Research
Mixed
Endurance exercise training increases muscle GLUT4 protein content and mitochondrial density, which shifts substrate utilization toward fat oxidation and spares muscle glycogen during sustained exercise.
If you train consistently, your body adapts by building more fuel pumps (GLUT4) and power plants (mitochondria). This allows you to burn more fat and save your sugar stores (glycogen) for longer or more intense efforts. Don't worry if you feel like you aren't 'burning' as much sugar; this efficiency is the goal of endurance training.
StrongSupportsVERY_HIGH confidence
The adaptations induced by endurance exercise training result in a marked sparing of carbohydrate during exercise, with an increased proportion of the energy being provided by fat oxidation.
Why this rating
The paper is a comprehensive review citing numerous studies on humans and rats confirming these adaptations.
Source
The regulation of carbohydrate and fat metabolism during and after exercise
John O. Holloszy · Frontiers in bioscience · 1998
narrative_reviewCited 177×
Read the paper This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →