When it comes to choosing your favorite supplement for getting a muscle pump, arginine should be near the top of the list. And if you’re really supplement savvy, citrulline will be up there, too. But have you considered glycerol for enhancing your muscle mass? Maybe we should ask, do you even know what glycerol is?

Also known as glycerin, glycerol is the backbone of fats known as triglycerides, the primary form of fat in your diet. (The prefix “tri” refers to the three fatty acids to which glyc- erin attaches.) Although we normally worry about eating too much fat, glycerol is the part of triglycerides that’s not stored as fat. Instead, the liver converts it to glucose and uses it as fuel.

Glycerol is used as an emollient and a laxative, in making explosives and antifreeze, and as a dietary supplement. Although it isn’t hugely popular with bodybuilders, glycerol is used by runners and other endurance athletes because it’s a powerful hydrating agent with strong osmotic properties. This means it attracts and binds large amounts of fluids, such as water, allowing athletes to increase their body fluid content and maintain it for longer, which can boost exercise performance.

A common constituent in protein bars, glycerol is used in low-carb bars as a sugar replacement. Although it still provides about 4 calories per gram, which is similar to carbs, it must be converted to glucose by the liver, so it doesn’t raise blood glucose levels or spike insulin. It also has a syrupy-sweet taste that mimics the taste and texture of fat. Glycerol has also been used in protein powders to encapsulate proteins and create a sustained-release effect, providing amino acids to the body over an extended period. But now glycerol is catching on with bodybuilders as a pump-enhancing product because of its hydrating effects.

A muscle pump occurs when fluid fills up the muscle cells. When you work out, your muscles create metabolic waste products that draw water into the cells. Since glycerol also attracts water, having more glycerol inside your muscle cells will enhance the pump you can achieve. It also pulls more water into your blood vessels, causing them to dilate and increasing their vascularity.

Researchers from the University of Glasgow (Scotland) found in a 2007 study that subjects who took both creatine and glycerol for seven days had nearly 40% more body fluid than a group that took just creatine, and almost 50% more fluid than a group taking just glycerol. This has important implications for hypertrophy: Muscle cell swelling stretches the muscle membrane and instigates processes that lead to long-term growth. For better muscle pumps, take 10–30 grams of glycerol with 20–32 ounces of water about one hour before workouts. Also be sure to take creatine with your pre- and postworkout shakes for a synergistic effect.