Sit tall with your leg extended and a resistance band looped around the ball of your foot. Gently press the foot away from you — as if pointing your toes — to tighten the band, then hold the position without moving for several seconds. This isometric contraction activates the calf muscles (gastrocnemius and soleus) and improves lower-leg strength, joint stability, and muscle endurance without placing excess stress on the Achilles tendon.