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Original Research
Reliability and Concurrent Validity of Seven
Commercially Available Devices for the
Assessment of Movement Velocity at Different
Intensities During the Bench Press
Alejandro P´erez-Castilla,
1
Antonio Piepoli,
2
Gabriel Delgado-Garc´
ıa,
1
Gabriel Garrido-Blanca,
2
and
Amador Garc´
ıa-Ramos
1,3
1
Department of Physical Education and Sport, Faculty of Sport Sciences, University of Granada, Granada, Spain;
2
Department of
Health Sciences, Faculty of Health Sciences, University of Jaen, Jaen, Spain; and
3
Department of Sports Sciences and Physical
Conditioning, Faculty of Education, CIEDE, Catholic University of the Most Holy Concepci ´on, Concepci ´on, Chile
Abstract
P´erez-Castilla, A, Piepoli, A, Delgado-Garc´
ıa, G, Garrido-Blanca, G, and Garc´
ıa-Ramos, A. Reliability and concurrent validity of
seven commercially available devices for the assessment of movement velocity at different intensities during the bench press. J
Strength Cond Res XX(X): 000–000, 2019—The aim of this study was to compare the reliability and validity of 7 commercially
available devices to measure movement velocity during the bench press exercise. Fourteen men completed 2 testing sessions.
One-repetition maximum (1RM) in the bench press exercise was determined in the first session. The second testing session
consisted of performing 3 repetitions against 5 loads (45, 55, 65, 75, and 85% of 1RM). The mean velocity was simultaneously
measured using an optical motion sensing system (Trio-OptiTrack; “gold-standard”) and 7 commercially available devices: 1 linear
velocity transducer (T-Force), 2 linear position transducers (Chronojump and Speed4Lift), 1 camera-based optoelectronic system
(Velowin), 1 smartphone application (PowerLift), and 2 inertial measurement units (IMUs) (PUSH band and Beast sensor). The
devices were ranked from the most to the least reliable as follows: (a) Speed4Lift (coefficient of variation [CV] 52.61%); (b) Velowin
(CV 53.99%), PowerLift (3.97%), Trio-OptiTrack (CV 54.04%), T-Force (CV 54.35%), and Chronojump (CV 54.53%); (c) PUSH
band (CV 59.34%); and (d) Beast sensor (CV 535.0%). A practically perfect association between the Trio-OptiTrack system and
the different devices was observed (Pearson’s product-moment correlation coefficient (r) range 50.947–0.995; p,0.001) with the
only exception of the Beast sensor (r50.765; p,0.001). These results suggest that linear velocity/position transducers, camera-
based optoelectronic systems, and the smartphone application could be used to obtain accurate velocity measurements for
restricted linear movements, whereas the IMUs used in this study were less reliable and valid.
Key Words: linear position transducer, linear velocity transducer, smartphone application, inertial measurement units, velocity-
based training, testing
Introduction
Velocity-based resistance training has gained in popularity over
recent years because of the proliferation of different commercially
available devices (e.g., linear position transducers, inertial mea-
surement units [IMUs], smartphone applications, etc.) that are
supposed to accurately measure movement velocity (3,5). It has
been proposed that the monitoring of barbell velocity could be an
appropriate alternative to prescribe the training load as compared
to the traditional approach that requires the determination of the
1 repetition maximum (1RM) (17,32). The use of movement
velocity to prescribe the training load is justified by the strong and
linear relationship that has been reported for multiple exercises
between movement velocity and the %1RM (13,26,31). In this
regard, instead of determining the 1RM through a single maximal
lift or by a set of repetitions to failure, the load can be prescribed
to match the desired velocity (17,34). Despite the encouraging
applications of velocity-based resistance training (6), little
research is available comparing the reliability and validity of
different commercially available devices used in training and re-
search to monitor movement velocity.
From a scientific standpoint, the three-dimensional (3D) mo-
tion capture has been recognized as the “gold-standard”in-
strument to measure movement velocity (22,36). However,
because this technology is not practical or affordable for strength
and conditioning professionals, other devices are typically used in
practice when implementing the velocity-based resistance training
approach. The linear position transducer has been the most used
device in scientific research (2,5,10,14). The linear position
transducer consists of an isoinertial dynamometer with a cable
that is typically attached to the barbell, and it derives velocity
from the recorded displacement-time data using the inverse dy-
namic approach (18). More recently, a linear velocity transducer
named “T-Force”(T-Force system; Ergotech, Murcia, Spain) has
been made commercially available, which directly provides ve-
locity measurements through the recording of electrical signals
that are proportional to the cable’s extension velocity (33). It is
reasonable to speculate that the linear velocity transducer could
be more precise than linear position transducers because it is
Address correspondence to Amador Garc ´
ıa-Ramos, amagr@ugr.es.
Journal of Strength and Conditioning Research 00(00)/1–8
ª2019 National Strength and Conditioning Association
1
Copyright © 2019 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
known that the successive manipulation of raw data increases
measurement errors (25,30). However, it remains unexplored
whether the reliability of velocity outputs significantly differs
between linear position and linear velocity transducers, as well as
their concurrent validity with respect to the “gold-standard”3D
motion capture.
It should be acknowledged that linear position/velocity trans-
ducers are not always practical or affordable. The need to attach
the cable to the barbell restricts exercise selection to the ones
predominantly performed in a vertical direction (5). Another
common drawback of linear position/velocity transducers is their
high price (2,000 US dollars), which may limit their use to
laboratory-based or professional sport settings (7,23,24). How-
ever, it should be noted that a new linear position transducer
named “Speed4Lift”(Speed4Lift
AU1 ; Madrid, Spain) has appeared
on the market with a considerably lower price (340 US dollars),
although there are no available data regarding its reliability and
validity. As an alternative to linear position/velocity transducers,
wearable technologies are increasingly gaining popularity in the
field of strength training and conditioning (3,5,12,28).
One of the wearable devices that have recently appeared on the
market is named “Velowin”(Velowin; DeporTeC, Murcia,
Spain). Velowin is a camera-based optoelectronic system
designed to measure movement velocity by the tracking of an
infrared reflective marker placed in the barbell. A high reliability
and concurrent validity of the Velowin to measure movement
velocity has been reported during the free-weight back squat ex-
ercise (12,21). The main advantage of Velowin as compared to
linear position/velocity transducers is that it does not require to be
attached to the barbell through a cable and, therefore, this would
eliminate the risk of cable rupture (21). However, the Velowin
cost (625 US dollars) and limited portability (e.g., a PC software
is needed) could limit its use for many strength and conditioning
professionals. Many practitioners can only afford more practical
devices such as smartphone applications or IMUs (2,28).
A smartphone application named “PowerLift”has been
designed to monitor movement velocity by the manual inspection
of a slow motion video recording by the smartphone high-speed
camera (4). The high reliability and validity of PowerLift to
monitor mean velocity has been confirmed in exercises such as the
bench press, full-squat, and hip-thrust (3,4). However, the main
limitation of PowerLift is that it does not provide real-time ve-
locity feedback because coaches are required to indicate manually
the start and end of the concentric phase. The PUSH band (PUSH
band, PUSH, Inc., Toronto, Canada) and Beast sensor (Beast
sensor, Beast Technologies Srl., Brescia, Italy), which are com-
posed by the combination of 3-axis accelerometers and 3-axis
gyroscopes, are 2 of the IMUs most commonly used in research
and practice (3,5). An advantage of IMUs is that they are able to
account for the anteroposterior displacement that is frequent
during free-weight exercises (28), whereas linear position/velocity
transducer cannot distinguish the direction of the cable dis-
placement. However, owing to the discrepancies found between
the studies that have evaluated the validity of the PUSH band
(3,5,36) and owing to the scarce number of studies that have
examined the reliability and validity of the Beast sensor (3), more
research is needed to explore the feasibility of both IMU devices.
To address the existing gaps in the literature, this study was
designed to provide a comprehensive analysis of different devices
(i.e., linear velocity transducer, linear position transducers,
camera-based optoelectronic system, smartphone application,
and IMUs) that are being used in practice for the measurement of
movement velocity during resistance training. Specifically, the
objective of this study was to compare the reliability and validity
of 7 commercially available devices to measure movement ve-
locity during the bench press exercise. We hypothesized that the
devices would be ranked from the most to the least reliable and
valid as follows: (a) linear velocity transducer; (b) linear position
transducers; (c) camera-based optoelectronic device; (d) smart-
phone application; and (e) IMUs. The results of this study should
provide practical information for strength and conditioning
coaches regarding the reliability and concurrent validity of dif-
ferent devices that can be used in practice for the assessment of
movement velocity.
Methods
Experimental Approach AU2to the Problem
This study was designed to explore the reliability and concurrent
validity of 7 commercially available devices for the measurement
of movement velocity. Subjects completed 2 testing sessions sep-
arated by 48–72 hours. The 1RM in the bench press exercise was
determined in the first testing session. The second testing session
consisted of performing 3 repetitions against 5 different loads (45,
55, 65, 75, and 85% of 1RM). The mean velocity of the barbell
was measured using an optical motion sensing system (V120:
Trio, OptiTrack; NaturalPoint, Inc. AU3, USA) that was considered
the gold standard in this study (27,38). In addition, the mean
velocity was also measured by 7 commercially available devices: 1
linear velocity transducer (T-Force system, Ergotech), 2 linear
position transducers (Chronojump; Boscosystem, Barcelona,
Spain; and Speed4Lift), 1 camera-based optoelectronic system
(Velowin, DeporTeC), 1 smartphone application (PowerLift),
and 2 IMUs (PUSH band; PUSH, Inc., and Beast sensor; Beast
Technologies Srl.). The 2 repetitions with higher mean velocity
recorded by the Trio-OptiTrack at each load were used for cal-
culating intrasession reliability (3,21), whereas only the repetition
with the highest mean velocity recorded at each load by the Trio-
OptiTrack was used for validity analyses.
Subjects
Fourteen physically AU4active men (age: 22.9 61.6 years; body
height: 1.76 60.06 m; body mass: 76.9 67.8 kg; bench AU5press
1RM: 86.1 611.9 kg) volunteered to participate in this study.
Subjects were recruited from a fitness center, and all of them AU6were
familiarized with the bench press exercise before the beginning of
the study. None of them suffered from physical limitations, health
problems, or musculoskeletal injuries that could compromise
tested performance. Subjects were instructed to avoid any stren-
uous exercise 2 days before each testing session. They were in-
formed of the study procedures and signed a written informed
consent form before initiating the study. The study protocol ad-
hered to the tenets of the Declaration of Helsinki and was ap-
proved by the institutional review board.
Testing Procedures AU7.The first testing session was used for an-
thropometric measures and to determine the 1RM during the
concentric-only bench press exercise following an incremental
loading test (11). The standardized warm-up consisted of jogging,
self-selected dynamic stretching and joint mobilization exercises,
and 1 set of 5 repetitions performed against external load of 17 kg
(mass of the unloaded Smith machine barbell) during the bench
press exercise. Thereafter, the external load was incremented
from 10 AU8to 1 kg until the 1RM load was reached. The average
Feasibility of Seven Devices to Measure Velocity (2019) 00:00
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Copyright © 2019 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
number of loads tested was 8.9 61.3. The interset rest was set to 4
minutes, and 1–2 repetitions were performed with each load.
The second testing session beganwiththesamewarm-up
described for session 1. Afterward, subjects performed the
concentric-only bench press exercise against 5 relative loads
(45, 55, 65, 75, and 85% of 1RM) that were implemented in an
incremental order. Lower loads (i.e., ,45%of1RM)werenot
tested because they are generally not used in training with the
bench press exercise, whereas higher loads (i.e., .85% of
1RM) were excluded to avoid high fatigue that could com-
promise reliability analyses. Three repetitions were executed
with each load. Interrepetition rest was set to 15 seconds, and
interset rest was fixed to 4 minutes. The barbell was held by the
safety stops of the Smith machine during the recovery periods.
Subjects were encouraged to lift the barbell at the maximum
possible velocity.
The standard 5-point body contact position technique (head,
upper back, and buttocks firmly on the bench with both feet flat
on the floor) was followed in the 2 testing sessions. Subjects self-
selected the grip width, which was measured and kept constant on
every lift. The barbell was held by the safety stops of the Smith
machine 1–2 cm above the subjects’chest at the level of the
sternum. From that position, subjects were instructed to perform
a concentric-only movement as fast as possible until their elbows
reached full extension. Two spotters were responsible for low-
ering the barbell after each repetition.
Measurement Equipment and Data Acquisition. The measure-
ment devices were not synchronized, and they separately collected
the mean velocity of the same repetitions (
½F1Figure 1). The specific
characteristics of each device are provided below:
Trio-OptiTrack. Trio-OptiTrack (V120:Trio; OptiTrack, Natu-
ralPoint, Inc.) is an optical motion sensing system, which included
3 infrared and precalibrated cameras fixed on a rectangular frame
that gives 3D position data of a reflective marker at a sampling
rate of 120 Hz. Raw data of marker position in space were ac-
quired using the software Motive v.1.5.0 (OptiTrack, Natural-
Point, Inc.) and then analyzed in Microsoft Excel (Microsoft,
Seattle, WA, USA). Instantaneous velocity was calculated by the
differentiation of the displacement data with respect to time. The
reflective marker was placed on the left side of the barbell, and the
Trio-OptiTrack was positioned at a distance of 2.5 m from the
marker.
T-Force. T-Force (T-Force system, Ergotech) is an isoinertial dy-
namometer that consists of a cable-extension linear velocity
transducer interfaced with a personal computer by means of a 14-
bit resolution analog-to-digital data acquisition board. In-
stantaneous velocity was automatically calculated at a sampling
rate of 1,000 Hz by the custom software v.2.28. The cable was
vertically attached to the right side of the barbell using a Velcro
strap.
Chronojump. Chronojump (Chronojump Boscosystem, Barce-
lona, Spain) is an isoinertial dynamometer that consists of a cable-
extension linear position transducer attached to the barbell
interfaced with a personal computer at a sampling rate of 1,000
Hz. Raw data were exported from the custom software v.1.6.2
and then analyzed in Microsoft Excel (Microsoft). Instantaneous
velocity was calculated by the differentiation of the displacement
data with respect to time. The cable was vertically attached to the
right side of the barbell using a Velcro strap.
Speed4Lift. Speed4Lift (Speed4Lift) is an isoinertial dynamome-
ter that consists of a cable-extension linear position transducer
attached to the barbell. Data were directly recorded by the dif-
ferentiation of the displacement data with respect to time at
a sampling rate of 1,000 Hz through Wi-Fi connection with an
Android smartphone using Speed4Lift application v.4.1. The
cable was vertically attached to the left side of the barbell using
a Velcro strap.
Velowin. Velowin (Velowin; DeporTeC) is an optoelectronic
system, which included an infrared camera interfaced with
a personal computer that measured displacement of a reflector
fixed to the barbell. Data were directly recorded from the custom
software v.1.6.314 by the differentiation of the displacement data
with respect to time at a sampling rate of 500 Hz. The Velowin
was placed at a distance of 1.7 m from the infrared reflector, and it
was calibrated according to the manufacturer’s instructions.
PowerLift. PowerLift is a smartphone v.6.0.1 application that
involves a frame-by-frame manual inspection of a slow motion
video recording by the smartphone high-speed camera at a fre-
quency of 240 frames per second and a quality of 720 pixels. The
mean velocity was computed as the individual range of motion
(i.e., vertical displacement of the barbell from the initial [1cm
above the subject’s chest] to the final [elbows at full extension]
position) divided by the lifting time (i.e., time between 2 frames
selected by the user). The smartphone (iPhone; Apple, Inc., CA,
USA) was held by a researcher in a portrait position and
recorded each lift from the front of the subject at approxi-
mately 1.5 m.
PUSH Band. PUSH band (PUSH band, PUSH, Inc.) is a wearable
wireless IMUs that consist of a 3-axis accelerometer and a gyro-
scope that provided 6 degrees of freedom in its coordinate system
(2). Data were directly recorded by the integration of the accel-
eration data with respect to time at a sampling rate of 200 Hz
through Bluetooth 4.0 LE connection with a smartphone (iPhone,
Apple, Inc.) using PUSH application v.1.1.26. The PUSH band
Figure 1. Distribution of the measurement devices during the
testing protocol: (1) Trio-OptiTrack, (2) T-Force, (3) Chro-
nojump, (4) Speed4Lift, (5) Velowin, (6) PowerLift, (7) PUSH
band, and (8) Beast sensor.
Feasibility of Seven Devices to Measure Velocity (2019) 00:00 |www.nsca.com
3
Copyright © 2019 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
was worn on the subject’s dominant forearm immediately inferior
to the elbow crease with the main button located proximally (2,5).
Beast Sensor. Beast sensor (Beast sensor, Beast Technologies Srl.)
is a wearable wireless IMUs that included a 3-axis accelerometer,
gyroscope, and magnetometer. Data were directly recorded by the
integration of the vertical acceleration with respect to time at
a sampling rate of 50 Hz through Bluetooth 4.0 LE connection
with a smartphone (iPhone, Apple, Inc.) using Beast application
v.2.3.7. The Beast sensor was placed on the barbell using a built-
in magnet (3).
Statistical Analyses
Descriptive data are presented as means and SDs, whereas the
coefficient of variation (CV) of the 5 loads is presented through
their median value. Reliability was assessed for each individual
load by the CV and the intraclass correlation coefficient (ICC
model 3,1). Acceptable reliability was determined as a CV ,10%
and an ICC .0.70 (8). The median CV value of the 5 loads was
calculated to compare the reliability between the 8 devices ex-
amined in this study. To interpret the magnitude of differences
observed between 2 CVs, a criterion for the smallest important
ratio was established as higher than 1.15 (37). Bland-Altman
plots were constructed to explore the concurrent validity of the 7
commercially available devices with respect to the Trio-
OptiTrack system. Because we observed proportional bias in 6
of 7 comparisons (r
2
.0.1) (1), the data were log transformed
before calculating the Pearson’s product-moment correlation
coefficients (r) (19). The criteria to interpret the strength of the r
coefficients were as follows: trivial (,0.1), small (0.1–0.3),
moderate (0.3–0.5), high (0.5–0.7), very high (0.7–0.9), or
practically perfect (.0.9) (19). Statistical significance was ac-
cepted at the p,0.05 level, and confidence limits were set at
95%. All reliability assessments were performed by means of
a custom spreadsheet (20), whereas other statistical analyses were
performed using the software package SPSS (IBM SPSS version
22.0, Chicago, IL, USA).
Results
Mean velocity values only reached an acceptable reliability at all
loads for the Trio-OptiTrack system, the linear velocity/position
transducers, and the smartphone application (CV ,6.24% and
ICC .0.73) (
½T1Table 1). Based on the comparison of the median
CVs of the 5 loads, the devices were ranked from the most to the
least reliable as follows: (a) Speed4Lift (CV 52.61%); (b) Velo-
win (CV 53.99%), PowerLift (3.97%), Trio-OptiTrack (CV 5
4.04%), T-Force (CV 54.35%), and Chronojump (CV 5
4.53%); (c) PUSH band (CV 59.34%); and (d) Beast sensor (CV
535.0%).
Bland-Altman plots revealed low systematic bias and random
errors (#0.05 m·s
21
) for the T-Force, Chronojump, Speed4Lift,
Velowin, and PowerLift as compared to the Trio-OptiTrack
system (
½F2Figure 2). Both IMUs showed larger random errors
(PUSH band 50.06 m·s
21
and Beast sensor 50.21 m·s
21
).
Heteroscedasticity of the errors was observed for all devices with
the only exception of the Speed4Lift (r
2
50.007). A practically
perfect association between the Trio-OptiTrack system and the
different devices was observed (rrange 50.947–0.995; p,
0.001) with the only exception of the Beast sensor (r50.765; p,
0.001) (
½F3Figure 3).
Discussion
This study compared the reliability and concurrent validity of 7
commercially available devices for the measurement of movement
velocity during the bench press exercise performed in a Smith
machine. The different devices were ranked from the most to the
least reliable as follows: (a) Speed4Lift; (b) Velowin, PowerLift, T-
Force, and Chronojump; (c) PUSH band; and (d) Beast sensor.
The concurrent validity of the T-Force, Chronojump, Speed4Lift,
Velowin, and PowerLift with respect to the Trio-OptiTrack sys-
tem was practically perfect. The 2 IMUs, especially the Beast
sensor, showed the lowest concurrent validity (i.e., lower rcoef-
ficients and larger random errors) as compared to the Trio-
OptiTrack system. The Speed4Lift was the only device that did
not report heteroscedasticity of errors. The results of this study
speak in favor of the Speed4Lift as the most reliable and valid
device for the measurement of movement velocity during the
Table 1
Reliability of mean velocity values obtained from the Trio-
OptiTrack method and 7 commercially available devices at
different loads during the bench press exercise.*
Device
Load
(%1RM)
Mean velocity
(m·s
21
) CV (95% CI) ICC (95% CI)
Trio-OptiTrack 45 0.84 60.05 3.47 (2.52–5.59) 0.73 (0.35–0.90)
55 0.71 60.05 2.22 (1.57–3.76) 0.93 (0.79–0.98)
65 0.58 60.05 4.04 (2.93–6.50) 0.84 (0.57–0.95)
75 0.46 60.05 4.15 (2.98–6.85) 0.83 (0.54–0.95)
85 0.35 60.05 4.64 (3.37–7.48) 0.88 (0.67–0.96)
T-Force 45 0.83 60.06 2.48 (1.78–4.09) 0.90 (0.70–0.97)
55 0.70 60.05 1.82 (1.32–2.93) 0.95 (0.84–0.98)
65 0.59 60.05 4.35 (3.15–7.01) 0.78 (0.45–0.93)
75 0.49 60.05 4.78 (3.43–7.89) 0.77 (0.40–0.92)
85 0.37 60.05 4.90 (3.55–7.90) 0.87 (0.64–0.96)
Chronojump 45 0.90 60.05 2.31 (1.67–3.72) 0.87 (0.64–0.96)
55 0.76 60.05 2.09 (1.51–3.36) 0.90 (0.71–0.97)
65 0.60 60.07 6.24 (4.47–10.3) 0.72 (0.31–0.90)
75 0.47 60.06 4.53 (3.25–7.48) 0.85 (0.58–0.95)
85 0.34 60.05 5.65 (4.05–9.32) 0.86 (0.60–0.95)
Speed4Lift 45 0.88 60.06 2.61 (1.80–4.77) 0.87 (0.55–0.96)
55 0.75 60.04 2.39 (1.73–3.85) 0.84 (0.57–0.94)
65 0.63 60.05 2.42 (1.69–4.25) 0.93 (0.78–0.98)
75 0.51 60.05 3.92 (2.81–6.47) 0.81 (0.49–0.94)
85 0.38 60.05 3.41 (2.38–5.98) 0.94 (0.78–0.98)
PowerLift 45 0.79 60.04 2.85 (2.02–4.83) 0.84 (0.55–0.95)
55 0.70 60.06 3.97 (2.81.6.74) 0.85 (0.57–0.96)
65 0.58 60.05 4.91 (3.48–8.33) 0.74 (0.32–0.92)
75 0.51 60.05 3.69 (2.58–6.48) 0.87 (0.58–0.96)
85 0.40 60.04 4.97 (3.47–8.71) 0.85 (0.54–0.96)
Velowin 45 0.91 60.06 2.89 (2.09–4.65) 0.83 (0.56–0.94)
55 0.77 60.05 3.27 (2.35–5.40) 0.79 (0.45–0.93)
65 0.64 60.06 3.99 (2.86–6.59) 0.83 (0.53–0.94)
75 0.51 60.05 6.01 (4.36–9.69) 0.68 (0.26–0.89)
85 0.38 60.06 7.64 (5.54–12.3) 0.69 (0.27–0.89)
PUSH band 45 0.79 60.07 5.02 (3.56–8.52) 0.69 (0.22–0.89)
55 0.63 60.07 7.84 (5.39–14.3) 0.46 (20.27–0.81)
65 0.46 60.08 9.34 (6.77–15.0) 0.78 (0.45–0.92)
75 0.31 60.06 14.6 (10.0–26.6) 0.50 (20.21–0.82)
85 0.24 60.06 19.1 (13.7–31.5) 0.47 (20.09–0.80)
Beast sensor 45 0.82 60.32 33.4 (23.5–58.9) 0.29 (20.42–0.72)
55 0.70 60.27 24.2 (15.6–53.2) 0.64 (20.28–0.89)
65 0.51 60.21 35.0 (22.6–77.1) 0.30 (20.91–0.77)
75 0.34 60.16 40.2 (28.1–70.5) 0.31 (20.40–0.73)
85 0.23 60.15 54.9 (38.9–93.2) 0.27 (20.38–0.70)
*1RM 51 repetition maximum; CV 5coefficient of variation; 95% CI 595% confidence interval;
ICC 5intraclass correlation coefficient.
Feasibility of Seven Devices to Measure Velocity (2019) 00:00
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bench press exercise performed in a Smith machine. Collectively,
the results of this study suggest that all devices, with the exception
of the IMUs (especially the Beast sensor), could be used to obtain
accurate velocity measurements for restricted linear movements.
However, strength and conditioning professionals should be
aware of the presence of heteroscedasticity between these devices,
which could limit the interchangeable use of different devices.
Linear position/velocity transducers have been routinely used
for training and testing purposes (5,16,29). These devices have
been considered the “gold-standard”to measure barbell velocity
Figure 2. Bland-Altman plots for the measurement of mean velocity between the Trio-OptiTrack system and
the 7 commercially available devices: T-Force (upper-left panel), Chronojump (upper-right panel), Speed4Lift
(upper middle-left panel), Velowin (upper middle-right panel), PowerLift (lower middle-left panel), PUSH band
(lower middle-right panel), and Beast sensor (lower panel). Each plot depicts the averaged difference and
95% limits of agreement (dashed lines), along with the regression line (solid line).
Feasibility of Seven Devices to Measure Velocity (2019) 00:00 |www.nsca.com
5
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in many studies (2,3,5). Specifically, the linear velocity transducer
used in this study (T-Force) has been frequently used to validate
other devices that were designed to measure movement velocity
(2,14,15). The preferential use of linear velocity transducers as
compared to linear position transducers could be justified because
the direct measurement of movement velocity is expected to
provide more accurate velocity outputs (30). However, there is
scarce information regarding the comparison of the reliability of
velocity outputs between linear velocity and linear position
transducers. Contrary to our hypothesis, the linear velocity
Figure 3. Relationship of mean velocity values between the Trio-OptiTrack system and the 7 com-
mercially available devices: T-Force (upper-left panel), Chronojump (upper-right panel), Speed4Lift
(upper middle-left panel), Velowin (upper middle-right panel), PowerLift (lower middle-left panel), PUSH
band (lower middle-right panel), and Beast sensor (lower panel). The Pearson’s correlation coefficient (r)
was calculated using the log transformation because the assumption of homoscedasticity was violated.
Feasibility of Seven Devices to Measure Velocity (2019) 00:00
6
Copyright © 2019 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
transducer (i.e., T-Force) was not more reliable than the 2 linear
position transducers used in this study (i.e., Chronojump and
Speed4Lift). In addition, to the best of our knowledge, this is the first
scientific article that has provided data regarding the validity of the
Chronojump and Speed4Lift. It should be noted that the Speed4Lift
was the most reliable device and the only device that did not report
heteroscedasticity of errors with respect to the Trio-OptiTrack sys-
tem. These results together with its lower price (340 US dollars)
and excellent portability (the software is installed in a smartphone
app that is wirelessly connected with the hardware) place the
Speed4Lift as an accurate, cost-effective, and practical device for
the measurement of movement velocity. It is worth noting that the
heteroscedasticity of errors observed for the other devices com-
promises their interchangeability. The T-Force and PowerLift
showed progressively larger values than the Trio-OptiTrack with
increasing velocities, whereas opposite results were observed for the
Chronojump, Velowin, PUSH band, and Beast sensor.
The Velowin has been recently developed as a more affordable
and practical device to measure movement velocity during re-
sistance training exercises. However, to date, only 2 studies have
examined its reliability and concurrent validity to measure move-
ment velocity. Garc´
ıa-Ramos et al. (12) found a comparable re-
liability (CV 54.29–4.60%) and high validity (r50.97–0.98)
between the T-Force and Velowin systems during the free-weight
back-squat exercise. Laza-Cagigas et al (21). also observed a high
validity (concordant correlation coefficient 50.96) and reliability
(CV 57.3% and ICC 50.97)oftheVelowinsystemtomeasure
mean velocity during the free-weight back-squat exercise with re-
spect to a 3D system. In line with these findings, our results showed
a high and comparable reliability and validity of the Velowin system
as compared to the data provided by linear position/velocity
transducers during the bench press exercise performed in a Smith
machine. More recently, an affordable (11 US dollars) smart-
phone application named PowerLift has been made commercially
available to measure movement velocity. The results of this study
corroborate the findings of Balsalobre-Fern ´
andez et al. who showed
a comparable reliability (ICC 50.93–0.99) and high validity (r5
0.94–0.98) of PowerLift with respect to the data provided by a lin-
ear position transducer (SmartCoach Europe, Stockholm, Sweden)
during free-weight exercises (3,4). Although it should be acknowl-
edged that it is possible to obtain accurate measurements of mean
velocity with PowerLift, the necessity of individually selecting the
start and end points of each repetition may be unpractical when
many athletes need to be assessed. In addition, the no provision of
real-time velocity feedback should also be considered a limitation
compared with the other devices analyzed in this study (39).
Wearable technologies such as the PUSH band and Beast sensor
are being increasingly used in the strength and conditioning field.
These 2 IMUs have been recently validated to measure movement
velocity during a variety of resistance training exercises (2,3,5,36). In
line with our results, the PUSH band provided highly valid meas-
urements of mean velocity when the data of several loads were
combined for the analysis during the bench press performed in
a Smith machine and during the free-weight shoulder press and
biceps/arm curl exercises (r.0.86) (2,36). However, the validity of
the PUSH band seems to be compromised when the data of in-
dividual loads are analyzed separately (specially for loads $80% of
1RM) (5). The PUSH band device should be therefore considered
with some caution given the controversial results and the lower re-
liability reported in this study. Regarding the Beast sensor, to the best
of our knowledge, only 1 study has investigated the reliability and
validity of this device with respect to the data provided by a linear
position transducer (SmartCoach Europe), reporting both a very
high reliability (ICC .0.95) and validity (r.0.98) during the bench
press, full-squat, and hip-thrust exercises (3). On the contrary, our
results suggest that the Beast sensor is the least reliable and valid
device among all the commercially available devices analyzed in this
study. It is plausible that the lower sampling frequencies of the IMUs
or the need to integrate acceleration-time data to obtain velocity
values could have caused their lower reliability (5,28). Therefore,
more evidence about the feasibility of wearable technology in the
field of velocity-based resistance training is needed.
Several limitations and directions for future research should be
considered. First, it should be noted that the mean velocity is not
the only velocity variable used in practice. The mean propulsive
velocity (i.e., average velocity from the start of the concentric
phase until the acceleration of the bar is lower than gravity) and
maximum velocity (i.e., maximum instantaneous velocity value
reached during the concentric phase) have been commonly rec-
ommended for training and testing (9,35). Therefore, future
studies should consider expanding the analysis of the reliability
and validity of different devices to these variables. It should be
noted that the mean velocity was the only variable analyzed in this
study because it was the only common variable for the 8 devices
analyzed. Second, the PUSH band was placed on the subject’s
forearm, whereas the other devices were attached to the barbell.
Therefore, although the measurement of the PUSH could be af-
fected by anteroposterior movements, the displacement of the
other devices was restricted to the vertical direction. Another
factor that could have promoted the lower reliability and validity
of the IMUs is their lower sampling frequency. In this regard, it is
plausible that the reliability and validity of the PUSH could be
improved with the current 2.0 version, which has a higher sam-
pling frequency (1,000 Hz), and it can be directly attached to the
barbell. Future studies should examine whether our findings
could be applicable to free-weight exercises in which the dis-
placement of the barbell is not restricted to the vertical direction.
Finally, because one of the main applications of the use of velocity
during resistance training is the prediction of the 1RM
(13,26,31), future studies should examine the precision of dif-
ferent commercially available devices for predicting the 1RM
during basic resistance training exercises.
Practical Applications
The devices were ranked from the most to the least reliable as
follows: (a) Speed4Lift; (b) Velowin, PowerLift, T-Force, and
Chronojump; (c) PUSH band; and (d) Beast sensor. All devices
presented a high concurrent validity with respect to the Trio-
OptiTrack system with the only exception of the Beast sensor,
whereas the Speed4Lift was the only device that did not report
heteroscedasticity of errors. Taken together, these results
suggest that the Speed4Lift is the most appropriate device for
the measurement of movement velocity during the bench press
exercise performed in a Smith machine. Note that linear ve-
locity transducers, linear position transducers, camera-based
optoelectronic systems, and smartphone application could all
be used to obtain accurate measurements of mean velocity
during the bench press exercise performed in a Smith machine,
although the presence of heteroscedasticity of errors should be
in mind. The 2 IMUs present a lower reliability and validity
and, consequently, more caution should be taken when using
PUSH band and Beast sensor devices for implementing
velocity-based resistance training programs.
Feasibility of Seven Devices to Measure Velocity (2019) 00:00 |www.nsca.com
7
Copyright © 2019 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Acknowledgments
The authors thank all the participants who selflessly participated in the
study. This study was supported by the Spanish Ministry of Education,
Culture and Sport under a predoctoral grant (FPU15/03649) awarded
to A.P.C. and by the University of Granada under a postdoctoral grant
(perfeccionamiento de doctores) awarded to A.G.R.
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