The clam exercise is a safe effective and well controlled exercise for the Glut Medius.
Unstable weak muscles around the pelvis, means that your body can’t provide a stable base when lifting, moving etc. and this instability can lead to strain injuries and pain in the knees, pelvis, and lower back. I find that people that have a strong musculature around their hips, pelvis and torsos tend to “hold” their adjustments for longer.
One of these important stabilizing muscles in the pelvis is the Glut Medius. It runs from the pelvis to the thigh bone and is used for abduction of the leg which is important to keep the pelvis level while standing/weight bearing on one leg.
To best strengthen you Glut Medius with the “Clam” exercise:
Lie on your side with your hips bent to about 60 degrees and the knees bent and feet positioned together. Position the top knee slightly in front of your bottom knee so the pelvis is facing slightly down toward the ground.
Put your hand on the upper hip to lock this position in, then separate your knees as far as you comfortably can with a smooth well controlled movement. Make sure to not roll your body back and keep your feet together through the movement.
You can hold the top position for 1-2 seconds and the move the knee back down to the starting position.
Repeat this movement until you start to lose your form or fatigue. If you want to add resistance, then you can put an appropriately stiff elastic exercise band around your thighs to make the exercise harder.