EFFICIENT MOVEMENT - properties of movement
Muscles contract to produce force required for movement. What is of critical importance in terms of improved effectiveness and efficiency of movement is how well the elasticity in muscle fibres and tendons is utilised.
The contractile and elastic components of muscles provide viscoelastic characteristics which when used correctly passively add considerable power to your performance. The muscle belly is the site of the contractile components, while the majority of the elastic properties come from the tendons. Contractile components of muscle can store up to 4.7 J/kg compared with 2000-9000 J/kg in tendons.
The elastic behaviour of the tendons is characterised by the relationship between the deformation (stretch – length change) and the applied force. Deformation of an elastic material has the potential to store energy and if released provide energy.
There are three phases of deformation of tendons: compliant, linear and failure. The compliant phase is the initial stretch of the muscle and little energy is stored as the length changes. As deformation increases the energy store is close to linear with deformation. As the muscle is stretched (over stretched) elastic energy stores decrease due to failure of the muscle fibres (muscle damage).
The Achilles tendon has a stiffness requiring 250N of force to stretch it 1mm enabling it to store 0.125 J of energy. During running the Achilles can be stretched up to 18mm, storing 42J of energy. When running, a 75kg person whose center of mass changes 5cm requires 36J of energy each stride demonstrating how beneficial the energy store of tendons can be if utilized correctly.
With specific technique training, the pre stretch of the muscle has the ability to store energy prior to muscle contraction significantly reducing the amount of force required by the muscle. Correct technique enhances the utilisation of tendon energy and the reason that some athletes perform much faster with lower energy costs.
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