You can do this exercise either at the gym or at home. If you prefer to do them at home, you may be more comfortable performing this exercise on a yoga mat, towel or any other soft surface you can put between you and the floor.

This exercise works your rectus abdominis muscles, which are the major muscle group in your core and the muscles responsible for the six-pack look. Side planks also work your deltoids, which are your shoulder muscles; your obliques, which are the muscles on the side of your torso, and your latissimus dorsi, which are the broad muscles of your mid-back.c 

1. Lie on your right side on your mat. Raise yourself onto your right elbow, balancing on feet so that your entire body resembles a inclined plank of wood turned on its side.
2. Contract your abs, especially the obliques on your right side (abdominal muscles closest to the ground) to keep from sagging towards the ground.
3. Hold for 30 seconds on each side for one set. Perform three to four sets.
   

Plank crunches: While in the side plank pose, place the hand closest to the ceiling on your hip. Use your abdominal muscles to move your hips up and down (towards and away from the the floor).

Reach-under plank: From the standard side plank, reach your top arm to the side so that it is parallel to your chest and perpendicular to the ground. Reach under the side of your torso closest to the ground and then back up to start.

Hip-abduction plank: Starting with a side plank, raise your top leg towards the ceiling and lower back down to start. This is more of an advance move, so if you experience any discomfort, stop.

*For each of these variations, do 10-15 reps on each side.