@atg Single leg movements like bulgarian split squats for high reps, then hindu squats or deep sissy squats to failure. When you get better at bulgarian split squats, elevate your front foot on a box or platform for a deeper stretch. If you have any weights, even a light dumbbell, I'd recommend holding it at the shoulder while you do the split squat.
If you do the hindu squats, replicate the way Indian wrestlers do them, rhythmically and when you get better add a small hop at the top. Eventually you'll be able to handle many reps, and it will become an explosive conditioning movement that trains your cardio while also challenging the legs.
If you do sissy squats instead, make sure you engage your glutes and abs to keep your low back neutral, and support with your hands to avoid balance problems.
This is assuming you can handle full knee flexion, make sure your body can handle that ROM before starting the higher reps for hindu squats or sissy squats. If your glutes need extra work, train movements like single leg glute bridges, hip thrusts, and shoulder bridges to failure.
