#1477 Why are your fingers stiff when you are cold?

Why are your fingers stiff when you are cold? Fingers are stiff when you are cold because the body moves the blood to more important organs, because muscles stiffen in the cold, because the joints become viscous, and because the cold can reduce nerve impulses.

When our hands are exposed to the cold for a long period of time without gloves, they become pretty much useless. The fingers will not move, there is little strength, and it I very difficult to grip or manipulate objects. There are several reasons why this is. The first reason is the body’s basic survival instinct. All of our organs need a certain temperature to be able to function. That varies slightly from person to person, but it is generally between 36.5℃ and 37.5℃. If body temperature goes above or below these thresholds, the organs will have trouble functioning. In our body, there are vital organs (hence the name), and expendable things. When our body temperature drops, the brain instructs the blood vessels to constrict in our extremities to reduce the blood flow there and bring it into the core in order to keep our organs warm. The extremities are considered expendable. This reduced blood flow into the hands means the muscles that operate our fingers don’t have enough oxygen to function properly. This makes the muscles stiff and slow.

Muscles also work far more slowly in the cold than they do in warmer weather. The first reason for this is that muscle fibers expand when they are warm and contract when they are cold. That makes them naturally stiffer and slower. The chemical reactions that take place inside the muscles also slow down in cold temperatures. Our body uses ATP for energy, and that has to be broken down in the muscles so that they can move. They do this with enzymes, such as myosin ATPase. Enzymes work best in the same temperature range as our internal organs, and when they get colder, they don’t work as well. Enzymes work by moving a lot and coming into contact with other substances, where they trigger a chemical reaction. When they are cold, they don’t move as much because there is less chance they will contact the other substances. Interestingly, a lot of the muscles that control the motor function of the fingers are found in the forearms. If you want to rapidly warm up your fingers, it is better to apply heat to your forearms than directly to your hands.

Another reason why our fingers become stiff and unwieldy is because of the synovial fluid in our joints. The joint is the flexible point between where two bones meet. The bones cannot rub against each other because the friction would chip them away, so they are covered in a layer of cartilage. This is then protected by a layer of synovial fluid that is contained in the joint between the two bones. It is a very thick, jelly-like fluid that reduces friction. When the temperature decreases, the synovial fluid gets thicker and more viscous. It doesn’t move as freely, and friction builds up in the joints, making them stiff. This is also why joint problems like arthritis get worse in the cold.

The last issue is the nerves themselves. The nerves are affected in two ways. Firstly, the constriction of the blood vessels in the body reduces blood flow to the nerves, and without blood, the nerves can’t function properly. The second reason is that the temperature itself can affect the speed at which the nerves can send and receive signals. The colder they are, the slower the signals pass up them. When your arms and hands are very cold, it is very difficult to send commands to your fingers.

All of the reasons why our fingers don’t work very well in the cold are the reasons why our hands hurt when they start to warm up after being very cold. If you rapidly warm cold hands, the blood flow will return in a rush, and the nerves will suddenly be able to function at normal speed. The blood rushing back causes a throbbing, aching feeling because they expand and press on the nerves that have only just started to work properly again. Lots of pain signals get sent to the brain. Although this pain is a good sign because it means that your hands are returning to normal. If you warm up your hands and feel no pain, it might mean the nerves are too damaged to send signals, and you have probably developed frostbite, which is a very serious problem. And this is what I learned today.

Sources

https://cyclingmagazine.ca/sections/training-guide/training/why-defrosting-your-hands-and-feet-after-a-cold-ride-hurts-so-much-and-how-to-avoid-the-pain

https://csep.ca/2021/02/17/cold-temperatures-can-reduce-muscle-strength-and-speed-but-increase-muscle-activity