Abstract

Introduction

Performance tests which measure a cyclist’s training status and are used to prescribe training have been used since the early 1900s.1,–,5 As maximal oxygen consumption (VO_2max) is related to exercise capacity,6 VO_2max has rapidly become the most popular measurement to determine training status in athletes, such as runners and cyclists.7,–,10 However, this parameter loses its accuracy to predict training status in a homogeneous group of well-trainedcyclists.11 12 In response, the measurement of peak power output (PPO) has gained popularity as a marker of training status.7 13 14 PPO can either be expressed as an absolute or relatively to body mass (W/kg), the latter being a predictor of a climbing capacity.7 In addition, a cyclist’s endurance capacity is normally tested by performing a laboratory-based time trial.14 The 40-km time trial (40-km TT) test has shown to be reliable12 15 and able to detect small meaningful changes in well-trained and elite cyclists.16,–,18

Although the performance parameters measured during these tests are valuable and potentially could assist in refining training programmes, these tests (VO_2max, PPO and 40-km TT) are strenuous and are therefore not practical for monitoring purposes. As a consequence, these tests are normally only performed twice or three times per season.19 However, if one test could accurately predict other performance indicators, the volume of testing per session could decrease and possibly allow more frequent testing (monitoring). Accordingly, Hawley and Noakes11 developed a stepwise protocol and reported a strong relationship between PPO and VO_2max (r=0.97), which allows the prediction of VO_2max from PPO. In addition, Hawley and Noakes11 also reported a good relationship between PPO and 20-km TT time (r=−0.91) in a small group of male and female cyclists (n=19), suggesting that PPO can also predict endurance cycling capacity. However, when PPO within this study was expressed in relative terms, the relationship between PPO (W/kg) and 20-km TT performance became substantially weaker (r=−0.67). A similar finding was reported by Balmer et al20 who reported a strong relationship between absolute PPO and mean power measured during a 16.1-km flat time trial (r=0.99, n=16), but when 40-km TT time was compared with PPO, a significantly weaker relationship was found (r=−0.46). A possible explanation for these discrepancies could be that the effect of body mass was not considered appropriately when determining the relationships between PPO and time trial performance.

In support of this, Swain has shown that body mass is an advantage when performing a flat time trial and is a disadvantage for climbing cycling capacity.21 22 Based on these findings, Swain has suggested that body mass should be adjusted to the power of 0.32 when predicting flat time trial performance.21 22 Subsequently, Mujika and Padilla9 have used this allometric scaling method profiling 24 professional road cyclists. This study showed that PPO adjusted for body mass (W/kg^0.32) was the strongest predictor of time trial specialists, which supports Swain’s allometric scaling method to predicting endurance cycling capacity.

Although this method has the potential to predict endurance cycling capacity, to our knowledge no study has confirmed the accuracy of this method in a large group of trained cyclists. Therefore, the aim of this study was to determine whether PPO or VO_2max adjusted for body mass (W/kg^0.32, ml/min/kg^0.32, respectively) is able to more accurately predict 40-km TT performance than absolute PPO or VO_2max (l/min) or relative PPO (W/kg) or VO_2max(ml/min/kg). A secondary aim was to confirm whether VO_2max can also be accurately predicted from PPO when using a continuous ramp protocol.

Methods

Forty-five competitive male cyclists of varying training status were recruited for this study. Subjects had a competitive cycling history of 8±5 years, ranging from 2 to 21 years, and trained on average 10±3 h per week, ranging from 5 to 20 h per week. Prior to participation, all cyclistscompleted a Physical Activity Readiness Questionnaire (PAR-Q)23 and signed a written informed consent. Ethical approval for the study was provided by the Research and Ethics Committee of the Faculty of Health Sciences of the University of Cape Town. The principles of the World Medical Association Declaration of Helsinki and the American College of Sports Medicine Guidelines for Use of Human Subjects were adopted in this study.24

In the 2 weeks before the performance tests, all subjects completed a PPO test, including gas analysis, and the 40-km TT test for familiarisation purposes. Subjects were asked to refrain from eating for 2 h before the test and from drinking any caffeine 3 h before the test. Measurements including height, weight and seven skinfolds (triceps, biceps, supra-iliac, subscapular, calf, thigh and abdomen)25 were performed at the start of the study while body fat percentage was calculated.26 All tests were performed on Computrainer cycle ergometers (Computrainer Pro 3D; RacerMate, Seattle, Washington, USA), which were calibrated before each test as recommended and described previously.12 The 40-km TT test was performed 72 h after the PPO test. All performance tests were conducted under stable environmental laboratory conditions (21.9±1.0°C, 51±4% relative humidity, 102.1±0.7 kPa).

Results

The general characteristics and performance parameters of the 45 trained cyclists are shown in table 1.

The relationships between absolute PPO and absolute VO_2max (l/min) and relative PPO (W/kg) and relative VO_2max (ml/min/kg) are shown in figure 1. Significant relationships were found between absolute PPO and VO_2max (r=0.96 (95% CI 0.93 to 0.98), p<0.0001) and relative PPO and VO_2max (r=0.94 (95% CI 0.89 to 0.97), p<0.0001).

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Figure 1

The relationship between absolute peak power output (PPO) and absolute VO_2max (A) and relative PPO and relative VO_2max (B).

Both relationships between PPO and VO_2max were linear and are characterised by the following regression equations:

VO_2max adjusted for body mass (VO_2max^0.32) and 40-km TT performance

The relationships between VO_2max adjusted for body mass (ml/min/kg^0.32) and 40-km TT performance expressed as time or as mean power (PO) are shown in figure 2A,B, respectively. Significant relationships were found between both VO_2max^0.32 and 40-km TT time (r=−0.93 (95% CI −0.88 to −0.96), p<0.0001) and VO_2max^0.32 and average 40-km TT PO (r=0.93 (95% CI 0.88 to 0.96), p<0.0001).

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Figure 2

The relationship between adjusted relative VO_2max (ml/min/kg^0.32) and 40-km time trial (40-km TT) time (A) and mean power output during the 40-km TT (B).

The relationship between VO_2max^0.32 and 40-km TT time and mean 40-km TT PO were characterised by the following regression equations:

40-km TT time

The SEE of 40-km TT time (s) from VO_2max^0.32 is 70 s.

Mean 40-km TT PO

The SEE of mean 40-km PO from VO_2max^0.32 is 12 W.

PPO adjusted for body mass (PPO^0.32) and 40-km TT performance

In figure 3A,B, the relationships between PPO adjusted for body mass (W/kg^0.32) and 40-km TT time and mean 40-km TT PO are shown. Even stronger relationships were found between the relative PPO^0.32 and 40-km TT time (r=−0.96, 95% CI −0.93 to −0.98, p<0.0001) and average 40-km TT power (r=0.92, 95% CI 0.86 to 0.96, p<0.0001).

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Figure 3

The relationship between adjusted relative peak power output (PPO) (W/kg^0.32) and 40-km time trial (40-km TT) time (A) and mean power output during the 40-km TT (B), relative PPO (W/kg) and 40-km TT time (C) and mean power output during the 40-km TT (D) and, absolute PPO and 40-km TT time (E) and mean power output during the 40-km TT (F).

The relationships between PPO^0.32 and 40-km TT time and mean PO were characterised by the following regression equations:

40-km TT time

The SEE of 40-km TT time (s) from PPO^0.32 is 52 s.

Mean 40-km TT power

The SEE of mean 40-km Power from VO_2max^0.32 is 12 W.

Discussion

The first important finding of this study was the strong relationship between PPO and VO_2maxeither expressed in absolute (r=0.96 (l/min)) or relative (r=0.94 (ml/min/kg)) terms. These findings are similar to the findings by Hawley and Noakes,11 who used a stepwise testing protocol instead of a continuous ramp protocol and reported a significant relationship between absolute PPO and VO_2max of r=0.97 (l/min). Although the regression equations are different, this finding confirms that VO_2max can be predicted from PPO determined by both a stepwise and/or continuous ramp protocol. As the standard error of estimate (SEE) of the predicted VO_2max in the current study (SEE 3%) is lower than the SEE in the study of Hawley and Noakes (SEE 6%), this finding suggests that PPO measured by a continuous ramp is slightly more reliable and able to predict VO_2max more accurately. However, other factors such as a different sample population or improved/new equipment for measuring PPO and/or VO_2max more accurately could also explain this finding.

The main finding of this study was that both VO_2max^0.32 and PPO^0.32 are able to accurately predict 40-km TT performance (r=−0.93 and r=−0.96, respectively). The strongest relationship and the lowest SEE when predicting 40-km TT performance was found when PPO was adjusted for body mass (W/kg^0.32) (r=−0.96, SEE: 52 s). This finding supports the allometric scaling method proposed by Swain.21 In addition, Swain reported a strong relationship between 40-km TT time and 40-km TT PO (r=−0.94),21 suggesting that both 40-km TT time and PO should be accurately predicted from PPO^0.32. This is similar to our findings, which show a strong relationship between PPO and both 40-km TT time (r=−0.96, 95% CI −0.93 to −0.98, p<0.0001) and 40-km TT PO (r=0.93, 95% CI 0.86 to 0.96, p<0.0001). The finding by Muijka and Padilla,9who reported that PPO^0.32 was the strongest predictor of time trial specialists, also support the proposed allometric scaling method of Swain to predict flat time trial performance. However, the current study is the first study to compare the relationships between 40-km TT performance and absolute PPO (W), relative PPO (W/kg) and PPO^0.32 (W/kg^0.32). As PPO^0.32 (W/kg^0.32) had a significantly better relationship with 40-km TT performance than absolute and relative PPO (both p<0.001), the allometric scaling method is able to more accurately predict flat 40-km TT performance in a heterogeneous group of trained cyclists.

As the current study only shows that PPO^0.32 is able to predict flat 40-km TT performance performed on a cycle ergometer, future research studies need to determine the capacity of PPO^0.32 to predict outdoor 40-km TT performance, as also suggested by Nevill et al.28However, as the main aim of 40-km TTs is to determine and monitor changes in the endurance cycling capacity, PPO^0.32 seems to be the most accurate prediction method. As we have conducted our research on a fairly heterogeneous group of trained cyclists (coefficient of variation for VO_2max was 11%), it is not known if the relationship between PPO^0.32 and 40-km TT is similar in a homogeneous group of elite cyclists, particularly since with this group other factors like cycling efficiency might also contribute to endurance cycling capacity.

In conclusion, the findings of this study show that in addition to PPO, both 40-km TT performance and VO_2max can be accurately predicted from a single PPO test. This suggests that the number of tests needed to determine a cyclist’s cycling capacity (peak and endurance) can possibly be reduced to a PPO test. In addition, minimal equipment is needed to perform a PPO, the duration of a PPO test is short (in most cases ranging from 8 to 12 min) and a cyclist recovers relatively quickly from a PPO test (in comparison to a TT). Collectively, this suggests that a 20 W/min continuous ramp PPO protocol can be used more frequently to monitor changes in PPO, VO_2maxand 40-km TT performance in (well)-trained and elite cyclists. However, it seems unlikely that it can fully replace submaximal cycle tests, such as the LSCT which can be performed on a weekly basis in elite cyclists.19 29

In summary, this study shows that PPO^0.32 (W/kg^0.32) is able to predict laboratory 40-km TT performance/endurance capacity in trained cyclists more accurately than absolute PPO and/or relative PPO (W/kg). In addition, PPO (absolute and relative) determined during the same continuous ramp protocol PPO test, is able to accurately predict VO_2max. These findings suggest that in addition to PPO, both VO_2max and endurance cycling capacity can be predicted from a single PPO test.

Acknowledgments

The authors would like to thank all cyclists who participated in this study.

Footnotes

• Funding This study was funded by the RA Noakes Fellowship, Medical Research Council of South Africa, Discovery Health and the University of Cape Town.

• Competing interests None.

• Ethics approval This study was conducted with the approval provided by the Research and Ethics Committee of the Faculty of Health Sciences of the University of Cape Town.

• Provenance and peer review Not commissioned; externally peer reviewed.

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