“The third or chronic form of general fatigue is found in men during a course of training in which the amount of endurance required daily is more than can be regained during the periods of rest. In this condition the temperature becomes subnormal, the weight goes down, the skin looks pale and flabby, the muscles lose their elasticity, the eye becomes dull and listless, interest in exercise ceases, every effort becomes a burden, and the patient sits without ambition or the power to rouse himself from his lethargy”
Exercise in Education and Medicine by Robert Tait McKenzie, B. A., M. D (1909)
The human brain is three times the size of an ape’s relative to body size (fig 1). It accounts for 20-25% of an adult’s resting oxygen and energy use, and 60-70% of total-body-glucose metabolism. This makes the human brain the most ‘expensive’ metabolic tissue found within all known species, and one of the most vulnerable to metabolic ‘stress’, especially during it’s growth and development (fig 2).
Despite it’s reliance on a constant supply of glucose, the brain stores only a tiny amount locally as glycogen*, so relies on the ‘glucostatic’ function of the liver (80-90% of circulating glucose comes from the liver) to maintain an adequate glucose supply. Brain function is compromised when blood glucose falls below (hypoglycemia), or exceeds (hyperglycemia), the normal physiological range (70-110 mg/dl). Consequently, humans have evolved a number of metabolic ‘emergency’ strategies to ensure the survival of the brain, often to the detriment of the rest of the body.
The progression of ‘Over Training Syndrome’, due to unintelligent-endurance training (see BTR Training Zones), shares many features with the progression of glucose starvation (fig 3). The ‘raiding’ of vital-structural and immune-system proteins, combined with the attempt to metabolise inferior ‘energy’ substrates (lactate, amino acids, and fatty acids), creates the physiological and psychological symptoms of Hysteria, Neurasthenia, Hypochondriasis, Malingering, Pyschoneurosis, Depression, Chronic Fatigue Syndrome (CFS), Myalgic Encephalopathy (ME), Post-Viral Fatigue Syndrome (PVFS), Under Performance Syndrome (UPS) and Over Training Syndrome (OTS).
These labels are historically and culturally dependent, but would appear to boil down to one thing; a de-energised brain.
* For every 1 gram of glycogen stored, 3 grams of water is stored with it so for the brain to store 100g of glycogen (the amount stored in the liver) it would weigh an additional 400g. The extra weight (and volume) would completely change the morphology and function of the human body.
Ruderman NB, Aoki TT, Cahill GF. (1976) Gluconeogenesis and its disorders in man. In Gluconeogenesis: Its Regulation in Mammalian Species.
SC Kalhan and IÁ Kilic (1999) Carbohydrate as nutrient in the infant and child: range of acceptable intake. European Journal of Clinical Nutrition.
Taylor RE (2001) Death of neurasthenia and it’s psychological reincarnation. British Journal of Psychiatry.
Lewin R. (1984) Human Evolution: An illustrated Introduction.
Muhammad Z. Shrayyef and John E. Gerich (2010) Normal Glucose Homeostasis: in Principles of Diabetes mellitus. L. Porestky (ed)