Indeed, in 1995 Toates already defined stress as a "chronic state that arises only when defense mechanisms are either being chronically stretched or are actually failing," while according to Ursin (1988) stress results from an inconsistency between expected events ("set value") and perceived events ("actual value") that cannot be resolved satisfactorily, which also puts stress into the broader context of cognitive-consistency theory. Biological background
Stress can have many profound effects on the human biological systems. Biology primarily attempts to explain major concepts of stress using a stimulus-response paradigm, broadly comparable to how a psychobiological sensory system operates. The central nervous system (brain and spinal cord) plays a crucial role in the bodys stress-related mechanisms. Whether one should interpret these mechanisms as the bodys response to a stressor or embody the act of stress itself is part of the ambiguity in defining what exactly stress is. The central nervous system works closely with the bodys endocrine system to regulate these mechanisms. The sympathetic nervous system becomes primarily active during a stress response, regulating many of the bodys physiological functions in ways that ought to make an organism more adaptive to its environment. Below there follows a brief biological background of neuroanatomy and neurochemistry and how they relate to stress.Stress, either severe, acute stress or chronic low-grade stress may induce abnormalities in three principal regulatory systems in the body: serotonin systems, catecholamine systems, and the hypothalamic-pituitary-adrenocortical axis. Aggressive behavior has also been associated with abnormalities in these systems.
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.