The tendons’ main role is to transmit forces from the muscle to the bone and absorbs external forces to prevent injury to the muscle. As the tendon runs from a very compliant tissue (the muscle) to a ridged stiff one (the bone), this role can become very difficult, this can result in strain concentrated at the site of merging tissues. This can be a common site of injury.
The make up of the tendon is now not thought to be the same throughout, research has discovered that the tendon itself may be more ridged in some parts and more compliant and elastic in others to overcome this concentration of strain and risk of injury. Each tendon will differ throughout the body depending on the rate in which they are strained. The behaviour of the collagen within the tendon depends on the intramolecular types, quantity and bond.
The tendon collagen fibres at rest are now thought to be organised in a crimped patter, when the tendon is put under strain of up to 2%, the fibres and fibrils are thought to flatten. Any further the fibres are said to be pulled into a more parallel and linear pattern.
If the strain remains lower than 4% the fibres and fibrils have been shown to recoil back to their normal resting state but strain greater than 8-10% there is evidence to suggest that microscopic damage occurs. As the strain on the fibrils continues the gap between the molecules increases and when the recoil they do not slip back into their normal alignment they can become disorganised, tangled and bunched. Strain above 8% can lead to complete failure and rupture. This is demonstrated clearly on the stress-strain curve graph of a tendon.