At the other extreme is the Olympic swimmer Dara Torres.

“I don’t need a ton of warm-up to be ready for my races,” she said. Her warm-up is just “some light swimming, kicking and drills,” followed by a few sprints.

Exercise researchers say they are not surprised by the lack of consensus on warming up. There is a theory of why it should improve performance, but there is dearth of good research on whether it actually does.

The theory, said Paul Laursen, a performance physiologist at the Millennium Institute of Sport and Health, in Auckland, New Zealand, is that muscles contract better after they have already been contracting.

As a muscle warms up, the force of its contractions can be charted like a staircase: when it starts to work, the contractions may be only half as strong as they are after it has contracted a few times. The explanation is that the contractions release calcium ions in the cells, enabling the muscle fibers to contract more forcefully. At the same time, muscle enzymes, which work best when slightly higher than body temperature, heat up and become more efficient.

That may be why the elite male marathoners did well after their slow shuffles. “Despite the fact that they can go so fast,” Dr. Laursen said, it will take only a few muscle contractions for their muscles to warm up effectively for their long duration event.”

But the story may be different for shorter events. Dr. Laursen said that athletes might do best with a high-intensity warm-up, the sort that Andy Hampsten did; that can allow fast-twitch muscle fibers to contract more efficiently and can prepare the nerve fibers and the cardiovascular system for an all-out effort.

That, at least, is the theory. What’s missing is evidence showing actual effects on performance.

There’s almost nothing credible, as Andrea J. Fradkin an exercise researcher at Bloomsburg University of Pennsylvania, discovered when she searched for published studies on warm-ups. Most of the research was done in the 1960s and ’70s, she told me, and its quality was poor.