It’s 2017 and everything but the kitchen sink has been turned into a fitness fad at some point. One casualty of this I’m particularly interested in highlighting is plyometrics. I’ve seen trainers and class instructors place them in programmes incorrectly and by observing the repetitions, sets and technique instructed, it appears these movements aren’t fully understood. I feel by explaining the methods behind plyometrics, people will better understand how to use them.
The definition of a plyometric is to produce maximal force in the shortest possible time. This can involve jumping, throwing, receiving loads at high speeds and/or returning them at high velocities also. Plyometrics are quick and explosive in nature, our body must utilise our muscles in rapid stretch shortening actions or counter movements in order to produce maximal force in the quickest time possible. This process is summarised as a stretch shortening cycle (SSC) and involves mechanical and neurophysiological processes.
The musculature and tendon mechanics behind the SSC, revolve around the series elastic component (SEC). The SEC occurs when our muscle is lengthened and quickly contracted, aka known as eccentric and concentric contractions. An explanation of these contractions can be done by extending your elbow to straighten your arm and lengthen your bicep, this is an eccentric motion, then close it again by bending your elbow shortening your bicep, this is a concentric motion on the bicep. If a pause is left too long between the eccentric and concentric actions, the elastic energy generated will become useless and be lost in the body. The elastic energy is generated deep within our muscles fibres thanks to their contractile filaments actin and myosin. If a concentric action occurs straight after an eccentric motion, this elastic energy will contribute to force production of that muscle. The muscles mechanics work similar to the mechanics of a bow and arrow, in which the draw back of the bow/lengthening of the muscle, contributes to the production of force.
The neurological process of the SSC is based off of our bodies stretch reflex. Once the muscles have been lengthened (as explained above), we have sensory organs known as muscle spindles that are located in our muscle and joints that aim to control the rate of lengthening to our muscles. If a rapid stretch action is perceived by these spindles, a neural signal is sent via our reflex arc increasing sensitivity of the muscle and subsequently increasing activation within it to prevent further stretch (imagine being scared and somebody unexpectedly tapping you, you would react very quickly, this is an example of how the muscle feels once it receives a sudden lengthening). This increased sensitivity increases the reactive force the muscle produces.
If you combine the stored energy created in eccentric and subsequent concentric contractions and also the increased sensitivity from our muscle spindles, you get an explosive muscular motion aka known as a plyometric. Join me in my podcast this week, where this topic continues and I discuss how you can correctly incorporate plyometrics into your programme and also how you can identify sub optimal instruction yourself.