polar pedaling index
Pedaling Index (PI) is the ratio between the minimum and maximum forces of a single pedaling cycle. A pedaling cycle begins when a magnet on the crank passes a relay on the circuit board, and ends when the magnet passes the relay again. The resulting ratio is averaged from the most recent pedaling cycles.
PI helps optimize pedaling technique by measuring the ‘roundness’ of force distribution, or how evenly the power is produced – the higher the PI percentage, the better. Values of 30% or more are very good. Breaks in continuous pedaling affect PI values adversely.
At the crest of a pedaling stroke, there is a weakening, or a "dead spot", in pedaling force before another stroke begins. Developing an even rotation helps maintain consistency over the whole circular pedal stroke, and produces a fluent, forward thrust.
PI enables continuous monitoring of pedaling technique. This is especially helpful at different intensity levels, since pedaling technique tends to become challenged at higher intensities.
A common technique is to use clipless pedals to help maintain a constant force, also during the upward stroke, and by ‘spinning’ the pedals at a higher cadence using a lower gear instead of ‘mashing’ the pedals at a higher gear. Other methods to smooth-out the pedal stroke include changing the length of the cranks to better suit one’s physique or trying to eliminate the dead spot by using variable geometry chain rings or other special products that change the geometry of the crank and bottom bracket.
At higher speeds, pushing against the force of the wind by ‘mashing’ at every pedal stroke will result in a small but constant fluctuation in speed. In races, even minor increases in speed will sharply increase wind resistance, or aerodynamic drag, which requires substantially greater effort to compensate for. Because of that, cycling with small but frequent variations of speed will be less energy-efficient than maintaining an even pedal rotation with constant power and speed, even if the overall average speed stays the same.
It is useful to compare average PI results between different exercise sessions when assessing long-term development.