When the mercury drops, it threatens your body's core temperature, which functions best at about 98.6° F. To stay warm, your body will send more blood toward your core. "The muscles in your legs and arms get less blood flow — and less oxygen — than they would in warmer temperatures. With less oxygen, the muscles are stiffer, they don't work as well, and they fatigue easily," says Dr. Sarah Eby, a sports medicine physician with Harvard-affiliated Massachusetts General Hospital.
Cold weather also affects nerves (which contribute to muscle function) and makes blood flow to muscles even less efficient.
All of these changes increase the risk for muscle and tendon injuries, especially if you're less active in the winter and your muscles are weak and tight.
