Core is the least worked muscle group of all the muscles. Why? Nobody likes sit ups! However, to exercise your core muscles you don't have to do sit ups. In fact, sit ups and crunches are not the best way to develop a strong core. When those two exercises are performed without a well rounded core routine, you could be setting yourself up for an injury. So what do you do instead? Glad you asked
#1 core exercise - Plank
The plank is an isometric exercise that uses all of the core muscles and then some. Here is how to do it:
Lay flat on the floor face down. Keeping your body as stiff as a board, push up to a plank position which can be:
a. Weight on your elbows that are directly beneath the shoulders
b. Weight on your hands (at the top of a push up position) that are beneath your shoulders.
Don't let your body sag and don't let it become a hill. Keep it straight. If you squeeze your cheeks together you will know when you are in a straight plank.
You should be able to hold a plank for 2 minutes 3 times, with a 1:30 rest between sets. See how long you can go and just do it. Start where you are and build up to the 2 minutes.
#2 Mountain Climbers
Mountain climbers are done in a plank, so all of your core muscles are engaged. The extra work is the one leg crunches that can be done fast or slow.
Here is how to do it:
Get in a plank position ("b" position above is best) and bring one knee into your chest. Place that leg back in a straight plank position and bring the other knee up to your chest. Remember to keep your butt down in a good plank position.
You should be able to perform 40-50 reps (each leg) using speed or 25-30 going slow for 3 sets. Rest 1 minute between sets.
#3 Side Plank
This exercise focuses on the oblique (muscles behind the "love handles"), but engages all the core muscles as well.
Here is how you do it:
Lay down on your side and then bring your elbow underneath your shoulder. You should have your entire torso off the ground. Remember to keep your body straight and your hips forward.
You should build up to be able to hold this position for 1 minute on each side 3 times with a 1 minute rest between sets. Start with where you are and work up to that.