Training Dictionary
Fats
Definition: Fats used for fuel are often found stored in the body as triglycerides. Triglycerides are made from a backbone of glycerol and three fatty acids.1
The body releases lipases to break down triglycerides into the utilized form, free fatty acids. Free Fatty Acids are used as a steady fuel supply to supplement the burning of glycogen. While exercise intensity increases, the total energy burned from fat remains fairly stable; however, the total energy burned from carbohydrate sources increases.2
Effects of Exercise
Have you ever looked at a nice sirloin steak? A good steak has lots of fat marbleized into the meat. Legs can store lots of energy in the form of fat, marbleized and vascularized for easy, readily accessed fueld. With aerobic training, one will utilize more fatty acids as a fuel source during exercise.3
While you may think that the fat comes from fat stores beneath the skin, the increased use of fatty acids comes from the ability to break down more fat from intramuscular storage (within the muscle). If you have ever wondered how ultra marathon runners, some who are practically skin and bones, have the fuel supply to run all day without additional fuel, this is your answer.4
High intensity efforts release hormones such as: growth hormone, testosterone, and epinephrine, which induce fat storage breakdown.5
Extensive exercise at a low intensity will help train the body to utilize fat better, sparing glycogen supplies. This will help you exercise longer and ride faster with less effort.
Important Details
The candles wax (fat) flames only in the presence of the the wick (carbohydrate). Your primary source of fuel during exercise should always be carbohydrates.
Sources:
1 Campbell, N. A., Reece, J. B., L. G. Mitchell 1999. Biology. 5th Edition. Addison Wesley Longman, Glenview, IL: 65-67 pp.
2 Hurley B. F., et al. Muscle triglyceride utilization during exercise: effect of training. Journal of Applied Physiology 1968: 5:62.
3 Mark Hargreaves, 1995. Exercise Metabolism. Human Kinetics, Champaign, IL: 188-190 pp.
4 McArdle, Katch, F. I., & V. L. Katch, 2001. Exercise Physiology: Energy, Nutrition, and Human Performance. 5th Edition. Lippincott Williams & Wilkins, Philadelphia: 31 p.
5 Gaesser, G. A., Rich G.A., Effects of high- and low- intensity exercises on aerobic capacity and blood lipids. Medicine & Science in Sports Exercise 1984: 16:269.
