Wednesday, July 11, 2012
Leg Speed vs Running Pace
Since this has come up in conversation at least twice recently, I decided to share my thoughts.
Many runners are talking about increasing their leg speed i.e. running cadence or stride rate. I frequently discuss it with my running analysis clients. It also happens to be a major component of the Chi method of running. I utilize stride rate as a method of modifying stride length. Many runners over stride which for the purpose of this discussion I define as landing with their foot in front of their center of gravity. This usually introduces a braking component to the stride which is not economical--each subsequent stride must be more powerful to overcome the increased resistance of braking. Also, this is associated with increased forces at impact and thus a higher risk of injury. Usually I try to help my runners decrease their stride length by increasing their cadence, possibly along with other changes outside the realm of this discussion.
So, the question is: How does this affect speed?
Leg speed and running speed are not necessarily related. For example, a person can run eight-minute miles or eleven-minute miles and have a cadence at 180 steps per minute in both cases. The difference would be related to the amount of forward lean and the power with each stride. Stride length may change too, but that is not necessarily desirable as I mentioned above.
Then, what does happen?
Increasing cadence will decrease stride length and thus, distance covered with each step. However, more steps are made per minute. This may or may not increase speed; it will depend on the person. The purpose of making this change with my clients is to limit their risk of injury and ultimately improve economy. So, as they train with better form and develop more power, they should be able to improve performance, either by going faster or farther with similar effort.