Can you please recommend more abdominal toning exercises suitable for those of us with lower back problems (osteoporosis and bulging discs)? I have been doing one you suggested a few weeks ago, but I don't feel it's doing any good. It doesn't make me sore, even a little.

For results, rather than feeling sore, you need to reach what's called the point of overload - the point where you feel you can do only one or two more repetitions with good technique. To help you achieve this, ensure the muscle you are wanting to target is the one that reaches the point of overload. For example, neck ache is often cited as a limitation to working the abdominal muscle effectively. Minimise this by pre-contracting your abdominal muscles before you lift your shoulders off the floor, lifting from the breastbone and not from the chin.

Classic abdominal toning exercises involve the two attachment points of the abdominal muscles, at the pubic bone and at the breast bone, moving closer together. This position is not recommended for your condition, but the heel slide suggested a few weeks ago is a suitable introductory exercise.

This week's suggestion, Dead Bug, is more challenging. Lie on your back and lift your legs off the floor, knees over hips, lower leg parallel to floor, arms directly over shoulders. Hold this position for 20 seconds, firmly pulling your abdominals into the base of your spine. Relax for 10 seconds and repeat five times. Experiment, extending the knees away a little so you feel some tension on your abdominals; progress by slowly lowering one leg at a time to the floor. Avoid a "popping out" of your tummy by placing a ruler across your lower abdominals, and keep it in place with as little movement as possible as you perform the exercise.

· Joanna Hall is a fitness expert (joannahall.com). Send your exercise questions to: Weekend, 119 Farringdon Road, London EC1R 3ER (weekend@theguardian.com).