Isometric single leg heel raise - soleus bias ("Heel raises" Soleus strengthening isometric, hands on wall, single leg)

Stand up straight facing a supportive surface such as a wall.
With your legs hip-distance apart soften your knees a little.
Rise up onto the ball of both feet.
Transfer your weight onto the leg to be exercised, lifting your other leg from the floor.
Keeping your heel raised and knee softened, hold this position.
Place the ball of your other foot back on the floor and lower yourself back down using both legs.
Repeat.