Standing can feel harder than running for a couple of reasons. Muscles, like your hip flexors, are actually in their tensed state when you are standing, which can lead them to feel fatigued over time.u003cbr/u003eu003cbr/u003eTensing the muscles in your legs is also what allows blood to flow through your veins. When you stand for too long without moving your leg muscles, it can lead your blood to pool in your lower legs.