by Edmund R. Burke, Ph.D.
Measurements of creatine kinase, an enzyme found in muscle cells, are frequently used to indicate muscle damage and stress after exercise. It is thought that the enzyme leaks from cells and into the bloodstream when cell membranes are ruptured.
A double-blind, crossover study by S. Ready, M.S. of St. Cloud State University in Minn. compared the effects of two sport-drink formulations on post-exercise muscle stress and performance time. Ten college-aged men and women drank either a carbohydrate/protein beverage or a carbohydrate/electrolyte beverage while participating in a simulated duathlon. Subjects ran for 45 minutes, rested 10 minutes, cycled for 90 minutes and then performed a duathlon time trial. They drank a 360-ml sports drink before they started cycling and again 30 minutes into the ride.
Blood samples were collected and analyzed for creatine kinase, lactic acid and glucose. Seven of the 10 subjects who drank the carbohydrate/protein beverage shaved an average of 27 seconds from their time trials. In addition, their creatine kinase levels decreased 36 percent during the 24 hours after exercise-an indication that extra carbohydrates and protein may reduce post exercise muscle stress.