Are you in Canada? Click here to proceed to the HK Canada website.

For all other locations, click here to continue to the HK US website.

Human Kinetics Logo

Purchase Digital Products

If you are looking to purchase an eBook, online video, or online courses please press continue


Booktopia Logo

Purchase Print Products

Human Kinetics print books are now distributed by Booktopia Publisher Services throughout Australia/NZ, delivered to you from their NSW warehouse. Please visit Booktopia to order your Human Kinetics print books.

Human Kinetics Logo

Purchase Courses or Access Digital Products

If you are looking to purchase online videos, online courses or to access previously purchased digital products please press continue.


Mare Nostrum Logo

Purchase Print Products or eBooks

Human Kinetics print books and eBooks are now distributed by Mare Nostrum, throughout the UK, Europe, Africa and Middle East, delivered to you from their warehouse. Please visit our new UK website to purchase Human Kinetics printed or eBooks.

Feedback IconFeedback

The crossover concept

This is an excerpt from Physiology of Sport and Exercise 8th Edition With HKPropel Access by W. Larry Kenney,Jack H. Wilmore & David L. Costill.

The crossover concept was first outlined by Brooks and Mercier1 to describe the relative balance between carbohydrate (CHO) and fat metabolism during sustained exercise. At rest and during exercise at low to moderate intensities (below 60% of maximal oxygen uptake), lipids serve as the main substrate for generating ATP. During high-intensity exercise (above 75% of maximal oxygen uptake), increases in muscle glycogenolysis and the recruitment of more type II muscle fibers promote a shift to CHO as the predominant substrate for generating ATP. The crossover point is the intensity where fat and carbohydrate utilization intersect (see figure 2.15) as the energy from fat decreases and the energy from carbohydrate increases. Beyond this crossover point, further increases in power are met with further increments in CHO utilization and decrements in fat oxidation.

Figure 2.15 The relation between the relative contributions of fat and carbohydrate (CHO) utilization to overall energy expenditure as a function of exercise intensity. The point at which the two lines intersect illustrates the classic crossover concept.
Figure 2.15 The relation between the relative contributions of fat and carbohydrate (CHO) utilization to overall energy expenditure as a function of exercise intensity. The point at which the two lines intersect illustrates the classic crossover concept.

The crossover point is affected by both the exercise intensity and endurance training status. Endurance training results in biochemical adaptations within the muscle fibers that promote and support oxidation of FFAs, including an increase in the number of mitochondria, increased oxidative enzymes, and changes in β-oxidation and the electron transport chain—all important determinants of fat metabolism. The result of training is to allow the body to spare muscle glycogen since carbohydrate stores within the body are limited. These training-induced adaptations shift the crossover point toward higher exercise intensities. Diet (energy supply and stores) and prior exercise play secondary roles in determining the balance of substrate utilization during submaximal exercise.