Animal studies have shown the following:
- Muscles immobilised in a shortened position lose sarcomeres.
- Anti-gravity and weight bearing muscles immobilised in a shortened position lose sarcomeres more quickly.
- Once sarcomeres are lost they are replaced by connective tissue. This results in a loss of muscle elasticity.
- Muscles immobilised in a neutral position maintain their sarcomeres.
- Muscles immobilised in a lengthened position gain more sarcomeres.
- Once a muscle has become shortened, if it is immobilised in a lengthened position it can regain sarcomeres.
As well as these biomechanical changes in the muscle, there can also be changes in other soft tissues such as tendons and within the joint. This makes the muscle stiffer, more resistant to passive stretch and can result in reduced joint movement.
- Muscle fibres are replaced with collagen and fatty tissue.
- Collagen proliferates into joint space, this occurs within the first 2 weeks.
- Connective tissue when immobilised forms cross bridges between collagen fibres and thus elasticity is removed = THIXOTROPHY.
- Prolonged immobilisation affects joint cartilage – it gets thinner at point of contact.
Relevance for your practice
Positioning has an impact on biomechanical changes in muscle, soft tissue and joints.
Good positioning from day one for every patient is vital in preventing these biomechanical changes.
All staff should know how to correct shortened positions and make positioning part of your care plan as soon as the person is admitted to hospital after stroke. This is very relevant to staff looking after patients in bed who will be returning to weight bearing and to physiotherapists involved in early mobilisation of patients, because muscles like soleus and gastrocnemius will be more affected.
The process of muscle shortening is reversible – so proactive treatment and good positioning from day one for every patient is essential and cost effective.
These findings are directly relevant to all stages of treatment and rehab – even if you are the best nurse, physio or occupational therapist in the world you cannot achieve the best treatment or outcome available if your patient can’t get their heels on the floor or reach out to grasp because of tissue shortening.
Muscle tension is important for contraction/function:
Muscles in neutral position do not develop significant changes in stiffness or sarcomere numbers
(Gracies 2005)
Page last reviewed: 04 May 2020