Which of the following is true as exercise intensity increases?

a. Energy is supplied in a smooth continuum where one system may predominate depending upon the intensity.
b. When the anaerobic threshold is reached muscles begin getting oxygen and suddenly begin producing lactate, which can be measured in the blood.
c. There is a point in ultraendurance activities where fat metabolism stops completely and protein metabolism supplies nearly all of the energy.
d. At a certain point aerobic metabolism is shut off and anaerobic metabolism is turned on.

The generally accepted model of energy systems has been used for many years. When exercise intensity rises and glucose uptake by working muscles is increased, a drop in circulating glucose is observed while in higher intensity exercise, muscle glucose uptake can increase by as much as 30 - 50 times, compared to the resting rate. Changes is glucose metabolism have been described by numerous authors and forms an integral part of the modification of energy systems to training stimulus. This is integral to understanding the changes that may occur in the use of blood borne glucose and intra muscular glycogen that may be a marker of exercise intensity. Further Increased cytosolic and more effectively mitochondrial calcium during high ATP turnover in exercise increases glucose phosphorylation while in some cells MAS converted lactate to pyruvate whereas glucose oxidation and lactate production are influenced by the activity of MAS when the intensity of exercise rises, it can lead to down-regulation of MAS activity, which leads to an increase in lactate production Where MAS is inhibited, there is a 50% decrease in lactate oxidation. Likely sites for the adaptation of MAS are highlighted and the effect that this can have on our view of how the energy systems function during high intensity exercise are also suggested. Through consideration of these metabolic events a new vision of energy system function is proposed. I hope u can find something in here lol