Running in heat and tough conditions

Potentially a lot, but there is no universal seconds-per-degree rule. Population studies show slower average marathon times as heat stress rises, while the individual response changes with humidity, sun, wind, acclimation, fitness, pace and time on course. The heat tool turns temperature and humidity into a modelled planning range. Use the conservative end, then adjust by effort and race-organiser guidance.

Yes. Slow down before the conditions force you to, start conservatively and use effort as the final check. The heat tool gives a modelled range from temperature and humidity, not a precise prescription. Sun, wind, acclimation, fitness, clothing and time on course can all move your real response outside that range.

If the race may be hot, planned heat acclimation is one of the most useful preparations. Repeated, controlled exposure for at least two weeks is often preferred, although a shorter block can still help. Reduce pace and total training load while you adapt. Day-of pacing and cooling still matter, but they do not replace preparation. Seek expert guidance with pregnancy, medical conditions or a history of heat illness.

Use cooling you have rehearsed: shade, light clothing, pre-cooling, water dousing, cold towels, ice or cold drinks where practical. No single method or body site is universally best. Cooling supports preparation and conservative pacing; it does not replace them. Confusion, altered behaviour, loss of coordination, collapse or inability to continue normally needs immediate medical help.