PezCranking: PowerCranks Baseline
Monday, February 14, 2005 6:20:16 PM PT

by Dr. Stephen Cheung, Ph.D.

Our long-time readers will know that we’re big fans of PowerCranks, with our resident Tech-geeks having used them long-term over the past couple of years. We now take them from the Tech bench to the Toolbox, and will start to look more closely at the science behind them in this continuing series…

What comes around goes around so the saying goes. This is especially true in cycling, where the fundamental motion of making the pedals go around in circles is repeated millions of times over the course of a season of riding. Unlike golfers or swimmers constantly twiddling with their technique in order to find that elusive perfect stroke, cycling seems dead simple in that the cranks simply keep the legs spinning around in perfect circles.

Little Improvements Means Big Gains
In fact, pedaling in circles seem so simple that most of us never give it any thought. Similarly, the concept of efficiency is very simple: it is a ratio of mechanical work (what actually propels the bicycle) versus biochemical energy expended. However, let’s think this through some more. All things being equal (i.e., same total amount of energy available), if we can be even a measly 1% more efficient with each pedal stroke in terms of oxygen use (i.e., each pedal stroke required 1% less energy), there are two possible results: 1) you can produce the same power for longer; 2) you can generate more power for the same time period. In other words, you will improve your efficiency.

If you’ve been hanging around other cyclists for a while, you’ve probably heard this same general arguments, coupled with advice to train your pedal stroke by consciously lifting your leg on your upstroke, riding fixed gears, doing high rpm drills, or one-legged pedaling on the trainer. All of these techniques have some basis and benefits, but they can be limited in effectiveness for various reasons. For example, the high momentum of the cranks and the short time window of each stroke with high rpm riding can mask any weaknesses in the stroke.

PowerCrank Initial Adaptation
Enter the PowerCranks, which is absolutely unlike any cranks you have ever ridden. The basic idea behind PowerCranks are to make each leg independent of each other, forcing each leg to truly pedal in circles and therefore eventually to optimize its mechanics. I won’t repeat the tech details, which we have discussed previously (see below for links). After analyzing the theory and having spent one week on the trainer and two weeks on the road (480 km on the road and 5000 m of climbing in hilly Dunedin) with them, here are my general comments and observations from a scientific perspective:

• The major muscles that you now demand work from are the hip flexors, the hamstrings, the tibialis anterior (shins) and the back. No matter how easy you take it, these muscles WILL be heavily stressed, especially in the initial adaptation. Therefore, it is essential that you gradually build up your time and distance, and that you stretch to minimize the risk of tendonitis or other overuse injuries.

• My initial Maximal Aerobic Power is 275 W, with a lactate threshold heart rate of 155 bpm. I will test myself again after about 4 weeks with the PowerCranks.

• Also, from the Spin Scan feature of the CompuTrainer, I expected that my right leg seemed a bit more powerful than my left (generally 53/47 split), but that my left leg was much smoother in force application throughout the pedal stroke. This latter observation was immediately and repeatedly borne out by the PowerCranks, as my right leg has been consistently the choppier of the two and always the first to tire and limit my riding. After two weeks, this disparity has generally been corrected.

• My general endurance level heart rates are 125-140 bpm. With the PowerCranks, I have found that riding at the same perceived effort raises my HR by 10-15 bpm, such that steady endurance rides on flats are in the 140-155 range. Why the difference and why would my endurance HR be near my LT HR? No research has been done measuring muscle activation and circulatory changes in the leg while using PowerCranks, but I think that the HR changes are due to the spreading of force generation across more muscle mass, requiring more overall blood flow required by the legs until the muscles adapt by becoming more efficient and building more blood vessels to these new muscles.

• Cadence drops dramatically with the initial adaptation phase, with my cadence being 70-75 rpm for prolonged riding. This should rise up in the coming weeks, as I’m now comfortable with 75-80 rpm sustained cruising. Coupled with the much higher average power outputs (they have increased from about 200 W average for a flat ride pre-PC to 230 W average), you must be careful about overuse injuries. This is especially the case for me, as I have jumped from off-season trainer riding to summer weather and summer form in training ride pace. I will avoid joining local group rides until I have three weeks of riding under my wheels.

• My Power Index (an indicator of pedaling smoothness based on the ratio of your minimum power versus your maximum power during a pedal stroke) on my Polar 625x was a measly 17% or so on flat rides pre-PC. My Power Index is now consistently up to 19-21% on flat rides, indicating a smoother application of power throughout each pedal stroke.

Reader Experience?
I will continue to report my numbers on the bike and in the lab over the coming months as I become more adapted to the PowerCranks. In the meantime, let me know your experiences with the PowerCranks, and I’ll publish a selection of reader comments in a future edition of Toolbox!