Rocker boards are excellent tools to challenge balance receptors. A rocker board moves in one plane of motion. It allows you to work a forward and back motion without wobbling side to side. The rocker allows you to stretch the calf and shift your center of gravity while trying to maintain a smooth transition. The rock should be very smooth. Excessive "clunking or ratcheting" is a sign of weakness. Concentrate on slow and smooth movements.
To make the exercises more difficult: