The onset of soft muscles can be a symptom of many possible diseases, as explained on Right Diagnosis from Healthgrades. It can also be an indicator of a more immediate problem, such as muscle overuse, an electrolyte imbalance, a spinal injury or dehydration. Soft and weak muscles are sometimes combined with a wide variety of other symptoms including respiratory, nerve, pain, sensory, skin and movement problems.
In fact, Right Diagnosis lists over 40 possible medical reasons for soft muscles. Some of the illnesses that most commonly have soft muscles as a symptom include muscular dystrophy, Parkinson's disease, diabetes, myasthenia gravis, lupus, anemia, peripheral neuropathy and brain tumors. Some tick bites can also produce muscle softness and weakness. A toxic level of aluminum in the body can result in muscle softness. Right Diagnosis reports that the drug Digoxin can produce muscle weakness as well. Avoidance or reduction in the use of Digoxin is especially important for pregnant women.
If the onset of soft, weak muscles is sudden or progressive, a doctor should be consulted to determine its cause. A doctor assesses muscle softness and weakness along with all other symptoms to assess possible causes and, if necessary, orders testing to accurately diagnose the cause.