What is the definition or description of: loss of strength?

Muscle weakness: Each muscle has a degree of function that is described as normal strength; this would usually be categorized as a strength of 5/5. Anything less than that would be a loss of motor strength, from which there are a number of possible causes.

Muscle weakness : Or decreased strength. This means that the muscle strength in that muscle is less than normal or previous strength. Sometimes this may be accompanied by decreased muscle bulk. Common causes include disuse atrophy, injuries and protein catabolism and vascular or immunological diseases