By Gretchen Reynolds

New York Times News Service

Can a shot of saltwater make you a faster runner?

The answer appears to be a resounding yes, if you believe the saltwater contains something that should make you a faster runner, according to a new study of the power of placebos in athletic performance.

Anyone who exercises knows from experience that our minds and mental attitudes affect physical performance. Who hasn’t faced a moment when, tiring at the end of a strenuous workout or race, we are about to quit before suddenly being passed on the path or shown up in the gym by someone we know we should outperform, and somehow we find an extra, unexploited gear and spurt on?

This phenomenon is familiar to physiologists, many of whom believe that our brains, to protect our bodies, send out signals telling those bodies to quit before every single resource in our muscles and other tissues is exhausted. We think we are at the outer limits of our endurance or strength when, in reality, we may still have a physical reserve available to us, if we can find a way to tap it.

Researchers at the University of Glasgow recruited 15 male recreational runners for a test of what the volunteers were told was a legal form of erythropoietin, or EPO, a substance that increases the number of red blood cells in the body. In many sports, EPO has been used for doping, because more red blood cells means more oxygen is carried to laboring muscles and endurance performance improves.

But the runners were assured that this was a formulation of EPO that was legal for use in research and would have few harmful side effects, since the dosage would be low.

On the other hand, the runners were told, the drug should improve athletic performance because it would increase red blood cells.

The “drug,” however, was saline, which would be given by injection, because past research had shown that the placebo effect tends to be stronger when a substance is injected instead of swallowed.

Before starting the “drug” regimen, though, the volunteers competed in a 3-kilometer track race to determine their baseline finishing times. Then some of the men continued their normal training for a week, while others received injections of the “drug.”

They all raced again.

Finally, for another week, the men switched, with those who had not received the shot before receiving the injections now, and vice versa.

Then they all ran a final 3-kilometer race.

Throughout, the scientists collected data about how the men felt physically and psychologically during their workouts and the races.

As it turned out, almost all of them thought that the “drug” had had real and substantial effects. The runners told the scientists that during the week when they were receiving the injections, their workouts felt easier and they were more motivated to push themselves. Most of the runners also reported that they recovered better when receiving the injections.

Most important, they almost all significantly improved their 3-kilometer race times by about 1.5 percent after taking the “drug,” compared with their times at the start of the experiment.