Q How do I know if the exercise I'm doing is effective and how can I tell if I'm exercising hard enough?

A Most of us know that some exercise is essential to our health and wellbeing but making the progression from a couch potato to reasonable fitness seems like a long and puzzling road. What we need to know is how much, how often and how hard our exercise should be.

As well as including activity in our everyday life - walking, or cycling to the shops, using the stairs instead of the lift etc - we can improve our overall fitness by setting aside at least three 30 minute sessions a week, longer if you can.

Like most working parents, I have a very busy life juggling all my commitments - and nobody told me that taxi driving was part of the job description!

An hour in the gym is a precious luxury so if I've only got 30 minutes I want to be sure I'm making the most of it.

First of all, warm up properly. An inadequate warm up means that you will fatigue early in the harder part of your workout, when you're getting down to the nitty gritty you'll get puffed out and your body will be telling you to stop. (Yes I know your body's telling you to stop as soon as you open the door to the gym, bear with me!) A gradual warm up should start to raise your pulse, get all your bits moving and start a sweat. You shouldn't be out of breath yet. Spend about five minutes doing this. After a short stretch, get down to business.

Most of us want to do the minimum, but to exercise heart and lungs and burn off our fat deposits we need to get moderately puffed out for about 20 minutes, doing something that uses the big muscles in the body. energy is burned in the fibres of the muscles when they get to work. Using big muscles means our bodies demand more energy, faster.

So, here's the science! You should be working at between 65 per cent and 80 per cent of your maximum heart rate (MHR). To find your MHR, deduct your age from 220. Then work out what your percentage range should be.

When you exercise, take your pulse rate by counting your pulse for 15 seconds then multiply by four to find out how many beats per minute you are working at. For example, a 40 year old would have an MHR of 180. They should aim for a pulse rate between 117 and 144 beats per minute.

And listen, lazy bones, don't just hover around your lower range, push yourself a bit even if only for a short burst! You'll immediately feel the sense of wellbeing that comes from a good exercise session and in the long term you'll start to notice the pounds dropping off.

You shouldn't neglect improving your strength and muscle tone either. I'm still working on an 'in car' strength training plan that we can do while ferrying our little darlings around. Next time you're stuck in the traffic in Fishergate look out for the woman doing press ups against the steering wheel, it's probably me!