The 7.7% Efficiency Gap: How Pedal Choice Dictates Power Output and Cardiovascular Strain

When researchers at the University of Colorado Boulder tested cyclists riding at a casual 50 to 150 watts in 2016, they found something that frustrated cycling purists: wearing running shoes on flat pedals burned no more energy than using stiff carbon-soled shoes clipped into the pedals. "There were no significant differences in the metabolic cost of low-intensity, submaximal, steady-state cycling," the researchers concluded, challenging a long-held assumption about pedaling efficiency.[2]

Cycling orthodoxy has long insisted that clipless pedals—which lock a specialized shoe to the pedal body via a metal or plastic cleat—are universally more efficient because they allow riders to pull up on the backstroke. This mechanical advantage is often cited as the reason nearly every professional rider uses them. However, biomechanical data reveals that the true advantage of a fixed foot connection depends entirely on the wattage being applied, rather than a universal metabolic superiority.[4]

At low mechanical powers, the metabolic cost is identical. If a rider is producing 100 watts on a commuter route, the body consumes the same amount of oxygen regardless of the pedal interface. The flexible foam midsole of a running shoe is perfectly adequate for transferring light loads without wasting energy, making the upgrade to a stiff cycling shoe unnecessary for casual riding.[2]

But cycling is rarely a steady 100-watt effort. When the intensity spikes, the foam midsole becomes a liability. In a 2020 study, biomechanists Burns and Kram tested maximal uphill sprints and found that stiff-soled cycling shoes with clipless pedals improved maximum sprint performance by 16.6% compared to flexible running shoes with toe clips. The rigid carbon or nylon sole acts as a lever, distributing pressure evenly across the metatarsals and preventing watts from being lost to shoe compression.[3][4]

What happens in the middle, during a sustained hard effort like a 20-minute Functional Threshold Power (FTP) test? A 2021 study from the University of Nevada, Las Vegas (UNLV) tested exactly this, measuring both power output and cardiovascular strain across the two pedal types to see if the sprint advantage translated to aerobic endurance.[1]

The UNLV researchers found that cyclists using clipless pedals averaged 226 watts during the 20-minute test, while those on flat pedals averaged 215 watts—a 5.3% power penalty for the flats. The rigid connection allowed riders to sustain a higher mechanical output over the duration of the test without altering their cadence.[1]

Even while producing less power, the riders on flat pedals experienced a higher cardiovascular strain. They averaged 138.5 beats per minute during the FTP test, compared to 135.2 bpm on the clipless setup. The flat pedals required the heart to work harder to produce fewer watts, indicating a leak in the biomechanical chain.[1]

When we normalize these figures to evaluate cardiovascular efficiency, the gap widens. By calculating the power-to-heart-rate ratio from the UNLV data, Factlen found that clipless pedals produced 1.67 watts per beat per minute, while flat pedals produced only 1.55 watts per bpm.[5]

That represents a 7.7% improvement in cardiovascular efficiency during threshold efforts for the clipless system. It contradicts the common claim that pedal type only matters for maximal, out-of-the-saddle sprints, proving that a fixed connection saves significant energy during sustained, high-intensity aerobic work.[5]

Why does this happen? It is not necessarily because riders are pulling up on the pedals. Studies using electromyography (EMG) show that the rigid shoe and fixed pedal interface stabilize the foot, allowing the quadriceps and glutes to drive force straight down without the stabilizing muscles of the lower leg wasting energy to keep the foot planted.[1]

The choice between the two systems depends entirely on the mechanical demands of the ride. The data shows no universal winner, only a sliding scale where the benefits of a fixed connection scale linearly with the wattage applied. If the effort stays below 150 watts, the foam midsole of a running shoe is perfectly adequate; push past 200 watts, and that same foam begins to absorb the power you are trying to put into the drivetrain.[2][3]