Pedal Stroke Efficiency
05 Jul 2004
An interesting TV documentary about the legendary French rider Jacques Anquetil has inspired me to return to the subject of pedaling efficiency.
The magnificent Normandy hero remains an unequaled example of physical movement technique, especially in time trials.
The way he “caresses” the pedals thanks to an extraordinary use of the ankles permits him to prolong the effective or useful phase of his pedaling, thus reducing the force peak of each pedal stroke.
But what do we mean by the “effective pedaling phase”?
When we push on the pedals, the applied force can be split into two vectors: one perpendicular to the crank arm, and one tangential or parallel to it.
The first vector transmits rotary force to the crank arm and is thus an application of ‘effective force’. The second vector tends to ‘prolong’ or lengthen or even deform the crank arm and, producing no rotary force, represents an ineffective application of force.
With regard to pedaling technique, these two forces can be more or less present. Obviously the more efficient technique is one where the ineffective force is reduced to a minimum.
Optimal ankle movement consists of reducing the vector of tangential force while prolonging the duration, in the pedaling cycle, of the application of effective force outside of the 180° of a so-called neutral lower point.
Perfect ankle movement consists of a progressive extension of the foot articulation from approximately 90° to 190° of the pedal stroke—an extension that then reduces progressively on the upstroke (from 190° to 360°) of the stroke, bringing the ankle back to its original position.