WHY: This exercise is great to activate the abdominals.
HOW: Start this exercise on your back with your hips and knees bent to 90 degrees. Keep the small of your back pushed into the floor by activating your core. Start with both arms directly in front of you. Lower one arm in a slow and controlled manner to the floor while maintaining abdominal activation for the entirety of this exercise as you focus on your breath.
FEEL: You should feel the abdominal muscles engaging while you perform this exercise.