Question

Ryan is finishing his trail half marathon and starts to sprint the last half mile of the race. During this time Ryan’s legs really start to burn. Describe, in detail, what is happening metabolically in his muscles during this last half mile. Elaborate on how this affects the rest of the metabolic pathways.

Answer 1

For every degree the body’s internal temperature rises, the heart beats about 10 beats per minute faster. The result is a dramatic increase of stress on your heart.
Heat stress occurs when the body cannot get rid of excess heat
exercise duration under conditions of heat stress favours the oxidation of carbohydrate (CHO) and appears to increase the rate of muscle glycogenolysis, total CHO oxidation is often less and levels of muscle glycogen remain much higher at the point of fatigue when compared with the same exercise without heat stress. Furthermore, supplementing CHO during exercise in the heat appears to exert an ergogenic effect that is not related to 'peripheral' but rather 'central' factors. However, there may be a role for the excess ammonia (NH3) produced in the exercising muscle during heat stress, as cerebral uptake and subsequent metabolism of NH3 may have detrimental effects on cerebral function. Recent exciting results point toward an increased cerebral CHO uptake relative to that of O2, termed the cerebral metabolic ratio (CMR) during exercise with heat stress, although a causative link between this and reduced exercise performance has yet to be identified. Therefore, it appears that despite a shift towards greater CHO utilisation in both skeletal muscular and cerebral metabolism, these responses have ultimately not proved limiting to exercise with heat stress.
Acclimatization state, aerobic fitness and hydration level are important factors influencing a person's ability to dissipate body heat to the environment.
The higher the ambient temperature, the greater the dependence on evaporative heat loss to maintain body heat balance.
During exercise, the elevation in core temperature is dependent on the metabolic rate, when the environment has sufficient capacity for heat exchange.
Heat stress reduces a person's ability to achieve maximal metabolic rates during exercise.
Heat stress increases the total metabolic rate and anaerobic participation during submaximal exercise, and these increases are somewhat abated by heat acclimatization.
Exercise-heat stress reduces hepatic blood flow and increases hepatic glucose release.
Individuals routinely have sweating rates of 1 liter per hour when working in hot environments.
Dehydration from sweat loss increases plasma tonicity and decreases blood volume, both of which reduce heat loss and result in elevated core temperature levels during exercise-heat stress.
During exercise-heat stress, competing metabolic and thermoregulatory demands for blood flow make it difficult to maintain an adequate cardiac output.