1. The Plank. If there is only one move you do of all the core exercise I recommend, it should be the simple plank. It works almost your entire body (including those abs!) and will help you with any posture issues you may have from sitting and leaning forward at a desk all day.
Check out this excellent instructional how-to from Wiki How and remember to keep your back flat the whole time by squeezing your glutes and drawing your navel to your spin. Start with just 30 seconds a day and work your way up to two minutes without rest.
2. Squats. I know what you are thinking: squats with my back, knees, hip issues? Nooo! Trust me, as someone who has had back issues on and off for many years, I can tell you that squats (with proper form) will increase your strength and stamina while also increasing your mobility.
Think about it: every time you go up a steep flight of stairs or exit a car you are moving from a crouched position. Squats, when performed properly, will help you gain agility while getting your backside in the best shape possible. Check out this demo from Pop Sugar Fitness and try to get a few circuits in two to three times per week.
3. Single Leg Squat with Balance Ball. Do you have a balance ball and a set of weights handy? Then you can mix in this core exercise during the week as well! Balance one leg on the ball (the shin) and then go as low as you can with all of the weight being on your balancing foot. Hold a weight in each hand and every time you descend into the squat be sure to draw your navel to the spine and exhale. Be careful to keep your chest up and not hunch your upper body forward as you lower into the squat. Go for three circuits — one minute on each side.
Don’t have a ball or a weight — or are a beginner just starting out? No worries. Here’s your modification:
4. Burpees. Do you hear that? That is the sound of a thousand CrossFit disciples yelling “heck yeah!’ at the mere mention of burpees. This is one of those core exercises that utilizes multiple muscle groups, including your core. Don’t be chicken and give it a go!
Begin in a standing position and your feet shoulder width apart. Lower your body to the ground placing your hands in front of you first as you bring your chest to the floor on the inhale. As you exhale, push yourself up from that position and finish with a jump as you land on the floor. Aim for a tuck jump, grabbing your knees to your chest before you land to really feel it in those abs. Go for three rounds of 30 seconds each with 30 seconds of rest in between.
5. Balance Ball Lower Abs. Truthfully I do not know the real name of this exercise, but I make my students perform this in every single one of my classes. You lie on your back and place the ball (most people need the 55-centimeter size) between your legs. This should be the lower half of your legs between the shin and ankles.
Keeping your head on the mat and placing your hands under your hips to protect the lower back, lower the ball to the floor (as low as you can) on the inhale. Then draw your navel to the spine as you bring it back to the ceiling with straight legs the whole time. Try this for four sets of 20 seconds each with 10 seconds of rest in between.
Too intense or don’t have a stability ball? Try this modifiction: