Posted on October 20, 2015 by Jenny Cromack
We all have our idols in the world, for some it was Chuck Norris, others it was the Hoff, and some it was Britney Spears, there I go again talking about myself! Seriously though, for me it’s got to be Yuri Verkhoshansky, for those that are not sure who he is, Yuri was a senior coach on the soviet national track and field team from 1964 onwards.
During the following years some of the most exciting developments in sport science emerged, one of which being shock training. We now loosely refer to shock training when we talk about plyometric exercises. Plyometric is derived from the Greek word ‘plethyein’ which means to increase and ‘isometric’, which refers to the static nature of the type of muscle contraction. Plyometric training has been butchered by the fitness enthusiasts of today and most of its core principals have been lost in novelty classes, extreme workouts, ridiculous buzz words and a poor understanding of the mechanisms responsible for true plyometric actions. So for the purpose of this blog we will try to return to the simple mechanics and reasoning of shock training.
The core principal of shock training is sharp, compulsory muscular tension initiated by the bodies collision with an external object. Sounds pretty violent doesn’t it? Well it is!
A good example of this principal can be observed in a depth jump, if we step off a box we begin to accelerate towards the ground at 9.81m/s (gravity), inevitably there will be a collision between the individual and earth. All collisions conserve momentum, this is a fundamental law of physics. The distinguishing characteristic of different types of collisions is whether the collision stores kinetic energy (E=mv2). If the collision stores both kinetic energy and momentum it is referred to as elastic energy. Or the collision maintains momentum but not kinetic energy, this is referred to as inelastic collision.
The energy preserved in elastic collisions via kinetic energy is where Yuri was most interested, from this he set out to determine which factor was the most important:
1. The mass of the falling weight
2. The height from which the weight fell
To do this he originally examined 36 high level Soviet athletes and instructed them to carry out 8 depth jumps of varying heights. Starting at 0.15m, increasing in 20m intervals to 1.55m. Each athlete was randomised to control for any experimental flaw. The athletes landed on a dynamometric force plate which records vertical forces allowing him to produce a force time curve. Interestingly Yuri’s research suggested that explosive strength was developed most efficiently at a height of about 0.75m. if the depth jump was conducted 1.10m or higher maximal strength (F max) was developed.
Performance through the stretch shortening cycle is influenced by the visco-elastic properties of the muscle-tendon unit. During the stretching phase the energy is absorbed in the tendon unit, this energy can be re-utilised if the shortening of the muscle immediately follows the stretching. This is referred to as the amortization phase. Research has since suggested that 72% of the elastic energy returned comes from the tendons and 28% the muscles.
Therefore in order for the shock training method to be effective, the external force should be high enough to store elastic energy in the muscle tendon units. The external force should be as rapid as possible, it has been suggested that the coupling time should be less than the half-life of an acto-mysoinic bridge (which is around 150 milliseconds).
So if we return back to the initial question of do you need some shock training? If you’re trying to improve speed or jump ability then yes, but it needs to be done correctly. Shock training requires a jump from height and a short ground contact time, sub 200 milliseconds is a good starting point. If you can’t bounce up and down on the floor with less than a 200millisecond contact time you’re not developing this property, you’re just getting hot and sweaty. Time would be better spent developing strength, so that you have the capacity to return to shock training and reap benefits down the line.