How do runners generate speed?
The aim of most running events is to complete a given distance in the shortest possible time. Whether it’s a 5km or a marathon, the person who covers the distance in the shortest period of time, wins. A runner’s speed is simply the number of steps taken per minute multiplied by their step length - this is an indisputable mechanical fact and there is no hiding from it.
In equation form: Speed = Cadence x Step Length
A group of runners in a group will all be travelling at approximately the same speed but each will be generating that speed with their own unique combination of cadence and step length. Some runners will be moving with a relatively high cadence and relatively low step length; others will be running with lower cadence but higher step length.
The specific cadence and step length that each runner selects for a given speed will be down to a range of physical, physiological and possibly tactical factors. An increase in speed requires the runner to increase either cadence or step length or a combination of both.
Reaching maximum speed
When running at their top speed a runner will run with their chosen combination of cadence and step length. Any attempt to increase speed from this point will create a “negative interaction” between cadence and step length. Continuing to increase cadence will ultimately require the runner to drop step length, and vice versa. When this negative interaction happens the runner has essentially reached their maximum speed for their current fitness level.
Training to improve speed
Overcoming this negative interaction for cadence and step length is where training helps. An athlete can train to improve their physical and physiological capacities to allow them to handle higher cadence (by neuromuscular activations) and longer step lengths ( through benefits from strength and conditioning) without undue fatigue.
Research has consistently shown that most runners self-select a cadence that is slightly lower than optimal and most would benefit from a 5-10% increase, which in turn should lead to an associated improvement in run economy (better running economy means less calories burned per km). A modest increase in cadence may also help minimise the risk of overuse injuries.
Focusing on weak points
Once a runner is aware that running speed/pace is a direct outcome of cadence and step length then they can aim to make pace improvements by focusing on the contributing factors. By focusing attention on making improvements to technique, improvements in speed will happen as a result. The great advantage of prioritising the underlying factors rather than purely just trying to run faster is that the runner will discover which of the two factors (cadence or step length) is limiting for them or is suffering as they fatigue. With this knowledge they can adapt their training and prioritise development of the weaker factor.