I plan to have just a few drinks at a holiday party tonight. How will that affect my workout tomorrow morning?
Well, that depends on what you mean by "a few."
Earlier this year, researchers in New Zealand published a surprising study that found significant delays in muscle recovery when the subjects drank a "moderate" amount of alcohol after a strenuous workout. The findings join a little-known body of research suggesting that alcohol can sap your morning-after strength even if you're not hung-over.
The subjects in the new study did a series of leg exercises, then had 90 minutes to drink either straight orange juice or a mix of vodka and orange juice before going to bed. Over the next three days, the alcohol group didn't report feeling any additional leg soreness compared to the OJ group - but their loss of strength in a series of tests was 1.4 to 2.8 times greater.
However, "moderate" in this case was 1 gram of ethanol per kilogram of body weight - corresponding to about 6.5 bottles of 5-per-cent-alcohol beer for the subjects, who had an average weight of 193 pounds.
"When you look at how much athletes are reported to drink in the scientific literature, this is actually a moderate dose," says Matthew Barnes, a researcher at Massey University and the lead author of the study, which appeared in the Journal of Science and Medicine in Sport. "This is not just in New Zealand but in the majority of Westernized countries where contact team sports are played."
Sure enough, researchers have recorded some fairly prodigious feats of drinking by athletes - Mr. Barnes points to one study of rugby players in which post-match consumption reached as high as 38 units of alcohol - or 22 bottles of beer.
If you're drinking that much at a holiday party, the next day's workout is the least of your worries.
Since most people are dealing with smaller quantities, Mr. Barnes conducted a follow-up study that cut the dose in half, to a more-modest 0.5 grams of alcohol per kilogram of body weight. The results, which will appear in a forthcoming issue of the European Journal of Applied Physiology, offer good news: He found no difference at all in recovery between the alcohol and orange-juice groups.
He and his colleagues are now conducting further experiments that suggest the higher dose of alcohol may affect the central nervous system rather than the muscles themselves, weakening the signals sent from the brain to the muscles. However, it's possible that there are also changes in the muscles, or in the levels of hormones such as cortisol and testosterone.
There are two other key factors that affect how well you recover after a workout-booze combo, Mr. Barnes says: rehydration, and refilling your carbohydrate stores.
Drinks containing more than about 4-per-cent alcohol have a diuretic effect; drinking a 25-millilitre shot of hard alcohol will make you expel about 100 ml of urine. The solution here is simple: Drink a glass of water for every alcoholic drink you have during the evening.
In order to recover properly after a workout, replenishing your energy stores during the two hours following exercise is crucial. Some studies of animals have suggested that alcohol can directly hinder your ability to restore carbohydrate levels, but these results remain disputed.
However, problems definitely arise if the calories you consume from alcohol displace more functional calories. A 2003 study of Australian cyclists found that simply adding alcohol to a post-workout meal didn't change the amount of carbohydrate stored. But if the alcohol replaced some of the calories in the post-workout meal, carbohydrate stores were 50-per-cent lower after eight hours, and still lower 24 hours later.
Overall, these studies fit with the prevailing wisdom that one or two drinks a night won't have any negative effects on your health and performance. Indeed, light to moderate drinkers appear to have 20- to 40-per-cent lower risk of heart disease, among other reported benefits.
But if you've arranged a big night out with a group of Kiwi rugby players, you might want to schedule a fairly light workout for that day - or at least, don't expect to set any personal bests in the days that follow.
Alex Hutchinson blogs about research on exercise at sweatscience.com.