Understanding Elasticity
Elasticity is the ability to exhibit high amounts of force upon an immediate stretch of a muscle. You can think of elasticity as having 2 key components, stiffness and reactive strength.
In order to store elastic energy, we must be “stiff” enough to allow for minimal deformation during the impact. If we are not stiff enough, it means we are not able to produce enough force fast enough. Producing force quick enough after an immediate stretch is dependent on reactive strength abilities. Reactive strength is not an independent quality, it is made up of other qualities such as max strength.
To understand elasticity, we must understand stiffness. Stiffness is the ability to resist deformation. Muscles create stiffness and thus allow other tissues to be stretched and store/release elastic energy. A few things that can stretch us are ground impacts, defenders, inertia, etc. When stiffness is optimal, it allows elasticity to take place.
There are 3 main structures involved in stiffness, these all work together to allow us to be elastic.
Muscles: the contractile element. Muscles are responsible for how much force we produce, the speed of force production and the timing of our force production.
Nervous System: organises our stretch reflex and when our muscles fire
Passive Tissues: tendons, fascia and other unknowns.
Muscles are the only force-producing element in the body, they use ATP to create motion. Muscles produce a force that allows individual joints and tendons in a system to work together. We must consider the types of muscles (single or multi-joint), the force capacity of the muscles and what role they play. Are they stabilisers in the movement, the main force producer, or do they act synergistically?
The nervous system is the skill-based factor of movement. Locally the nervous system is responsible for the stretch reflex, the rate of firing, and the timing of the muscles firing. Systemically it is responsible for our joint organisation, the pre-tensing of muscles, and the actual skill component of the movement.
Elastic tissues are those that store and rapidly release energy, some are well-defined and some are poorly defined and some are still lacking enough research.
Tendons: are part of the muscle-tendon unit, and transmit force (not produce)
Fascia
Titan
Unknown
Remember, elasticity is initiated by a stretch. This stretch can be controlled or uncontrolled. The magnitude of stretch is dependent on mass and velocity. Slow and fast stretches require different impulses. An approach jump has a high velocity and requires a more developed stretch-shortening cycle. The heavier you are, the more demand you place on your body which also requires you to have a more developed stretch-shortening cycle.
The body is able to organise itself based on the movement, independent of the load which means there is a skill factor and a mechanical factor. You are able to modify your stiffness if your neuromuscular capacity is greater than the demand of the movement. For example, from a 24-inch box, you can choose if you want to drop and jump up focusing on max stiffness (short ground contact time) or max jump height. But, if it is now a 6-foot box, you are only able to focus on not getting injured, because the demands are too great for us to handle.
Elasticity can be contextual, even an elastic athlete can be in situations where they are not expressing elasticity. For example, if someone comes into an approach jump faster than they can handle, or lower than they can handle, they will either have a reduced jump height or bailout of the jump halfway through.
If an increased stretch does not improve performance, then it is reactive strength that is lacking.
Key Takeaways:
In order to be elastic, there must be some sort of stretch.
Stiffness is the ability to resist stretching or deformation from an applied force. The optimal stiffness is dependent on neuromuscular qualities.
The capacity of your neuromuscular system needs to be higher than the applied forces in order to optimise stiffness. If forces are too high for us to handle, our focus shifts from maximising performance to not getting injured.