Balance of carbohydrate and lipid utilization during exercise: the "crossover" concept.
Level 5 - mechanism / opinion, no new human data
Narrative review and theoretical concept paper without original empirical data or systematic review methodology
PubMed 7928844 · doi:10.1152/jappl.1994.76.6.2253
What was done
This narrative review and theoretical paper outlines the "crossover" concept describing how exercise intensity and prior endurance training interact to regulate the balance of carbohydrate and lipid metabolism during sustained exercise.
What was found
The abstract reports conceptual synthesis and ranges from existing literature rather than new empirical data. Following endurance training, low-intensity exercise (<= 45% maximal O2 uptake) utilizes lipid as the main substrate. In contrast, hard-intensity exercise (~75% maximal O2 uptake) relies predominantly on carbohydrate. The crossover point is defined as the power output where energy derived from carbohydrates exceeds that from lipids.
Why it matters
It introduces the foundational crossover concept in exercise physiology, reconciling divergent literature regarding substrate utilization as a predictable function of exercise intensity and training adaptations.
Limits
As a theoretical narrative review, it presents no original empirical dataset, sample sizes, or formal systematic review methodology.
Cited by
- supports Running a marathon in under two-and-a-half hours burns approximately 70% to 80% carbohydrates as fuel.