If your hips feel tighter than usual when the temperature drops, you're not imagining it. That sluggish, stiff stride you feel at the start of a cold run is a real physiological response not  a personal problem or something to just stretch your way through. This is what happens: Joint fluid becomes more viscous  in colder temps, which means your joints don’t move as freely. Blood flow to your muscles decreases , making them feel slower, tighter, and less responsive. Your nerv