Tell me I'm not the only fan of the post-workout shower beer. You know, when you've had a long day and then a hard workout, and your need for a hot shower is surpassed only by your need for a cold beer. So, unable to decide, you have them both at the same time. Ahhh.

But, shower beer in hand, sometimes I wonder: is indulging in an alcoholic beverage such a good idea during that important window for post-workout nutrition? And what if, rather than a single shower beer, you're out partying and partaking of way more? Are you sabotaging all your hard work in the gym?

First of all, here's what's actually in an alcoholic beverage, nutritionally speaking: Alcohol has seven calories per gram, compared to the familiar numbers of nine from fat and four from carbs and protein. The USDA's database breaks down a typical 12-oz beer (brand unspecified) as having 63 percent of its 153 calories from alcohol, 33 percent from carbs, 4 percent from protein, and no fat. Meanwhile, a 5-oz glass of wine, at 123 calories, is 87 percent alcohol and 13 percent carbs, with no fat or protein. Hard liquors have 100percent of their calories from alcohol, (96 calories in an 80-proof shot) and I'll leave mixed drinks as a do-it-yourself math problem.

Lab studies show all kinds of bad news associated with alcohol and sports: athletes who drink are more likely to get injured, and studies in rats have shown that drinking, over time, leaves the rodents with smaller muscle fibers and fewer capillaries. That's not to mention the better-known effects of alcohol: risks for liver damage, heart disease, cancer, and weakening of the immune system.

Still, most athletes drink at least a little, making alcohol a very widely-used drug: Most of the 88 percent of college athletes who drink are probably doing it in spite of, or in ignorance of, its effects on their muscles. (A century ago, the research was less clear: Thomas Hicks, winner of the 1904 Olympic marathon, had a shot of brandy around mile 20 on the theory that it would help perk up his tired legs. It probably didn't work, although it's hard to say. He was dehydrated—this was thought to help performance—and also took a near-lethal amount of strychnine, an effective and then-legal performance enhancing drug.)

So what's that post-workout beer really doing to your muscles?

That's the question that a pair of New Zealand researchers were trying to answer when they served dinner and screwdrivers to a half dozen "healthy men" (apparently not trained weightlifters) after a workout. They had done the equivalent of 300 reps of lowering the weight on a knee extension machine—but only with one leg. Six others got plain orange juice with their meal, and on another day, the experiment was repeated with each person working their opposite leg and downing the opposite drink.

A day and a half after each workout, the subjects' strength was tested. Everybody was a little weaker, which was to be expected, but the alcohol drinkers were worst off: they stood at a 39-44 percent loss of strength, compared to 27-29 percent after plain orange juice.

The study was a bit suspect, though, because the researchers threw out data from two subjects who didn't produce the expected results. Another important note is that the amount of alcohol the subjects drank was fairly high—the equivalent of a six-pack each. The authors defended the dose as being moderate compared to, for example, what rugby players typically drink at an after-party. A follow-up study showed that drinking half that amount, about three drinks' worth, produced no difference between the alcohol drinkers and controls.

Diving deeper into what's going on in the muscles, a group of Australian scientists decided to test nine actual rugby players, giving them screwdrivers or OJ four hours after a match. The next morning, the alcohol drinkers scored worse on a jump test (about 10 inches lower than they jumped before the match; controls only lost two inches). They also scored poorly on cognitive tests, including slowed reaction time. Happily, even though animal studies have linked alcohol consumption with lowered testosterone, the players' T levels were normal.

And where does that leave you, standing in your kitchen after a hard day with a protein shake in one hand and a beer in the other? Let's look at one more study that combined alcohol with different post-workout drinks. This one put eight "physically active" men through a circuit-type workout with leg extensions and cycling, then gave them a shake with whey protein powder and/or maltodextrin (a carbohydrate), followed by, again, orange juice with or without vodka.

The key result here was the rate of muscle protein synthesis. That means, how much muscle are you building, how fast? Alcohol seemed to hurt that process, while protein helped. Importantly, combining protein and alcohol was better than alcohol alone, but didn't totally cancel out alcohol's effect. So you should definitely still have the protein shake, whether or not you drink the beer.

But there's one big caveat. All of these studies were performed with a lot of alcohol—for this last one, the dose was equivalent to a whopping 12 drinks. I think it's safe to say that if you're chugging that much, it's not a calculated decision based on muscle protein synthesis rates.

Actually, there's a second big caveat. These studies were all done on men. We already know that women and men metabolize alcohol differently, and an informal study done for Runner's World magazine found a very interesting result. Giving runners two or three beers after a run was supposed to hurt their performance on a treadmill test the next day (compared to drinking non-alcoholic beer), which was true for most. But it seemed to have the opposite effect on some of the women, who put in their best performances the night after drinking. Performance booster or statistical fluke? We'll have to wait for more research to find out.