by Developing Speed
Kinetic Select May 2017
The following is an exclusive excerpt from the book Developing Speed, published by Human Kinetics. All text and images provided by Human Kinetics.
Two factors that determine running speed are stride cadence and stride length.
Stride cadence refers to the number of strides taken per second, and stride length refers to the distance traveled by each stride. The product of these factors gives a mathematically accurate description of running speed. Traditional thinking has suggested that if one of these can be improved with the other remaining constant, running speed will increase. Therefore, the focus of speed training has been on improving stride cadence, improving stride length, or improving both. However, recent research suggests that while improving these factors plays a role in determining running speed, they may provide the coach limited tools when developing speed training programs.
In particular, the concept of stride length, traditionally measured as the distance between each successive foot contact, can be problematic. Too much focus on artificially lengthening an athlete’s stride can result in placing the foot ahead of the athlete’s center of mass. This position compromises the athlete’s ability to generate force and ultimately slows running speed. Instead, an effective stride length should be the focus. This is the distance traveled by the athlete’s center of gravity per stride. An effective stride length is generated by applying a force into the ground (pushing off the ground) and propelling the athlete forward rather than reaching forward with the legs in an attempt to pull the athlete forward. The force producing capacities of the athlete are fundamental to achieving optimal stride and length and maximal speed.
Stride cadence is a function of contact time (the time spent on the ground with each stride) and flight time (the time spent in the air on each stride). Research has shown little variation in flight time between runners of different speeds, and the greatest variations in cadence are a result of differences in ground contact time (Weyand et al. 2000). Therefore, efforts to improve stride cadence should focus on shortening ground-contact times rather than focusing on cycling the legs faster.
Stride length is largely a function of the impulse and velocity generated at toe-off. The velocity of the athlete’s center of gravity, which is a key factor in dictating stride length, does not alter between successive steps. Like impulse, it is generated during the time the athlete’s foot is in contact with the ground (the stance phase). Therefore, efforts to enhance stride length by technical means during the flight phase, the time the body is not in contact with the ground, are limited and should instead focus on generating impulse and velocity during the time the athlete is in contact with the ground.
The discussion of stride length and stride cadence requires an analysis of the phases of a running stride. Each running stride can be divided into two components: a stance phase and a flight phase. These phases are outlined in figure 1.1. The stance phase occurs when the athlete’s foot is on the ground and consists of the time between the initial contact with the ground and the subsequent toe-off.
The stance phase can be further divided into an early stance, a midstance, and a late stance. During the early stance, when the foot makes contact with the ground, the athlete’s body absorbs the landing forces, which can vary from two and a half to five times the bodyweight, depending on the speed and distance of a sprint. The leg muscles absorb the landing forces through eccentric contraction, which lengthens the muscles. This has the potential to cause significant braking forces unless the athlete has the strength capacities and required muscle stiffness to effectively repel this force.
During this phase, the athlete can develop elastic energy, which is beneficial in later stages. During the midstance, the athlete switches from absorbing force to exerting a concentric force, which shortens the muscles and generates maximal vertical force. The elastic energy generated in the early stance can contribute to the force produced through the mid and late stance. In late stance, the body accelerates forward as a result of the concentric forces generated.
The flight phase is the period between toe-off and the next foot contact (see figure 1.2). During this phase the athlete makes no contact with the ground, so in essence is in flight. Velocity during the flight phase cannot be increased, and the athlete must cycle the leg in preparation for the next footfall. An inability to cycle the leg effectively results in suboptimal ground contact on the next stance phase, and therefore limits speed expression. Because athletes can propel themselves forward only when their foot is in contact with the ground, the stance phase should be the main focus of speed enhancement programs.
With Developing Speed, the National Strength and Conditioning Association (NSCA) has created the definitive resource for developing speed training programs that optimize athletic performance. Including assessments and the application of speed training to eight specific sports, this authoritative guide provides all the tools needed for maximizing speed. The book is available in bookstores everywhere, as well as online at the NSCA Store.