Squats can be broken down into two main categories: squats done with weights or without weights. A secondary categorization divides squats into those which build large muscle groups and those which tone muscles. Barbells, dumbbells and machines are used in squats, with many variations with and without weights.
CalisthenicExercise.com calls squats "one of the most important exercises, with or without weights." Weighted varieties of squats include the barbell squat, front squat, hack squat and sissy squat. Squats that use machines include the Smith Machine squat and front squat, plus hack machine squats. Squats that involve dumbbell movements include the dumbbell squat, Bulgarian split squat, dumbbell lunges and many more listed by Muscle & Strength.
Squats without weights include prisoner squats, jump squats and lunges. CalisthenicExercise.com suggests plyometric high-energy squats including half squats, box squats, Hindu squats, split squats and one-legged squats. These exercises work most of the major muscle groups of the body, including the abs, calves, glutes, hamstrings, hips, thighs and lower back.
According to WebMD, squats are one of the most effective exercises, thanks to the multiple muscle groups worked. WebMD stresses the need to keep one's back straight and knees over the ankles when properly performing a squat.