I’d like to ask you a question: is the goal of a competitive triathlete to maximize efficiency? Is the goal to use the least amount of energy possible? Or is the goal to be as fast as possible? Do you strive to cross the finish line declaring, "I only burned an average of 600 calories per hour!" or rather "That was a new PR for me!"
While efficiency is important, your overall goal as a competitive triathlete is not to be efficient, but to be as fast as possible. While efficiency and economy usually go hand-in-hand with speed, it is often the case that the fastest way the finish line is not always the most efficient, and cycling cadence is a prime example.
Let's define cycling efficiency. The simplest definition of efficiency is the ratio of the work accomplished to energy expended, that is, the effectiveness of converting chemical energy into mechanical work. In the case of human beings, our energy source is oxygen, and we convert that energy into mechanical work. Someone who uses less oxygen, or fuel, for a given amount of work is therefore more efficient, just like gas mileage with a car. You can have two cyclists turning out identical power, but one churning away at a cadence of 45 and the other at 90. Both are doing the same amount of work, but one may be more efficient than the other.
As the science of cycling exploded in the late 70s and early 80s, there was a significant focus on cycling efficiency. For example, a 1979 study in the Journal of Applied Physiology indicated that cadences of 50 to 60 were the most efficient, using the least amount of energy for the same amount of work. In fact, there are studies going all the way back to 1913 that have consistently proved that cadences of 50 to 60 are the most efficient cadences, with efficiency decreasing as cadence increases. Primarily because at higher cadences, you have to lift the weight of your own legs more often, and use more energy. However, in the early 80s, the Journal of Sports Medicine took a look at cycling efficiencies at different power outputs, and found that at lower power outputs of 140 watts, higher cadences were still less efficient, but at higher power outputs of 290 watts, there was only a small decrease in efficiency for higher cadences. A 1992 study from the Journal of Sports Medicine took this one step further when it found that as a subject was able to cycle at a higher percentage of his VO2max, the higher cadences of up to 100 became less and less inefficient. Meaning, as your intensity increases, you can increase your cadence without too much loss of efficiency, with the journal reporting the cutoff to be at about 70% of your VO2max. So, the take-home from these studies is, if you can either maintain a high power output, let’s say 250 watts or more, or if you can cycle at 70% of your VO2max, a higher cadence does not cause too much of a decrease in efficiency.
Another fascinating study from a 1993 study performed by ASU, and published in the journal Medicine and Science in Sports and Exercise took experienced runners with no cycling experience, but of equal aerobic capacity to experienced cyclists. These runners were asked to pedal at their freely selected cadence at a constant power output of 200 W. Their average preferred cadence was 92 rpm, but their most economical cadence was approximately 63 rpm, essentially the same as the cadences recorded for the experienced cyclists. It is amazing that a runner’s instinct, and the most economical runners run at about a 90 cadence, but their instinct when getting on the bike is to mimic that 90 cadence.
So, even though higher power output or intensity means that you can cycle with a higher cadence and lose less efficiency, lower cadences are still more efficient. So why do we want to ride at a cadence of around 90 as a triathlete? A few reasons:
First, ASU’s study also indicated that perceived exertion for the same amount of work was higher for cadences at the extremes of 50 or 100. Meaning, the subject felt that more work was being done for the same power output at those extreme cadences. One benefit of being closer to the middle is that you will feel less tired.
Second, higher cadences use more slow twitch muscle fibers. You’ll recall that slow twitch muscle fibers are used for endurance, and that fast twitch muscle fibers are used for explosive power and speed. At the same power output, a lower cadence requires more force, therefore more fast twitch muscle fibers need to be recruited. A 1992 study published in the European Journal of Applied Physiology took eight men cycling for 30 min at approximately 85% of individual aerobic capacity at cadences of either 50 or 100. Muscle biopsy samples were taken immediately prior to and after exercise. The 30-min exercise bout resulted in no statistically different decrease in slow twitch fibers between the 50 and 100 cadence. However, fast twitch fibers glycogen levels decreased 49% during the 50 cadence, compared to a 33% decrease observed in the 100 cadence. You will experience less neuro-muscular fatigue at higher cadences.
Third, because you are using more slow twitch muscles at higher cadences, you will be using more fat for fuel instead of glycogen, giving you a better reserve of energy for a string finish.
In summary, while cycling at higher cadences may be less efficient in terms of energy use, the fact that you will have less perceived effort, less neuro-muscular fatigue for the run, and use more fat for fuel instead of glycogen, put together mean that as a triathlete, the best cadence is somewhere between 80 and 100, with most elite triathletes hovering around a cadence of 90.
This topic was one of several topics covered in Episode 31 of the Tri Talk Triathlon Podcast.