I grabbed the following paragraph from my article, Heat Production and Dissipation, from seriousexercise.com:
Subjects sometimes complain that their hands and feet are cold. Realize that your
core temperature can be overheating simultaneous with your hands being
frostbitten. Many people die shoveling snow. I suspect that part of this is due to
exertion—including overheating of the trunk. Note that this life-threatening heat
is produced as they are struggling to protect their hands from frostbite. The
shoveler responds to the cold of his hands, feet, nose and arms by overheating the
core.
Heat Production and Dissipation
So is this product safe?
As I explain in my referenced article, heat is produced relative to the body’s mass and dissipated relative to the body’s surface area per that mass. And as a body part is larger in mass, its surface area per mass is smaller!
If any body part needs a warmer it’s the extremities, not the trunk!
Of course, vests are often preferred to provide better mobility to the arms.
As a youth living in Toronto, winters provided for my very first source of income as a (professional) snow shoveler for many of my neighbours’ driveways on our street (as well as my own). I once shovelled the driveways of nearly every neighbour on my street (a profitable day) so I can attest to the challenges of cold weather exertion. When you’re shovelling snow, you have all sorts of competing adversities to deal with and I believe that the annual stories of death-by-shovel are not far removed from our concerns with exercise: Intense and protracted bouts of Valsalva (breathing in ice cold air), mated with excessive gripping of the shovel combine with rapid overheating due to excessive layering which can cause massive arterial blood pressure spikes. When you factor in the fact that many who go out to shovel are not well-conditioned, you have the makings of a killer avocation. I learned very early on that my body could generate enough heat that I would sweat even in double digit minus temperatures (that’s Celsius). I remember the neighbours being absolutely aghast at my shovelling “attire” during blizzard conditions: T-shirt, joggers, boots and gloves but no coat and certainly no tuque on my head... I got off on their reactions but somewhere in my head I also knew that there was more to my instinct than just teenage hubris. I knew that overheating during vigorous activity, particularly when the ambient temperature is low, could be dangerous. In the 1922 documentary Nanook of the North, audiences marvelled at Nanouk's occasional shirtless outings in the Arctic. And more recently, Wim Hoff climbed mount Everest in just shorts. And Remember Sylvester Stallone being forced by John Lithgow to rock climb in a nearly vertical glacial cliff-face in just a t-shirt in the freezing cold in the movie Cliffhanger? Perhaps Lithgow's character knew full well that Sly would not freeze to death because he would generate so much heat while scaling the monolith... There’s an aphorism that says, there is no such thing as bad weather, only bad clothing… I think that this saying is as circumstantial as much as it is weather-based. In fact, a heated vest is a marvellous device, and I have worn one when riding my motorcycle in very cold weather. Curiously, a heated vest worn on a motorcycle is often barely enough to balance the extremes of the elements. While riding with the vest turned on—if it truly is cold enough—I often have to check on the vest's functioning because it can be hard to tell if the heat is actually on. Plus the exertion level is relatively low so overheating remains unlikely (unless the temperature rises dramatically, in which case you’d turn it off). I suppose the same is true for snowmobiling …However, I remain far less less sanguine about the use of a heated vest for any activity that may raise body temperature by exertion. Last year on the slopes, I admonished a good friend for wearing a heated vest while snowboarding for the same concerns as snow shovelling…
Did I just read you using the word "core"? I know in this context it may be fitting. Enjoying these!