Validity and Reliability of the PowerTap P1 Pedals Power Meter

Abstract

To validate the new PowerTap P1® pedals power meter (PP1), thirty-three cyclists performed 12 randomized and counterbalanced graded exercise tests (100–500 W), at 70, 85 and 100 rev·min-1 cadences, in seated and standing positions. A scientific SRM system and a pair of PP1 pedals continuously recorded cadence and power output data. Significantly lower power output values were detected for the PP1 compared to the SRM for all workloads, cadences, and pedalling conditions (2–10 W, p < 0.05), except for the workloads ranged between 150 W to 350 W at 70 rev·min-1 in seated position (p > 0.05). Strong Spearman’s correlation coefficients were found between the power output values recorded by both power meters in a seated position, independently from the cadence condition (rho ≥ 0.987), although slightly lower concordance was found for the standing position (rho = 0.927). The mean error for power output values were 1.2%, 2.7%, 3.5% for 70, 85 and 100 rev·min-1, respectively. Bland-Altman analysis revealed that PP1 pedals underestimate the power output data obtained by the SRM device in a directly proportional manner to the cyclist’s cadence (from -2.4 W to -7.3 W, rho = 0.999). High absolute reliability values were detected in the PP1 pedals (150–500 W; CV = 2.3%; SEM < 1.0 W). This new portable power meter is a valid and reliable device to measure power output in cyclists and triathletes for the assessment, training and competition using their own bicycle, although caution should be exercised in the interpretation of the results due to the slight power output underestimation of the PP1 pedals when compared to the SRM system and its dependence on both pedalling cadence and cyclist’s position (standing vs. seated).

Full text

©Journal of Sports Science and Medicine (2018) 17, 305-311
http://www.jssm.org
Received: 20 November 2017 / Accepted: 16 April 2018 / Published (online): 14 May 2018
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Validity and Reliability of the PowerTap P1 Pedals Power Meter
Jesús G. Pallarés  and José Ramón Lillo-Bevia
Human Performance and Sports Science Laboratory, University of Murcia, Murcia, Spain
Abstract
To validate the new PowerTap P1® pedals power meter (PP1),
thirty-three cyclists performed 12 randomized and counterbal-
anced graded exercise tests (100–500 W), at 70, 85 and 100
revꞏmin-1 cadences, in seated and standing positions. A scientific
SRM system and a pair of PP1 pedals continuously recorded ca-
dence and power output data. Significantly lower power output
values were detected for the PP1 compared to the SRM for all
workloads, cadences, and pedalling conditions (2–10 W, p <
0.05), except for the workloads ranged between 150 W to 350 W
at 70 revꞏmin-1 in seated position (p > 0.05). Strong Spearman’s
correlation coefficients were found between the power output val-
ues recorded by both power meters in a seated position, inde-
pendently from the cadence condition (rho ≥ 0.987), although
slightly lower concordance was found for the standing position
(rho = 0.927). The mean error for power output values were 1.2%,
2.7%, 3.5% for 70, 85 and 100 revꞏmin-1, respectively. Bland-Alt-
man analysis revealed that PP1 pedals underestimate the power
output data obtained by the SRM device in a directly proportional
manner to the cyclist’s cadence (from -2.4 W to -7.3 W, rho =
0.999). High absolute reliability values were detected in the PP1
pedals (150–500 W; CV = 2.3%; SEM < 1.0 W). This new port-
able power meter is a valid and reliable device to measure power
output in cyclists and triathletes for the assessment, training and
competition using their own bicycle, although caution should be
exercised in the interpretation of the results due to the slight
power output underestimation of the PP1 pedals when compared
to the SRM system and its dependence on both pedalling cadence
and cyclist’s position (standing vs. seated).
Key words: Cycling, mobile power meter, testing, cycle ergom-
eter, power output.
Introduction
Mobile power meters became commercially available in
the 1980’s, allowing direct measurement of power output
in field conditions (Nimmerichter et al., 2017). Since then,
scientists, coaches and cyclists have been able to measure
bicycle power output during cycling training and competi-
tion, as traditionally performed in a laboratory setting. The
SRM power meter soon became the gold standard of the
mobile power meters. It consists of a crankset that allows
the measurement of torque via strain gauges, located be-
tween the crank and the chain rings, and angular velocity
from the cadence. Therefore, power output is calculated as
the product of torque and angular velocity.
Several valid and reliable laboratory-specialized er-
gometers and power meters have been developed so far to
monitor exercise performance while cycling: Lode
(Earnest et al., 2005; Reiser et al., 2000), Ergoline
(Maxwell et al., 1998), Monark (MacIntosh et al., 2001;
Maxwell et al., 1998), Velotron (Abbiss et al., 2009;
Astorino and Cottrell, 2012), Wattbike (Hopker et al.,
2010; Wainwright et al., 2017). It should be noted that it is
not possible to use them for field testing, moreover their
size, weight and especially their price, could make difficult
their use in laboratories with low financial resources
(Peiffer and Losco, 2011). In addition, even if the cyclist
can customize the position of the ergometer´s handlebars,
saddle and pedals (not always possible), there would be
considerable variations with their own bicycles in some de-
cisive metrics such as the crank width (Q-factor), crank
length, and other differences related to the specific geome-
try of the bicycle itself, which could affect comfort, pedal-
ling performance and might even increase injury incidence
(Disley and Li, 2014).
Currently, there are some mobile power meters
whose validity and reliability have been confirmed, such as
Garmin Vector (Bouillod et al., 2016; Nimmerichter et al.,
2017; Novak and Dascombe, 2016), or PowerTap Hub
(Bertucci et al., 2005b; Bouillod et al., 2016; Gardner et al.,
2004). Nevertheless, there are others whose results are re-
producible, but whose validity remains in question, such as
Stages (Bouillod et al., 2016; Granier et al., 2017). Finally,
there are others considered unreliable power meters, for ex-
ample, Look Keo Power pedal (Sparks et al., 2015).
The validity and reliability of power meters is
linked to the usefulness of the information obtained, since
it is well known that poor reliability in power output meas-
urement does not allow for optimisation of the training pro-
gram, in comparison with previous or future tests, nor an
accurate analysis of the data (Jeukendrup et al., 2000).
Changes in performance and training status cannot be de-
termined without a high level of reliability for the measure-
ment of power output (Garcia-Lopez et al., 2016; Hopkins
et al., 2001; Jeukendrup et al., 2000; Pallares et al., 2016;
Paton and Hopkins, 2001). For the evaluation of the effect
of training or detraining with power output measurement,
it is important to know the variation due to the technical
error of the power meter (Bertucci et al., 2005a). Specifi-
cally, Vanpraagh et al. (1992) suggested that the range of
the technical error for workload recorded using ergometers
should be within 5%. When using a power meter to test
high-level athletes, it would be advisable for this technical
error to be closer to 2%, due to the fact that elite male cy-
clists have typical variation of ~1% for time trials lasting
~1 hour (Paton and Hopkins, 2001).
The recent development of the PowerTap P1 pedals
(PP1, CycleOps, Madisson, USA) has introduced another
mobile power measuring tool to the market with a reduced
price (~$999.99). In a similar way to others, this manufac-
turer claims that the PP1 pedals are accurate to within
Research article

Validity of PowerTap P1 pedals power meter
306
1.5%, with a very limited extra weight (~150 g) compared
with mid or top range clipless road pedals. They are built
with eight strain gauges, which work with a ‘Multipole
Ring’, a sensor made of 20 small magnets around the pedal
spindle. It allows cyclists to use their own bicycle in tests
or training sessions carried out on laboratory ergometers,
indoor trainers, rollers or in the field, by just replacing the
pedals. The power measurement comes directly from the
point of contact with the bicycle, reducing the loss of
power output due to mechanical connections (Jones, 1998).
As far as we know, the PowerTap P1 pedals have
not been previously validated. For this reason, the purpose
of this study is to examine the validity, reliability and ac-
curacy of a new powermeter placed in the pedals of the
bike under laboratory cycling conditions.
Methods
Experimental approach to the problem
A descriptive, cross-sectional, quantitative study was con-
ducted. During a period of three weeks, each participant
performed several tests, conducted on separate days, in the
same exercise laboratory, under standardized conditions
(22.9 ± 2.0 oC; 39.3 ± 3.0 % humidity). The study, which
was conducted according to the declaration of Helsinki,
was approved by the Bioethics Commission of the Univer-
sity of the University of Murcia, and written informed con-
sent was obtained from all participants prior to participa-
tion.
Participants
Thirty-three well-trained male cyclists and triathletes vol-
unteered to take part in this study (age 32.4 ± 9.0 yr; height
1.86 ± 0.08 m; body mass 78.6 ± 12.9 kg; VO2max 57.7 ±
6.6 mlꞏkg-1ꞏmin-1; maximal aerobic power (MAP) 399 ± 31
W; cycling training experience 11.2 ± 2.7 years). All par-
tici pants train ed for 6 h ours or mor e per w eek du ring a min-
imum of twelve months preceding the study. Participants
were asked to avoid strenuous exercise, caffeine and alco-
hol for at least 24 hours prior to each testing session.
Testing procedures
A brand new PowerTap P1 power meter (CycleOps, Mad-
ison, USA) was compared against an SRM crank-based
power meter (scientific model with adjustable 7075 Alu-
minium crank length; Schoberer Rad Messtechnik, Julich,
Germany, ±1% accuracy). For all testing sessions, PP1
were mounted on the SRM cranks with the manufacturer-
recommended torque. Additionally, a medium size road bi-
cycle (Giant Defy 3, 2010 Giant Bicycles, Taiwan; Alu-
minium alloy frame with carbon fibre fork) was fitted with
the SRM 172.5 mm crank power meter. This precision
strain gauge-based crank and sprocket dynamometer trans-
mitted data to a unit display fixed on the handlebars.
The relationship between the frequency output and
the strain gauges and torque is determined during manufac-
ture and considered constant. The validity of this SRM sys-
tem has been previously demonstrated and therefore taken
as the gold standard power meter device (Jones, 1998;
Martin et al., 1998; Passfield and Doust, 2000). To mini-
mize the possible influence in the validity and reliability
values of the PP1 data, the same bicycle and SRM power
meter were used in all testing conditions. A dy-
namic calibration of the SRM crankset was performed by
the manufacturer prior to the beginning of the study.
The rear wheel of the bicycle was removed and at-
tached to a direct drive pedalling unit Cycleops Hammer
(Cycleops, Wisconsin, EEUU) (Lillo-Bevia and Pallares,
2017) with 10 speed (11–25 tooth) rear gear ratio and 39–
53 tooth front gear ratio. For all tests, the gear ratio 39:15
was selected, and cyclists were not allowed to change it to
prevent a potential effect of this variable on pedalling tech-
nique. Prior to each testing session, the calibration of the
Hammer ergometer was carried out according to the man-
ufacturer’s recommendations. In this way, the Hammer can
accurately determine the power required to overcome bear-
ing and belt friction, and set the zero offset of strain gauges.
Furthermore, the zero offset of the PP1 pedals was set be-
fore each testing session. Likewise, the front fork of the
bicycle was attached to the accompanying steering appa-
ratus for stability purposes. The bicycle seat height position
was matched to the cyclist’s own training geometry. Cy-
clists used their own cycling shoes fitted with Look cleats.
The absolute and relative validity of this direct drive device
has been recently confirmed (Lillo-Bevia and Pallares,
2017).
Testing protocol
All testing protocols began with a standardized warm-up of
5 minutes at 100 W with a freely chosen cadence. Follow-
ing this period, the validity and reliability of the devices
were assessed in the laboratory during three different test-
ing protocols:
All participants performed three randomized and
counterbalanced graded exercises tests, one for each se-
lected fixed cadence (70, 85 and 100 revꞏmin-1), at six sub-
maximal workloads (100, 150, 200, 250, 300 and 350 W)
of 75 seconds duration (Jones, 1998). The three graded ex-
ercise tests were separated by 5 min of recovery at 75 W,
performed in seated position and with freely chosen ca-
dence. The order of the three cadence levels was random-
ized to ensure that the validity of the results was not af-
fected by increments on the ergometer break temperature
or by the cyclists’ fatigue. After 5 min of recovery at 75 W,
cyclists performed a 75-second seated free cadence 500 W
workload. Finally, they performed a graded exercise test at
three sub-maximal workloads (250, 350 and 450 W) of 75
seconds with a freely chosen cadence, in a standing pedal-
ling position. Two minutes of recovery at 75 W with freely
chosen cadence were kept between the three workloads
tested. The pedalling power output was registered by the
PP1 and SRM simultaneously.
Following the recommendation of Jones (1998),
only power outputs and cadence values from the 10th to the
70th second of each 75-second step were analysed, to allow
the Cycleops Hammer enough time to stabilise the assigned
breaking workload. During each test, power output (W)
and cadence (revꞏmin-1) of PP1 were recorded at a fre-
quency of 1 Hz using a Garmin 1000 cycling computer
(Garmin International Inc., Olathe, KS, USA). Addition-
ally, power output and cadence of the SRM crankset were
recorded at a frequency of 1 Hz using the Power Control
V.

Pallarés and Lillo-Bevia
307
Statistical analysis
Standard statistical methods were used for the calculation
of means, standard deviations (SD), coefficient of variation
(CV) and standard error of the mean (SEM). Data were as-
sessed for heteroscedasticity by plotting the predicted vs.
the residual values for power and cadence measurements.
The Kolmogorov-Smirnov test and complementary anal-
yses of normality were used. The SRM and PP1 power out-
put and cadence data were not normally distributed. Thus,
the analysis of differences between the mean of power out-
puts and cadences values of each device were assessed with
a non-parametric Mann-Whitney U test. Spearman's rank
order correlation coefficients were calculated comparing
the power outputs values of the SRM and the PP1 power
meters during every graded exercise test. Additionally,
given the fact that a high correlation does not necessarily
imply that there is good agreement between any two meth-
ods, Bland-Altman plots were used to assess and display
the agreement and systematic difference among the SRM
and PP1 power outputs values (Bland and Altman, 1999).
The power outputs differences were drawn in relation to
the mean values and 95% of the differences, which were
expected to lie between the two limits of agreement (LoA).
LoA was defined as mean bias ± 2 standard deviation (SD)
(Atkinson and Nevill, 1998). Statistical significance for all
tests was regarded as p < 0.05. The recorded data were
downloaded from the previously described units and
further analysed using publicly available software (Golden
Cheetah, version 3.4) and Microsoft Excel 2016 (Microsoft
Software). Analyses were performed using GraphPad
Prism 6.0 (GraphPad Software, Inc., CA, USA), SPSS soft-
ware version 19.0 (SPSS, Chicago, IL) and Microsoft Ex-
cel 2016 (Microsoft Corp, Redmond, WA, USA).
Results
Validity
No significant differences were detected in power output
values between SRM scientific model and PP1 pedals at 70
revꞏmin-1 in seated position for workloads ranged between
150 W to 300 W (p > 0.05). However, in the rest of the
workloads, cadences, and pedalling positions assessed, sig-
nificantly lower values were detected in the PP1 compared
to the SRM power meter (p < 0.05) (Table 1). Nevertheless,
high levels of Spearman’s correlation coefficients were de-
tected between the power output values recorded by the
PP1 and the SRM devices in seated position (rho ≥ 0.987;
p < 0.001), independently from the cadence condition (70,
85 and 100 revꞏmin-1). However, for standing pedalling a
slightly weaker correlation coefficient was found (rho =
0.927; p < 0.001) (Table 1 and Figure 1). Confirming the
means difference data analysis, the Bland-Altman analysis
revealed low bias, but not negligible, between the power
output values of the SRM power meter and PP1 pedals for
all seated tests. Specifically, the PP1 pedals underestimated
the power output data obtained by the SRM device in a
directly proportional manner to the cyclist’s pedalling
cadence (bias = -2.4 W (LoA -12.1 to 7.3) at 70 revꞏmin-1,
Table 1. Results from the validity and reliability analysis.
POWER OUTPUT CADENCE
SRM (W) PT P1 (W) SEM
(W)
Rho
Spearman
value
Bland
Altman SRM (rpm) PT P1 (rpm)
Mean
±SD CV Mean
±SD CV Bias
(W)
SD Bias
(W)
Mean
±SD CV Mean
±SD CV
70
CAD
SITTING
100 W 99±6 5.6% 97±4* 4.2% 0.7
0.989#
-2.4
4.8
LoA
(-12.1 to 7.3)
70.4±1.0 1.4% 71.7±1.1 1.5%
150 W 150±5 3.4% 148±5 3.0% 0.8 70.7±0.9 1.3% 70.7±1.0 1.5%
200 W 200±5 2.4% 198±4 2.1% 0.7 70.6±1.1 1.5% 70.9±1.1 1.5%
250 W 251±5 2.0% 248±5 1.9% 0.8 70.7±1.0 1.4% 70.8±1.0 1.3%
300 W 303±5 1.5% 300±5 1.6% 0.8 70.4±0.9 1.3% 70.9±0.9 1.3%
350 W 356±4 1.2% 352±5* 1.4% 0.9 70.0±1.0 1.5% 70.6±1.0 1.5%
85
CAD
SITTING
100 W 101±6 5.9% 96±6* 5.7% 1.0
0.987#
-5.3
6.1
LoA
(-17.6 to 7.0)
84.7±0.8 0.9% 85.0±0.8 0.9%
150 W 149±6 4.0% 145±5* 3.7% 0.9 84.7±0.8 0.9% 84.8±0.8 0.9%
200 W 201±6 2.7% 196±5* 2.7% 0.9 84.8±0.9 1.1% 85.0±0.9 1.1%
250 W 252±5 1.9% 246±5* 2.2% 0.9 84.8±1.1 1.3% 85.0±1.1 1.8%
300 W 303±6 1.8% 298±6* 2.0% 1.1 84.9±1.2 1.4% 85.1±1.2 1.4%
350 W 355±5 1.5% 349±6* 1.7% 1.0 84.9±1.0 1.2% 85.1±1.0 1.7%
100
CAD
SITTING
100 W 96±8 8.6% 91±7* 7.2% 1.1
0.999#
-7.3
7.9
LoA
(-23.1 to 8.4)
98.9±1.3 1.3% 99.7±1.2 1.3%
150 W 145±7 4.9% 139±5* 3.9% 0.9 98.9±1.4 1.4% 99.2±1.5 1.5%
200 W 197±8 4.1% 191±7* 3.7% 1.2 99.6±1.2 1.2% 99.1±1.2 1.3%
250 W 248±7 2.9% 241±7* 2.8% 1.2 99.6±1.3 1.3% 99.7±1.3 1.3%
300 W 298±7 2.4% 291±7* 2.4% 1.2 99.5±1.5 1.6% 99.8±1.6 1.6%
350 W 352±5 1.9% 342±8* 2.3% 1.3 99.8±1.9 1.9% 99.7±1.9 1.9%
FC
S
TAND
250 W 253±7 2.6% 241±5* 2.2% 0.9
0.927# -9.0
5.3
LoA
(-19.7 to 1.7)
75.9±6.1 8.0% 74.9±11.0 14.7%
350 W 352±6 1.8% 345±5* 1.5% 0.9 74.8±9.1 12.1% 73.5±12.9 17.6%
450 W 455±8 1.7% 446±6* 1.2% 1.0 69.6±7.7 11.1% 68.5±10.7 15.7%
FC
SIT
500 W 499±9 1.8% 492±11* 2.2% 1.9
-7.0
3.5
LoA
(-14.1 to 0.0)
90.0±10.1 11.2% 89.8±10.5 11.7%
STAND = Standing; SIT= Sitting; CAD = Cadence; FC = Free cadence; SD = Standard Deviation; CV = Coefficient of variation; rho Spearman = Spearman
correlation coefficient; LoA = Limits of Agreement; * Significant differences compared to the SRM device; # significant Spearman correlation coefficient;
(p < 0.05).

Validity of PowerTap P1 pedals power meter
308
-5.3 W (LoA -17.6 to 7.0) at 85 revꞏmin-1 and -7.3 W (LoA
-23.1 to 8.4) at 100 revꞏmin-1, rho = 0.999). A slightly
greater underestimation was found for standing tests (bias
= -9.0 W (LoA -19.7 to 1.7)) (Table 1 and Figure 2).
Figure 1. Spearman´s Correlation Coefficient of the
PowerTap PP1 pedals under three different cadences, during
the submaximal graded exercises tests, compared to the sci-
entific SRM power meter at 70, 85 and 100 revꞏmin-1.
Reliability
The mean CV for the sitting graded exercise tests were
2.7% vs. 2.4%, 3.0% vs. 3.0% and 4.1% vs. 3.7% for the
SRM compared with the PP1 at 70, 85 and 100 revꞏmin-1,
respectively. These values were considerably lower if the
100 W workload was excluded (2.1 vs. 2.0%, 2.4 vs. 2.5%
and 3.2 vs. 3.0%). The mean CV for standing pedalling
tests of both devices (SRM vs. PP1) were 2.0% vs. 1.6%,
respectively, while CV for the high workload (i.e., 500 W)
in seated position remained very low (1.8% vs. 2.2%). The
SEM for the PP1 remained at very low values for all testing
conditions (ranging between 0.7 W and 1.9 W) (Table 1).
Discussion
The main finding of this study is that the PP1 is a highly
valid and reliable tool for testing and training purposes in
cycling under all assessed workloads (100 W to 500 W),
cadences (70, 85 and 100 revꞏmin-1) and pedalling posi-
tions (seated and standing). To our knowledge, this is the
first study that validates the PP1, which is a portable power
meter with some important advantages with respect to
other portable devices such as the use of the cyclist's own
bicycle, maintaining the usual riding position and the
wheelset and the crankset of the bicycle, the reduced extra
weight compared to other high performance portable
power meters (installed at crankset or hub), and finally the
ease of installation, which allows exchanging it between
various bicycles.
Nevertheless, it is important to be conscious that
this portable power meter slightly underestimated the
power output data in a directly proportional manner to the
pedalling cadence (from -2.4 W at 70 revꞏmin-1 to -7.3 W
at 100 revꞏmin-1), independently of the cycling workload
or pedalling position. This fact could be due to the strain
gauges’ sensitivity, or due to the signal processing (ampli-
fication, filtering, analog to digital conversion and data
analysis).
Figure 2. Bland-Altman plots of the PowerTap PP1 pedals,
assessed during the submaximal graded exercises tests, com-
pared to the scientific SRM power meter at 70 (A), 85 (B) and
100 (C) revꞏmin-1.
Laboratory based ergometers (e.g., SRM, Lode, Ve-
lotron, Wattbike) are still considered the “gold standard”
power meters due to their high levels of validity and relia-
bility (Abbiss et al., 2009; Earnest et al., 2005; Hopker et
al., 2010; Hopkins et al., 1999; Jones, 1998; Paton and
Hopkins, 2001; Reiser et al., 2000; Wainwright et al.,
2017). Thus, for a cycle trainer or power meter to be useful
in a research setting it must have similar qualities of meas-
urement. Different researchers have tested the validity of
other mobile ergometers such as Tacx Fortius (Peiffer and
Losco, 2011), KICKR Power Trainer (Zadow et al., 2017;
Zadow et al., 2016), LeMond Revolution (Novak et al.,
2015), and Elite Axiom Powertrain (Bertucci et al., 2005a),
as well as other mobile power meters, including PowerTap
Hub (Bertucci et al., 2005b; Bouillod et al., 2016; Gardner

Pallarés and Lillo-Bevia
309
et al., 2004) and Garmin Vector (Bouillod et al., 2016;
Nimmerichter et al., 2017; Novak and Dascombe, 2016). It
should be noted that the SRM, as the reference power me-
ter, is also affected by some measurement error. Jones
(1998) reported extremely low variability (± 0.3% and ±
1.0% for two different 20 strain gauge, and ± 1.8% for a 4
strain gauge models), while the accuracy claimed by the
manufacturer of these devices is also very high (± 0.5 %
and ± 2.5 %, for the 20 and 4 strain gauge, respectively).
Additionally, most of these validation studies have used the
SRM scientific model comprising 20 strain gauges (Ber-
tucci et al., 2005a, Duc et al., 2007; Jones, 1998) or the
SRM professional model (4 strain gauge) (Gardner et al.,
2004; Hurst and Atkins, 2006) as the gold standard devices.
Despite the fact that, according to the data collected
in the present study, there are small but significant differ-
ences between the mean power output values obtained by
the PP1 pedals and the SRM scientific model, there are
highly significant, “near perfect”, relationships
(rho ≥ 0.987; p < 0.001) from 100 W to 350 W with seated
position at low, medium and high cadences. The previous
concordance is reduced for standing, freely chosen cadence
pedalling (rho = 0.927; p < 0.001).
It is also important to note that this study has found
very small bias and SD of bias in the agreement between
the SRM and PP1 power output data, as well as between
SRM and PP1 cadence (from -2.4 ± 4.8 W to -9.0 ± 5.3 W),
both for the standing and seated pedalling positions, even
though it is known that standing pedalling causes lateral
sways and affects the biomechanics of pedalling (Stone and
Hull, 1993). These results are consistent but progressive.
When used in the laboratory and compared to the SRM
crankset, similar mean and SD biases, as well as the 95%
limits of agreement data, were reported for other mobile
power meters, such as Garmin Vector Pedals (Bouillod et
al., 2016; Nimmerichter et al., 2017) (0.6 ± 6.2 W, 11.6 to
12.7 W; -11.6 to 12.7 W, -3.7 to 9.5 W), PowerTap Hub
(Bertucci et al., 2005b) (2.9 ± 3.3 W; -3.7 to 9.5 W), and
Look Keo Power Pedal (Sparks et al., 2015) (4.6 ± 0.4 W;
-15.9 to 13.9 W). Bouillod, et al. (2016) found higher mean
and SD biases when the SRM crankset was compared with
the Stages (-13.7 ± 12.4 W, -37.9 W to 10.6 W).
Paton and Hopkins (2001) suggested that in elite
athletes, a magnitude lower than 2% is required to detect
changes in performance from an ergogenic or training in-
tervention. Besides, Hopkins (2000) suggested that an 84%
confidence interval is a more reasonable threshold than the
traditional 95% interval when attempting to detect changes
in athletic performance. Based on a workload of 350 W,
changes of ≥ 2% (7.0 W) and ≥ 1% (3.5 W) would be re-
quired to be confident (84%) that a trained cyclist had
changed power output because of a training intervention.
When compared to the SRM, the mean error of the PP1
shows that, in the present data, it falls within this range.
Based on the current study’s evaluation of the PP1, a mean
error of ~2% compared to the SRM would be acceptable
for talent identification purposes. These results suggest that
the PP1 power meter is sufficiently accurate to track per-
formance changes over time, and thus would serve as an
acceptable training tool. Regarding reliability (Table 1),
when we compare the PP1 with other mobile power meters
from previous studies, mean CVs are similar to these find-
ings. Bertucci et al. (2005b) reported a CV from 1.7 to
2.7% for the PowerTap Hub and from 1.2 to 2.0% for the
SRM crankset over a workload range of 100 W to 420 W.
The mean CVs reported in laboratory and field trials by
Nimmerichter et al. (2017) were 0.95 vs. 1.00% and 2.82
vs. 3.05%, for the SRM and a Garmin device, respectively.
These results mean that CV for the SRM and the PP1 in the
current study concur with the reliability data from previous
studies.
Cycling technique and type of ergometer can affect
cycling efficiency (Arkesteijn et al., 2013). In our opinion
the inclusion of cyclists as participants adds more ecologi-
cal validity to the real use of the pedals. From this point of
view, the reliable results of the current research confirm
that this biological variability does not affect the validity
of the power output data, nor the cadence, of this power
meter. What is more, the pedals and cyclists were tested
with three different and representative cadences to analyse
if the cadence affects the reliability of the power output and
cadence. Besides, the number of participants and their fit-
ness level (i.e., well-trained cyclists) are consistent with
other published research studies assessing the reliability
and validity of cycle ergometers (Pallares et al., 2016;
Passfield and Doust, 2000; Wainwright et al., 2017).
It is important to note that PP1 pedals have some
limitations in their use, in spite of the practical advantages
they offer. As the SRM power meters are checked for va-
lidity and reliability against a first principles dynamic cal-
ibration rig, the PP1 pedals cannot be easily checked by
this method because of the difficulty of applying a known
force dynamically to the pedals. The application of the
torque at the bottom bracket will not cause any deflection
within pedals axles. On the other hand, a static calibration
cannot be performed either due to the fact that the PP1 ped-
als will not transmit any data to a recording device if a ca-
dence reading is not available (Bini and Hume, 2014). As
stated earlier, the best current method to assess the varia-
bility of the PP1 pedals was to compare them with a scien-
tific model SRM crankset, which has been shown to be ac-
curate and reliable. Additionally, the slope of the power
curve cannot be adjusted, meaning that PP1 will always be
limited by the factory calibration. Accordingly, PP1 pedals
should be checked regularly against a calibrated scientific
SRM crankset. If this process is done regularly, PP1 pedals
provide an acceptable method of power output measure-
ment and their use in detecting changes in performance and
monitoring external training power output is supported.
Since the tests were developed with workloads up to 500
W, additional research must be done to test the reliability
and validity of the PP1 for sprint cycling tests above 500
W. Also, further research is needed to evaluate this power
meter system in field conditions (Bouillod et al., 2016).
Conclusions
This study confirms that, despite the slight but consistent
underestimation found at 85 and 100 revꞏmin-1 (2–7 W),
which slightly depends on both pedalling cadence and cy-
clists’ position (i.e., seated vs. standing), this new PP1 is a
valid, reliable and accurate mobile power meter, compared

Validity of PowerTap P1 pedals power meter
310
with the recognized gold standard scientific SRM, to meas-
ure power output and cadence in cyclists. This new porta-
ble power meter provides an alternative to more expensive
laboratory ergometers, allowing cyclists to use their own
bicycle for testing, training or competition purposes. Cur-
rent results demonstrate that the PP1 provides valid read-
ings of power output from 100 to 500 W, in either seated
or standing positions, at cadences of 70, 85 and 100
revꞏmin-1, or even at freely chosen cadences.
Acknowledgements
The authors wish to thank the participants for their invaluable contribution
to the study. The experiments comply with the current laws of Spain.
There are no conflicts of interest.
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Pallarés and Lillo-Bevia
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International Journal of Sports Physiology and Performance 11,
1115-1117.
Key points
 PP1 pedals slightly underestimate power output at
medium to high cadences (2 to 7 W).
 PP1 pedals provide valid readings of power output
from 100 to 500 W, in either seated or standing po-
sitions, at fixed cadences of 70, 85 and 100 revꞏmin-
1, or even at freely chosen cadences.
 These results suggest that the new PP1 pedals is a
valid, reliable and accurate mobile power meter to
measure power output and cadence in cyclists using
their own bicycles.
AUTHOR BIOGRAPHY
Jesús G PALLARÉS
Employment
Professor of Exercise Physiology (Human
Performance and Sport Science Labora-
tory, University of Murcia, Spain)
Degree
PhD
Research interest
Exercise physiology and training; perfor-
mance analysis; ergogenic aids.
E-mail: jgpallares@um.es
Jose Ramon LILLO-BEVIA
Employment
PhD student at Faculty of Sport Sciences,
University of Murcia, Murcia, Spain
Degree
MSc, PhD candidate
Research interests
Exercise physiology and training, perfor-
mance analysis
E-mail: joseramon.lillo@um.es
 Jesús García Pallarés
Faculty of Sport Science, Argentina S/N, Santiago de la Ribera,
Murcia, Spain