REPRODUCIBILITY OF OUTDOOR FLAT AND UPHILL CYCLING TIME TRIALS AND
THEIR PERFORMANCE CORRELATES WITH PEAK POWER OUTPUT IN MODERATELY
Performance Laboratory, Sports Medicine & Research Centre, Singapore
Sports Council, Singapore
24 March 2005
Journal of Sports Science and Medicine (2005) 4, 278
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aims of the present study were firstly to examine the reproducibility
of outdoor flat and uphill cycling time trials (TT), and secondly
to assess the relationship between peak power output (Wpeak)
obtained in the laboratory and outdoor cycling performance in moderately
trained cyclists. Eight competitive male cyclists first performed
a progressive cycle ergometer test in the laboratory to determine
Wpeak (W). Thereafter, they performed three 36 km TT (TT36)
on a flat course on separate days and at the same time of the day.
On a different day, they also performed three 1.4 km uphill TT (TT1.4)
in a single day. The coefficient of variation (CV) values across three
TT36 and TT1.4 ranged from 1.1 - 1.4% and 2.6
- 2.9%, for performance time (min) and mean power (W), respectively.
The correlation between absolute Wpeak (W) obtained in
the laboratory and mean power during TT36 and TT1.4
was 0.90 (p < 0.01) and 0.98 (p < 0.01), respectively. Absolute
Wpeak (W) correlated significantly with performance time
in TT36 (r = -0.72, p < 0.05) but not in TT1.4
(r = -0.52, p > 0.05). The correlation between relative Wpeak
(W·kg-1) and performance time in TT36 and TT1.4
was r = -0.65 (p > 0.05) and r = -0.91 (p < 0.01), respectively.
In conclusion, under stable environmental conditions, performance
time and mean power are highly reproducible in moderately trained
cyclists during outdoor cycling TT. Laboratory determined absolute
Wpeak (W) may predict cycling performance on a flat course
but relative Wpeak (W·kg-1) is a better predictor
of performance during uphill cycling.
WORDS: Field-based, reliability, performance time, mean power,
heart rate, PowerTap powermeter.
tests are an integral component of assessment for competitive cyclists
in practical and research settings (Paton and Hopkins, 2001).
In order to evaluate the effectiveness of nutritional strategies,
ergogenic aids or training regimens, practitioners have traditionally
used criterion tests that include sub-maximal performance rides
to exhaustion at a fixed percentage of peak oxygen uptake (VO2
peak) or peak power output (Wpeak) (e.g. Coggan
and Coyle, 1987;
Coyle et al., 1991;
McLellan et al., 1995).
However, Krebs and Powers (1985)
and Jeukendrup et al. (1996)
have shown that the reproducibility of time to exhaustion protocols
are poor and suggested that time trial (TT) protocols may result
in better performance evaluation.
The ease of measuring laboratory-based variables during simulated
cycling TT has resulted in a comprehensive evaluation of the reproducibility
of performance and physiological variables. Several studies have
examined and reported high reproducibility of laboratory-based cycling
TT performance in well-trained cyclists (Hickey et al., 1992;
Jeukendrup et al., 1996;
Laursen et al., 2004;
Palmer et al., 1996).
However, due to changeable environmental factors and non-standardized
field conditions, limited research is available on the trial-to-trial
variations of such protocols in field conditions and in particular,
with moderately trained cyclists. Smith et al. (2001)
were reportedly the first to examine the reproducibility of field-based
40 km cycling TT performance using the SRM (Schoberer Rad Messtechnik,
Welldorf, Germany) powermeter, but only in well-trained cyclists.
Relative to the biological changes that occur during repeated tests,
knowledge of the reproducibility of performance and physiological
variables may help practitioners interpret 'real' or significant
changes more appropriately.
Peak power output (Wpeak) obtained during a progressive
cycle ergometer test in the laboratory has been used to predict
performance of well-trained cyclists because of its strong relationship
with mean power and performance time during cycling TT (Balmer et
Bentley et al., 2001;
Hawley and Noakes, 1992).
However, data on the relationship between outdoor cycling TT performance
and Wpeak in moderately trained cyclists is lacking.
The large discrepancy between the air-conditioned laboratory environment
and the hot and humid outdoor environment in the local climate coupled
with the non-specificity of laboratory test protocols results in
a considerable challenge of making the test results meaningful and
specific to the actual cycling environment. Moreover, moderately
trained rather than well-trained cyclists are often employed as
subjects during interventional studies. Therefore, there is a need
to investigate field-based cycling performance in moderately trained
cyclists and its correlation with laboratory tests. As a result,
the aims of the present study were firstly to examine the reproducibility
of outdoor flat and uphill cycling TT, and secondly to assess the
relationship between laboratory determined Wpeak and
outdoor cycling performance in moderately trained cyclists.
Eight moderately trained, competitive male cyclists volunteered
to take part in the study. Their mean age, height, body mass, Wpeak
and VO2 peak were 22.5 ± 3.4 years, 1.73 ± 0.04 m, 64.8
± 9.8 kg, 343 ± 27 W and 3.81 ± 0.36 L·min-1, respectively.
These subjects had been actively cycling on a regular basis (>
4·week-1) for at least 2 years and their physiological
characteristics were lower than those of well-trained cyclists (mean
Wpeak = 439 W; mean VO2 peak = 5.4 L·min-1)
(Mujika and Padilla, 2001).
Written informed consent and pre-participation medical questionnaire
were provided prior to the commencement of the study that was approved
by the institutional ethics review committee.
Subjects first performed a progressive cycle ergometer test to exhaustion
in the laboratory to determine peak oxygen uptake (VO2 peak)
and peak power output (Wpeak). Following that, they completed
three outdoor 36 km TT (TT36) on a flat course on three
separate days and three outdoor 1. 4 km uphill TT (TT1.4)
on another day. Subjects performed all tests within a three-week
period, with at least 72 h separating each test day. Subjects were
requested to perform the same type of training for the duration
of the study and to refrain from heavy physical exercise 24 h before
a test day. Subjects completed a food diary on which they recorded
their food and fluid intake for the day preceding a TT as well as
for the day on which they performed their TT. They were then instructed
to repeat this dietary regimen before each subsequent trial. They
had trained and participated in local TT races prior to their involvement
in the study and were familiar with the field locations in the study.
Progressive exercise test
VO2 peak and Wpeak were determined on an electronically
braked cycle ergometer (Lode Excalibur Sport, Groningen, The Netherlands).
After a self-selected warm-up of 5 min, the incremental test commenced
at an initial workload of 100 W with increment of 15 W every minute
thereafter. Throughout the test, minute ventilation (VE),
oxygen uptake (VO2), carbon dioxide expired (CO2)
and respiratory exchange ratio (RER) were measured breath-by-breath
using an open circuit spirometry system (Vmax 29, SensorMedics Corporation,
USA). The oxygen and carbon dioxide gas analysers were calibrated
prior to the VO2 peak test with known concentrations
of standard gases and the flow meter was calibrated using a three-litre
syringe. Heart rate (HR) was monitored continuously using a short-range
telemetry monitor (S610, Polar Electro OY, Kempele, Finland). Subjects
were considered to have attained VO2 peak when any two
of the following criteria were met: i) volitional exhaustion, ii)
maximal RER > 1.05, and/or iii) HR > 95% of age-predicted
maximum HR (HRmax, based on the formula of 220 - age
in years). VO2 peak was recorded as the highest value
obtained over any 60 s period. The measurement of Wpeak
was based on the calculation of completed work in (W) plus the fraction
of time spent in the final non-completed workload multiplied by
15 W (e.g. a subject abandoned the test 30 s after beginning a workload
of 305 W, his Wpeak would be calculated as 290 W + (0.5
x 15 W), which would amount to 297.5 W).
36 km flat TT
Subjects completed three TT36 on a flat course on three
separate days and at the same time of the day. Warm-up was self-selected
and recorded and remained consistent throughout all trials. For
each trial, the subjects wore the same clothes and used their own
bicycles fitted with a mobile cycling powermeter, PowerTap ProTM
(PT) (Graber Products, Madison, WI, USA) in the hub of the rear
wheel. Bertucci et al. (2004)
and Gardner et al. (2004)
had previously showed that the PT is both reliable and valid. Two
sets of PT were used in the study and each subject would use the
same set for all his trials. The PT torque was zeroed before each
trial according to the manufacturer's instructions. Environmental
temperature, humidity and airflow were monitored continuously with
a heat stress system fitted with an air probe (QT36, Quest Technologies,
USA). Tires were inflated to 110-120 psi and kept consistent throughout
all trials. Each trial consisted of three 12 km loops. Subjects
were allowed to choose their preferred cadence and gear ratio and
were instructed to adopt similar strategies and complete the distance
in as fast a time as possible. During each trial, time, power output,
and heart rate were continuously monitored and subjects were blinded
to this information. Environmental conditions were consistent on
all test days (temperature: 30.0 ± 1.3 °C; relative humidity: 56.0
± 1.4 %; wind speed: 0.8 ± 0.5 m·s-1).
1.4 km uphill TT
Subjects completed three TT1.4 on an uphill course in
one day. A rest interval of 40 minutes separated each trial in order
to eliminate any possible fatigue effects. The trials were performed
on a hill with an average gradient of 7.1% calculated as the ratio
of the overall elevation (100 m) (GPSports SPI10, Canberra, Australia)
by the distance (1400 m). The instructions given to the subjects,
warm-up and measurements obtained were similar to those described
for TT36. Environmental conditions were consistent on
all test days (temperature: 28.6 ± 0.7 °C; relative humidity: 64.5
± 4.6 %; wind speed: 0.9 ± 0.3 m·s-1).
The SPSS software (11.5 for Windows) was used for all statistical
analyses. Descriptive data (means and standard deviations) of all
the subjects and their performance in the trials were computed.
Mean values for all trials were compared using one-way analysis
of variance (ANOVA). Reproducibility of the performance and physiological
variables were examined using the within-subject random variation
as represented by the coefficient of variation (CV) and the intraclass
correlation coefficient (ICC) (Model: Two-Way Mixed Effects; Type:
Consistency). CV values for individual subjects were calculated
by dividing each subject's SD by their mean values. The 95% confidence
intervals (95% CI) were calculated using the methods of McGraw and
Pearson product moment correlation was used to examine the relationships
between Wpeak (W and W kg-1) and mean power
and performance time in TT. For all analyses, the alpha level of
statistical significance was established at p < 0.05.
subject data for mean power and performance time are presented in
Tables 1 and 2,
respectively. There were no significant differences between trials
(p > 0.05) for all variables measured.
The coefficient of variation (CV), intraclass correlation coefficients
(ICC) and 95% confidence intervals (CV [95% CI] and ICC [95% CI])
for each variable across all trials are presented in Table
Table 4 shows the correlation
matrix between absolute and relative Wpeak (W and W kg-1)
obtained in the laboratory and mean power and performance time during
TT36 (W36, T36) and TT1.4
main finding of the present study was that outdoor flat and uphill
cycling TT performance was highly reproducible in moderately trained
cyclists. It is known that the reproducibility of laboratory-based
cycling performance is high for well-trained cyclists when the exercise
durations were familiar to them (Hickey et al., 1992;
Jeukendrup et al., 1996;
Laursen et al., 2004;
Palmer et al., 1996).
Smith et al. (2001)
were reportedly the first to demonstrate that field-based 40 km
cycling TT performance using the SRM powermeter was highly reproducible
in well-trained cyclists. The authors in the cited study reported
a CV of 1.7% for performance time across three outdoor 40 km TT.
Comparatively, low CV values of 1.4% and 1.1% for performance time
in TT36 and TT1.4, respectively, showed that
even in moderately trained cyclists, performance was highly reproducible
in the present study. Possible factors that might have contributed
to the high reproducibility were that subjects rode their own bikes
and were accustomed to the distances of the test protocols. In addition
to these factors, we also attribute the high reproducibility of
performance time to stable environmental conditions. These postulations
were supported by Palmer et al. (1996)
who showed that the CV values for performance time during laboratory
simulated cycling, when subjects rode their own bikes, were 1.1%
and 1.0% for 20 km TT and 40 km TT, respectively, in well-trained
In the present study, the CV values for mean power were 2.9% and
2.6% for TT36 and TT1.4, respectively. Similarly,
Smith et al. (2001)
reported a CV of 2.6% for outdoor 40 km TT. Analyses by Hopkins
estimated that the CV values for mean power in Palmer et al's (1996)
laboratory-based study were 2.4% and 3.3% for 20 km TT and 40 km
TT, respectively. Based on these data, we observe that the variations
of mean power produced by moderately trained cyclists during outdoor
TT are comparable with those of well-trained cyclists in both indoor
and outdoor conditions. Additionally, there seemed to be a trend
indicating higher CV values for mean power when compared to performance
time. It is noteworthy that mean power is not less reproducible
than performance time but rather an artifact of the non-linear time-power
relationship (Seiler et al., 1998;
Schabort et al., 1998).
The relationship between a change in muscular power output and the
corresponding change in movement velocity of an object moving through
air or water is not linear because of the exponential relationship
between movement velocity and the resulting drag force acting on
the object (Sanderson and Martindale, 1986;
Power is a third-order polynomial function of velocity. The impact
of wind drag is highly significant in cycling TT as cyclists are
riding at high speeds and wind velocity is the primary resistance
It has been proposed that heart rate may not be a good indicator
of exercise intensity as it can be affected
by environmental changes, hydration status and positional changes
on the bike (Jeukendrup and van Diemen, 1998).
In the present study, the ICC for mean heart rate was 0.60 for TT36
and 0.90 for TT1.4. Since the duration for TT36
was more than ten times that for TT1.4, the factors that
may affect heart rate response were likely to have greater influence
on the former, thus resulting in a higher variation. Bishop (1997)
reported an ICC of 0.91 for mean heart rate during repeated 1 h
cycling TT in the laboratory. In the cited study, mean power was
reportedly more reliable (ICC = 0.97). Overall, the reproducibility
of sub-maximal heart rate response is moderate to high, but practitioners
need to be watchful of the factors that may increase the likelihood
The second finding of the present study was that mean power during
TT36 (W36) may be predicted with some confidence
from absolute Wpeak (W) obtained in the laboratory (r
= 0.90, p < 0.01). This finding is in agreement with data from
previous studies using well-trained cyclists (e.g. Balmer et al.,
Bentley et al., 2001;
Hawley and Noakes, 1992).
Balmer et al. (2000)
reported a highly significant correlation (r = 0.99, p < 0.001)
between absolute Wpeak (W) and mean power during outdoor
16.1 km TT. In the present study, a highly significant relationship
was also found between mean power during TT1.4 (W1.4)
and absolute Wpeak (W) (r = 0.98, p < 0.01). The higher
correlation for the latter can be attributed to the greater emphasis
of muscular power during an uphill climb.
In contrast, absolute Wpeak (W) was only modestly correlated
with performance time in TT36 (T36) (r = -0.72,
p < 0.05), and differences in T36 may be attributed
primarily to variations in individual aerodynamics since environmental
conditions were consistent on all test days. This is not surprising
as Balmer et al. (2000)
also reported a low correlation (r = -0.46, p > 0.05) between
absolute Wpeak (W) and performance time in 16.1 km TT.
In the cited study, the correlation was even lower than that of
the present study because the environmental conditions were not
standardized as subjects competed in separate TT races. Therefore,
factors such as wind speed, direction, temperature and humidity
might have additional influences over and above individual aerodynamics
on performance time. With well-trained cyclists, Hawley and Noakes
showed that absolute Wpeak (W) correlated strongly with
20 km cycle time (r = -0.91, p < 0.001) under standardized environmental
conditions when all subjects completed their TT in the same event
held on the same day. In the cited study, the course of the TT was
mainly flat and consisted of four laps of 5 km oval circuit.
The non-significant relationship between absolute Wpeak
(W) and performance time in TT1.4 (T1.4) (r
= -0.52, p > 0.05) in the present study reiterated the importance
of power-to-weight ratio during uphill cycling in comparison with
riding on a flat course. Some of the riders who attained higher
absolute Wpeak (W) also had larger body masses and thus
were at a disadvantage during climbing. However, when riding on
a flat course, a larger rider has an advantage (in terms of absolute
oxygen consumption and power output) due to a lower frontal surface
area to body weight ratio than a smaller rider (Swain et al., 1987).
This advantage is lost when cycling uphill. This argument is supported
by a strong relationship (r = -0.91, p < 0.01) found between
relative Wpeak (W·kg-1) and T1.4
and a non-significant relationship (r = -0.65, p > 0.05) between
relative Wpeak (W·kg-1) and T36.
Hawley and Noakes (1992)
also reported that the correlation between Wpeak (W)
and outdoor 20 km cycling time was decreased when Wpeak
was expressed relative to body mass (W·kg-1) (r = -0.68,
p < 0.01).
conclusion, under stable environmental conditions, performance time
and mean power are
highly reproducible during outdoor cycling TT in moderately trained
cyclists provided they are familiar with the test protocol and duration.
Laboratory determined absolute Wpeak (W) may predict
cycling performance on a flat course but relative Wpeak
(W·kg-1) is a better predictor of performance during
technical assistance of Frankie Tee and Lee Hong Choo throughout the
study is kindly acknowledged and appreciated.
stable environmental conditions, performance time and mean power
are highly reproducible in moderately trained cyclists during
outdoor flat and uphill cycling time trials.
determined peak power output (Wpeak) (W) may predict cycling performance
on a flat course.
determined relative Wpeak (W·kg-1) is a better predictor of performance
during uphill cycling
Frankie H. Y. TAN
Employment: Exercise Physiologist, Human Performance Laboratory,
Sports Medicine & Research Center, Singapore Sports Council.
Degree: BSc (Honors), MSc.
Research interests: Exercise and sports performance training
Abdul Rashid AZÝZ
Employment: Head, Human Performance Laboratory, Sports Medicine
& Research Center, Singapore Sports Council.
Degree: BPE (Sport Studies).
Research interests: Exercise and sports performance training