How do our muscles age?
By the age of 70, a person has lost on average 40 - 50% of the muscle strength that they had when they were younger. This loss of muscle mass, strength and function, known as ‘sarcopenia’, means that the person has little or no reserve, has poor balance and can’t react quickly to a trip in the same way as a younger person.
Think about someone who is frail - this could be you, a parent, grandparent or friend - they may struggle to walk for any distance, open a can of food or bottle, lift their kettle etc. This frailty commonly leads to a fall, a situation which can be, more often than not, life threatening to an older person.
In order to develop appropriate treatments, we need to understand why we develop sarcopenia as we get older. Studies using transgenic ageing models have shown us that this muscle loss is not inevitable, providing an exciting prospect that a treatment for such muscle loss can be developed.
Our muscles are made up lots of long cells (called muscle fibres) that often run the length of the muscle. As we age, these cells get smaller and we also lose some of them completely. By the age of 70, we have lost approximately 30-40% of our muscle fibres. Once lost, muscle fibres cannot currently be replaced, not even by exercise.
A CT section of a mid thigh from a healthy female in her twenties (above) and a healthy female in her eighties (below). Featured here with kind permission from Professor A Young at the University of Edinburgh.
What exercise can do is simply make the remaining 60% of fibres bigger (hypertrophy) although muscles of old mammals are pretty resistant to this. This improves strength acutely, but we don’t know how long this lasts. As if this loss of muscle fibres wasn’t enough, if the remaining muscle is damaged, by excessive or unaccustomed exercise, or surgery, there is evidence that it may never repair.
Every muscle fibre has a nerve supply, originating from the spinal cord. As we age, nerve connection is poor and muscle fibres become denervated. Experiments in transgenic models have suggested that this is a major way in which the fibres are lost. Current research is focusing on understanding the process of denervation in the muscle of old people to develop interventions that can help maintain the number of fibres in our muscles into old age.
© University of Liverpool/The University of Sheffield/Newcastle University