Speed Development Part 1: Why Relative Strength is the Foundation of Speed Development

First off I want to apologize because I’m going to have to talk about physics a decent amount in this blog, but I’ll try to keep it simple. When talking about speed development we usually separate acceleration and maximum velocity as the mechanics are very different, but for the purpose of this blog I will focus on maximum velocity. Here are some of the facts that you need to know:

1. Stride Length is primarily determined by an athlete’s anthropometrics and the Ground Reaction Force (GRF) they are applying into the ground.

2. Impulse = Force x Time

3. Speed = Stride Rate x Stride Length

Speed can be looked at as being equal to an athlete’s stride length multiplied by stride rate. Today we are going to focus on stride length and stride length is largely determined by anthropometrics (bodily measurements) and GRF. As we can’t coach an athlete to get taller, we will focus on their GRF.

If two athletes have similar anthropometrics and running mechanics, the athlete who has a better relative strength will most likely be faster. I say most likely because the athlete with the superior Rate of Force Development (RFD) will be faster, but that will in most cases be the stronger athlete. Now notice in the title I said relative strength and not just strength (Relative strength is strength divided by body weight). If the athletes are equal in all other aspects, the lighter athlete will be faster. This is because every time your foot strikes the ground while running you first have to absorb the eccentric force necessary to decelerate your body weight and then project your body forward. For every pound of muscle or body weight added to an athlete, 2 pounds of additional ground force are needed to offset the weight. This might not seem like a big deal as the decrease in stride length is so minimal, but in a 100 meter sprint an athlete will be taking approximately 50 strides so that little decrease in stride length could be the difference between winning and losing a race. In other words if you are a track sprinter or trying to get a good 40 yard dash time, trying to get a bigger chest and biceps isn’t a good idea.

Let’s examine some of the benefits improved strength has on ones running:

1. First off, increasing an athlete’s strength will increase the amount of force they are able to apply into the ground. Strength and power training targets type II muscle fibers and larger motor units, which are the same muscle fiber type and motor units used when predominately when sprinting. If the ground contact time (GCT) remains the same, this will result in an increased stride length due to a greater impulse.

2. Stronger runners will most likely be more efficient runners. While at maximum velocity a weaker runner will have more vertical displacement of their center of gravity (COG) during each ground contact because of a less stiff support leg. While at maximum velocity a runner wants to strike the ground underneath their COG with a stiff support leg in order to help minimize GCT and wasted forces. A weaker runner’s support leg will not be as stiff, resulting in an initial lowering of the COG as the foot strikes the ground. This results in increased GCT and wasted vertical force to overcome the downward shift in the athlete’s COG. A more stiff support leg will also help better utilize the athlete’s stored elastic energy.

3. Stronger runners also have the ability to stabilize their torso while running. The most successful sprinter is the one who is able to produce the greatest amount of beneficial force, and on that notion, a stable torso is critical to be able to optimize the forces generated by the legs.

Here is an important disclaimer. Being strong does NOT mean you are necessarily fast, as there are a lot of other factors required in order to be fast. The purpose of this blog is to state that you won’t be fast without good relative strength. This is why strength development is one of my primary focuses when first getting an untrained athlete. I coach a lot of 14 to 16 year old athletes who want to be faster and getting them stronger is usually step one as strength is a precursor for power and speed development.

In review, improving an athlete’s strength will provide them the capabilities to increase stride length, increase running efficiency, and decrease GCT. My next blog will be discussing the importance of Rate of Force Development when running and in sport.