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VALIDITY AND RELIABILITY OF GLOBAL POSITIONING
SYSTEM UNITS (STATSPORTS VIPER)FOR
MEASURING DISTANCE AND PEAK SPEED IN SPORTS
MARCO BEATO,GAVIN DEVEREUX,AND ADAM STIFF
School of Science, Technology and Engineering, University of Suffolk, Ipswich, United Kingdom
ABSTRACT
Beato, M, Devereux, G, and Stiff, A. Validity and reliability of
global positioning system units (STATSports Viper) for mea-
suring distance and peak speed in sports. J Strength Cond
Res XX(X): 000–000, 2018—Previous evidence has proven
that large variability exists in the accuracy of different brands
of global positioning systems (GPS). Therefore, any GPS
model should be validated independently, and the results of
a specific brand cannot be extended to others. The aim of this
study is to assess the validity and reliability of GPS units
(STATSports Viper) for measuring distance and peak speed
in sports. Twenty participants were enrolled (age 21 62 years
[range 18 to 24 years], body mass 73 65 kg, and height 1.78
60.04 m). Global positioning system validity was evaluated by
comparing the instantaneous values of speed (peak speed)
determined by GPS (10 Hz, Viper Units; STATSports, Newry,
Ireland) with those determined by a radar gun during a 20-m
sprint. Data were analyzed using the Stalker (34.7 GHz, USA)
ATS Version 5.0.3.0 software as gold standard. Distance re-
corded by GPS was also compared with a known circuit dis-
tance (400-m running, 128.5-m sports-specific circuit, and 20-
m linear running). The distance bias in the 400-m trial, 128.5-m
circuit, and 20-m trial was 1.99 61.81%, 2.7 61.2%, and
1.26 61.04%, respectively. Peak speed measured by the
GPS was 26.3 62.4 km$h
21
, and criterion was 26.1 62.6
km$h
21
, with a bias of 1.80 61.93%. The major finding of this
study was that GPS did not underestimate the criterion dis-
tance during a 400-m trial, 128.5-m circuit, and 20-m trial, as
well as peak speed. Small errors (,5%, good) were found for
peak speed and distances. This study supported the validity
and reliability of this GPS model.
KEY WORDS training, circuit, team sports, velocity
INTRODUCTION
Team sports are characterized by an intermittent
model where aerobic and anaerobic components
are highly taxed (7,18,25). Athletes generally per-
form specific actions during official matches and
training sessions including high-speed running and accelera-
tions (35,40). It is well known that the correct evaluation of
external load parameters is crucial for sports scientists
(13,29,34). This information has a critical impact on daily
basis decisions and periodization (24). Global positioning sys-
tems (GPS) are instrumentations used to quantify the external
load parameters in team sports (6,10,16). Global positioning
systems have a better time efficiency and greater practicality
(e.g., allows for real-time feedback and less operator work)
compared with video-tracking systems during training ses-
sions, and for such reasons, GPS represent the most common
technology for players’ external load evaluation (4,12,17).
Global positioning systems are used especially during training
sessions to collect and analyze kinematic data such as total
distance covered, accelerations, and sprints, as well as distance
at high intensity (17,36,37). Across sports, high-intensity speed
running is associated with different speed bandings; therefore,
a univocal speed threshold does not exist (7,13).
Global positioning system accuracy, validity, and reliability
have been commonly investigated in sports (5,16,27,32). The
measures of validity explain the difference between the values
recorded by GPS and the criterion measures, whereas reliabil-
ity refers to the reproducibility of values of a test on repeat
occasions (8,17,28). Several studies underlined that a higher
sampling rate (10–15 Hz) provides a more valid and reliable
measure of the athlete’s movement demands compared with
less sophisticated devices (1–5 Hz) (32). Despite such im-
provements, the validity and reliability of the most recent
units decrease when tested in small-distance tracks (sports-
specific circuits), high-intensity change of directions (e.g.,
short shuttle runs), and during high-speed movements (e.g.,
peak speed) (4,26,27,32). Previous evidence has also proved
that large variability exists in the accuracy of different GPS
brands, as well as variability observed between GPS units of
the same model (16,27). Therefore, any GPS model should be
validated independently, and the results of a specific brand
cannot be extended to others (1).
Address correspondence to Marco Beato, M.Beato@uos.ac.uk.
00(00)/1–7
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STATSports Viper units are devices widely used at the
national and international level (e.g., Premier league, Italian
Serie A, etc.). Up to now, only one study has evaluated the
validity of these GPS models (Viper Units; STATSports) (4)
and has found an average error of 0.31 60.55 m compared
with the criterion measure during a 10-m short shuttle runs
(distance bias = 2.53%). Moreover, GPS average speed was
different compared with video analysis (25 Hz) during short
shuttle runs at different speed, with an average error that
decreases as the distance increases (from 8.7 to 3.5% at
5 m and 20 m, respectively) (4). However, this study presents
some limitations because of the lack of a gold standard cri-
terion instrument to evaluate peak speed, and distance was
not evaluated during a sport-specific circuit but only during
linear short shuttle runs (16). Moreover, no information
about STATSsports reliability is reported in this study.
Therefore, it is not possible to consider such information
and the research on this device as exhaustive.
The validation process is a critical step for the application of
this technology in sports and in research studies. Sports
scientists and coaches need to know the limitation of such
GPS model to better lead and organize their practice. Such
information is paramount because sports scientists can use GPS
data to manage player training load, recovery, and subsequent
training sessions (3,19). It is also fundamental to understand the
validity and reliability of such GPS units to better compare the
metrics during training sessions and among the players. Such
interpretation and decisions can only be made when the reli-
ability and validity of a GPS technology are well known. STAT-
Sports Viper unit technology is largely used in professional
sports (e.g., Premier league and Italian Serie A), as well as for
research purposes; therefore, its validation can have critical
implications for sports scientists and researchers. Therefore,
the main purpose of this study is to assess the validity and
reliability of STATSports Viper units by evaluating distance
and peak speed during sports-specific activities.
METHODS
Experimental Protocol and Data Analysis
The current observational study was designed to examine
the validity and reliability of GPS units (STATSports Viper)
for measuring distance and peak speed in sports. The
validation process of this technology is crucial for its
scientific acknowledgment and credibility.
Subjects
Twenty students (age 21 62 years [age range 18 to 24
years], body mass 73 65 kg, and height 1.78 60.04 m,
Figure 1. A) 400-m athletic track. B) Specific team sports circuit of 128.5 m. C) 20-m sprint.
Validity and Reliability of Global Positioning Systems
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all mean 6SD) were considered in this study (data recorded
during 2017). The experimental protocol was in accordance
with the Declaration of Helsinki for the study on human
subjects. The institutional ethics board of the University of
Suffolk approved the experimental protocol. Signed
informed consent documents were obtained for all subjects.
Procedures
Global positioning system data collection was performed on
an athletic track clear of large buildings to enhance satellite
reception (38). Global positioning system validity was eval-
uated by comparing the instan-
taneous values of speed (peak
speed) determined with these
devices and with those deter-
mined by a radar gun (Stalker
ATS 2, 34.7 GHz, Dallas,
Texas, USA) during a 20-m
sprint. Data were analyzed
using the Stalker ATS Version
5.0.3.0 software. ATS II radar
uses high-frequency radio
waves and measures the
change in the frequency after
it bounces off a moving object
(Doppler radar). Radar gun
and laser devices are consid-
ered a gold standard instru-
ment for evaluating peak
speed (17,32,36). Stalker ATS
validity and reliability have
been previously reported (21).
GPS accuracy for recording distance was evaluated using
the criterion distance of a 400-m athletic track, as well as
using a specific team sports circuit of 128.5 m that replicated
the movement demands of team sports (performed on syn-
thetic surface) and during a 20-m linear running (24). The
validation of this circuit was reported in previous studies
(9,16). The researchers explained to all subjects to remain
in a standing position for 30 seconds, after their signal to
start the trial. All subjects returned exactly to the starting
point where they waited for another 30 seconds in a standing
position. The start time for each trial was determined by the
Figure 2. STATSports Viper 10 Hz.
Figure 3. A) STATSports Viper unit outside the harness. B) STATSports Viper unit inside the harness.
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increase above zero on the velocity trace. Subjects completed
two 400-m trials at a self-selected speed (jogging pace), 128.5-
m trials, 20-m linear running (jogging pace), and a 20-m sprint
at maximum speed (Figure 1). Each subject was verbally in-
structed during each trial to perform the correct procedure.
Every player performed a familiarization trial (week 1) before
the beginning of the experimental period (week 2). In 400-m
trial, 128.5-m circuits, 20-m trial, and 20-m sprint were per-
formed by the participant of this study (validity evaluation,
week 2), and each trial was repeated with the same procedure
(test-retest) a week later (reliability evaluation, week 3). Each
session was performed in similar weather conditions (e.g., no
rain or clouds). Validity and reliability procedures adopted in
this study were previously used in literature and are considered
appropriate to simulate movement patterns of sports in a stan-
dardized manner (24).
The GPS units were turned on about 10–15 minutes
before the beginning of the test while the subjects were
familiarized with the equipment, as well as the protocol
procedures (Figure 2). During the experiments, a GPS unit
(10 Hz, Viper Units; STATSports) was placed on the back of
the subjects by means of a harness at the level of the chest
(Figure 3). Global positioning system Viper has the following
characteristic: dimension 33 mm (wide) 388 mm (high),
body mass 48 g, 10-Hz GPS, 100-Hz gyroscope, 100-Hz
triaxial accelerometer, and 100-Hz magnetometer. The same
GPS unit was used for all participants to avoid interunit
variability (a possible confounding factor). Global position-
ing system data (speed and distance) recorded by the GPS
were downloaded and further analyzed by the STATSport
Viper Software (firmware 2.7.1.83). The number of satellites
visualized by this unit, as well as the horizontal dilution of
position, is not reported by this GPS model, and therefore,
are not reported in this study.
Statistical Analyses
Data are presented as mean values 6SD. A Shapiro-Wilk test
was performed for the evaluation of normality (assumption)
for statistical distribution. Validity was assessed using the bias
(%) between the known distance and the GPS (absolute
error). Bias was interpreted as poor (.10%), moderate
(5–10%), or good (5%) (23). Differences between GPS speed
and criterion were reported as a mean of change with confi-
dence intervals (CIs 90%) (22). A paired ttest was used to
compare the peak speeds recorded. Statistical significance was
set at p,0.05. Effect size (ES) was interpreted by Cohen as
trivial ,0.20, small 0.20–0.59, moderate 0.60–1.19, large 1.20–
2.00, and very large .2.00 (15). Threshold values for benefit
or harmful effect were evaluated based on the smallest worth-
while change (0.2 multiplied by the between-subject SD) (23).
Hopkins’s spread sheet (validity by simple linear regression)
was used to evaluate criterion and GPS peak speed (23).
Regression analysis was used to show the relationship
between actual and measured peak speed. A correlation sys-
tem from trivial (,0.1), small (0.1–0.3), moderate (0.3–05),
large (0.5–07), very large (0.7–0.9), nearly perfect (0.9), to
perfect (1.0) scores was used (23). The reliability (between
the weeks 2 and 3) was assessed using the typical error of
measurement and expressed as percentage of coefficient of
variation (CV). Statistical analysis was performed using SPSS
(Statistics 20.0) for Mac OS X Yosemite.
RESULTS
Global positioning system distance covered in the 400-m
trial, 128.5-m circuit, and 20-m trial was 395.9 610.1 m,
131.7 61.5 m, and 20.17 60.28 m, respectively, with an
absolute error of 7.9 67.2 m, 3.48 61.5 m, and 0.25 6
0.21 m, respectively. The bias in each trial was 1.99 6
1.81%, 2.7 61.2%, and 1.26 61.04%, respectively. Peak
speed measured by the GPS was 26.3 62.4 km$h
21
, and
criterion was 26.1 62.6 km$h
21
. Mean difference was 20.27
(20.48 to 20.05), p= 0.045, ES = 0.07 (trivial). The absolute
error of the GPS was 0.40 60.45 km$h
21
, and the bias was
1.80 61.93% (good). A nearly perfect correlation was found
between GPS and radar gun peak speed (r= 0.98 CI [0.96–
0.99], p,0.001) (nearly perfect). Global positioning system
reliability is reported in Table 1 as mean of change with CI
90% and CV. Test-retest parameters (distance covered in the
400-m trial, 128.5-m circuit, 20-m trial, and 20-m sprint and
peak speed) recorded in week 3 were 397.8 68.6 m, 131.2 6
1.3 m, 20.31 60.5 m, and 26.1 62.2 km$h
21
, respectively.
Smallest worthwhile change of the within parameters
TABLE 1. Reliability data recorded during 400-m trial, 128.5-m circuit, 20-m trial, and 20-m sprint (20 participants).*
Variables
Mean of change
(CI 90%)
Typical error as
CV (%)
Test-retest
p-level ES (Qualitative)
400-m distance (m) 1.91 (21.52 to 5.34) 1.6 (1.3–2.3) 0.348 0.20 (small)
128.5-m distance (m) 20.57 (21.18 to 0.04) 0.8 (0.7–1.2) 0.122 0.41 (small)
20-m distance (m) 0.14 (20.08 to 0.36) 0.4 (0.3–0.5) 0.274 0.34 (small)
20-m peak speed (km$h
21
) 0.24 (20.12 to 0.60) 0.7 (0.5–0.9) 0.256 0.09 (trivial)
*CI = confidence interval, CV = coefficient of variation, ES = effect size.
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(test-retest of distance covered in the 400-m trial, 128.5-m
circuit, 20-m trial, and peak speed) was 2.1, 0.3, 0.04 m, and
0.44 km$h
21
, respectively.
DISCUSSION
Global positioning system is a technology commonly used
to evaluate external load parameters (e.g., total distance,
peak speed, etc.) in sports (1,2,7,10,13,30); therefore, the val-
idation process of this technology is crucial for scientific
acknowledgment and credibility. Sports scientists and
coaches need to know the limitation of such GPS model
to better use and interpret the data recorded. The aim of
this study was to assess the validity and reliability of STAT-
Sports Viper units by evaluating distance and peak speed
during sports-specific activities. The major findings of this
study were that GPS STATSports showed small bias (,5%,
good) for peak speed (20 m) and distance (400-m linear
running, 128.5-m circuit, and 10-m linear running); therefore,
data reported in this study supported the validity of these
GPS units. Moreover, this study reported high levels of reli-
ability (CV), and a small mean of change (test-retest) in
every variable (Table 1).
Literature shows that high-intensity activities and sports-
specific movements (e.g., short sprints) are associated with
a low level of GPS accuracy (10,11,33). However, this study
did not find these limitations in the parameters analyzed.
Scientific literature has revealed that sampling rate is a param-
eter closely associated with validity and reliability (17). Cur-
rent GPS have a higher sampling frequency than previous
GPS models (10 Hz and 5-1 Hz, respectively) on the market;
therefore, new GPS could report higher accuracy than pre-
vious models (4,14,24). The data recorded in the current study
can be compared with only one study that analyzed the same
GPS model used in this research (4). It was previously re-
ported that Viper units underestimated speed and distance
(20 m) with a bias of 3.5 and 2.53%, respectively. The results
of the current study showed a lower bias in both the evalua-
tions that was equivalent to 1.80% (sprint 20 m) for peak
speed and 1.99, 2.7, and 1.26%, for distance evaluated using
a 400-m circuit (linear running), 128.5-m circuit (sports-
specific running), and 20-m linear running, respectively. The
discrepancies between these 2 studies could be explained by
considering the activity performed by the athletes (different
circuits were used in the current study). In the previous study,
subjects performed shuttle runs (with a 1808change of direc-
tion) on an athletic track at 3 different velocities: slow (2.2
m$s
21
), moderate (3.2 m$s
21
), and high (3.6 m$s
21
) over the
following distances: 5, 10, 15, and 20 m. Moreover, the main
limitation of the previous study was associated with the cri-
terion value considered that was not a gold standard (video
analysis) (4). Both the studies showed that GPS STATSports
units have a good level of accuracy (bias: ,5%, good) in the
measurement of distance and speed.
Ten-hertz Viper units used in this study showed low errors
in total distance for circuit laps and peak speed. These results
are supported by previous publications that showed general
advantages of current 10-Hz technology (e.g., greater
accuracy and reliability) compared with the previous 1–5
Hz units (16,24,30). In several previous studies, sprint speed
was evaluated indirectly (e.g., correlation between time gates
and average speed); thus, the peak speeds were not directly
measured with a criterion measurement (32). Contrariwise,
this study presented a direct comparison with a gold stan-
dard criterion (for the first time for STATSports). The rela-
tionship (r= 0.98, nearly perfect) between radar gun peak
speed and GPS peak speed during 20-m sprint provided
evidences to support the utilization of such GPS to assess
sprint performance in team sports (31). However, sports
scientists should be conscious that a statistical difference also
exists between peak speed assessed using GPS and radar gun
(mean difference = 20.27 km$h
21
,p= 0.045, ES = 0.07).
This new evidence could offer several advantages to sports
scientists that could integrate the evaluation of athletes’ aver-
age speed using time gates with the evaluation of peak speed
using GPS. Current GPS on the market seem able to evalu-
ate peak speed with sufficient accuracy (24); therefore, sports
scientists could use such technology during athletes’
evaluations.
This study reports innovative and practical implications
regarding the reliability of the STATSports Viper units. It is
not possible to compare these data with previous studies that
evaluated the reliability of these same GPS units; however, it
is possible to compare these data with other GPS models. In
a recent study, the GPXE PRO (18 Hz) and MinimaxX S4
(10 Hz) were analyzed and reported a small bias (%) in each
parameter considered (24). It was reported a bias in distance
covered during 10-m sprinting (0.6 61.6 and 2.5 63.5%),
20-m sprinting (0.2 61.1 and 2.2 62.2%), 30-m sprinting
(0.7 60.8 and 1.2 61.3%), 129.6-m circuit (0.9 60.4 and 2.0
60.8%), and peak speed (0.6 61.1 and 1.4 61.1%), for
GPXE PRO (18 Hz) and MinimaxX S4 (10 Hz), respectively
(24). STATSports reliability data recorded in this study pres-
ent small CV for 400-m trial, 20-m trial, 128.5-m circuit, and
peak speed that are in line with the bias reported for GPXE
PRO (18 Hz), which are smaller than MinimaxX S4 (10 Hz).
The current GPS technology seems able to offer reliable data
in different conditions such as distance covered during short
and long linear activities (20-m trial and 400-m running) as
well as during a sports-specific circuit (128.5 m)
(20,24,26,32).
This study presents 4 main limitations: First, sport-specific
movements were evaluated using a circuit, and human error
should be taken into consideration (e.g., movement away
from the track). For instance, during the 400-m trial, human
error could have affected the results (395.9 610.1 m). Studies
that conduct trials with humans could present variability
between the designs; therefore, sports scientists and coaches
should consider such limitations. Future studies could repli-
cate our results to confirm the bias (%) reported in the current
study using mechanical devices moving at known distances
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and speeds. Second, a recent review reports that sport-specific
movement and peak speed could be evaluated using a VICON
motion analysis system that can offer additional information
of GPS validity (32). In this study, a radar gun was used to
evaluate the peak speed during 20-m sprint; however, this
technology is not suitable to evaluate speed during sports-
specific movements that are not linear; therefore, future stud-
ies could evaluate the GPS STATSports considering the inclu-
sion of VICON motion analysis. Many team sports allow for
the use of GPS technology during official matches; however,
literature suggests that professional teams may still be cautious
when GPS technology is used in such a context because
stadium and spectators could affect GPS precision and reli-
ability (32,39). Sports scientists should be conscious that data
reported in this study were obtained in optimal conditions
and cannot be extended to any other environment/
conditions (e.g., stadium and poor weather condition). How-
ever, future studies could evaluate the same parameters inside
a stadium to analyze their validity and reliability in such cir-
cumstances. Another limitation of this GPS technology is the
inability to report the horizontal dilution of precision; there-
fore, the findings reported in this study need to be interpreted
considering such a limitation (20,24,32). The last limitation
could be associated with the number of GPS units used in
this study that is not a representative of the cohort of units,
which generally clubs, used. Professional clubs can receive up
to 50–80 units at a time; therefore, sports scientists should be
conscious of such limitation.
PRACTICAL APPLICATIONS
The evaluation of GPS STATSports units’ validity and reli-
ability was a paramount step for its application in a sports
context and for research purposes. Considering that such
units are largely used in professional sports (e.g., Premier
league and Italian Serie A), as well as for research purposes,
this study offers innovative implications for sports scientists
and researchers. The findings reported underline that dis-
tance and speed data reported by STATSports Viper units
showed good levels of accuracy and reliability. Moreover,
coaches could use such technology to better compare the
metrics during training sessions and among the players, as
well as to manage player training load, recovery, and sub-
sequent training sessions. However, sports scientists should
be conscious that this GPS technology presents some errors
(around 1–2%); therefore, metric variations among players
and training sections should be analyzed with these errors
in mind. Future studies could be required to confirm our
results.
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