“So clearly, being wet and in the wind with bare skin is really going to chill you. And being dry and in cold wind is going to chill you. The nuance I wanted to communicate was if you compare being damp with sweat under a rain jacket with being dry but having no wind-break at the same temperature, is there a difference in the chilling effect? Or is there perhaps a cross-over temperature where one becomes more heat-depleting than the other? Thinking that it could come into play when racing or training on rolling terrain where having no wind break would be more comfortable on the climbs but having a wind break would be more comfortable on the descents.”
This is a great question from Dan. I’m not aware right away of any particular threshold temperature or cross-over effect because there are some individual variations in the cold response to consider. I do think there are some basic things that need to be in place, but those need to be adjusted to your individual needs (e.g., body composition, any medical conditions, etc.)
My personal experience with this, living in Colorado, where we can see all four seasons in any given day has trained me to focus on staying dry as the main priority. Wet and windy conditions seem to be the worst combination. Wet skin cools faster, reaches a lower temperature, and freezes at a higher threshold than dry skin. (1, 2, 3)
The lower your body fat percentage, the greater shivering response that may take place to aid in maintaining body temperature. And with this response, comes a massive increase in metabolic rate, so you need to be fueled (and continue fueling as much as possible) if you are experiencing cold stress to that degree.
There are differences in the individual response to cold, so trial and error in relatively safe locations are key to figuring out what you can handle. Personally, I aim to keep my hands, feet, and head covered and as windproof as possible in temps below 40 degrees F. If I’m doing a hard ride in the cold, I’ll aim to keep it no more than about 90 minutes because I can’t handle much more than that, even with adequate coverage. It’s really a balance of riding just hard enough to stay warm, but not so hard that you are sweating a lot underneath your jacket.
Also consider clothing and layers that you can peel or zip/unzip as necessary. I just picked up a surprisingly warm jacket that holds heat in very nicely, and all I have to do is unzip a little bit when climbing to allow some airflow through (and heat out), and then zip back up before a descent to lock in some of that heat I just built up on the climb.
Resources:
Castellani JW, Young AJ, Ducharme MB, et al. American College of Sports Medicine Position Stand: prevention of cold injuries during exercise. Med Sci Sports Exerc. 2006;38:2012-2029.
Keatinge WR. Freezing-point of human skin. Lancet. 1960;1(7114):11-14.
Molnar GW, Hughes AL, Wilson O, Goldman RF. Effect of skin wetting on finger cooling and freezing. J Appl Physiol. 1973;35:205-207.