More body fat means a lower specific gravity and hence greater buoyancy (so chubby yet unfit people often seem to swim fast and efficiently). But Michael Phelps is lean and muscular. So what makes HIM such an efficient swimmer - some subtle muscular movements perhaps, unconsciously mastered during years of swimming practice?

If so, a top swimmer could presumably remain afloat even when quite heavily weighted down. How heavy a steel bar could Michael Phelps carry in a backpack, say, without drowning?

Finally, are inefficient swimmers justified in thinking that they at least get a decent workout when they swim, in a way that Michael Phelps doesn't?

I work on a submarine which entails long trips away from home dived in the sea. Our only light is from fluorescent strip lights and the water we drink is de-mineralised. What affects would this have on the human body?

Whenever I buy cheap ice cream (i.e. Mac Donalds Soft Serve) or service station slurpies I almost always get a brain freeze when I consume it too fast, I know how to prevent getting these (slow down consumption) and I assume that it's caused by the temp. of the food/liquid I'm consuming, but what is the science behind it? Is it muscles or something contracting really hard and fast causing a cramp? And why do i predominately get it from the cheap stuff.

P.s. I’ve theorised that I don’t get it from more expensive ice cream because it tastes so good that I take my time and enjoy.

my majure is clinical psychology

I read that bruising increases white blood cells and that asthmatics are short of white blood cells

Being a regular athlete, i have visible veins standing out from both my arms. However, many more veins protude from my right arm than my left, and those that do, protude further. I can only assume that this means i have greater blood circulation in my right arm. I am right handed - could these 2 facts be linked? I have noticed this in other people too, with all having more veins in their favoured arm. Does the hand we favour need more oxygen to function, or does the factc that the arm has more oxygen make the arm ones favourite?

I have noticed, as others may have, that as a race humans have everything done for them; travel (cars, planes etc.), hunting (guns, breeding food etc.), and also there is no longer a need too compete for homes (we can simply build more). is there any need to evolve any further? have we reached our final stage in our long evolutionary chain? 

The snow at the base of our small apple trees melts before snow elsewhere has melted. We've seen this under other trees too. Why?

Robert Campbell, Uetendorf, Switzerland

(Image: Mattox, stock.xchng)

If the sun was extinguished or there was a permanent worldwide eclipse, how long would it take for us all to freeze to death, and what could we do to try to avoid it?

Darren Darby, London, UK

(Image: Lucien Rudaux, Wikimedia Commons)

Asked by listeners on BBC Three Counties Radio, UK

(Image: tellgraf, stock.xchng)