Exercise very high intensity

During very brief but very high-intensity exercise (sprinting, running upstairs), when there is not sufficient time for the arterioles to dilate to permit increased blood flow to the muscle. 

Very high intensity exercise is characterized hy rapid glycogen breakdown, glycolysis, and lactate production, with almost instantaneous ATP buffering by creatine phosphate. 

Fig. 13-30 Fuel distribution during very high intensity exercise.

Most team games (e.g. soccer, rugby, hockey, football) and some individual sports (e.g. squash, tennis) involve intermittent high-intensity bursts of exercise interspersed with rest periods (i.e. mostly less intense periods), although the whole period of activity can be very long. These are known as multiple sprint sports. In experiments that involved a study of short bursts of activity followed by short rest periods, repeated for 30 minutes, the increase in blood... 

A number of studies have shown that caffeine may favorably affect long-term endurance performance (ref.3) but research results concerning high intensity, short-term exercise have been a bit mixed (ref.4). Still, it seems very likely from an analysis of the biochemical effects of caffeine that is has a beneficial effect on short-term fatigue and muscle fiber in high intensity, short-term exercise like weightlifting (ref.5 6). 

At the onset of very rapid muscle contraction, ATP levels fall. This canses an increase in AMP concentration. Both phosphofructokinase and glycogen phosphorylase are sensitively stimnlated by AMP. After several seconds, glycogen phosphorylase becomes fully activated because of the arrival of epinephrine in the blood that stimulates the cAMP cascade. Epinephrine is rapidly secreted at the onset of high-intensity exercise and is a mediator of the fight or flight response. 

A rate of 15 litres per minute is remarkably high it is not very different from that achieved during intense sustained exercise by an athlete. 

The fact that the incubation times can vary by as much as three orders of magnitude for steels that are composition-ally very similar provides the technical basis for exercising caution in using the WOL displacement controlled test specimen on new alloys to measure the threshold stress intensity. A rapid drop in load would produce an artificially high threshold stress. 

Haber s laboratory version of ammonia synthesis was indisputably effective, but even after Brunck made the decision that BASF should proceed with the commercialization of the discovery doubts persisted inside the company about the success of such a costly, and seemingly open-ended, exercise. Given the absence of any precedent for running continuous catalytic synthetic reactions at snch high pressures and temperatures, it was only reasonable to expect that even with intensive effort it would take a very long time to transform Haber s bench model to a smoothly operating commercial plant. ... 

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