Most cyclists will get interested in the biomechanics of cycling at some point. One of these moments is when looking into advancing from platform pedals to clipless systems, or when they had a crash caused by clipless pedals and trying to find out if the risk is worth the benefit.
My interest in the scientific aspects of cycling started with reading the book "Cycling Science: How Rider and Machine Work Together" by Max Glaskin. Even almost ten years later, it is still a great starting point for any cyclist. It is a beautifully designed book, visualizing the often relatively dry scientific facts with aesthetic graphics and charts. Thus, it is more a clever tease than a scientific compendium.
Coming to clipless pedals and bike shoes, you will find myths long debunked by scientific studies but still almost religiously repeated in the media and among cyclists. Sometimes the age of these studies works against the facts, are ignored by the cycling world, and are easily dismissed as "old data." For example, the myth of the upstroke has been debunked since the 1980s and is still out there.
We developed the Bythlon pedal system for the ambitious cyclist. Bythlon offers additional performance allowing cycling with purpose-designed bike shoes but without the risk of clipping in. Our customers switching from regular sports shoes to rigid-soled cycling shoes report back average performance gains around 15 to 25%. However, supporting scientific data beyond this study from 1995 has been rare.
Fortunately, there is a new refreshed interest in cycling science. We find associate professor Rodger Kram at the University of Colorado at the forefront of the research into the efficiency of bike shoes. In recent years he has published three related studies in the journal Footwear Science.
The first one is from 2016 and came to the somewhat surprising conclusion that the shoe type and shoe–pedal interface do not affect the metabolic cost of bicycling. Wait, what? Yes, the researcher found that the energy required pedaling at defined watt output and cadence with sneakers on a flat pedal, then an identical shoe with toe clips, and finally clipless pedals was all the same.
A closer look at the methods reveals the answer: The participants were ten healthy, injury-free, experienced competitive, or experienced recreational cyclists and were asked to pedal 5 minutes with steady cadence at 50, 100, and 150 watts with 5-minute breaks in-between. Everyone with a power meter or a smart home trainer will recognize that these output levels are very low and brief, particularly for experienced riders. So yes, to us, this is obvious: For short steady-state rides with low effort, shoes don't matter.
I guess someone pointed the researchers in the right direction, and they repeated the test in 2019 for a second study—this time aiming at maximum power levels. Comparing running shoes with toe clips versus cycling shoes with click-in pedals showed the cycling shoes enhanced the maximum power output by 16.6 +/- 10.2%. This finding is again no surprise to us – our customers report similar figures.
Maybe there is one question left: Bike shoe soles come with different grades of stiffness. The stiffest are the most expensive and made from carbon versus the less rigid nylon versions. Is there a performance difference?
The title of the third study published in 2020 answers this already by name: "No effect of cycling shoe sole stiffness on sprint performance." The researchers tested three different bikes shoes with various levels of stiffness and found no difference for the peak power.
In conclusion, rigid-soled bike shoes help the cyclist transfer more power to the pedal, but you don't have to buy the most expensive bike shoes.
The bicycle pedal upstroke, the impact of pulling
The myth of the upstroke has already been debunked in the 1980s by Dr. Jeff Broker, but the pulling technique to improve the pedal stroke in road cycling is still controversially discussed today. Two misunderstandings of scientific data are responsible for the debate.