Exercise leads to changes in blood sugar levels and depletes muscle glycogen, the sugar stored in your muscles. Some of the glycogen gets excreted in your urine. Much of the glycogen you use when training gets burned for energy. The remainder either is excreted or winds up stored as fat. If you suspect a sugar-related disorder, consult your physician.
Glycogen
Glycogen, a sugar found in both your blood and your muscles, is the primary fuel your body uses for energy. Two different energy systems in your muscles -- the slow-oxidative glycolytic, or SOG, and the fast-oxidative glycolytic, or FOG systems -- use sugar as a source of energy. The SOG system is used primarily for endurance related activities such as manual labor or a marathon, the FOG system is used primarily for heavy lifting.
Glycogen and Water
Each gram of glycogen that you store holds 4 g of water. When you deplete your muscle glycogen through exercise, you lose more water. Some of the water will carry stray glycogen molecules, which are then excreted through your urinary tract. The greater your training volume at higher intensities, the more sugar you will burn. You will continue to burn calories following training, but much of the expended glycogen has no where to go but out when you finish training.
Excessive Exercise
Excessive exercise can result not only in a depletion of your muscle glycogen, but also in your blood sugar as well. Exercise can stimulate the release of various hormones, including epinephrine, which cannibalize your sugar reserves. This can cause a sudden drop in your blood sugar, otherwise known as exercise-induced hypoglycemia. This condition results not only in more sugar in your urine, but also not enough in your blood stream. If you feel dizzy or light-headed, stop exercising at once. If you suspect low-blood sugar, consume a small supply of simple sugar.
Diet
While consuming a high-carbohydrate meal prior to training can give you more energy, you may be over-consuming carbohydrates, or eating too many of the wrong foods. A small meal, without a lot of fat or simple sugar, should give you plenty of energy. If you are carb-loading for a very high volume of exercise, expect some of the sugar to slop over into places you would not normally find it. Some of the excess will be excreted as urine.
References
- "Textbook of Biochemistry With Clinical Correlations"; Thomas M. Devlin; 2010
- "Physiology of Sport and Exercise, Fourth Edition"; Dr. Jack H. Wilmore, et al.; 2007
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