From Miami City Ballet doctor of physical therapy Elizabeth Maples:

Plank tendus emphasize movement through the feet while energizing the entire core and upper body and increasing your heart rate.

• In a forearm plank position, engage inner thighs and sit bones. Slowly lift heels for a slow relevé and lower them for a calf stretch. This will result in the body sliding back and forth slowly.
• Add a tendu with alternating feet. From the calf-stretch plank position, with heels lowered as much as possible, let one foot continue to sweep along the floor like a cat pawing the surface until you point the toe off the floor, keeping hips and thighs level. Lift the standing foot into a relevé to complete the motion. Return to a calf-stretch position, lower the lifted toes and repeat with the other foot.

Eccentric relevé exercises are great for teachers who suffer from Achilles tendinitis because they work the stabilizing muscles of the lower legs and work the tendon from a contracted to an extended position, with control. Here are two.

• In parallel, move through a forced arch plié to straighten legs to demi-pointe. Then coupé one foot to the opposite leg and lower the heel slowly without a plié. If possible, do this on a stair or yoga block so you can extend the heel below flat on the floor. You can repeat that turned out.
• Practice stepping onto demi-pointe in a piqué with or without the barre for support, extending the working leg in a low arabesque and then rolling down to flat on the standing leg. Start parallel en croix, then repeat, turned out.