Desperate for a flatter stomach? Our fitness expert Mark Hibbitts can help. Don't do these exercises just after having a baby, but a few months down the line, and they may make all the difference

Mums often ask me "What am I doing wrong? I do sit-ups every day and my stomach still isn't flat!" Well, I'm surprised it's not common knowledge by now that there's a lot more to working the waistline than doing endless amounts of this quite ineffective exercise.

In actual fact, thinking of your waist as one muscle group and concentrating on only one exercise is not a sensible thing to do at all. We often find that if one muscle group is worked at the expense of others then the others become dysfunctional, resulting in postural problems such as kyphosis - a curvature of the upper spine.

This is often seen in inexperienced male gym-goers whose idea of a good workout constitutes set after set on the bench press, leaving them with tight pectoral muscles and an ape-like appearance!

Working your stomach in the same way can leave you with the same kind of result. Concentrating only on the rectus abdominus (abs) will result in them becoming short, giving you a hunched over appearance, and possibly leading to a weak lower back and all the problems associated with it.

So what should I do?

The very best way to build a tight and strong waistline is to choose a variety of exercises that will target the midsection as a whole. This will include the abs, the lower back (erector spinae), and the internal and external obliques. You will also need to learn how to activate the deep muscles that help to give your body stability. The most well known of these core muscles is the transverse abdominus or TVA, that wraps around your trunk like a corset.

To find your TVA, lie on your back and put your fingertips inside your hip bones. Cough, and you’ll feel your TVA twitch beneath your fingers. To contract the TVA take a deep breath in, and then breathe out and at the same time pull your belly button in towards your spine. When you've mastered this, try holding the contraction for 10 seconds while continuing to breathe. It will be tricky at first but once you've learned to 'fire and sustain' the TVA, you will be able to switch it on any time you exercise or do anything else that requires effort. Although your core also consists of other muscles, contracting one part, (in this case the TVA) will engage the other parts synergistically.

A great way to make sure your core muscles are working is to do your exercises on a Swiss ball. These can always be found in the gym, and many of you will have one at home. They work so well because the instability of the ball makes your core work just to stop you falling off!

Below are some great ball exercise that will work the whole of your waistline. They can be tricky at first, but do persevere as 20 minutes three times a week should get your waistline looking fit and trim!

Hyperextensions                                                                            
Lay face down with your tummy on the ball. Cross your arms in front of your body and contract your TVA. Using your lower back muscles, raise upper body until parallel to the floor. Slowly return to start position and repeat 12-15 times

Trunk Rotations                                                                           
Lay face down on the ball. Contract TVA and lift arms out to the side. Rotate torso to one side, then return and repeat on other side. 12-15 reps. To aid balance keep feet wide apart and one hand on the floor.

Crunch with a twist
Sit on the ball and roll out until lower back is on ball. Place hands loosely on head (no pressure on neck) and contract TVA. Slowly curl your upper body toward your pelvis whilst rotating torso to the left. Return to start position and repeat on other side. Repeat 12-15 times