Sir, Sir Roger Bannister’s letter (July 15) did not deal with another aspect of the effect of heat stress on the human frame.

The mass of an individual is approximately proportional to the cube of his height, whereas the area of skin is proportional to the square. Take two men, one 5ft tall, the other 6ft 3in. If both are the same shape in all regards, the taller would weigh 1.9 times the weight of the smaller. If both do an identical task, for example, running a mile, the work done is in similar proportion and so is the body heat produced.

Body heat is mostly lost through sweat but this depends on the area of skin. The taller man has only 1.5 times the surface area of the other through which to lose 1.9 times the quantity of heat. This results in a greater degree of heat stress for the taller man as his body core temperature rises. Performing strenuous tasks in hot conditions is inherently more stressful for larger men than smaller men of the same shape but this phenomenon is rarely recognised.

J. G. Wishart
Edinburgh

Sir, The standard dress of the Parachute Regiment some years ago was “smock and denims”, wherever we were serving, from the Middle East, which was reasonably warm, to the Arctic Circle in Norway. It was always the assumption at that time that should Great Britain land a man on the Moon he would go in “smock and denims”.

Colin J. Butcher
Brecon

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