The Sandbag Plank with Drag is an awesome strength exercise for both the core and the shoulders.
1. Begin in a plank position with your feet wide apart and your sandbag to one side of your body.
2. Bring the opposite arm under your body, palm up, to reach the outside handle of the bag.
3. Drag the bag under your body (keeping your hips flush to the floor) and release the bag to the opposite side of your body.
4. Repeat with opposite hand.
To make this move more intense, bring your feet closer together or increase the weight of your sandbag. To modify this move drop to your knees.