Distinctions of Speed and Force Expression

Training for explosiveness, power training, and speed training oftentimes are used interchangeably, but after looking at these training are closely, you realize these are different attributes and training for one does not necessarily mean you are training for all of them.  In the world of track, speed is king.  But when you compare the speed of the 100m dash to the 400m hurdles, are you comparing the same thing? Not necessarily. This article dives into the distinctions of speed and expressions of force.

When people talk about explosiveness in sports, they are really talking about a term called rate of force development.  This concept has been exemplified by Hakkinen’s classic study (1985) showing a quicker production of strength after a strength training.

Although athletes training for rate of force development might not be as strong as powerlifters, they can use 80% of their strength faster than a power lifter can use 70%.  If this concept is applied to a stride, sprinters are able to apply higher force to the ground and remain on the ground for minimal time.  This means they will either accelerate faster or maintain a faster speed.  In other sporting events it means a basketball player doesn’t have to preload a jump as long or a thrower can transfer the leg strength to the shot put quicker (throwing it further).

When training to improve rate of force development, it’s usually best to:

  • 1st. Develop leg strength
  • 2nd. Focus on speed of movement

(JM McBride 1999D Baker 2001MH Stone 2003).

Power is easy to get mixed up with rate of force development because power = force x velocity (measured in Watts).  At initial glance this equation may look like the same thing as explosiveness as we usually describe explosiveness as ‘fast strength’.  What is not so obvious is that power can be used to describe strength/any amount of time.  For example, an endurance cyclist can ride at 300 Watts for HOURS.  This cyclist is producing a relatively high amount of power, but it is expressed over such a long time that we would not consider him explosive.  An easy way to make the distinction between power and explosiveness is to ask two different questions:

  1. “How much force can you produce at a given velocity?” (Power)
  2. “How much time is needed to achieve high amounts of force?” (Rate of force development)

Understanding this distinction between power and explosiveness does not mean power is irrelevant or should not be trained.  A high rate of force development (explosiveness) is related to an athletes peak power ability (peak power is achieved with maximal speed movements near 30% 1RM; Haff, 2012).

Training for peak power often uses exercises like medicine ball throws/slams, Olympic lifts with light weights, and plyometrics.  Athletes who have trained for peak power can improve rate of force development (Haff, 2005) but a mixed strength and velocity approach is best for sport optimization (Harris, 2000).

Speed training in sport often deals with the mechanics of a movement and predominately sprinting.  Sprinting ability is critical in most sports, but is often assumed either you are slow or you are fast.  What is not discussed is the capacity of improvement for speed.  Much of the improvement in sprinting comes from increasing stride frequency and the force vector quantity (direction and magnitude of force; Weyand, 2000).  Stride frequency improvements first come from learning how to sprint.  This involves learning how to quickly turn sprinting muscles on and off and synchronize the legs like pistons in a motor engine (Young, 2014).

However, the trump card for speed is the force vector quantity relative to body weight (Weyand, 2000). Stated another way:

  1. How hard is your foot striking the ground? (Force)
  2. How much force is produced relative to your body weight?
  3. Is the foot strike propelling you STRAIGHT FORWARD? (Direction)

When your foot strikes the ground it produces a ground reaction force.  If your foot is landing directly under your center of gravity you will have an optimal force direction.  If your ground reaction force is large relative to your body weight, you will be able to accelerate fast and maintain a faster speed.

It’s important to know that heavier athletes (lineman, throwers, etc.) are striking the ground with more force than traditional sprinters, but the sprinters are applying more force/body weight and that is why they are faster.  Top sprinters (or even fast athletes) are able to strike the ground with a lot of force due to:

  1. Their joint angles at ground contact are optimal for muscle strength production.
  2. Their ability to quickly absorb force (ie. They do not collapse after striking the ground hard).
  3. Utilizing the stretch shortening cycle (Young, 2015).

-Remember your last Doctor’s visit when the Doctor hit your knee with the rubber hammer?  That is the stretch shortening cycle and fast athletes use it to run faster.

So what does this have to do with explosiveness and power?

Speed training has shown to improve power both vertically (Markovic, 2007) and horizontally (Lockie, 2012); therefore, improving your ability to maintain force at higher speeds.

The synchronization of speed training can enable an athlete to reach higher forces in shorter amounts of time (Bellon, 2016).  This results in explosiveness improvements.

Finally, the importance of strength has been honored in previous articles (Shea, 2017Shea 2017) but not formally discussed here.  Strength is a very important prerequisite to the capacity of improvement in all the variables listed above.

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