Many diseases and conditions can lead to this imbalance, either through the disease itself or disease associated appetite-changes. Causes of muscle atrophy, include immobility, aging, malnutrition, certain systemic diseases (cancer, congestive heart failure; chronic obstructive pulmonary disease; AIDS, liver disease, etc. ), deinnervation, intrinsic muscle disease or medications (such as glucocorticoids). Immobility
Disuse is a common cause of muscle atrophy and can be local (due to injury or casting) or general (bed-rest). The rate of muscle atrophy from disuse (10-42 days) is  approximately 0.5–0.6% of total muscle mass per day although there is considerable variation between people. The elderly are the most vulnerable to dramatic muscle loss with immobility. Much of the established research has investigated prolonged disuse (>10 days), in which the muscle is compromised primarily by declines in muscle protein synthesis rates rather than changes in muscle protein breakdown. There is evidence to suggest that there may be more active protein breakdown during short term immobility (<10 days). Cachexia
Certain diseases can cause a complex muscle wasting syndrome known as cachexia. It is commonly seen in cancer, congestive heart failure, chronic obstructive pulmonary disease, chronic kidney disease and AIDS although it is associated with many disease processes, usually with a significant inflammatory component. Cachexia causes ongoing muscle loss that is not entirely reversed with nutritional therapy. The pathophysiology is incompletely understood but inflammatory cytokines are considered to play a central role.
One side effect of cycloplegic drops is that they often have BAK as a preservative ingredient, which, with daily use, can erode the tear shield:

At each administration of an eye drop containing benzalkonium chloride, its detergent effect disrupts the lipid layer of the tear film. This cannot be regenerated and can no longer protect the aqueous layer of the tear film, which evaporates easily. In these circumstances, the cornea is exposed and eye dryness occurs. In addition, benzalkonium chloride has a cellular toxicity on caliciform cells, entailing a reduction in the amount of mucin, an additional reason for disrupting the tear film. In fact, none of the cycloplegic drops used to treat Spasm of Accommodation in the United States are available without BAK. This unfortunately makes treatment much more difficult as the side effect of dry eyes and corneal damage can occur. France, Australia, Canada, and the United Kingdom do have limited availability of BAK-free eye drops available in unidose, and they must be imported to the United States with a physicians letter to the FDA enclosed with the imported prescription. Due to the high potential of tear shield damage with long-term use and the associated dry eye condition caused by cycloplegic eye drops with BAK (preservative), many physicians do not recommend cycloplegic eye drops.