During strenuous activity, the glycogen in your muscles is converted into this "milky" acid, C3H6O3
[DOC] [TLE] 1999 Shils, Shike, and Ross - Modern Nutrition in Health and ... [PAR] Body Composition: Influence of Nutrition, Physical Activity, Growth, and Aging ...... 
Role of Skeletal Muscle in Whole-Body Amino Acid Metabolism ..... production as 
for carbohydrate) and (b) conversion of amino acids into other products.