This muscle sits on the outside of your pelvis and keeps your hips level when you stand on one leg. In calisthenics, it's critical for pistol squats, side planks, and any movement requiring lateral stability. Weak gluteus medius leads to knee valgus (knees caving in) and lower back pain. Train it with side-lying leg raises, clamshells, and single-leg balances. Strong gluteus medius means stable hips and healthier knees.