soft tissue injuries, respectively.
16
Given its cyclical nature and dynamics, endurance running
essentially consists of a series of collisions with the ground and does
not generally involve large changes in speed or direction, nor does it
imply variations in locomotor skills such as jumping, sliding, or
cutting.
2
Thus, the main surface property that can affect runners’
safety and performance is the ability to absorb impact forces during
foot landing,
17
so endurance running performance is influenced by
shock absorption (SA), vertical deformation (VD), and energy
restitution (ER).
12,13
In this regard, the International Association
of Athletics Federations has established that the SA and VD values
of track-and-field surfaces must range between 35% and 50% and
0.6 to 2.5 mm, respectively, while no reference values are available
for ER.
18
Regarding some other popular running surfaces such as
concrete or asphalt, they typically yield SA and VD values close to
0, especially for concrete, although no regulation applies on them as
they were not originally conceived for running purposes. However,
the mechanical properties of treadmill surfaces have not been
previously reported, and the only regulation concerning this type
of surface, the European Standard EN 957-6+A1 (ie, Stationary
Training Equipment—Part 6: Treadmills, Additional Specific Safety
Requirements and Test Methods), provides no recommendation or
reference values for SA, VD, or ER.
19
Yet, treadmills represent one
of the most commonly used running surfaces worldwide.
This investigation aimed to characterize, for the first time, the
mechanical properties of treadmill surfaces, along with a practical
interpretation of their influence on physiological and perceived
demands during endurance running compared with other widely
used surfaces such as asphalt and tartan tracks.
Materials and Methods
Subjects
A total of 10 experienced male endurance runners (competing in
races ≥10 km) were recruited from local training groups (age: 28
[5] y; height: 174 [6] cm; body mass: 70 [6] kg). All of them had
been injury-free and on a systematic training program for at least
the last 6 months, did not take part in any competition during the
course of the study, and were familiarized with the running surfaces
used in this trial. Written informed consent was obtained from all
participants. The study protocol was approved by the local ethics
committee (Toledo Hospital) and was conducted in accordance
with the Declaration of Helsinki.
Design
Two weeks before the start of the study, subjects performed a
familiarization session with the treadmill used in this study (HP
Colino, Garcia-Unanue, and Gallardo are with IGOID Research Group, University of
Castilla-La Mancha, Toledo, Spain. Foster is with the Dept of Exercise and Sport
Science, University of Wisconsin-La Crosse,LaCrosse,WI,USA.LuciaandFelipeare
with the School of Sport Sciences, Universidad Europea de Madrid, Madrid, Spain.
Felipe (Joseluis.felipe@universidadeuropea.es) is corresponding author.
685
International Journal of Sports Physiology and Performance, 2020, 15, 685-689
https://doi.org/10.1123/ijspp.2019-0539
© 2020 Human Kinetics, Inc. ORIGINAL INVESTIGATION
Cosmos Quasar, Nussdorf-Traunstein, Germany) and an incremen-
tal running test until volitional exhaustion for maximum heart rate
(HR
max
) and maximum oxygen uptake (VO
2
max) determination.
Thereafter, they completed 3 standardized running trials in a
randomized, counterbalanced order over a 3-week period (1 trial
per week, each performed on the same day of the week and at the
same time of the day) on the following surfaces: (1) conventional
asphalt, (2) a rubber-based tartan track, and (3) a treadmill (HP
Cosmos Quasar).
Rescheduling of test was foreseen in the case of adverse
weather conditions. To maintain similar experimental conditions
throughout the study, participants were asked to use consistently
the same running shoes and to reproduce the same routine across
the 3 trials. Diet, liquid intake, and sleeping hours were controlled
from the day before each test by completing a diary that was
handled to each participant at the beginning of the study. Partici-
pants were asked to write down their routines before the first trial
and to reproduce them during the following 2 trials. They were also
told to refrain from doing strenuous exercise and drinking caffeine-
containing drinks within the 48 and 2 hours, respectively, prior to
each trial, and to present for the tests in a well-hydrated state. The
subjects were blinded to the information provided by the treadmill
display panel and, like for the trials on the other 2 surfaces, the only
information given to them was time elapsed (every 10 min).
Each trial consisted of a 40-minute run at a constant speed
that was preceded by a 10-minute self-selected warm up and a
subsequent 3-minute active rest. Running speed was the same for
the 3 surface conditions. The first test was performed at a self-
selected, moderately vigorous constant pace, which was allowed
to be interpreted by each subject. This constant speed was
reproduced in the second and third tests, so that each participant
covered the same distance across the 3 trials. Asphalt trials were
carried out on a level promenade using a 0.8-km round trip, and
running pace was determined every 400 m to ensure constant
speed. Tartan track trials were performed on a 400-m rubber-
based track, where lap time was controlled. Treadmill trials were
conducted in an open-air laboratory environment, where an air
stream was created by using industrial electric fans placed in front
of the subjects. Air flow was set equal to the participants’running
speed, so that air resistance experimented across the 3 conditions
was controlled for. No inclination of the running surface was
applied for any of the 3 conditions. Wind speed, air temperature,
and humidity were monitored using an anemometer. In over-
ground trials, running speed was determined using time and
known distances, and it was recorded with commercially avail-
able Global Positioning System receivers (SPI-HPU; GPSports
Systems, Canberra, Australia). In the treadmill trials, running
speed was controlled by the treadmill control system, although
subjects also carried the Global Positioning System units to
ensure equal loading conditions. For the 3 surface conditions,
HR was continuously monitored using radiotelemetry (Polar
Electro, Kempele, Finland), and rating of perceived exertion
(RPE) was assessed every 10 minutes using the Borg 6 to 20
scale, which was explained to the participants before the start of
the study.
The SA and VD of running surfaces were assessed by an
artificial athlete device following European standards EN
14808:2005
20
and EN 14809:2005,
21
respectively, in accordance
with current International Association of Athletics Federations
regulations.
18
ER was assessed with an advanced artificial athlete
device following the Fédération Internationale de Football
Association Test Method 13.
22
The description of the artificial
athlete and the advanced artificial athlete apparatus and the rela-
tionship between the 2 devices have been described elsewhere.
23
Statistical Analysis
Five time intervals (0−10, 10−20, 20−30, 30−40, and 0−40 min)
were considered for data analyses. Mean HR (meanHR), the
percentage that meanHR represented relative to each participant
HRmax (%meanHR), peak HR (peakHR), and the percentage
that peakHR represented relative to each participant’s HRmax
(%peakHR) were obtained after the tests for all 5 time intervals.
MeanHR was calculated as the mean of all HR values recorded, and
peakHR was the highest HR registered at any point within each
interval. RPE assessed at 10 (Borg10), 20 (Borg20), 30 (Borg30),
and 40 (Borg40) minutes, respectively, was analysed, as it was the
average of these values (Borg
mean
). Finally, time spent in different
intensity zones was calculated as a percentage of total time. Four
different intensity zones were identified relative to athletes’HR
max
and following previously established criteria
24
: low (<75% of
HR
max
), moderate (75%–85% of HR
max
), high (85%−95% of
HR
max
), and maximal (>95% of HR
max
). Given the relatively small
size of the study sample, the nonparametric Kruskal–Wallis test
was used to compare variables between different surfaces. When a
significant trial effect was identified, post hoc pairwise compar-
isons were performed using Dunn–Bonferroni tests. Effect sizes
(ESs) were calculated and defined as follows: trivial, <0.19; small,
0.2 to 0.49; medium, 0.5 to 0.79; and large, >0.8.
25
SPSS software (version 21.0; SPSS Inc, Chicago, IL) was used
for all statistical analyses, with significance set at .05. All data are
presented as mean (SD).
Results
The VO
2
max of the participants averaged 58.2 (7.5) mL/kg/min.
SA, VD, and ER values for each surface are shown in Table 1.
All subjects were able to successfully reproduce the same
speed and total distance covered across the 3 surface conditions
(with no rescheduling of the sessions needed due to changing
weather conditions), with the maximum within-subject variation
between trials being 1.1%. The maximum prevailing wind speed
observed during overground trials was 0.6 m/s. As wind speed was
consistently below 2 m/s,
26
this variable was dismissed, and
relative air flow was considered to be equal to the runners’speed.
Within-subject variations in temperature and humidity during the
trials did not exceed 2.4°C and 15%, respectively.
Figure 1shows the relationship between HR and time for the 3
running conditions. A different behavior was observed in the tartan
with respect to the other 2 surfaces.
Table 2shows the values for all HR-related variables. When
comparing treadmill and tartan conditions, %meanHR3040 (+2.6;
P=.027; ES: 1.06), %peakHR2030 (+2.5; P=.033; ES: 1.02), %
peakHR3040 (+2.7; P=.012; ES: 1.10), and %peakHR0040 (+2.7;
Table 1 Mechanical Properties of Running Surfaces
Surface
Shock
absorption, %
Vertical
deformation, mm
Energy
restitution, %
Asphalt 0.0 0.3 90.8
Tartan 37.4 2.2 62.6
Treadmill 71.3 6.5 37.0
IJSPP Vol. 15, No. 5, 2020
686 Colino et al
P=.012; ES: 1.10) were significantly higher for the former. No
other significant differences were found. However, ES values
ranged between 0.52 and 1.10 for all the variables except for
meanHR1020 (0.35), peakHR0010 (0.32), and peakHR1020
(0.39), thereby indicating that the treadmill overall imposed higher
physiological demands compared with tartan. On the other hand,
when comparing asphalt versus tartan, ES values ranged between
0.39 and 1.11 for all HR variables, reflecting the more demanding
effect of the asphalt. Regarding the treadmill versus asphalt
comparison, no differences were observed in HR variables.
Figure 2shows the percentage of total time spent on each of
the 4 HR zones. Time spent at >95% of HR
max
was significantly
greater for treadmill compared with tartan running (+12.0%;
P=.038; ES: 1.77). No other significant difference was found
for HR-based intensity zones, although ES exhibited large differ-
ences in treadmill versus asphalt comparisons for zones 3 (−10%;
P>.05; ES: 1.25) and 4 (10%; P>.05; ES: 1.36).
Figure 3shows RPE values in each time interval for the 3
surfaces. Except for the first 10 minutes on asphalt, all mean RPE
values were significantly higher in asphalt and treadmill compared
with tartan. No significant differences were identified between
treadmill and asphalt.
Figure 1 —Relationship between HR (beats per minute) and time
(minutes) during the 40-minute running trials on 3 different surfaces.
HR indicates heart rate.
Table 2 HR Values While Running on Different
Surfaces
Asphalt Treadmill Tartan
meanHR0040 173 (7) 173 (7) 169 (8)
meanHR0010 164 (7) 165 (7) 161 (8)
meanHR1020 173 (7) 172 (8) 169 (8)
meanHR2030 175 (7) 176 (8) 171 (8)
meanHR3040 178 (8) 179 (8) 174 (9)
%meanHR0040 90 (2) 90 (2) 88 (2)
%meanHR0010 86 (3) 86 (3) 84 (3)
%meanHR1020 90 (2) 90 (2) 89 (2)
%meanHR2030 92 (2) 92 (2) 90 (2)
%meanHR3040 93 (2) 93 (3)* 91 (2)
peakHR0040 181 (8) 182 (9) 177 (8)
peakHR0010 172 (7) 172 (7) 169 (8)
peakHR1020 176 (7) 176 (8) 173 (8)
peakHR2030 178 (7) 179 (8) 174 (9)
peakHR3040 181 (8) 182 (9) 177 (8)
%peakHR0040 94 (2) 95 (3)* 92 (2)
%peakHR0010 90 (2) 90 (2) 88 (2)
%peakHR1020 92 (2) 92 (2) 90 (2)
%peakHR2030 93 (1) 94 (2)* 91 (2)
%peakHR3040 94 (2) 95 (3)* 92 (2)
Abbreviation: HR, heart rate. Note: Data are mean (SD). The last 4 digits in the
variables’names indicate the beginning (first 2) and the end (last 2) of the time
interval.
*P<.05 compared with tartan.
Figure 2 —Time (% of the total) spent at the 4 different HR-based
intensity zones (zones 1, 2, 3, and 4: <75%, 75%–85%, 85%–95%, and
>95% of maximum HR). Data are mean (SD). HR indicates heart rate.
*Significantly different from tartan (P<.05).
Figure 3 —Differences in RPE (on a 6–20 Borg scale) while running on
different surfaces. Data are mean (SD). Borg10–40 or Borg
mean
: RPE value
at 10–40 minutes or mean RPE value for the test. RPE indicates rate of
perceived exertion. *Significantly different from tartan (P<.05).
IJSPP Vol. 15, No. 5, 2020
Effect of Treadmill Surface on Running Performance 687
Discussion
The main purpose of this study was to assess the isolated effect of
the treadmill surface (vs asphalt and tartan) on physiological stress
and perceived demands during endurance running, as well as to
provide for the first time data on the mechanical properties of
treadmill surfaces. Results showed a mechanical difference among
the 3 surfaces assessed in the present study, with the treadmill being
the most compliant surface (VD =6.5 mm), almost 3-fold higher
than the value for tartan (VD =2.2 mm) and both being higher than
the asphalt surface, which as expected yielded a VD value close
to 0. In accordance to their compliance, the SA ability ranged from
over 70% for the treadmill to be negligible in the asphalt, while the
ER evolved in the opposite direction. Further studies should clarify
whether this is a generalizable assumption or an isolated case due to
the model used in this study.
Besides the differences in surface properties, our results also
showed differences in physiological and perceived demands of
running between the 3 running conditions. Treadmill seems to be
the most demanding surface for runners once air resistance and
other environmental constraints are controlled for. When compared
with the tartan track, the significant differences and medium-to-
large ES in HR and RPE variables we found indicate that physio-
logical and perceived demands of running were overall higher on
the treadmill. On the other hand, when compared with the asphalt,
the results of time spent at each HR zone showed that the intensity
during the treadmill run also tended to be higher, although differ-
ences did not exhibit statistical significance. Regarding the asphalt
versus tartan comparison, statistical significance in RPE and small-
to-large ES values in HR suggest that trials performed on the tartan
required lower physiological stress and perceived effort compared
with asphalt running. Our results contradict the common assump-
tion that the more compliant a surface is (eg, treadmill), the more
energy will return to the athlete during the stance phase thereby
reducing the metabolic cost of running.
3,27
Regarding the asphalt
versus tartan comparison, our results agree with those of previous
studies reporting that the greater cushioning ability of the tartan and
its elastic behavior result in a spring effect, which allows for this
surface to store energy at initial contact and return it to the runner at
toe off, thus reducing the cost of running.
28
However, regarding the
treadmill, the effect of the moving belt was theoretically expected
to save energy.
29
As physiological and perceived demands remain
unaffected or somewhat penalized once other environmental con-
straints are controlled for, it appears that the mechanical properties
of this surface compromise performance, overcoming the energy
saving provided by the moving belt.
McMahon and Greene
2
reported that running performance is
severely compromised when the spring stiffness of the surface is
lower than the stiffness of the runner’s leg and musculature. Thus,
highly compliant surfaces with very low spring stiffness, such as
foams or dry beach sand, have proven to cause a reduction in the
elastic energy recovery and thus to compromise running efficiency
and performance.
30
Further, Baroud et al
1
reported that the energy
returned from a sport surface to an athlete can only be effective
when returned at the right location, time, and frequency. Thus, in
running or sprinting, energy should be returned to the forefoot
during the second half of ground contact phase with at least a
frequency that corresponds to the length of the ground contact time.
Otherwise, a reduction in elastic energy recovery and of general
muscle-tendon efficiency would occur,
14
thereby increasing the
energy cost of running and compromising performance. According
to our results, this seems to be also the case for treadmills. This
hypothesis is partially supported by Sassi et al
14
research, one of the
very few reporting the SA and VD of running surfaces. When
comparing natural grass, artificial turf, and asphalt, they reported
that the cost of running on both natural grass and artificial turf was
∼5% higher than on asphalt. As SA and VD values for the 2 grass
surfaces were similar and both significantly higher than for asphalt,
their results confirm that the low spring stiffness of the surface can
increase the cost of running despite its more compliant behavior.
However, on surfaces of intermediate spring stiffness such as
tartan, a slight performance enhancement would occur in compari-
son with running on a hard surface, as the elastic energy return
provided by the tartan would assist the runner by assuming some of
the cost necessary to operate the leg spring, giving them back part
of the potential energy lost in each drop as they propel away from
the surface and reducing the amount of mechanical work
required.
27
Our results are supported by those of DiMichele et al,
11
who did
not find differences in physiological variables when comparing
treadmill and natural grass running at different speeds, despite the
fact that natural grasshas been reported to increase the energy cost of
running compared with asphalt,
14
and that the lack of air resistance
and the assistance of the belt would have expected to reduce
physiological stress during treadmill running. This suggests that
the mechanical properties of the treadmill surface might increase the
physiological effort needed for running regardless of running speed,
and it challenges the assumption that differences in energetic cost of
running between indoor treadmill and outdoor asphalt are not
affected by differences in the elastic properties of the surface.
26
Practical Applications
The present study describes for the first time the SA, VD, and ER of
a treadmill surface and provides a novel interpretation of the effect
of these variables on the physiological and perceived demands of
endurance running. Our results show that the treadmill surface does
not reproduce faithfully the mechanical properties of some outdoor
surfaces (asphalt and tartan) that are widely used for running.
Conclusions
The considerably more compliant behavior and higher SA ability of
the treadmill lead to a reduction in the amount of energy returned to
the athlete, which in turn compromises running efficiency and
increases physiological stress and RPE during endurance running.
Mechanical properties of treadmill surfaces have previously been
received little attention, and questions on energy losses and injury
risk related to this type of surface have rarely been studied.
Although our study provides a new insight into the behavior of
treadmill surfaces, further research is needed to fully characterize
their mechanical properties, the extent to which they might depend
on different models, operating hours or construction of the tread-
mill, and the influence that they might have on running perfor-
mance and injury risk.
Acknowledgments
The work of E.C. was funded by a postgraduate scholarship from the
Spanish Ministry of Education, Culture, and Sport for the development of
his PhD (grant number: FPU15/04700). J.G.-U. acknowledges the finan-
cial support from Fondo Europeo de Desarrollo Regional, Programa
Operativo de la Regio´n de Castilla-La Mancha (2018/11744).
IJSPP Vol. 15, No. 5, 2020
688 Colino et al
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IJSPP Vol. 15, No. 5, 2020
Effect of Treadmill Surface on Running Performance 689
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