Q: Why can't some of my dancers keep their heels down while in demi-plié?
A: There are two primary reasons why heels pop up during demi-plié. The first is tight soleus muscles. This muscle runs from just below the knee to connect with the gastrocnemius muscle to form the Achilles tendon that connects at the heel bone. This muscle determines the muscular depth of your demi-plié. The shorter and tighter it is, the shallower the demi-plié will be. To stretch the soleus muscle, do a traditional calf stretch with a straight back leg, then slightly bend the knee to bring the stretch toward the ankle.
The second reason heels lift is due to misalignment during the descent. Students are generally trying hard to work their turnout, and end up tucking their pelvis under and shifting toward the front of the feet. Not only do the heels lift when this happens, but it puts a lot of strain on the knees, too.
Have your students monitor the weight on their feet during the demi-plié, striving to always keep the weight equal between the pads of the big toe, little toe and heel. This will then stretch the soleus at the bottom of the demi-plié and help to maintain anatomical alignment.