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Current issues in exercise metabolism: the crossover concept

C M Tipton1

  • 1Department of Physiology, University of Arizona, Tucson 85721, USA. tipton@u.arizona.edu

Clinical and Experimental Pharmacology & Physiology
|November 18, 1997
PubMed
Summary
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Athletes use carbohydrates and lipids for energy during exercise, not protein. Exercise intensity and training status significantly influence which fuel source is primarily used.

Area of Science:

  • Exercise Physiology
  • Sports Nutrition
  • Metabolic Research

Background:

  • Historically, athletes consumed protein believing it enhanced performance, a notion disproven by the 19th century.
  • Metabolic studies since 1939 identified lipids and carbohydrates as primary energy sources for muscular exercise.
  • Factors like exercise intensity, training, and fuel availability influence energy metabolism during physical activity.

Purpose of the Study:

  • To explore the controversy surrounding substrate utilization during exercise.
  • To reconcile conflicting findings regarding fuel selection in trained versus untrained individuals.
  • To address uncertainties for researchers and educators in exercise physiology.

Main Methods:

  • Review of metabolic investigations and respiratory exchange ratio changes.
Keywords:
Non-programmatic

Related Experiment Videos

  • Analysis of the 'crossover' concept proposed by Brooks and Mercier (1994).
  • Examination of glucose kinetics in trained and untrained subjects at 80% VO2max (Coggan et al., 1995).

    • Main Results:

    • Metabolic studies confirm lipids and carbohydrates are key energy substrates.
    • The 'crossover' concept explains substrate shifts but faced challenges in fully explaining trained subject metabolism.
    • Coggan's findings indicated limitations of the crossover concept for trained athletes at high intensity.

    Conclusions:

    • Substrate utilization during exercise is complex and multifactorial.
    • The 'crossover' concept provides a framework but requires refinement.
    • Further research is needed to fully understand exercise metabolism in trained individuals.