Prolonged physical activity

It is unlikely that the rate of ATP generation in the hver under normal conditions will be decreased to such an extent that ATP/ADP concentration will be seriously affected. However, some extreme physiological conditions, such as intense and prolonged physical activity, prolonged starvation and haemorrhagic shock may result in reduced perfusion of the liver and lack of oxygen that could result in a marked decrease in the rate of ATP generation. The effect... 

After prolonged physical activity, the uptake of fatty acids is directed to the muscles involved in the activity and away from adipose tissue and the inactive muscles, due to a change in the activity of one enzyme. This allows restoration of the triacylglycerol store within the muscle. 

In an adult, it is only after about 24 hours of fasting or during prolonged physical activity that fatty acid oxidation plays a major role in energy provision. Neither condition is common in developed countries, so that an inability to generate ATP from fat oxidation is not normally apparent. 

Prolonged physical activities require the complete oxidation of a fuel to provide a sufficient rate of ATP generation. A marathon run requires the oxidation of about 700 g of glycogen, provided no other fuel is used. To generate the same amount of ATP from the conversion of glycogen to lactate, approximately 7 kg of glycogen would be required. 

Table 13.5 Arterial concentrations of some fuels during prolonged physical activity in human volunteers "...

Quantitative studies of energy metabolism and fuel utilisation in very prolonged physical activity were performed by Mike Stroud during his Antarctic expedition with Ranulph Fiennes in 1992. One part of the study was measurement of energy expenditure by the dual isotope techniques (Chapter 2). Calculated over the whole expedition, the average daily energy expenditure of Stroud and Fiennes was 29 MJ but on particularly arduous days it increased to... 

Figure 13.23 Depletion of muscle glycogen content during prolonged physical activity. The units of glycogen are xmoLs glucose-equivalent per gram fresh muscle. Glycogen content was measured in biopsy samples taken from the vastus lateralis muscle. Exhaustive physical activity was performed on a bicycle ergometer. Exhaustion coincided with the glycogen content when it was close to zero. (Data from Hermansen et ai, 1967).

There are a number of conditions that are considered to reduce the effectiveness of the immune system and hence increase the risk of infections. These include malnutrition, stress and intense prolonged physical activity. 

The plasma concentration of ketone bodies in fed, healthy humans is very low (about 0.1 mmol/L) so that the rate of utilisation is very low. However, it is elevated in several conditions, e.g. starvation, hypoglycaemia, affer physical activity. In starvation in normal adults, it increases to about 3 mmol/L after three days and to 5-6 mmol/L after several more days (Figure 7.24). Nevertheless, it can increase to 3 nunol/L or higher within a few hours of completing a prolonged period of physical activity if food, particularly carbohydrate, is not eaten (known as accelerated starvation ) (Table 7.3). Ketone bodies are particularly important in children, since starvation can quickly result in severe hypoglycaemia. This is due to the fact that the amount of glycogen stored in the liver of a child is... 

Low energy intake with prolonged and intense physical activity... 

So, there s actually a biological basis to the euphoric sensation associated with high-level physical activity, such as the runner s high described by long-distance runners and exercise gurus The euphoria is caused by the body s release of endorphins and enkephalins produced by prolonged exercise or stress on the body. 

The patient tires abnormally early during prolonged mental or physical activity or cannot sustain the same level of activity as normal. 

Exercise performance seems to be greatly affected by the chronic level of physical activity experienced by the animal or Individual. For example, differences In the capacity for prolonged exercise seem obvious between wild and domesticated animals. This Is probably due. In part, to Inherent biochemical differences between the muscles of active and less active species ( 1 ). Muscles of wild animals appear darker than those of their domesticated counterparts ( ). Further, variations In activity patterns due to seasonal change (3 ) or hibernation ( ), are associated with differences In the enzymes related to oxidative metabolism. Thus, In a general sense physical activity seems to be associated with biochemical changes that enhance the muscle s capacity for aerobic metabolism. 

Saltin, B. Hermansen, L. (1967) Glycogen stores and prolonged severe exercise. In Nutrition and Physical Activity (Blix,... 

In general, a relatively acute deficiency is involved in the central nervous system lesions of the Wernicke-Korsakoff syndrome, and a high-energy intake, as in alcoholics, is also a predisposing factor. Dry beriberi is associated with a more prolonged, and presumably less severe, deficiency, with a generally low food intake, whereas higher carbohydrate intake and physical activity predispose to wet beriberi. 

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