Are there any scientific studies proving the benefits of clipless pedal systems?

Question

Has there been done any scientific studies that proves that clipless pedals actually improve pedaling efficiency etc. over flat pedals? Clipless pedal enthusiasts are quick to say that you must use clipless pedals to improve efficiency when cycling, but I have never seen this being backed up by any scientific sources actually proving this claimed efficiency boost.

Answer 1

The Pedaling Technique of Elite Endurance Cyclists: Changes With Increasing Workload at Constant Cadence was published in the International Journal of Sport Biometrics 7:29-53, 1991. However, it seems to come to the conclusion that they don't really make any difference as far as pedaling efficiency goes.

"...while torque during the upstroke did reduce the total positive work required during the downstroke, it did not contribute significantly to the external work done because 98.6% and 96.3% of the total work done at the low and high workloads, respectively, was done during the downstroke."

This is echoed in Physiological and biochemical determinants of elite endurance cycling performance published in the Medicine and Science in Sports and Exercise 23:93-107, 1991. There are numerous graphs showing that pedal force is only exerted between the top and bottom of the downstroke, represented by a very sharp parabola spiking at 90 degrees from vertical.

That said, I think it's obvious to anyone who has ever done any particularly technical riding that with and without clipless pedals that clipless pedals significantly improve the handling of a bicycle. A fact which is probably more difficult to verify through scientific studies.

Answer 2

The case for/against clipless, or even straps, is sort of summed up in this piece from the Rivendell Bicycles website. They mention studies, albeit without citing the exact source, that actually pulling up on the pedal is extremely unlikely, except maybe on short uphill or sprint bursts, and so being attached to the pedal is far from being a must. And they suggest, without supporting evidence, that it may actually make you a better cyclist, because without attachment your legs have to learn to go in circles, and not simply be taken along for the ride.

There is also the issue with positioning your foot on the pedal: all that careful messing around with the cleats so that the ball of the foot is exactly over the pedal axle. But then there is that other blog from Joe Friel, who is an evidence nut, suggesting that there is no proper support for that being best, and that it may be more efficient to put your cleat under the arch.

Joe's blog, together with the (again, inadequately referenced) story of the Japanese competitor in Ironman New Zealand that forgot to put his shoes in the transition bag, and went to a bike personal best riding barefoot on clipless pedals, have really changed my outlook on the need for attachment to the pedals. I ride with clips on my fixie, but am more and more considering changing to plain pedals and see where that takes me.

Answer 3

It's not a study per se, but the Wattbike gym machine has a useful power output meter which shows the power being applied by each leg (explained in more detail on their website).

The basic premise is that by smoothing out the push and the pull you can see a visible effect on the power curve on the display. The real key (from personal anecdotal experience) is that clipless pedals assist in these actions because the pull isn't just employing a different set of muscles in the leg and adding more power (although it is doing that), you're also reducing the total down time in each cycle. If you're just pushing, there's going to be periods where either neither is pushing and thus the bike/revolving weight is decelerating or even where both are pushing and counteracting each other.

Clipless pedals aren't going to assist in the latter case, but they will in the former. So by pulling you're helping to compensate for the lag in the cycle until the other leg starts pushing and we all know that maintaining a speed is generally easier than accelerating to that speed. So if you've got even 5-10 degrees (or more) of arc in every cycle where neither foot is pushing (see the wattbike examples of a bad transition, the curve that looks like a figure-of-eight) then you're having to work to regain the previous power. While if you're managing the leg-to-leg transition, the effort doesn't drop off so much (resulting in a 'peanut' curve) and you're not losing as much power.

Additionally, as suggested here, the clip is allowing you to attach at a better point on the base of foot, rather than on the ball of the foot which is demanded by your not being attached.

Answer 4

Foot retention, in some form, has been around since the dawn of cycling.

There are multiple reasons for it:

• Having a foot slip off the pedal during a hard effort is dangerous (especially on fixed gear bikes, but also during a race in close quarters). This isn't a risk at slow speeds, but at high cadences, it can be hard to stay on pedals without retention.

• If you ride a lot, your pedal stroke will get more efficient just like a runner becomes more efficient with running. What this means on the bike is that your feet are not resisting each other on the upstrokes and wasting energy. It also means that on the upstroke your foot is applying little-to-no force on the pedal and it can easily shift position if it is not retained by clipless pedals or straps. If your foot is not in the right position, your stroke is less efficient and there is the danger of coming off the pedal during an exertion.

I think if you want scientific evidence for foot-retention, all you need to do is find evidence for having the foot placed properly on the pedal.