Bodybuilding workouts are fueled primarily by glycogen stored in muscle. Glycogen is nothing more than long, repeating chains of glucose. When you need energy, the glycogen is broken down in a process called glycolysis. Glycogen stored in the liver is used to maintain a certain narrow range of blood glucose levels between meals, since your brain and nervous system depend on a steady trickle of glucose to keep the engines running. The best way to replenish depleted glycogen stores is to take in carbohydrates. In fact, how quickly and efficiently the body replenishes glycogen stores in muscle largely determines the rate of exercise recovery.
In recent years several techniques have improved on the usual consumption of carbs following a workout to restore muscle and liver glycogen levels. One involves the use of a carbohydrate and protein concoction, usually featuring a 4-to-1 ratio of carbs to protein. It works because it involves the use of high-glycemic-index, or simple, carbs, which elicit maximum insulin release. Insulin, in turn, promotes the increased activity of the rate-limiting enzyme required for glycogen synthesis. Adding protein to carbs produces an even greater insulin release and, consequently, a more efficient glycogen replenishment.
Japanese scientists think they may have found another way to enhance muscle and liver glycogen synthesis following training. In a new study using rats as subjects, they found that giving acetic acid to the rodents increased the efficiency of muscle and liver glycogen repletion.1 The most common source of acetic acid is vinegar, and the study found that the same amount of vinegar used in food provided enough acetic acid to do the job.
Vinegar contains acetic acid at a concentration of 3 to 9 percent, and foods such as sushi, marinated meats and vegetables prepared with vinegar contain 0.2 to 1.5 grams of acetic acid. Apple cider vinegar is a good source of acetic acid and has been used as a folk medicine for many years. A diet still in vogue on the Internet has apple cider vinegar as a key ingredient.
How acetic acid enhances glycogen repletion is complicated, and the process in the liver is different from what happens in muscle. Both processes, however, alter enzyme systems, the net effect of which is enhanced glycogen replenishment. Although the initial study used rats as subjects, there’s no reason to suggest that the technique won’t work in the human body, which has the same enzymes involved in the glycogen-repletion system. Those who want to try acetic acid can use apple cider vinegar itself or tablets or capsules, which are cheap and readily available.
1 Fushimi, T., et al. (2001). Acetic acid feeding enhances glycogen repletion in liver and skeletal muscle of rats. J Nutr. 131:1973-1977.