1. Transversus Abdominis Activation
Lie on your back with your legs bent up. If you want, place your hands on your lower belly. Imagine that you are moving your navel inwards towards your back, or imagine that you are bringing your navel and pubic bone closer towards each other. Hold for 5 - 10 seconds, then relax. Repeat 10 times. Variation: Stand on your hands and knees, and do the same thing. Work towards being able to hold for a longer time.
If you are having difficulty finding this muscle, try coughing once - you'll feel your lower belly shrink inwards and become hard. In the exercise, imagine that you are willfully contracting the same muscle, but slower and more controlled.
[The aim is to find this contraction and that it is always active before and throughout other movements involving more muscle groups and coordination. Once that is achieved, this exercise is no longer needed]
Lie in the same position as in the previous exercise. Tighten the transversus abdominis, then tighten your buttocks and lift your hips off the floor, bringing your shoulders, hips and knees into a straight line. Hold for 5 - 10 seconds, then come slowly down. Repeat 10 times, rest and repeat another 10 times. Work towards repeating 10 times three.
3. Bridging with Leg Lift
As in the previous exercise, with the addition that once you have gone up in a bridge, lift one leg and hold it straight. Be careful to not sway while doing this. Bring your leg down, and come back down again from the bridge. Repeat 10 times for each leg. Work towards repeating 10 times three.
Lie on your belly, face down, arms forward. Tighten the transversus abdominis, then lift your left arm and right leg slightly off the ground. Hold for 3 - 5 seconds, then come slowly down. Change sides, lifting your right arm and left leg. Repeat 10 times for each side.
5. The Quadruped
Stand on your hands and knees, facing down with a straight neck. Tighten the transversus abdominis, then raise one leg and stretch it backwards, until it is straight. The idea is not to lift it as high as possible but to straighten it as far as it will go. Hold for 3 - 5 seconds (or more, for the eager), then come slowly down. Change legs. Repeat 10 times for each leg. Work towards doing this 10 times three.
For added challenge, lift the diagonally opposite arm in the same way at the same time as you lift the leg, again aiming more for a straightening/stretch than raising your arm high. As before, hold, then come slowly down.
6. The Plank
A popular exercise but it must be performed correctly to give the best reults. Start on your elbows and knees: elbows straight under your shoulders and knees and feet hip-width apart. Straighten your legs and lift your hips so that your body becomes a straight "plank", resting on your elbows and toes. Hold for 20 seconds, or as long as you can. Repeat 3 - 5 times. You can work to extend the time you hold it, up to 45 seconds.
When doing the plank, again, imagine moving your navel in towards your spine, tilt your pelvis back, and tighten your buttocks. It is important to keep the spine neutral in this exercise: face down and keep your neck straight, and keep your lower back straight as well, meaning no big curve and sagging hips, nor letting your bottom stick up.
The very best exercises are the ones that get done, regularly. If you choose to do only a few of these exercises above, let that be 1, 2, 3, and 5. Aim to run through them once a day, or at least on week-days for a period of 6 - 8 weeks. Be curious - you never know what could happen if you work on your core strength for a set period! The next group of exercises will be for the shoulders.