Not all watts are created equally.

By Roland Kemp ASCC


How you produce wattage is the first consideration to think about when developing a time trial strategy.  You can create 1,000 watts by pedalling in the 53:12 gear at a very high force but with low cadence, or you can produce 1000 watts by pedalling in the 39:21 gear at a low force but with very high cadence. The power output is the same in the end, but you utilise very different muscle fibres to produce it.

Most fast-twitch (Type II) muscle fibres are recruited in a high-force, low-cadence situation, whereas more slow-twitch (Type I) fibres are recruited in a low-force high-cadence, situation.

Why does this matter when it comes to getting the most out of your time trial efforts? It matters because of the energy expenditure in both situations. When fast twitch muscle fibres are recruited, more muscular glycogen is used in the contraction than when slow twitch muscle fibres are recruited.

Pedalling as smoothly and steadily as possible is key in time trials. By keeping the normalised power and average power as close to each other as you can, you save valuable energy. When normalised power is very high relative to average power, this means your power has fluctuated too much. By saving your efforts on hills and avoiding bursts of wattage, you can keep your index low and therefore really maximise your energy efficiency throughout the course. When considering power output and smooth pedalling, even an effort that isn’t full gas is a ‘match’ which is already ‘burned’.

This will cost you more than you want to spend. This is critical waste of muscular energy which could impact negatively later on in the race. In the same way as when you are driving a car, your fuel consumption will be much higher if you are constantly braking and accelerating hard at every opportunity, than if you just drove smoothly and consistently. Your muscles will react in the same way with energy expenditure when fluctuating between low and high power than retaining a constant, steady output.

KempFitness coaching looks at client data using Traning Peaks. One useful data field to look at is Variability Index:

Variability index (VI): algorithm showing how smooth or evenly paced an athletes power output was during a race or work out.

A properly paced time trial should have a VI value of 1.05 or less while a road race or criterium may have a VI as high as 1.1 or more.

Variability Index can be calculated by dividing Normalized Power by Average Power. 

It’s not necessarily about advocating high cadence, but we recommend that you adopt greater consideration about how you race. Use your gear range to keep your cadence consistent and practice trying to achieve a more steady, smooth power output during training sessions.

Reference adapted from: training and racing with power meter Second edition Hunter Alan and Andrew Coggan.

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