If you have time for only one lower-body exercise, squats should be it. They strengthen your quadriceps, hamstrings, and butt, giving you a firm foundation and a toned, great-looking lower half. What’s more, they are easy to do and require no fancy equipment — just a little bit of know-how.

If you’re ready to go beyond the basics — and get even faster results — try these three variations on the theme:

Dumbbell Squats: The added weight of the dumbbells helps strengthen your legs and backside even more while also engaging your core muscles. To do these squats, hold a dumbbell in each hand with arms by your sides. Perform a basic squat, keeping your arms straight (don’t lock those elbows!) and chest up. Repeat.

Squat Jumps: These are a terrific way to add some calorie-blasting cardio to an already great exercise. Here’s what to do: Perform a basic squat, then jump up, raising your arms overhead. Land softly back in squat position. Repeat.

Speed Squats: Looking for a way to increase your agility? Look no further! These squats are also ideal for athletes who want to improve their reaction time. To perform them, simply do quick repetitions of the basic squat. For an added challenge, place a barbell across your shoulders.

When doing squats, remember to watch your form to avoid injury. Never let your knees extend past your toes, and push your heels into the floor for stability throughout the move. If you have pain in your knees when you do squats, stop doing them.