Flats vs Clipless Pedals
Power comparison using flat pedals with mid-sole foot placement versus conventional "clipless" clip-in pedals
by Jerry Nolan
When I took up the sport of triathlon. I soon discovered I had a problem with my calf muscles cramping after transitioning from the bike to the run. To solve the problem, I decided to minimize the use of the calf muscle by placing my foot mid-sole on the pedal. Naturally I had to switch from "clipless" clip-in pedals to flats to do this. My initial impression with the mid-sole foot placement was "Wow! I feel so much stronger this way." I rode mid-sole for the duration of my triathlon career, about six years, then continued to ride this way for the next four years. I took a lot of grief from my roadie friends ranging from disbelief to being told I could gain 30% more power by switching to clip-in pedals. In Fall of 2019 I decided to try clip-in pedals again. My reaction was "Wow! I feel so much stronger this way." Okay, what's going on here? I decided that I'd better conduct a scientific experiment to see what's going on.
I felt that the mid-sole foot placement meant more power because the calf muscle is the smallest and weakest muscle in the power chain of the cycling stroke. Most power comes from larger muscles in the body, namely, the gluts, hamstrings, and quads. I thought the small calf muscles were a power bottleneck for the larger muscles. This was the reasoning behind my sticking with mid-sole flats for so long.
When I switched back to the clip-in pedals, I seemed to be ride stronger than ever, but I learned long ago not to trust my judgement in such matters. I needed to be scientific. I designed an experiment where I would ride one day with mid-sole flats and the next with clip-in pedals. I could quantify the results with a heart rate monitor and power meter and then use statistical analysis to see if there was any significant difference.
I used Garmin Vector 3 power meter pedals to measure power. My plan was to ride my Specialized Roubaix on a Kurt Kinetic Road Machine fluid trainer for three months, December, January, and February. For the mid-sole foot placement, I used a pair of Flypedals. Flypedals are adapters that convert clip-in pedals to flat pedals. They are designed for bike commuters who don't want to deal with two pairs of shoes when commuting to work.
In my experiment I rode 18 times with the clip-in pedals and 18 times with the mid-sole foot placement. Each ride was targeted for 1 hour and 40 minutes in duration. Some rides were longer and some shorter depending on how I was feeling, but the average time for riding with clip-in and mid-sole flats was close to equal. It should be noted that indoor riding can seem harder than outdoor riding because there is no stopping for traffic, no coasting downhills, and no slowing for safety. My Garmin Aerobic Training Effect was greater than 3.0 for 88% of the indoor workouts. By comparison, my outdoor rides have been greater than 3.0 for only 25% of the rides. The indoor rides were not boring as I watched “Jerry’s Scenic Cycling” videos on YouTube. Occasionally I put in a sprint which I can identify in the data by bursts over 300 watts.
At the end February I exported the Garmin data to a spreadsheet and compared the averages for all the data. Power was the first thing I looked at. The averages for the clip-in and mid-sole flats were different, but the difference could be due to variability in my performance. To correct for this, I ran T-tests on the data. If the result of the t-test was less than .05 then there would be a 95% probability the difference was not due to the variability in my performance. It would mean there was a significant advantage to one pedal over the other.
RESULTS
Power
The results of my experiment showed no significant difference in Average Power, Max Power, Max Avg Power (20 min), or Normalized Power (NPA). There was also no significant difference in Calories, Aerobic Training Effect, Max Bike Cadence, Training Stress Score, and Total Strokes.
Cadence and Heart Rate
There was a significant difference in Avg Bike Cadence and Avg HR. The clip-in pedals produced significantly higher Avg Bike Cadence and Avg HR. But there was no significant increase in power.
DISCUSSION
Power
It would appear from the results of this experiment that the only way to produce more power is through more fitness. Clip-in pedals or mid-sole flats will not increase power according to this experiment. Other studies cited below agree with this finding.
Maximum power
Maximum power averaged for all rides was clip-in 312 watts and mid-sole 332 watts. There was no significant difference. In the experiment I sprinted only when I felt like it, so some rides had no sprints. We can look at the maximum power during sprints by averaging the maximum value for power bursts over 300 watts. Results show a value of 406 watts with clip-in pedals. The flat pedals averaged 408 watts. No significant difference. My trainer does not allow me to come out of the saddle for sprints, so all sprints were seated. That these two numbers are so close is extraordinary. I thought for sure I had more sprint power with the mid-sole foot placement. I might try an experiment outdoors where I can stand up during the sprint.
Cadence, Heart Rate, and Gears
Higher HR likely corelates with higher cadence because it takes increased HR to move the legs faster.
When riding with resistance and producing power to overcome the resistance, the power output remains the same if an easier gear is used to achieve the higher cadence. My legs did indeed demand that I spend more time in an easier gear with the clip-in pedals. The calf muscles and ankle joints are relatively weak compared to the larger knee and hip joints so an easier gear was naturally preferred.
A higher cadence might be advantageous because of the pulsing application of power. Power is not evenly applied through the 360o rotation of the propulsion cycle. Most power is applied through a 50o to 60o arc. Since there are two cranks that would 100o to 120o of one propulsion cycle. The other 50% is spread through the remaining 160o to 140o. The faster you go the more important a high cadence becomes because of the greater wind resistance and less glide between strokes. Similarly, high cadence might be better for hill climbing because it is important to hit that next stroke quickly to minimize the loss of momentum between max power arcs. (See Cycling Dynamics graphics below to see graphic of the uneven propulsive nature of cycling.)
The Fatigue Issue
The placement of the pedal under the ball of the foot might be advantageous because the calf muscle is contributing more than when the pedal is mid-sole. According to a study titled Joint Motions of the Lower Limb during Ergometer Cycling “…the ankle ROM (range of motion) was 24 degrees ranging from 2 degrees plantarflexion to 22 degrees dorsiflexion.” I measured my own ankle ROM and it came to 18o. Although the mid-sole foot placement probably has similar ankle ROM, the leverage is not there to allow the calf muscles to contribute as much to powering the bike. It is worth noting that the calf muscles contribution is during the peak power phase of the stroke. (See graphic in Cycling Dynamics section at the end of this article.)
If the calf muscles contribute more, the knee and hip muscles contribute less to achieve the same amount of power. Is this advantageous? It apparently is since virtually all road riders ride with the ball of their foot on the pedal. It does result in a higher cadence, but not more power according to this study.
Given that this study shows that ball of the foot placement results in a higher cadence and higher HR, perhaps pushing a harder gear with mid-sole foot placement will tire the legs more quickly than the heart, or perhaps a higher HR from a higher cadence will tire the heart more quickly than the legs. It is a complex physiological issue beyond the scope of this study.
Pulling up on pedal during recovery
Although riders have long said that a big advantage of clip-in pedals is the ability to pull up on the pedal during recovery, virtually all scientific studies have shown that this is a myth. In Cycling Biomechanics: A Literature Review in the section titled “Force Application” several studies are cited that show riders don’t pull up on the pedal. Here is one paragraph from the section:
In a study of steady-state riding of pursuit team riders and recreational riders, only a few examples of pulling up were observed. Occasionally, some unloading of the pedals occurred, but rarely did the riders actually pull up. When an upward force was demonstrated, the force was small and of short duration (2). The results contradict reports in bicycling magazines claiming that pulling up during the recovery phase can increase one's efficiency by as much as 30 percent. If that were true, elite cyclists would show some upward force during the recovery phase (2).
Cycling Dynamics
Garmin provides cycling dynamics data. This study didn’t look for significant difference in cycling dynamics. Below is a graphic of two typical rides, one for each condition.
Garmin’s Cycling Dynamics
Small Dark arc is 50% of power for each foot
Lighter shaded arc is other 50% of power for each foot
The percentage in the middle of each circle is the amount of power each foot contributed to the output of both legs.
Clip-in
Flats
Studies related to this experiment:
Is economy of competitive cyclists affected by the anterior–posterior foot position on the pedal?
Gross cycling efficiency is not altered with and without toe-clips
Effect of Toe Clips during Bicycle Ergometry on [Vdot]O2 max
Torque-velocity relationship during cycle ergometer sprints with and without toe clips
Bike Fitting: The Myth of the Upstroke
The Body Mechanic: Stop pulling up on your pedals
Joint-specific power production during submaximal and maximal cycling
From the Abstract: Use of a posterior foot position instead of an anterior decreased the dorsiflexing ankle load moment, increased the gluteus medius and rectus femoris activity, and decreased soleus muscular activity but did not significantly change the hip or knee moments.
Muscular activity during ergometer cycling.
From the Abstract: Use of a posterior pedal foot position increased the activity in the gluteus medius and rectus femoris muscles, and decreased the activity in the soleus muscle.
Joint Motions of the Lower Limb during Ergometer Cycling.
Cycling Biomechanics: A Literature Review
Are Clipless Pedals Actually More Efficient Than Flat Pedals? The Answer Might Surprise You.
Posted April 2020
Jerry Nolan
jerry@coloradomesa.edu
January 13, 2021 - NOTE: During 2020 outdoor season I used flat pedals. I started with ball of foot on the flat pedal. By mid-season my legs and feet started migrating to mid-sole. Most of second half of outdoor season my legs and feet preferred the mid-sole position. I apparently got stronger because so far my average watts for 100 minutes on the indoor trainer this winter is about 20 to 25 watts higher than last winter. My average HR is about also 10 BPM higher. I guess I'm just more fit this year. Maybe I should mention that I am 77 years old.