A good core strength exercise.

Kneel on a gym mat. Adopt the Neutral Spine Position then drop forwards onto your hands. Walk your hands forwards, and then lower yourself onto your elbows as you approach full stretch, forearms forwards. Then lift your knees so your body forms a nearly straight line from heels to shoulders, and be supported between your elbows and toes. Keep the Neutral Spine Position.

The exercise is now all about holding the "plank" position and resisting the urge of your hips to drop down; use your core muscles to achieve this.

There is no movement in this exercise, simply holding the body position exercises your muscles.