Weight training presents an array of potential problems different from those encountered in running or contact sports. For bodybuilders, small muscle injuries are inevitable and necessary for muscles to grow. When overtrained, however, muscles sustain large amounts of damage, and muscle, joint, and nerve dysfunctions are possible; biochemical dysfunction can also affect the body as a whole. One example is reduction of adrenal function, which can compromise overall health.
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The adrenal glands are located above each kidney. They produce the majority of necessary steroid-based hormones. Some hormones that are important during weight training are epinephrine and norepinephrine, which are produced in the medulla region of the adrenal gland, and cortisol and testosterone, which are produced in the adrenal cortex. Epinephrine helps the body deal with expected stress, such as weightlifting. The adrenals release norepinephrine in response to unexpected stresses and release cortisol for any type of stress. Testosterone is the male sex hormone -- also produced in smaller quantities by females -- and is necessary in conjunction with cortisol for heavy training.
In "Lore of Running", author Timothy Noakes discusses how symptoms reminiscent of those seen in Addison's disease had been rumoured to afflict chronically overtrained Eastern European athletes. Addison's disease results from damage to the adrenals that keeps them from producing enough hormones. Symptoms include weight loss, depression, low blood pressure upon standing, and general physical incapacitation. According to Noakes, overtrained athletes from multiple disciplines, including weightlifting, demonstrate similar but not as severe symptoms, and in general tend to have lowered adrenal hormones.
Overtraining is defined as any increase in volume or intensity which results in long-term performance problems. It is not to be confused with overreaching, which is a temporary increase in volume and/or intensity of training to improve performance. The chronic stress associated with overtraining leads to inability of the adrenals to react correctly to stress. Testosterone levels decrease, and the adrenals are not able to secrete sufficient cortisol in stress situations. This can be tested experimentally by measuring cortisol levels after a very mild stress, such as administering insulin to induce temporary hypoglycemia, states Noakes.
Poor nutrition may contribute to adrenal insufficiency. Competitive weight trainers often have diets high in protein but deficient in vegetables, which can lead to vitamin and mineral insufficiency. The production of steroid hormones depends on the presence of cofactors and enzymes derived from dietary vitamins and minerals, so their lack can contribute to relative adrenal insufficiency.
Since the systemic effects of overtraining centrally involve insufficient adrenal hormones, early research focused on the idea that excessive training damages the adrenals directly. However, Noakes cites studies implicating the hypothalamus instead. The hypothalamus is the part of the brain that produces corticoid releasing hormone, or CRH. This stimulates the pituitary to release adrenocorticotrophic hormone, or ACTH, which in turn influences adrenal hormone production. In "The Endocrine System in Sports and Exercise", William Kraemer describes reduced adrenal responsiveness to ACTH during heavy endurance training, which also supports the theory of hypothalamic disruption.
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- "Optimal Muscle Training"; Ken Kinakin; 2009
- "Lore of Running"; Timothy Noakes; 2003
- "Strength and Power in Sport"; Paavo Komi; 2003
- "The Endocrine System in Sports and Exercise"; William Kraemer and Alan Rogol; 2005
- National Endocrine and Metabolic Diseases Information Service: Adrenal insufficiency and Addison's Disease