Muscles, tendons, and ligaments: What are their roles; what are the differences; and what are the relationships between them?
As dancers we’re familiar with talking about muscles, tendons and ligaments, but are we clear about their roles, their properties, and the differences between them?
The degree of mobility in a joint is determined by three main factors – the bones, in terms of the form, size and fit of the joint; the ligaments, in terms of their course and strength; and the muscles in terms of the course and number of muscles acting upon the joint.
Muscles are soft tissues, made up of millions of muscle cells; Liane Simmel (2014) refers to them as ‘the Motor of Movement’! There are actually three different types of muscle found in the body, each having a different function and therefore a different structure. As dancers, when we speak of muscles we are referring to skeletal muscles. These are voluntary muscles, controlled as the name suggests by the voluntary nervous system via conscious thought. They are attached to the bones and they move the skeleton. Smooth muscles are involuntary muscles, controlled only by the autonomic nervous system, and not by conscious thought. We find smooth muscles in our digestive system, for example. Heart muscle is the third type of muscle, and as you would expect it is only found in the heart. Interestingly, heart muscle shares attributes of both skeletal and smooth muscles; the make-up of the individual muscle cells is cross-striated like skeletal muscle, yet controlled, like smooth muscle, by the autonomic nervous system.
Tendons connect skeletal muscles to the bones, serving to move the bone or the structure. Ligaments connect bones to bones and serve to hold structures together, promoting stability. Tendons are white in colour, ligaments have a yellow appearance.
As tendons connect our muscles to our bones their primary role is in allowing us to move our limbs and structures. Tendons also help prevent muscle injury by absorbing some of the impact from movement as we run and jump for example. They transfer the tensile force (tensile – relating to tension) produced by the contraction of the muscles, to the bones and are therefore required to be extremely strong with a low degree of elasticity. The elasticity of the tendon is estimated to be considerably lower at 4% than the elasticity of the muscle, which Simmel (2014) suggests can stretch up to 50% in extreme cases. As well as playing an active role in joint movement, some tendons are present to increase muscle movement distances rather than the movement of the joint. Although tendons are remarkably strong they are prone to injury. With a slower metabolism they take longer to respond and adapt than muscles. Resistance training can be effective to help strengthen tendons, but they remain the weakest part of the tendon, muscle and bone system. The Achilles tendon is the thickest, strongest tendon in the body; it is resistant to tearing with very minimal elasticity.
And finally, we come to ligaments, which are composed of a tough, fibrous type of connective tissue, made up of collagen fibres that give strength with a low level of elasticity. They attach bone to bone, usually serving to hold structures together and promote stability. Ligaments restrict actions outside of normal joint range. Some ligamentssucceed in increasing their flexibility by penetrating their fibres into neighbouring muscles. An important aspect of ligaments for dancers is the plentiful presence of receptors that provide proprioceptive feedback to the nervous system regarding joint position. This promotes the development of both coordination and balance. One can see how ligament injuries have the potential to affect these skills. One of the ligaments main roles is to transfers compressive load into a tensile loading of the ligaments, thereby finding an optimal joint position that transfers this compression into a responsive tightening of the ligaments.
Blommaert Ballet School recommends Liane Simmel’s Dance Medicine in Practice for a very comprehensive yet readable account of the muscular system.
Simmel, L. (2014). Dance medicine in practice. Routledge.
Denise Horsley, MSc. – Blommaert Ballet School Dance Science Advisor