Side Plank Reach Through (Left Side) Start in side elbow plank on your left side with your feet stacked. Raise your right arm in the air. Lower your right arm in front of your chest and reach it underneath your rib cage through the space behind your left arm. Reach your arm back up into the air to complete the rep. Keep going for 40 seconds, followed by a 10-second rest. Image Source: POPSUGAR Studios