Elastic energy can be looked at as the body’s way of using the spring-like properties of muscles and tendons to move more powerfully and efficiently. Hooke’s law tells us that stiff tissues require a high amount of force to be stretched compared to a compliant tissue. Shorter muscles attached to longer tendons; such as the gastrocnemius-Achilles tendon complex, are favourable.
Elastic energy and MTU stiffness are crucial for tasks which have very short contact times, such as maximal sprinting. However this requires larger muscular forces according to the impulse-momentum relationship. The reason the SSC is important for these types of movement is due to the relatively inefficient nature of muscle tissue and the parallel elastic component at recovering potential elastic energy when compared to tendons; shown as the series elastic component in the Hill’s model diagram (figure 1). Muscle fibres can stretch up to 3% before cross bridge cycling occurs and the concentric power output will be greatly reduced. The increased viscosity of muscle can also slow down muscular contractions, losing energy as heat.
When the stiffer tendons are stretched they have an almost limitless recoil speed, meaning MTUs are able to shorten at far greater speeds than if relying solely on concentric muscle contractions. Training to improve these qualities means that players will produce more power without increasing muscle activity; due to a more efficient MTU.
“The scientific principle known as Hooke’s Law tells us that all tissues stretch when force is applied to them. Stiff tissue requires high force to be stretched and recoil quickly. Tendons are efficient at doing this, muscles are not!”
Tendon – Series elastic component returns 80-90% of energy!”
Muscle - Parallel elastic component returns approx 60% of energy.