What is Power All About?

Knowledge is Power

Most of us love gadgets, especially when we believe they will make us faster. In cycling, the ultimate gadget is the power meter.This measurement tool doesn’t look bling and isn’t the lightest or most aerodynamic piece of kit out there. What it gives you is information about how hard you are working. It’s like having a mini sports science laboratory attached to your handlebars! I must admit that I’ve become more of a purist as I’ve got older. My perspective has changed and I’ve learnt just as much about sporting performance through yoga and Vipassana mediation as in Medicine and Science in Sport and Exercise. However, understanding cycling power has helped me link the feeling and the physiology to performance optimisation.

In this blog I talk about how the information from a power meter can be used to help you achieve your personal best.

Chris Hoy

Introduction

So you’ve been training for your big race all year, your motivation is high and the adrenaline is pumping. Your start time comes and you fly out of the starting blocks, getting up to your target heart-rate quickly. Your breathing becomes deeper and more rapid. The effort starts to hurt. That’s ok, though. Simply backing off a little gets you back into your rhythm and you feel you have performed well. But have you performed to the best of your ability? Read on and find out.

One of the reasons the British Cycling World Class performance programme is so successful is it is set up to allow riders to perform optimally; that is to produce the best performance possible under specific conditions. Simply focussing on winning isn’t enough because the performance of the opposition cannot be controlled. The use of power meters is fundamental to the step-by-step approach used to achieve the marginal gains required to optimise rider performance at the very highest level. Of course, not all of us can justify the cost of a power meter. However, by understanding cycling power could help you on the way to achieving a personal best.

A screen dump of TrainingPeaks WKO
A screen dump of TrainingPeaks WKO

What is a Power meter

A power meter typically consists of strain-gauges contained within the cranks, rear-wheel hub or in the pedal axle, a ‘switch’ to measure cadence and a small computer unit to collect and display the data. As the rider applies force at the pedals, the electrical resistance in the strain gauges change. This measurement of change, which is proportional to the force applied, is ‘sent’ to the computer unit and in conjunction with the cadence measurement, power is calculated. Therefore, in simple terms power, measured in watts (W), provides a very accurate measurement of how hard a rider is working. Most computers also record speed, heart-rate and GPS data. In short, a power meter is the bike’s equivalent of a black box on an aircraft, providing information on every turn of the pedal.

Understanding the Data

You don’t need to be a physicist or sports scientist to interpret the data collected from a power meter. Following a few basic steps will help you do so:

  • Use a good computer software package to upload your data to. Many coaches and riders at use TrainingPeaks because it is so user friendly. This powerful online programme is suitable for experts and beginners alike because it can be configured to suit the analysis needs of the individual.
  • Learn to ‘crawl before you run’. To develop an understanding of power requires is similar to designing a training programme. You must build strong foundations, understanding the basics of power measurement and link that to the basics of human energy production. If you attempt to do the complex analysis without strong foundations, you are unlikely to get the most from your investment.
  • Enrol on a course. I developed one in my day job with British Cycling, details of which are found here.

The next course we’re delivering is Saturday 22nd February 2014 – 11:00 – 18:00 – Stirling, Scotland. 

Using the Data

Top coaches and scientists working in cycling probably understand the demands of their event more than in most other sports. That is because they can analyse and optimise performance effectively using power data. For example, it’s possible to quantify the demands of a BMX event in minute detail, through every turn of the pedal. Power data will tell me that a female rider needs to deliver around 2000W out of the start-gates to gain the best racing line. Then she will deliver 5-10 efforts exceeding 1500W in a race lasting under 50 seconds, double what a typical male club-level athlete can produce in a one-off effort.

Tony in the SRM Workshop
Tony in the SRM Workshop

By understanding the power demands in a race provides valuable information on what training sessions are required to prepare for and improve performance for future races. For example, on-bike training is probably not sufficient to be able to produce 2000W. Rather, a supplementary and highly specialised lifting programme in the gym is required. The rider also needs to be able to do repeated hard sprints at power greater than Cav produces in his race to the line. A power meter gives the coach almost instantaneous and accurate feedback on whether the aims of the session are being achieved or not. Additionally, with more complex analyses in separating power into its component parts, force and angular velocity(cadence), it is possible to identify what the most effective gearing on the bike is likely to be for optimal performance.

Power output also allows us to accurately monitor training volume and intensity in the short-, medium and long-term. Looking at a few easy to understand graphs will tell us if we are improving or not. Coaches will know exactly what power output a rider is likely to achieve in specific sessions, even if they are on the other side of the world. If the riders are unable to hit these numbers, it may suggest that the rider is not sufficiently recovered from their previous sessions and the coach will adapt subsequent sessions to aid recovery.

In individual races such as time trials, all but the most experienced riders set off too hard. This is because the rider’s perceived effort in the first few minutes of exercise does not reflect the intensity they are riding at. By the time it does, fatigue will begin to set in and the rider will slow down. It is very common for a 20-30% power-overshoot at the start of a time trial, resulting in a loss of several minutes from what could be optimally achieved. A power meter will help a rider get closer to what is considered to be optimal.

Top Tips

  • Power meters are great tools, but it’s important that you don’t get too caught up in the numbers. There’s no point in getting a personal best maximum power number if it’s not reflecting in your race results because you can’t go round a corner.
  • Power meters are precision instruments and should be treated as such. Therefore, you should get your power meter calibrated at least once per year, ensuring this cost is factored in to your purchase decision.
  • Don’t become over reliant on a power meter as doing so can limit your performance. Using one during group rides could mean you being dropped on climbs or you trying to ride at 100km.h on descents just to stay in your power zone. Don’t do it or bananas may fly at your head.
  • Consider hiring a power meter before buying one.
  • Invest in a specialist software package such as TrainingPeaks. It tends to be far more user friendly that the ones that are supplied by the power meter manufacturers.
Hunter Allen a power guru!
Hunter Allen a power guru!
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