Resistance bands work similarly to free weights, but there are a few key differences. Like dumbbells, barbells, or any other free weights, resistance bands provide external resistance that your muscles have to work against. When you’re pushing against a resistance band during an exercise, your muscles have to engage to fight the tension
For example, if you are doing a squat with a mini band around your quads, you have to press your legs against the band even when you’re standing in the starting position. You have to then press out when you’re lowering into a squat, and again when you’re standing back up, to keep your knees in line (not collapsing in toward each other).
Because of this, your muscles are often under tension for an extended period of time when bands are involved, which means they’re pretty much constantly working. If you've ever done glute bridges or lateral walks with a mini band looped around your legs, you know that the burning sensation sets in almost immediately—that’s because you’re never really giving your muscles a solid break until you actually stop doing the exercise.