The Physiology of Fat Loss Part 2

From the fat cell to the furnace, find out exactly what causes the body to burn fat. 
By: Mike Deyhle, Christine Mermier, and Len Kravitz
Fitness Journal- January 14

Adaptations to Exercise That Improve Fat Usage 

Trained people can use more fat at both the same speed or power output and the same relation percentage of heart rate maximum than untrained people.  Lipolysis and fat release from adipocytes are identical in untrained and trained people.  This shows that trained people are better able to burn fat because of differences in the muscle’s ability to take up and use fatty acids, not because of the adipocytes’ ability to release fatty acids.  Adaptations that enhance fat usage in trained muscle can either improve fatty-acid availability to the muscle and mitochondria or improve the ability to oxidize fatty acids.

Fatty-Acid Availability

Exercise causes specific proteins to deliver more fatty acid to the muscle and mitochondria.  Exercise also increases the amount of FAT/CD 36 on the muscle membrane and mitochondrial membrane and boosts CPT1 on the mitochondrial membrane.  Together, these proteins improve fat transport into the muscle and mitochondria to be sued for energy.  Exercise may also cause changes in the intramuscular lipid droplets, which contain IMTAGs that usually reside near the mitochondria.  The close proximity allows an efficient release of fatty acids from the lipid droplets to the mitochondria.  Exercise also boosts IMTAG availability by causing lipid droplets to conform more closely to the mitochondria.  Exercise may increase total IMTAG stores.  Another training adaptation that may improve fatty-acid availability is an increase in the number of small blood vessels within the muscle.  Fatty acids can enter the muscle through small capillaries.  By increasing the number of capillaries around the muscle it enables increased fatty-acid delivery into the muscle.