Have poked around the web a bit on this issue and haven’t found a definitive answer. Almost got answered on Slowtwitch, but the article really doesn’t compare a having a top on, vs. no top at all. Took a lot of heat xfer and thermo in college, but I’m still not sure what the answer is.
Background for the question:
I live in Georgia so the summers are hot and humid. Your body dumps tons of fluids trying to cool itself but the relative humidity is so high, much of it just pours off.
Shirt (or hat). Advantages: Conduction heat loss “may” be up because high surface area of high-tech material allows more evaporation of perspiration. Evaporation cools jersey which cools skin. More efficient then sweat dripping off. Radiation heat absorption down because sheltered from direct sunlight Disadvantage: Convection heat loss down because reduced air-flow to skin.
No shirt or hat. Advantages: High convection heat loss. Disadvantages: Heat loss due to perspiration might not be as high as shirt scenario because low surface area. Sun beats down on skin so radiation heat absorption is an issue.
So the question becomes, I guess, does the increased cooling due to the efficiency of sweat evaporation (due to surface area of shirt/hat) and shade, make up for the reduced cooling caused by the loss of convection cooling (caused by still air near skin)?
Anecdotes are good, but it’s hard to be both the study group and control group simultaneously. Anyone seen a real study on this?
Personally, for me topless is a little bit cooler. However, if it is a “her” going topless in a race, it is definitely hotter. But seriously folks, it seems all the tri races are going to mandatory tops, and I always recommend practice what you race. Your question may be acadamic already. Slightly off topic, I’d banned the “man bras” before I would ban shirtless.
I can’t see them requiring tops for men in the Southeast anytime soon. The humisery’s just too brutal that the RDs would never hear the end of the complaints if they tried.
Hmmm. A) There was that little thread a couple of months back regarding The Disney half-IM and a penalty… B) Do you mena to tell me that the women in the Southeast can handle the heat and humidity but the guys can’t? I think the guys down there just got tagged.
I don’t know if this answers your question, but the Army did their heat clothing standards in your neck of the woods and decided a soldier will last longer with a shirt on than off. By that, you’d be better in a singlet.
I appreciate the response, but having spent most of my adult life in the Marines and Army, I am cautious in accepting information about any technical issue from the military. Almost no one in the Army (or Marines), for example, has a technical degree. As a result, they are so rift with wives-tales on every technical issue that their ideas on some things are likely to make you burst out laughing.
When your mom tells you to put a hat on or you’ll catch a cold, you appreciate the fact that her heart’s in the right place. But you don’t go to her when you have a question about viral infections.
I here ya there, the thought was that when it’s really hot, like in the desert, people put on more clothes the keep the hot air off you, as anything over you body temp adds heat to you. When humid, cooling isn’t going to happen so keeping the sun off you will keep your temp down. This does coincide with survival manuals that tell you to keep your clothes on.
Having done many an interval workout in 100+ temps in Texas, for me it’s definitely shirtless. Maybe scientifically the singlet is the way to go, but for me shirtless feels much cooler. Plus you’re not carrying around a 2lb. sopping wet shirt
You sweat. The sweat obviously wets the top. The wet top then cools you.
Perhaps you need to go back to physics class. Sweat cools you because latent heat (i.e. energy) from your body is used to evaporate it. That wet top you refer to simply blocks the cooling mechanism - that’s why we use wicking fabrics nowadays. A light coloured top may help simply by reflecting sunlight.
I don’t have a definitive answer to your question, so I will muddy the waters a bit instead. If you are wearing a top (and I believe a singlet is cooler) does wearing a darker or lighter color have an effect? My personal opionin is a white or light colored singlet is cooler than no singlet or a dark color.
I have done tris and training with tri top and without, with hat and without. Even with the relatively cool summer we’ve had in MI, the only question for me is HOW MUCH cooler “without” is.
I have been told, reading about it in the Badwater Ultra marathon web sites that to run with some sort of top that wicks moisture away is good but more important something that reflects solar radiatin away…so these guys racing in the desert, direct sun wear white or other light color that reflects and gives better protection. I have found I am a bit cooler in hi heat and humidity when I wear a white hat and shirt that covers my shoulders against direct sunlight…
I think it also depends on the humidity. Here in CO with dry 90deg+ days, I find shirtless is significantly cooler. If you can keep the shirt wetted down, as in a race with water stations provided, the shirt is cooler. I usually train shirtless and race with a shirt when possible.
When I lived in N Carolina, the humidity meant there was no evaporative cooling effect to speak of. In this case, for sunny days, a close-fitting white shirt in some hightech material was my guess. On cloudy days, I’d go shirtless to get the convection cooling as best as possible.
Never seen any studies either… spent some time in PubMed, but didn’t find anything.
Over the past week I’ve been back wondering about this same issue. So I went poking around Google and, to my very great surprise, I stumbled upon this thread, started by one of my earliest posts here at Slowtwitch. But even this thread never really resulted in the kind of science based hard answers I was looking for. Altho some folks in the thread pointed out that people in desert environments wear loose fitting clothes, there is near consensus from those that train and race in the heat that shirtless is cooler. My guess is that the more clothes in the desert anecdote doesn’t account for the fact that the racer is creating most of his heat and needs to dump it. Whereas the dude in the desert isn’t so much creating heat as trying to shield himself from radiant heat.
Humidity is a big issue too. I could imagine that when humidity is pretty high, a shirt could help evaporative heat losses because of the high surface area of high tech shirts. Certainly with no shirt you don’t get much evaporative heat loss because in high humidity your sweat just drips off. But convection is a big deal and a shirt is certainly going to reduce convective heat losses.
What we need is some studies that look at optimum solutions for different temps, sunlight intensity, and humidity.
