RESEARCH ARTICLE
Open Access
Comparison of vertical ground reaction forces
during overground and treadmill running.
A validation study
Bas Kluitenberg1*, Steef W Bredeweg1, Sjouke Zijlstra1, Wiebren Zijlstra2,3 and Ida Buist1
Abstract
Background: One major drawback in measuring ground-reaction forces during running is that it is time consuming
to get representative ground-reaction force (GRF) values with a traditional force platform. An instrumented force
measuring treadmill can overcome the shortcomings inherent to overground testing. The purpose of the current
study was to determine the validity of an instrumented force measuring treadmill for measuring vertical
ground-reaction force parameters during running.
Methods: Vertical ground-reaction forces of experienced runners (12 male, 12 female) were obtained during
overground and treadmill running at slow, preferred and fast self-selected running speeds. For each runner, 7 mean
vertical ground-reaction force parameters of the right leg were calculated based on five successful overground
steps and 30 seconds of treadmill running data. Intraclass correlations (ICC(3,1)) and ratio limits of agreement (RLOA)
were used for further analysis.
Results: Qualitatively, the overground and treadmill ground-reaction force curves for heelstrike runners and
non-heelstrike runners were very similar. Quantitatively, the time-related parameters and active peak showed
excellent agreement (ICCs between 0.76 and 0.95, RLOA between 5.7% and 15.5%). Impact peak showed modest
agreement (ICCs between 0.71 and 0.76, RLOA between 19.9% and 28.8%). The maximal and average loading-rate
showed modest to excellent ICCs (between 0.70 and 0.89), but RLOA were higher (between 34.3% and 45.4%).
Conclusions: The results of this study demonstrated that the treadmill is a moderate to highly valid tool for the
assessment of vertical ground-reaction forces during running for runners who showed a consistent landing strategy
during overground and treadmill running. The high stride-to-stride variance during both overground and treadmill
running demonstrates the importance of measuring sufficient steps for representative ground-reaction force values.
Therefore, an instrumented treadmill seems to be suitable for measuring representative vertical ground-reaction
forces during running.
Keywords: Running, Kinetics, Biomechanics, Validity, Overuse injuries
Background
One major drawback in measuring ground-reaction
forces during running is that it is time consuming to get
representative ground-reaction force (GRF) values with a
traditional force platform. A single force platform is only
capable of measuring GRFs of one single stance phase
per trial [1,2]. Therefore, multiple force platforms are
necessary for measuring consecutive steps which is space
consuming and expensive. The limited length of a run-
way, also makes it difficult to simulate natural running
at a constant speed in a laboratory situation [3]. For de-
tection of small differences in GRFs during running,
however, it is important to record sufficient steps during
a stable running pattern [4]. An instrumented treadmill
capable of measuring GRFs can overcome the limitations
inherent to overground GRF testing during running
at a short runway. With an instrumented treadmill
it is possible to measure GRFs of multiple steps during
* Correspondence: b.kluitenberg@umcg.nl
1Center for Sports Medicine, University Medical Center Groningen,
Hanzeplein 1, Groningen, GZ 9713, The Netherlands
Full list of author information is available at the end of the article
© 2012 Kluitenberg et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the
Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
Kluitenberg et al. BMC Musculoskeletal Disorders 2012, :
http://www.biomedcentral.com/1471-2474//
one trial without interruptions in running speed, result-
ing in a more stable running pattern during the
measurements [3].
In running, most runners make first ground contact
with the posterior part of the foot, this is called heel-
strike running. This running style results in a typical ver-
tical GRF force-time curve that is characterized by two
peaks, the impact peak and the active peak, as depicted in
Figure 1. Magnitude of the impact peak is speed depen-
dent and occurs during the first 10% of stance (10-30ms)
[5]. The active peak is reached approximately during mid-
stance and can last up to 200ms. The absence of a separ-
ate impact peak in the force-time curve is typical for a
non-heelstrike runner, as depicted in Figure 1 [6]. Besides
a vertical component, GRFs also have an anterior-
posterior and medio-lateral component. During running,
the anterior-posterior force component shows a typical
braking and propulsive phase while the medio-lateral
force component is characterized by more variability [7].
Compared to the vertical GRF component, anterior-
posterior and medio-lateral forces are small [7].
An underlying assumption when using a treadmill for
running analysis is that running on a treadmill is similar
to
overground
running.
A
comparison
of
spatio-
temporal variables during overground and treadmill
running was made in several studies. During treadmill
running, runners tend to run with a shortened stride
length and an increased stride rate [3,8,9]. Despite of
these spatio-temporal differences, only small differences
in knee flexion and a more flattened landing style during
treadmill running were observed [3,10]. An overground-
treadmill comparison with respect to GRFs was made in
only two studies [1,3]. No systematic errors or extraor-
dinary differences in vertical GRFs were found. Impact
peaks and loading rates, however, have not been studied
in these previous studies.
The purpose of this study was to determine the valid-
ity of a custom made instrumented force measuring
treadmill to measure vertical GRF parameters during
running. Validation of the treadmill was performed by
comparing overground and treadmill measured vertical
GRF parameters during running.
Methods
Participants
Twenty-four experienced runners (12 male, 12 female)
between 18 and 35 years old participated in this study.
The runners were voluntarily recruited by contacting
two local track and field clubs. The criteria for inclusion
in this study included a minimal training frequency of
two times a week for at least a period of one year. Run-
ners who reported an injury at time of measurement
were excluded. Both heelstrike and non-heelstrike run-
ners were allowed to participate in this study. All partici-
pants signed an informed consent before measurements
started. The study was approved by the Medical Ethical
Committee at the University Medical Center Groningen,
The Netherlands; M12.112668.
Overground measurements
During the overground measurements, GRFs were mea-
sured at three different individual speed conditions. Par-
ticipants were instructed to run at their preferred speed
(running speed for a normal endurance run), slower
speed (running speed during a warming-up), and a faster
speed (10km race speed) respectively. GRFs were col-
lected with a force platform (0.60m x 0.40m) which was
mounted in the middle of a 17.5m long runway. The
sample frequency of the force platform was set at
1000Hz. Running speed was monitored with two pairs of
photocells placed 2.5m before and after the force
platform.
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% Of Stance
Vertical-GRF (BW)
Fz2
Fz1
LR
tFz1
tFz2
Contact Time (CT)
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% Of Stance
Vertical-GRF (BW)
Fz2
tFz2
LR
Contact Time (CT)
Heelstrike landing
Non-Heelstrike landing
Figure 1 Outcome measures in a typical vertical ground-
reaction force (GRF) curve for a heelstrike runner and a non-
heelstrike runner. Figure is created from personal data.
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Before the actual overground measurements started,
the participants performed several accommodation runs.
During these accommodation runs, the exact start pos-
ition for the measurements was determined. The start
position was based on the position of foot placement at
the force platform. Foot strike of the right foot should
be completely at the force platform without an alteration
in running pattern. An alteration can indicate aiming for
the force platform, which modifies the GRF pattern [11].
Position of foot placement and running pattern were
evaluated on sight. When participants were able to run
several trials at the same speed, while landing with the
right foot completely placed at the force platform, with-
out visible alterations in running pattern, the actual
measurements started. Since the participants were tested
at three different speed conditions, accommodation runs
were performed for each speed condition (preferred,
slow and fast). The accommodation runs for the pre-
ferred speed were combined with a short warming-up
and took longer (approximately 10 min), where the
subsequent accommodation runs took approximately
5 minutes.
During the actual measurements, GRF data were cap-
tured until five clean strikes of the right leg within a 5%
speed range were recorded for all speed conditions.
Trials with visible alterations in running pattern were
not included in these five clean strikes. Afterwards, the
mean running speed of the five steps was calculated for
each speed condition.
Treadmill measurements
In this study, an instrumented treadmill (Entred, Force-
link, Culemborg, The Netherlands) with a running sur-
face of 1.60m by 0.60m that was driven by a 1.8 kW
motor was used to measure vertical GRFs during
running. The treadmill was equipped with three strain
gage
force
transducers
(ACB-500kg, Vishay
Revere
Transducers, Breda, The Netherlands) which were con-
nected to bridge
amplifiers. The force
transducers
were mounted on a stiff plate which was enforced with a
non-deformable frame and were positioned as shown in
Figure 2. The signals from the amplifiers were sampled
at 1000 Hz, digitized into a 16-bit signal by an AD con-
verter (PCI-6220, National Instruments, Austin, TX,
USA) and were connected to a computer.
Before the treadmill measurements started, partici-
pants started with an accommodation run of 10 minutes
at 10 km·h-1. After this accommodation period, partici-
pants were tested at three different individual speed con-
ditions (slow, preferred and fast). Treadmill speed was
matched to the average overground running speed for
each speed condition because GRF parameters are speed
dependent [7]. The three speed conditions lasted three
minutes and were offered in random order. GRFs were
recorded during the last 30 seconds of each speed condi-
tion. When treadmill measurements were finished, parti-
cipants were given the opportunity for cooling-down at
the treadmill. All measurements were conducted while
participants were running in their personal running
shoes.
Data analysis
Vertical force data from both the force platform and the
treadmill were processed using custom programs written
in MATLAB R2010a (The MathWorks, Inc, Natick,
MA). All steps which were recorded during the treadmill
measurement were entered into the analysis. A 13-point
moving average low-pass filter with a cut-off frequency
of 33.3Hz was used to filter the GRF data that was
recorded during the overground and treadmill measure-
ments. Foot strikes in the overground and treadmill data
were detected with a threshold of 30 Newton for impact
and toe-off phase. Outcome measures for all right foot
steps were identified, as described in Table 1. For each
speed condition outcome measures of each participant
were averaged. A distinction between heelstrike and
S1
S2
S3
Front
0.60m
1.60m
Figure 2 Positioning of the three strain gage force transducers
S1, S2 and S3.
Kluitenberg et al. BMC Musculoskeletal Disorders 2012, :
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non-heelstrike landing patterns was made based on the
existence of an impact peak Fz1. Peak values Fz1 and
Fz2 and the loading-rate were normalized to bodyweight.
Statistical analysis
A within-subject repeated measures design was used to
determine the validity of the instrumented treadmill for
measuring vertical GRF parameters during running.
Therefore, a two-way mixed-effects, consistency, single
measure
intraclass
correlation
coefficient
(ICC(3,1))
model was used to examine the agreement between
overground and treadmill measured GRF-parameters.
Interpretation of the intraclass coefficients were as fol-
lows: poor (0 – 0.39), modest (0.4 – 0.74), or excellent
(0.75 – 1) [12]. ICCs were calculated by using SPSS
(SPSS inc. Version 18.0, Chicago, IL, U.S.A.). Besides the
intraclass correlations, Bland-Altman plots were used to
examine the agreement between overground and tread-
mill measurements [13]. These plots were made for each
outcome measure and each speed condition. The limits
of agreement (LOA) were calculated (mean difference
+/− 1.96 times the standard deviation of the difference).
Also ratio limits of agreement (RLOA) were calculated
to
express
the
LOA
as
percentage
of
the
mean
overground-treadmill value. The upper and lower LOA
and the RLOA provide insight into how much random
variation may be influencing the measurements.
Results
Ground-reaction force (GRF) parameters of a different
landing strategy cannot be compared, therefore only
GRF parameters of participants who showed a consistent
landing strategy during overground and treadmill run-
ning within a speed condition were examined. During
overground running at preferred speed, 19 participants
showed a heelstrike (HS) landing, while 16 of these run-
ners showed a HS landing during treadmill running.
This shows that 82.4% of the runners used a similar
landing strategy during treadmill running at preferred
speed. Results for the two other speeds can be found in
Table 2.
Qualitatively,
the
overground
and
treadmill
GRF
curves for both HS and NHS running at slow, preferred
and fast running speeds, were very similar, as can be
seen in Figure 3. In Table 3 a quantitative evaluation of
the vertical GRF-parameters of both HS and NHS run-
ners can be found. The levels of agreement between
overground and treadmill running for the time related
variables (tFz1, tFz2 and CT) were excellent (ICCs be-
tween 0.76 and 0.95 and RLOAs between 5.7% and
15.5%). Also the active peak (Fz2) measured with both
devices showed excellent agreement (ICCs between 0.77
and 0.89, RLOAs between 7.8% and 9.9%). Modest
agreement was found for the impact peak, Fz1 (ICCs be-
tween 0.71 and 0.76, RLOAs between 19.9% and 28.8%).
Maximal loading rate (LR) and average loading rate
(ALR) also showed modest to excellent intraclass corre-
lations (ICCs between 0.70 and 0.89), however the ratio
limits of agreement were higher (RLOA values between
34.3% and 45.4%).
Discussion
The instrumented treadmill is capable of measuring ver-
tical ground-reaction forces (GRFs) during running and
seems to be a usable tool for simulating overground run-
ning kinetics. The results of this study demonstrated
that the instrumented treadmill is a highly valid tool for
the assessment of the vertical GRF parameters: tFz1,
tFz2, CT and Fz2 and moderately valid for the assess-
ment of Fz1, LR and ALR for runners who showed a
consistent landing strategy during overground and tread-
mill running. A qualitative evaluation of the overground
and treadmill vertical GRF curves as shown in Figure 3,
Table 1 Definition of outcome measures, as displayed in
Figure 1
Outcome measure
Description
Fz1
Local maximum in the vertical GRF data,
normalized to body weight (BW).
Fz2
Maximum value in the vertical GRF data,
normalized to BW.
LR
The steepest part of the vertical GRF curve,
from stance to impact peak. Expressed
in BW/s.
ALR
Average loading rate, the slope of the line
from 20% to 80% of Fz1. Expressed in BW/s.
tFz1
Time from heelstrike to Fz1 in ms.
tFz2
Time from heelstrike to Fz2 in ms.
CT
Contact time, from heelstrike to toe-off in ms.
Outcome measures for the overground and treadmill data were identified with
the same routine. Foot strikes were detected with a threshold of 30 Newton
for both heelstrike and toe-off.
Table 2 Overground landing strategy compared to treadmill landing strategy, displayed as number of persons and
corresponding percentages of runners who showed a consistent landing strategy
Heelstrike landing
Non-heelstrike landing
Overground
Treadmill
Consistency
Overground
Treadmill
Consistency
Slow
17
14
82.4%
7
5
71.4%
Preferred
19
16
84.2%
5
5
100.0%
Fast
12
12
100.0%
12
6
50.0%
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demonstrated that the vertical GRFs for both the heel-
strike (HS) runners and the non-heelstrike (NHS) run-
ners were similar during overground and treadmill
running. The excellent intraclass correlations and low
limits of agreement for contact time (CT), time to im-
pact peak force (tFz1) and time to the active peak (tFz2)
reflect this qualitative similarity. After all, these para-
meters show that the timing of peak values in the verti-
cal GRF curve is not different for overground and
treadmill running. The qualitative similarity of these
GRF curves was also observed in other studies [1,3]. In
the current study, the overground and treadmill mea-
sured active peak (Fz2) showed no noteworthy differ-
ences. This is in accordance with the results of Riley
et al., who also compared overground and treadmill run-
ning kinetics in a group of 20 runners [3]. Overground
and treadmill measured impact peaks (Fz1), maximal
loading rates (LR) and average loading rates (ALR),
showed less consistent results with modest to excellent
intraclass correlations and wider limits of agreement. To
our knowledge this study is the first to compare
overground and treadmill measured impact peaks and
loading rates during running, therefore it is not possible
to evaluate these results with previous studies.
For an overground-treadmill comparison with respect
to vertical GRF parameters, a consistent landing strategy
during both running conditions (overground and tread-
mill) is required. While most runners showed a consist-
ent landing strategy during overground and treadmill
running, some runners switched to another landing
strategy. During slow and preferred running speed, these
inconsistent runners mostly switched from an over-
ground HS landing to a NHS landing during treadmill
running. Considering that this behavior is in line with
the more flattened landing style as observed in a previ-
ous study [14], it is likely that these inconsistencies in
landing strategy are the result of accommodation to
treadmill running. At fast self selected speed, however,
the inconsistent runners switched from a NHS to a HS
landing during treadmill running. These differences in
landing strategy may indicate overground and treadmill
differences in anterior-posterior GRFs which were not
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% of stance
Vertical-GRF (BW)
Slow running speed (N=14)      
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% of stance
Vertical-GRF (BW)
Preferred running speed (N=16)
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% of stance
Vertical-GRF (BW)
Fast running speed (N=12)
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% of stance
Vertical-GRF (BW)
Slow running speed (N=5)
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% of stance
Vertical-GRF (BW)
Preferred running speed (N=5)
0
20
40
60
80
100
0
0.5
1
1.5
2
2.5
3
% of stance
Vertical-GRF (BW)
Fast running speed (N=6)
Overground
Treadmill
Overground
Treadmill
Non-heelstrike running
Heelstrike running
Figure 3 Average GRF plots from all runners for overground (mean, solid black line; ± SD, dotted black lines) and treadmill
running (mean, solid grey line) at slow, preferred and fast running speed for heelstrike and non-heelstrike runners. Forces are in
body weight (BW).
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Table 3 Outcome measures for overground and treadmill running
OG mean ± SD
TM mean ± SD
ICC(3,1) (95%CI)
Mean diff (LOA)
diff (lowLim, upLim)
RLOA
(%)
Fz1 (BW)
HS
Slow
1.67 ± 0.26
1.70 ± 0.23
0.74 (0.37, 0.91)
0.03 (−0.32, 0.38)
20.8
Preferred
1.94 ± 0.45
1.93 ± 0.30
0.71 (0.35, 0.89)
−0.01 (−0.57, 0.55)
28.8
Fast
1.94 ± 0.25
2.06 ± 0.32
0.76 (0.35, 0.92)
0.12 ( −0.28, 0.52)
19.9
Fz2 (BW)
HS
Slow
2.54 ± 0.20
2.53 ± 0.18
0.77 (0.49, 0.91)
−0.02 (−0.27, 0.23)
9.9
Preferred
2.70 ± 0.26
2.65 ± 0.25
0.89 (0.76, 0.96)
−0.03 (−0.25, 0.17)
7.9
Fast
2.77 ± 0.24
2.70 ± 0.22
0.86 (0.67, 0.95)
−0.06 (−0.27, 0.15)
7.8
NHS
Slow
2.56 ± 0.17
2.55 ± 0.20
Preferred
2.61 ± 0.15
2.58 ± 0.13
Fast
2.79 ± 0.15
2.78 ± 0.20
LR (BW/s)
HS
Slow
81.11 ± 25.62
87.28 ± 23.39
0.76 (0.47, 0.90)
3.25 (−28.62, 35.12)
39.9
Preferred
95.34 ± 26.67
105. 33 ± 25.08
0.80 (0.57, 0.91)
6.11 (−26.21, 38.42)
34.3
Fast
104.40 ± 29.29
118.08 ± 33.73
0.70 (0.36, 0.88)
7.17 (−37.69, 52.02)
42.7
NHS
Slow
70.03 ± 14.68
65.09 ± 13.74
Preferred
77.00 ± 22.35
74.25 ± 16.47
Fast
95.81 ± 26.02
87.41 ± 18.74
ALR (BW/s)
HS
Slow
68.89 ± 20.26
73.92 ± 20.22
0.84 (0.63, 0.93)
2.98 (−24.74, 30.70)
45.3
Preferred
82.14 ± 21.38
88.70 ± 20.75
0.89 (0.74, 0.95)
3.60 (−23.01, 30.21)
36.4
Fast
90.70 ± 23.66
100.77 ± 29.10
0.86 (0.67, 0.95)
4.08 (−31.26, 39.42)
45.4
NHS
Slow
33.96 ± 6.07
31.21 ± 5.01
Preferred
47.09 ± 22.92
33.78 ± 4.20
Fast
43.63 ± 13.89
36.00 ± 4.20
tFz1 (ms)
HS
Slow
35 ± 4.08
35 ± 4.86
0.76 (0.40, 0.92)
0.0 ( −5.4, 5.4)
15.5
Preferred
34 ± 4.42
34 ± 3.35
0.82 (0.56, 0.93)
0.3 ( −4.4, 5.0)
13.8
Fast
32 ± 5.00
33 ± 4.88
0.87 (0.61, 0.96)
0.6 ( −3.7, 4.8)
13.0
tFz2 (ms)
HS
Slow
112 ± 13.55
109 ± 10.22
0.84 (0.63, 0.94)
−1.8 (−15.4, 11.8)
12.6
Preferred
102 ± 13.28
100 ± 12.19
0.94 (0.85, 0.97)
−1.6 (−10.1, 6.8)
8.5
Fast
99 ± 10.00
96 ± 11.47
0.87 (0.68, 0.95)
−3.0 (−13.5, 7.5)
11.0
NHS
Slow
102 ± 13.00
103 ± 15.00
Preferred
99 ± 12.00
98 ± 11.00
Fast
92 ± 80 0
91 ± 10.00
CT (ms)
HS
Slow
258 ± 22.00
254 ± 21.13
0.92 (0.80, 0.97)
−4.0 (−21.4, 13.4)
6.9
Preferred
232 ± 23.34
232 ± 20.49
0.92 (0.82, 0.97)
−2.0 (−17.2, 13.2)
6.6
Fast
223 ± 21.00
220 ± 21.14
0.95 (0.87, 0.98)
−3.3 (−15.6, 9.1)
5.7
NHS
Slow
240 ± 17.00
237 ± 19.00
Preferred
229 ± 12.00
222 ± 12.00
Fast
213 ± 12.00
206 ± 12.00
Intraclass correlations, mean-differences with limits of agreement (LOA), and ratio limits of agreement (RLOA) were reported. Both HS and NHS runners were taken
into account in the statistical analysis. Number of participants: HS (slow: N=14, preferred: N=16, fast: N=12), NHS (slow: N=5, preferred: N=5, fast: N=6).
HS: Heelstrike-runner, NHS: Non-Heelstrike-runner, CI: Confidence Interval, LOA: Limit of Agreement, RLOA: Ratio Limit of Agreement, OG: Overground, TM:
Treadmill, BW: Body Weight.
Slow running speed: HS runners: 11.0 ± 1.3 km·h-1, NHS runners: 10.9 ± 1.5 km·h-1.
Preferred running speed: HS runners: 12.7 ± 1.6 km·h-1, NHS runners: 11.8 ± 1.5 km·h-1.
Fast running speed: HS runners: 14.1 ± 2.0 km·h-1, NHS runners: 13.9 ± 1.9 km·h-1.
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compared in the current study. The results of this study
demonstrated that the inconsistencies in landing strategy
are smallest during running at preferred speed. There-
fore, to maximize certainty, it can be recommended to
determine landing strategy with a treadmill measure-
ment at preferred running speed.
The use of a treadmill in a research setting has been
subject of much debate. Several factors are mentioned
which may cause biomechanical differences between
overground
and
treadmill
running
[9].
First,
non-
mechanical factors as accommodation to the changed
visual and auditory surroundings or fear during treadmill
running may result in differences between overground
and treadmill running biomechanics [15]. Second, differ-
ences in air resistance may have an effect on treadmill
running form [16]. The effects of air resistance on run-
ning kinematics, however, will only be visible during
running at high speeds [17]. Third, intra-stride belt
speed variations, due to an energy exchange between the
treadmill and the runner, can cause differences in run-
ning kinematics compared to overground running. In
particular low powered treadmills are more sensitive for
opposite forces acting on the belt during running, result-
ing in larger belt speed variations. These variations in
belt speed may lead to biomechanical differences during
treadmill running when compared to overground run-
ning
[15].
Fourth,
during
running,
leg
stiffness
is
adjusted to the stiffness of the running surface [18].
Adjusting leg stiffness results in subtle changes in the
kinematics of the lower extremity [19]. Therefore, differ-
ences in running surface may lead to biomechanical dif-
ferences when comparing overground and treadmill
running.
Several studies compared overground and treadmill
running biomechanics [3,8,14]. Even though runners
tend to run with a shortened stride length and an
increased stride rate during treadmill running [3,8,9],
overground and treadmill running kinematics are re-
markably similar [3,9,14]. Only small differences in knee
and ankle joint kinematics were reported. Nigg et al.
observed a more flattened landing style during treadmill
running [14]. Riley et al. did not find differences in ankle
joint kinematics, but did find differences in minimal and
maximal knee flexion [3]. Maximal knee flexion was
lower and minimal flexion was higher during treadmill
running, which could be a result of the observed de-
crease in flight phase and higher stride rate [3]. Thus,
despite the theoretical factors which may influence
treadmill running biomechanics, only small differences
in overground and treadmill kinematics were observed.
In the current study, also no significant differences in
GRF parameters between overground and treadmill run-
ning were found. These findings are in line with previ-
ous studies where overground and treadmill running
kinetics were compared [1,3]. The between person vari-
ance in Fz1, LR and ALR during both overground and
treadmill running was high, as indicated by the high
standard deviations for these parameters. Stride-to-stride
variance for these parameters was also high, which
demonstrates the importance of measuring sufficient
steps for representative GRF values. This is especially
important for detecting small differences between differ-
ent conditions or persons [20]. Because a treadmill
makes it possible to measure multiple steps during one
test trial, it can be argued that a treadmill measurement
is more suitable for detecting small differences in verti-
cal GRFs during running. However, this assumption was
not assessed in the current study.
Since the treadmill used in the current study only is
capable of measuring vertical GRFs it cannot be used to
assess joint kinetics using the standard inverse dynamics
methodology, because anterior-posterior and medio-
lateral GRFs are also needed for these calculations. It
should also be noted that the inconsistencies in landing
strategy may indicate differences in anterior-posterior
GRFs between overground and treadmill running. Fur-
thermore, this instrumented treadmill would have lim-
ited usefulness for walking studies, because the double
support phase in walking cannot be measured directly.
For measuring GRFs during walking, an instrumented
split-belt treadmill may be more convenient.
A limitation of this study was that participants first
performed the overground measurements after which
the treadmill measurements started. Due to this fixed
order of the measurements, fatigue may have influenced
the later treadmill measurements [21]. Nevertheless, this
influence is expected to be low, since all participants
were experienced runners who did not have to deliver a
maximal performance and participants did not show
signs of exaggerated fatigue during the measurements.
Conclusions
The results of this study demonstrated the treadmill is a
moderate to highly valid tool for the assessment of verti-
cal GRFs during running for runners who showed a con-
sistent landing strategy during overground and treadmill
running. Therefore, an instrumented treadmill can be
used to measure vertical GRF parameters which corres-
pond to normal overground values during running.
In a future study, the treadmill can be used to measure
vertical GRF parameters in a large group of runners, for
instance to identify possible kinetic risk-factors for run-
ning related injuries prospectively.
Abbreviations
GRF: Ground-reaction force; HS: Heelstrike; NHS: Non-heelstrike; Fz1: Impact
peak; Fz2: Active peak; LR: Loading Rate; ALR: Average Loading Rate;
CT: Contact Time; tFz1: Time to impact peak; tFz2: Time to active peak;
Kluitenberg et al. BMC Musculoskeletal Disorders 2012, :
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BW: Body Weight; ICC: Intraclass correlation; LOA: Limit of Agreement;
RLOA: Ratio Limit of Agreement.
Competing interests
In this study, an instrumented treadmill was used. The research group had
no financial or other interest in the treadmill product or distributor of the
treadmill. The project was not dependent on external financial assistance
and the authors declare that they have no competing interests.
Authors’ contributions
SB, SZ, WZ and IB provided advice on the study design. BK recruited the
participants, was responsible for the data acquisition/analysis and wrote the
article. WZ provided advice on the data analysis. SB, SZ, WZ and IB
contributed to the content of the article. All authors read and approved the
final manuscript.
Author details
1Center for Sports Medicine, University Medical Center Groningen,
Hanzeplein 1, Groningen, GZ 9713, The Netherlands. 2Center for Human
Movement Sciences, University Medical Center Groningen, P.O. Box 196,
Groningen, AD 9700, The Netherlands. 3Institute of Movement and Sport
Gerontology, German Sport University Cologne, Cologne, Germany.
Received: 22 May 2012 Accepted: 1 November 2012
Published: 27 November 2012
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doi:10.1186/1471-2474-13-235
Cite this article as: Kluitenberg et al.: Comparison of vertical ground
reaction forces during overground and treadmill running. A validation
study. BMC Musculoskeletal Disorders 2012 :.
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Comparison of vertical ground reaction forces during overground and treadmill running. A validation study.
Kluitenberg, Bas,Bredeweg, Steef W,Zijlstra, Sjouke,Zijlstra, Wiebren,Buist, Ida