The “true reasons” why you should use a power-meter on your bike

I recently stumbled across an article about the main reasons for cyclists/triathletes to use a power-meter. Although I could not agree more on the importance of measuring power output for such athletes, I think the article completely misses the point on the reasons “WHY” power-meters are important since the reasons given were at least trivial and at most unsubstantiated. Here are a few better reasons I selected for you to use a power meter on your bike:

  • You will have another extra tracking variable: Bike speed is affected by aerodynamics (air resistance), frictional resistance, rolling resistance, inclination, and many other factors (Burke, 1996) that sometimes make it difficult to judge how much effort one is doing or to check performance improvement, whereas power output is not, or at least not so much affected by these aforementioned factors. However, different from what some people may think, power output is NOT more or less accurate than speed or HR, it is actually another monitoring variable that brings extra information. I understand “accuracy” in the context of precision, validity, and reproducibility. Yes, we also have to use other variables to check these things, but normally we should compare accuracy between two instruments or methods that measure the same variable. Long story short, each instrument has its on accuracy, while each variable would have its own characteristics, peculiarities, and limitations. Claiming that “power output” is more accurate than HR, speed, blood saturation, pressure or any other variable simply because it measures “something else” does not sound exactly right to me. In my view, the athlete should use as many monitoring variables as possible as long as he or she knows how to interpret correctly the data.
  • You will be able to measure or infer about cycling efficiency: briefly, what the power meters out there “measure” is the energy/time against the external resistance. Strain gauges are commonly used to measure torque (“strain” x crank lever), that integrated to angular speed allows for power output calculation; and that’s why it’s called power OUTPUT. In order to measure the power “INPUT”, or the energy/time our own body requires to produce that output, we need a calorimeter/metabolic analyzer to measure oxygen uptake (VO2) that can be converted into energy, or we can use HR to infer about VO2. Gross efficiency would be then calculated as follows: power input/power output during cycling (Burke, 1996). Measured in lab set-ups with healthy populations this cycling efficiency is about 9-11mL of O2/ watt, or approximately 30% (Poole et al, 1997). However, cycling efficiency can vary among people and as a result of training (Hopker et al, 2007; Hopker 2012); and to me that’s the “BEAUTY” of the power-meter: we can infer about cycling efficiency live!
  • You can build your “training zones/thresholds” also based on power: If power is an extra variable, one would also have his or her power training zones and thresholds. But care should be taken here! Since power output is an EXTRINSIC variable, it DOES not tell you anything about what’s going on inside your body. HR, in turn, is closely related to your metabolism. Hence it’s a MISTAKE to try to stay at certain “power zone” blindly. Considering that efficiency is affected by fatigue (Noordhof et al, 2015; Castronovo et al, 2013) we should also pay attention to other variables such as HR and RPE. You might think you are at “certain zone”, but it may not correspond to your actual metabolic state.
  • You can use it during your races (really?): I have mixed feelings about this one. Although it’s good to monitor your variables during competition, some athletes may over do it. This might create an extra source of stress to your body and mind. In the end, you want to check how you perceive effort and how you perform. Here is the question: would you slow down even feeling you could go faster just because you are out of you ideal power zone? Or because according to a certain index you would not finish this race at certain “pace”? I don’t have a strait answer to these questions, but perception of effort and fatigue should not be disregarded (Schallig et al, 2017); to me, RPE is the main “integrator” of all internal variables our own computer called “body” interprets and tells us what we are capable of. A trained athlete should know when he or she should go faster or slowdown regardless of anything else.

Measuring power output can be a potent weapon if used wisely. It shows how much power you are producing regardless of other things that affect speed; so during a climb, or under intense wind, you will still be able to know how “intense” you are pedaling. With the help of HR it is also possible to infer about efficiency and use power-zones in conjunction with HR-zones. Nevertheless, power output is merely another variable with its own limitations: it’s an extrinsic variable that, different from HR and RPE (both intrinsic), is insensitive to your metabolism and psyche. Finally, I believe the ultimate goal of the great majority of endurance athletes is “going faster”, and therefore RPE and speed become the decisive “monitoring” variables during any race.

 

References:

1- Burke ER. High-Tech Cycling.  Champaign, IL, Human Kinetics (1996).

2- Poole DC, Richardson RS (1997). Determinants of oxygen uptake. Implications for exercise testing. Sports Med. 24(5):308-20 (1997).

3- Hopker JG, Coleman DA, Wiles JD. Differences in efficiency between trained and recreational cyclists. Appl Physiol Nutr Metab. 32(6):1036-42 (2007).

4- Hopker J, Coleman D, Jobson SA, Passfield L. Inverse relationship between VO2max and gross efficiency. Int J Sports Med. 33(10):789-94 (2012).

5- Noordhof DA, Mulder RC, Malterer KR, Foster C, de Koning JJ. The decline in gross efficiency in relation to cycling time-trial length. Int J Sports Physiol Perform. 10(1):64-70 (2015).

6- Castronovo AM, Conforto S, Schmid M, Bibbo D, D’Alessio T. How to assess performance in cycling: the multivariate nature of influencing factors and related indicators. Frontiers in Physiology, 4, 116 (2013).

7- Schallig W, Veneman T, Noordhof DA, Rodríguez-Marroyo JA, Porcari JP, de Koning JJ, Foster C. The Role of the Rating of Perceived Exertion Template in Pacing. Int J Sports Physiol Perform. 3:1-22 (2017).