The grand plié, for example, requires you to squat with your pelvis tucked under, feet pointing out, and heels off the floor. It's a barre staple, but you may want to consider banning this exercise from your routine. While it's meant to strengthen your legs and glutes and improve your range of motion, the pelvic tuck stresses the lower back, and squatting with feet turned out stresses the pelvis' sacroiliac joint. What's more, to really work your glutes, you need to stretch them before contracting, which the grand plié doesn't do.
Instead, try the ball-squeeze parallel squat with calf raise. Position your feet hip-width apart, toes pointing forward. Hold a sponge ball between your legs as you descend into a squat, squeezing the ball throughout the exercise, then rise out of the squat and extend your legs till you're standing on your toes. This move will work your calves and glutes (while going easy on your joints).
The folks over at Shape put together an essential roundup to help you max out your workout without getting injured. Click through for the best and worst, barre none. (Shape)