Rain at 5 °C makes even hard running colder and costlier: rectal temperature was lower from 10 minutes, and oxygen uptake and perceived exertion were higher by 50–60 minutes
Key Findings
Rectal temperature was lower with rain than without at 10, 40, 50 and 60 minutes of running at 80% VO2max at 5 °C; oxygen consumption and perceived exertion were higher with rain at 50 and 60 minutes.
Twelve healthy men ran for 60 minutes on a treadmill with or without rain.
The authors attribute it to heat loss growing as the wet area grows, with energy expenditure and lactate rising from cold stress.
Practical Application
Wet, not the temperature alone, is what justifies a shell: around 5 °C in rain the body cools even at a hard effort, and the cost shows after 40–50 minutes.
For a long or easy session in cold rain, dress for staying dry at the trunk; for a short hard one, the rain matters less than the time spent standing wet before and after.
At low intensity in cold, wet and windy conditions heat production does not cover heat loss (Weller 1997, DOI 10.1152/ajpregu.1997.272.1.R226): the easy, slow session is the one that needs the most clothing.
Limitations
Small, young fit men, 5 °C only; performance was not measured. Abstract only was read.