This is a great all-round exercise that focuses mainly on toning your oblique muscles (the muscles at the side of your waist) while at the same time strengthens your deeper core muscles needed for good torso stability and strength. It is tough but well worth it!
How to do this exercise:
Lie on your side. Place your elbow under your shoulder and bend your lower leg to 90 degrees and straighten your top leg.
1. Lift and lower your hips for 10 reps focusing on using your oblique muscles
2. Hold your hips high in a side plank for 10 seconds while stretching your arm overhead for a full side stretch.
3. Raise your top leg using your bum muscles and hold for 10 seconds
4. Bring your top elbow to your top knee into a side crunch for 10 reps.
And your done! Now do it the other side!
If it is too much initially, practice each of the 4 parts separately and then gradually add in each part until you can do all 4 parts together.
If you want to make this more difficult, straighten both legs and stack your feet.