Dude.....OUTSTANDING question!!!!!!! Love to get into these subjects!
A friend of mine is encouraging me to join him at the local boxing club where he swears I'll get the toughest work-out of my life, etc. He also mentioned how they have this one class where he wears a sweat suit....and I'm thinking that's all old-school and long-since dismissed, much like coaches used to discourage athletes from drinking while training...or how smoking used to be thought beneficial to your health!
Now...I'm sure there's some kind of logic to it....perhaps an over-heated & taxed body will learn to cope with it and thus a boxer could go further during a fight or something, who knows....BUT, I'm of the complete impression that everything mentioned on this thread thus far is correct.
Sweat is just sweat, basically water. My background is that of being an insulation contractor, coupled with that is my affinity to see hot/steamy woman...so from that knowledge base I'd like to make the following observation:
When your body generates energy there is heat associated with it. As a means to cool your body, you sweat, this perspiration is intended to cool you. This is one of your bodies mechanism attempting to regulate your body temperature. As your perspiration transitions from a liquid state to a gas state (evaporate), the process requires energy and as such draws heat from your body...thus cooling you. When you wear layers of clothes you inhibit this cooling effect....your body attempts to sweat even more trying to cool you down. At some point it'll realize your hydration level is lowering and you'll sweat a bit less...but still, all your doing is playing with hydration levels: I entirely fail to see how this will somehow increase your caloric burn or offer any benefits other then to help flush your system and maybe give you that overall body-cleanse sensation of having purged a lot of fluids (like a sauna). Perhaps somebody else here can offer some better explanation or benefits of this intentional inhibiting/restriction of your bodies need to cool itself.
The one thing I have learned here is that ANYTHING that will improve your workout or add to getting a better workout is good! I used to ride my bike on an empty stomach and I'd be out there grinding away figuring I was forcing my body to burn more fat. From this forum I was encouraged to try fueling-up before AND during my ride. By adding just a few hundred calories my rides and swims have been thoroughly turbo-charged and I'm getting more out of them...in 2 manners:
1) Whereas I used to burn 1,700 calories on my fairly powerful rides, I now burn 2,200 calories because I'm rippin' it up with a bit o' carbs in my tummy. Notice that the overall increase in calories burned (500 more) are in excess of the calories eaten (a few hundred)....and
2) The more intense ride includes several burst of intense intervals thus giving me some EPOC (by theory) and so I continue my thermogenic and fat-oxidative journey hours after my ride is concluded.
Would you spend 350 calories (in) to burn-off an extra 500-750 (out)?? Oh hell yeah!
It would seem you experienced this same effect when you ran with just your shirt & shorts. More calories burned and you had better energy. Hey: just imagine if you ran naked!!!

Uhhh....don't go there! But newsflash: your body is more efficient & effective as a machine when you fuel it, let it breath and let it run cool.

On a personal note...I used to mountain bike with those grunge-style bulky mountain biking shorts. As the weather got hotter my ridin' budz harped on me to (like everyone else) transition to the lycra shorts. I avoided it because, ya know...I'm straight...but I finally gave in. Dude... I immediately noticed more power, stamina and everything felt light & quicker. Maybe it was the muscle-compression, ventillation or what-not...but my riding took a bump for the better. The improvement was nearly as noticable as when I transitioned from wearing regular shoes to real clip-in's!
Other things that improved my riding:
Eating properly before, during & after the ride
Lots of hydration, wearing a 100-ounce camel-pack w/diluted gatorade mixed-in
Listening to kickin' music via my ipod
Clip-in shoes
Lycra shorts
A helmet with LOTS of ventillation!!!!! (no more waterfall when I lean forward)
A lighter/better bike
Running higher air-pressure and just standing up with bent knees on downhills
Find what works for you and strive to get the most out of your workout. And don't stress all the little details. Look how you are now....eating right, exercising more then 90% of the population...whereas how was it a couple years ago? Fast food, little exercise and you were watching Desperate Housewives & Grey's Anatomy on tv; oh dude, those were lowly days indeed!
Eat Less, Eat right, Move more....rip it up, keep it up and as Chillen is fond of saying, Rock on my Brother!
