Re: why do our hands feel limp when we are very cold?

Hi Rana,

There are several reasons for weakness in your hands when they are cold, and we could go into a lot of detail about the specifics of how cold affects your nerves and muscles. However, the short answer is: to grab and hold things, your nerves need to be able to transmit bursts of signals from your brain and then release a chemical (the neurotransmitter acetylcholine) onto the muscles to tell them to contract. Then a bunch of biochemical steps need to happen in the muscles to enable them to contract and make your hand 'squeeze' something. If any of these steps don't work so well, your hand can't squeeze.

Cold affects all of those things. Basically, out bodies are big mushy bags of chemical reactions, and chemical reactions slow down as the temperature drops. In fact, that's one reason why our bodies work so hard to keep our temperature a pretty even 98-99 degrees F (about 37 C) -- so that all the chemical reactions keep going at an even clip.

When your hand gets cold, the speed with which nerve impulses go is slowed, until finally they can stop altogether. Also, the release of acetylcholine on to the muscle is reduced, and the subsequent reactions inside the muscle that make it shorten are reduced. There is nothing really that makes your hand 'stiff', like an old rusty machine or something -- it's more that things just don't work. And if your brain is sending messages down to your hand saying "squeeze! squeeze!" and your hand doesn't squeeze, or does so only weakly or slowly, we tend to say that it's 'stiff'. (Of course, if your hand gets REALLY cold, like with severe frostbite, it can obviously freeze solid. That's pretty stiff, but I don't think that's what you're asking about).

Interestingly, your body is mainly concerned with keeping your brain and other vital organs alive when it gets cold, so if you're not dressed warmly enough, your body will divert blood from your hands and feet, then arms and legs, in order to keep from cooling any further (a lot of heat is lost from your limbs). Thus, your hands and feet can get really cold, but your guts and brain will stay happy. ( Ducks and moose are particularly good at preserving their body heat, since they stand in cold water a lot of the time. -- and part of their method is to just let their feet get really cold while keeping their bodies cozy.) That's why you have to measure human body temperature as close to the 'inside' as you can (deep in the mouth, ear, rectum) to get an accurate temperature. Most people's hands and feet are quite a bit cooler (maybe 80-85 F) than their 'core' body temperature. Since your brain and heart and lungs and other important organs don't work so well when they're cold (for the same reason your hand doesn't when it's cold), it's obviously a very serious problem if they get cold. 'Exposure' or 'hypothermia' is basically when your core (brain, vital organs) body temperature gets too low.