The dorbarre plie + heel raise in first position gives you all the benefits of a plie and heel raise together. The plie movement is one of the most powerful exercises to reduce knee pain and strengthen the quadriceps muscle group. While the heel raise adds strength to your calf muscles, improves ankle mobility, and increases stability.
Regression
Make this exercise easier by performing less repetitions.
Progression
Make this movement more challenging by performing more repetitions, or doing a "pulse" version where you perform the move in double time.