Cadence, muscle fibre and getting results

by Angela Reed-Fox

Every part of the session you design should have a rationale behind it, and cadence is one of the components which will help determine whether a challenge is safe, effective and efficient – or not.  

You'll have come across that one rider who, no matter what you have planned for the class, ends up pedalling at around 40-50rpm at such a high resistance that they're having to recruit their upper body to help power every. single. pedal stroke. 

Doing this puts too much strain on the joints and the back – and the risk is exacerbated if they haven't warmed up adequately to start with. This is a problem that you'll most often encounter in newer riders who think that they need to make the session as hard for themselves as possible if they're to get any benefit.  

So what's happening in the muscle? 

Muscle fibres are fast or slow twitch. Slow twitch fibres (type I fibres) have more mitochondria which means they're able to create more energy through the aerobic system, using oxygen and burning fat. Fast twitch muscle fibres (type IIa and IIb) are a little different. Type IIb fibres create energy anaerobically (fuelled by glucose stored in the muscles) – these are the powerful short-burst fibres. Type IIa can use both aerobic and anaerobic metabolism and so share features of both type I and type II fibres. Hill-climbing at 70-80rpm uses more of the aerobic fibres which enables greater aerobic endurance (and therefore great fat burn).  

Thinking about the different muscle fibres then with regard to class challenges, you'll be using more fast-twitch (type II) fibres during short, intense challenges such as sprints (up to 1100rpm) and heavy climbs (around 60-70rpm), and conversely, using more slow-twitch, aerobic-friendly muscle fibres during endurance sets such as timetrials and flats at 80-90rpm, and working climbs around 70-80rpm. 

Keeping an idea on what muscle fibres you're wanting to use, or what energy system you want to concentrate on will determine how you design your session. You'll be targeting fast-twitch muscles for short periods of intense power (whether slow or faster cadence), and slow-twitch muscles which take longer to fatigue for extended challenges and longer intervals at a moderate cadence.  

So the cadence, and the power that you'll be coaching along with it will determine the result you'll expect your riders to get. If you're coaching short intervals with high power and a cadence above 100rpm or below 70rpm, you'll be training for strength and using more of your fast-twitch muscles; if you're coaching longer intervals at a moderate cadence (70-90rpm) you'll be coaching endurance, improved aerobic capacity, and fat burn.

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