Who even needs a chair behind them when their hips, glutes, quads, hamstrings, and core can support them in thin air? Get a workout in at your standing desk by perfecting the bodyweight squat, aka "the king of exercises."
How to: Stand with your hips just wider than shoulder-width apart, and stack your hips over your knees and your knees over your ankles. Keeping your back neutral and your chest and shoulders up, sit down into an imaginary chair. Get your thighs as parallel to the floor as you can, keeping your knees over your ankles and your weight back in your heels. Keeping your abs tight, push through your heels to return to the starting position.
Variations: Just when you think it can't get worse, oh, yes it can. Turn your feet out to 45 degrees, slightly tuck your pelvis, then stay tall through the crown of the head and say hello to your inner thighs as you squat it out plié-style. And to increase the burn in either squat position, go to your lowest point and add micro bounces.