Over the next month, thousands of high school and college football teams will get ready for fall by practicing in torrid conditions where heatstroke is a constant danger.
That has some trainers and doctors worried about increasingly popular thermometers that, in their view, sacrifice accuracy for convenience.
The devices use infrared light to scan heat radiation in the ear or on the forehead.
The infrared thermometers have produced lower readings in athletic settings -- or in lab tests meant to simulate them -- than rectal thermometers or other devices.
After testing a forehead scanner that is made by Exergen, researchers with the Institute for Exercise and Environmental Medicine at Presbyterian Hospital in Dallas, Texas, warned that low readings from the device could deprive patients of critical, perhaps lifesaving medical care.
In the test in the journal Medicine and Science in Sports and Exercise, the infrared thermometer gave readings below 37.8oC when rectal thermometers topped 40oC, a temperature at which some patients begin to become vulnerable to heatstroke.
Douglas Casa, the director of athletic training education at the University of Connecticut who completed a study of 10 types of thermometers used in intense training situations, said the infrared forehead and ear scanners were among those producing misleadingly low readings in his test.
And William Roberts, a University of Minnesota researcher and former president of the American College of Sports Medicine, said his tests of the forehead device on runners in the Medtronic Twin Cities Marathon led him to similar conclusions.
Both have submitted their results to peer-reviewed journals.
Exergen said that it was apparent from the report on the Texas test, which used healthy subjects in heated wet suits, that the researchers did not duplicate realistic conditions for athletes.
Exergen also said that the thermometer, the Temporal Scanner, was not marketed for use in athletic settings and came with instructions specifically stating that it was not for outdoor use.
That goes for both the consumer version, which costs US$30 to US$50 at drugstores and other chains, and a more durable model sold for about US$350 to doctors' offices and hospitals, it said.
The company Web site includes a 2005 news release noting that its thermometers had been used for 17 years at the Boston Marathon.
But Francesco Pompei, the company president, said the release made it clear that the device had required special handling at the marathon.
The changes, including use of a piece of film to deal with perspiration, have been shared with a small number of trainers who sought more information for their own studies, Pompei said.
"We use sports medicine for research," he said. "But we are not selling into the athletic market."
He added that the association with the Boston Marathon, which began in 1989, ended last year with the retirement of Marvin Adler, longtime medical director of the race.
Critics said the device might attract coaches looking for something simpler than rectal thermometers and less costly than the most accurate devices available outside of hospitals -- radio-transmitting temperature-sensing pills that athletes swallow.
Pompei said his company would be glad to work with critics to discourage using the Temporal Scanner in athletic settings.