Cadence in cycling refers to the speed at which you are pedaling measured in revolutions per minute, or rpm. The power you produce is a direct product of pedal speed, with Power = Angular Velocity (pedal speed) x Torque (force applied at the pedal).
Based on this formula, it’s easy to see that as your pedaling speed increases, the force per pedal revolution drops to maintain the same power.
Less force per pedal revolution means less strain on your muscles. Less strain means less muscular fatigue, which ultimately results in an increased time to failure. You can ride at a given power for longer before your legs give out. Imagine trying to hold 100% of your MAP at 30 rpm. Most people wouldn’t make it to the 2.5-minute mark, let alone a full 5 minutes.
At the same time, you would also struggle to hit the 2.5-minute mark at 100% of MAP riding at 140rpm. Riding at high cadences results in a higher cardiovascular strain, which is entirely due to decreased efficiency. Most riders will have an efficiency of around 23%, meaning 23% of the energy the body uses turns into the power you can deliver to the bike.
At higher than regular cadences, efficiency can easily drop by 10%. In fact, during various cadence testing we have completed in our Boulder Lab, we have recorded sustained (4+ minutes) efficiency as low as 5.4%. So what does your body do with the rest of that energy if only 23% turns into bike power? Most of that energy converts to heat. That means riding at 250W results in around 800W of heat production, the same heating power as most bread toasters!
Extra heat production is not what happens to that 10% change when riding at higher cadences. This decreased efficiency is due to a neuromuscular phenomenon known as “co-contraction.” Before diving in too deep, it’s important to remember that muscles exert force by shortening. Co-contraction is when two sets of muscles around a joint (flexors and extensors) are active (trying to shorten) simultaneously. An example of this is flexing your biceps (elbow flexor) and triceps (elbow extensor) simultaneously. Your lower arm would not move despite the fact both muscle groups are using energy to contract.
Your muscles react to nerve signals to both contract and to relax. When riding at super high cadences, your body runs into the issue of not contracting and relaxing your leg muscles fast enough. You end up contracting your muscles at the wrong phases of the pedal stroke. This results in more “negative” force during each reset phase of the pedal stroke. In this sense, your legs are producing more power when at these higher cadences. It’s just that less of that power actually makes it to your wheel to help propel you forward. We refer to this co-contraction limiter in terms of neuromuscular coordination (NMC).
All of our movements, large and small, utilize co-contractions, meaning all movements have some level of required NMC. Think about are typing on a keyboard. The NMC of the muscles in your fingers and hands allows you to hit the right key at the right time with enough force to trigger the key but not so much you end up with bruise fingertips. Most people remember first learning how to type or write. At first, you are slow and a bit clumsy. You make mistakes. Over time you can type/write faster and faster with better accuracy. Your ability to type/write faster is mainly down to the improved NMC of your hands. Your finger muscles might have gotten stronger, but the ability to hit a key harder doesn’t result in faster typing.
You can view cadence on the bike in the same way. When most people first start riding, their cadence is naturally low, often below 60rpm. As NMC improves, the cadence at which co-contraction starts to occur increases. As NMC improves, people will ride at higher and higher cadences until around the 80-90 rpm mark. This improved NMC is strictly down to time “practicing” pedaling. While some of you might have actively trained to type faster, most people get faster at typing over time.
The main differences between typing and pedaling are the size of muscle groups involved and the “need” for co-contraction to control the movement. Larger muscle groups (legs vs. fingers) use significantly more energy, which requires oxygen. Our leg muscles can produce more power and therefore need more oxygen than our cardiovascular system can handle. You would have to type pretty fast to start breathing as hard as you do riding at your FTP.
Now consider that your legs will make perfect circles when pedaling because you are physically attached to a circular crank. When typing, you don’t just happen to hit the right key every time. You can actively try and type faster, but once you cross that NMC threshold, you might be hitting keys more quickly, but they won’t be the correct ones.
Why does this matter? It matters because improving your NMC on the bike means you can ride harder for longer. Fixed cranks by their design allow you to have very poor NMC and still make perfect circles. You wouldn’t even be able to complete most other sporting movements or day-to-day tasks with such poor NMC.
This is why Cadence Builds, Cadence Drills, and Cadence holds occur so frequently in all of our training plans. The only way to improve NMC is to push past your current limit of NMC. Since you are ‘locked in’ to your pedals and will always make perfect circles, pushing past your current pedaling NMC means riding at uncomfortably high cadences. These are also the best sessions to maintain a high level of NMC even once you feel you have “mastered” cadence builds and think you never need to do them again.
The increased efficiency from improved NMC impacts all intensity levels, not just top-end power. No one has ever ridden faster by being less efficient. Improving and maintaining your NMC will put you in a better position to achieve your cycling goals regardless of what those goals are.