Muscular weakness

Poor muscle tone
Muscle weakness
Low muscle tone

Weakness is a symptom of a number of different conditions. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy and inflammatory myopathy. It occurs in neuromuscular junction disorders, such as myasthenia gravis.

Source: Wikipedia

People that are bedridden lose over 80% of their muscle strength during a four to five month period.
(G) Very specific problems