How to: Start on the ground with feet and hands shoulder width apart. Head and neck are neutral, back is flat, core is contracted, shoulder blades are retracted (ensuring stability in the joint), and hips are square with the ground. Take one hand off the ground and touch it to the opposite shoulder, without allowing the rest of the body to move.
What it strengthens: Primary muscles are the core musculature, deltoids (shoulder), and triceps. Secondary muscles are the pectorals (chest) and hip flexors.
Equipment needed: There is no equipment required to perform this exercise.
Modifications: An easier modification would be to put the knees on the ground or position the feet wider. To make this exercise more challenging, try putting the feet closer together, wearing a weighted vest or placing the feet on an unstable surface such as an AirDex pad or a disk.
Applications: Increasing core strength is very important and useful for making any physical task easier. Posture, form, and power all start with having a strong core. This exercise, in particular, improves the "anti-rotational" capabilities of the core musculature, meaning that it will be able to resist excessive or unwanted rotation through the trunk. Keeping the body in better alignment and decreasing the risk of injury, especially injuries to the back.