One of the causes of weakness in muscles in MS is the poor transmission of messages by damaged nerves, mainly within the spinal cord. It is often associated with fatigue. As the nerve damage makes muscles less responsive, it requires more energy to carry out actions. Feeling weak can cause an individual to become less active in an attempt to conserve energy, but this can cause weakness to increase. An already weak muscle that is not used will become weakened further, a process known as atrophy.
However, as muscle weakness in MS is primarily due to problems with nerves rather than within muscles, expending a great deal of energy by exercising to the point of exhaustion can also make weakness worse.
For many years people with MS were advised to avoid exercise due to the impact it could have on weakness and fatigue. It is now felt that exercise is beneficial if it works on gently building up endurance and strength in muscles without increasing weakness and fatigue.
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