running exercise, heat stroke

Most athletes, particularly those doing running exercise, only worry about heat stroke in hot conditions. But a case report of a near-fatal incident during a cool-weather marathon in the US suggests they may need to think again.

A well-trained male runner in his late 30s collapsed 10m before the finish of a race run in autumn temperatures ranging from 6-9.5ºC. In the medical tent his condition continued to deteriorate, with an erratic heart rate and breathing difficulties.

At the local emergency department, his rectal (core) temperature was measured at 40.7ºC – well above the threshold for exertional heat stroke – and he had heat-induced damage to his heart, kidneys, liver and blood clotting system.

After drastic cooling, the runner’s core temperature returned to normal and the organ damage was eventually reversed. He was able to leave hospital after five days but took a long time to recover and wasn’t able to resume regular running until six months later.

The underlying question, as the researchers point out, is: ‘Why on a cool, clear morning would a runner wearing a singlet and shorts experience a near-fatal heat stroke?’.

They suggest two possible explanations:

1. The runner had been ill with a sore throat in the week before the race and was still recovering on race day. This illness ‘may have been the factor that altered his body heat loss’;
2. In search of a fast qualifying time for the Boston Marathon, he was paced by a ‘fresh’ runner during the last 16k of the race. This external pressure may have allowed him to override his body’s natural protective response to heat stress – to slow down or stop altogether.

The key learning points, conclude the researchers, are that:

• Medical teams should always consider the possibility of heat stroke in a collapsed athlete, which means checking rectal temperature even in cool conditions;
• Runners should not run hard – or even at all – when ill;
• Outside pacing should be abandoned because it makes athletes less likely to slow the pace when feeling ill;
• Running with a ‘buddy’ would enable runners to watch each other for signs of heat stroke.

Med Sci Sports Exerc, vol 38, no 7, 1197-1203