Q. I set off with good intentions this year and started going to exercise classes. I began with a legs, bums and tums class but felt I should try something harder.

So for the past two weeks I've been to aerobics. But these classes seem to exhaust me and my feet ache like mad, half way through the class I start to feel sick.

I'm in my thirties, am I too old for this?

A. You want to progress - good for you! And you did the sensible thing by starting at a basic level. You need a level that's appropriate and achievable for you.

If you fancy leaping about in an aerobics class - and in my opinion you can't beat aerobics classes for burning fat and strengthening heart and lungs - then listen to what your body tells you.

You should be exercising at a level where you can still speak, although if you could hold a full conversation you're probably not working hard enough. I ask my participants to go just beyond their comfort level.

Think of a scale of 1-12, where 1 is doing nothing and 12 is total exhaustion.

Work at level 6-8 to start with. Tell the instructor that you're new to aerobics. He or she should give you low-impact alternatives. That means moves where you don't have to jump.

Listen to their instruction throughout the class and make sure you stick with these moves no matter what Flossie next to you is doing.

Leave out arm moves and make your steps smaller if you start to feel tired. Feeling sick in the middle of the class indicates you're going too hard too soon. Ease off.

Don't be afraid to take breaks, go to the side of the room and sip your water until you feel OK.

Achy feet? When did you last change your trainers? If you wear them three times a week for a hard workout then check them every six months.

Don't buy the most expensive pair then you won't mind changing them often. Your footwear is an important part of your equipment.

Go for 'cross trainers' which will give you stability in sideways movements.

If you like an aerobics-style class then persevere. You should keep up with your other exercise sessions too.

Thirty minutes of aerobic activity three times a week will keep you at a good level of fitness. I have taught exactly the same class to university students and to seniors.

"Too old" is not in my vocabulary!