Pedalling a bike: the importance of True Measurement

A power measurement example that shows how true data has made a significant difference to this rider’s approach to pedalling.

Bryan Taylor

Bryan Taylor

Verve Cycling President

Many years ago, the only measurement that really mattered for the bike racer or the aspiring kid on their tricycle was the finishing post. A line across the road or a lamp post, it didn’t matter – first one there WON!

Racing a bike is still the same. Gran Fondo, Zwift race, Olympics or Tour de France stage – all the same – it is about getting across the line.

What is different now is that we are able to measure things. We can measure the speed, our heart rates, our position relative to the finish or the terrain, our power. Here, the importance lies in ensuring that the measurements are true, as even just a very small percentage of inaccuracy can make an exercise wholly redundant.

Let’s take what appears to be a very simple concept – pedalling a bike. Our example today is as simple as we can make it with true measurement. It aims to demonstrate why the truth is so important and how it has made a significant difference to this rider’s approach to pedalling.

The test was completed on a Standard Road InfoCrank using an air-braked trainer. The data was logged by a custom Verve Cycling data logger and analysed using the VINC Pro software.

The first graph below depicts the entire left and right pedal strokes of a rider doing a 16 minute test ride – altogether about 2m data points. There are many metrics available, but we will just start with one of them; 53/47 left/right balance. This outcome over the full ride is pretty normal for this cyclist who goes through life with the view that his left leg is stronger than his right.

His physios tell him that both legs are quite different. He is a little confused, because after a hard event (or during) his left leg always cramps prior to the right – ‘why would the strong cramp first?’ – but all in all satisfied with the ‘diagnosis’ of all concerned that he is stronger in the left than the right.

Now we will look more closely at the pedal action during the second 8 second effort from the test.   

Surprisingly, the right(green) leg produces higher peaks over the exercise – in fact about 8% higher. We also can observe that the right leg has lower troughs on every pedal stroke than the right.

The overall pedal stroke of the right leg is inferior to the left.  We have also calculated that the right leg is ‘tiring’ twice as fast as the left.

The effect is easier to see on the Verve Maximum Sustained Output Analysis. Here the same effort is seen simultaneously as Torque per rotation and Power over time.

What is obvious here is that the Peak Torque – the top red/green/grey lines – show that the right peak is always higher than the left by a significant margin. But the torque applied through the entire pedal stroke tells a different story – both lines (lower red/green) are very close, but the left leg is slightly more powerful. The end result on the last rotation measured was only 0.5nm different.

We have added in the power Maximum Sustained output (now in the lower left corner) which is more marked, the left leg is consistently more powerful than the right. (Power and Torque are a little different, because torque doesn’t take into account speed of rotation – basically torque reduces as speed increases – power takes into account both force and speed).

So what was the aim of this simple exercise in reality?

  1. The general prognosis that this rider’s left leg is stronger than his right may be correct but it is not totally correct.
  2. The right leg is able to exert considerably more force on the cranks than the left leg when called upon to do so.
  3. The therapy that has been applied (for the past seven years on this cyclist) has involved increasing the strength of some muscles in the right side of the body and leg.
  4. But the true measurement suggests that there is a problem rotating the right leg that may not be a strength issue, because we have evidence that the right leg is stronger to push down than the left. However, at the ‘bottom’ of the pedal stroke there is a problem that causes the leg to tire faster and reduces the effectiveness of the entire stroke.
  5. The question now for the experts is, ‘where and what is the hindrance?’
  6. Once found and worked on, can we then strengthen the LEFT leg to the point of the right and therefore gain 8-10% more power overall?

The true power measurement has given the rider an insight into what is really happening when he is pedalling, providing him with a real opportunity to truly achieve that gain in power overall.

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