Many athletes swear by expensive compression shorts, socks, tights, and other garments. These tight-fitting items are thought to hold muscles firmly in place and improve blood flow to the muscles, thereby boosting athletic performance. But according to a new study of elite male runners, none of that actually happens.

The men in this study first ran on treadmills wearing no compression and then a second time while sporting compression sleeves on their lower legs. Researchers measured their oxygen uptake, stride, body positioning, and other markers throughout both runs. They noted no difference in exercise efficiency or biomechanics between the compression and no-compression runs. "Running economy, which is a measure of efficiency that is closely tied to endurance performance, was exactly the same with and without compression garments," says Abigail Stickford, a researcher at the Institute for Exercise and Environmental Medicine in Dallas. "Running gait, which includes stride length and stride frequency, was also unchanged."

This lack of effectiveness flies in the face of the claims often made about compression clothing, by both their manufacturers and users. For example, Stickford says, the garments used in her study supposedly increase blood circulation — and, thus, oxygen delivery — for improved sports performance and recovery, while also regulating skin temperature. Other supposed benefits include increased blood return to the heart, improved clearance of metabolic byproducts of exercise, increased proprioception (which means a person's perception of his body positioning), and enhanced comfort. But when these purported perks have been put to the test in actual scientific studies — not counting the trials conducted by clothing manufacturers — Stickford says the results have been mixed, and have primarily shown no real performance benefits of compression.

This is not to say that compression doesn't help muscles recover post-workout, which is another reason why athletes wear these items. But that would happen when the garments are worn after a workout, not during, says Stickford. "As far as I am aware, the scientific evidence supporting a positive effect of compression garments on recovery is more convincing than on any performance-enhancing effect," she says. "It's possible that this is a placebo effect, though, given that reduced soreness is probably the most consistently reported finding."

Stickford says that a placebo effect may also have played a role in her study. The vast majority of participants did not usually wear compression sleeves outside of this trial, but there were a few who did. Those guys, she says, believed very strongly in compression's effectiveness on training, performance, and recovery. And while the group as a whole did not see performance gains when they ran in compression sleeves, those individuals did show slight improvements in running economy.

So, should you wear them? "Based upon the results of this study, I think lower-leg compression sleeves are unlikely to improve endurance running performance," Stickford says. "However, if you think they could improve your performance, it may be worth a shot. The placebo effect is a very real phenomenon that affects everything from exercise performance to health outcomes. If there is a 'comfort,' whether physiological or psychological, for an individual wearing compression garments, then it could certainly affect his performance."

Stickford also points out that compression clothing might be more effective when worn for other sports, such as basketball or tennis, than for running. "There is some evidence to suggest that jumping and power performance can be maintained over a longer period of time when wearing compression shorts," she says.

And while there may not be a drastic benefit of compression clothing, there's really no harm in it either. "Unless you're wearing something that's cutting off your circulation," Stickford says. "But most garments have a mild to moderate level of compression and shouldn't do anything like that. Both anecdotal and experimental results show no significant harm in wearing the garments." The most significant damage of compression clothing would be to your wallet.

For access to exclusive gear videos, celebrity interviews, and more, subscribe on YouTube!