Kristi Storoschuk, a Ph.D. student at Queen’s University, and Mike Giardina sit down at the 2022 CrossFit Games to discuss metabolic flexibility. Metabolic flexibility is the body’s ability to alter fuel sources based on metabolic demands. Storoschuk explains how exercise can be a stimulus to improve metabolic flexibility as well as a way to determine one’s metabolic flexibility. Those who are metabolically flexible will be able to perform a higher workload while still utilizing fat as the main fuel source, and they will be able to use glucose effectively when the workload surpasses fat oxidation capacity. Contrary to that, those who are not metabolically flexible will be in a high state of glycolysis early in exercise or even during times of rest.
Storoschuk also explains how her Ph.D. experience has brought her to the conclusion that exercise is the only stimulus to truly improve metabolic flexibility in human muscle. Exercise provides the metabolic stress necessary to improve mitochondrial density. Storoschuk provides some insight into which types of exercise to prioritize to improve metabolic flexibility. Both zone 2 cardio and high-intensity training have been shown to improve mitochondrial function and density, though high-intensity exercise might be able to get similar results in less time.
Storoschuk finishes with a brief explanation on how exercise can help regulate metabolism when coming off a prolonged fast or even after a night of insufficient sleep. Both scenarios can cause an acute state of metabolic inflexibility, which can be overcome by a single bout of exercise.