I'm 28 and slightly underweight for my height. By eating more healthy food and working out three times a week, I've put on 4kg. But despite being more toned, I can't get rid of my "pot belly". What should I do?

I firmly believe that your abdominal muscles can be trained every day. As they provide a major functional and postural role 24/7, abs exercises done three times a week really won't deliver the results you seek. You need to do exercises that encourage the connective tissue of all four abdominal muscles to interweave and draw in to form a cummerbund tightening effect around your torso. Add the following specific exercise to your existing workouts, complement with two additional abs sessions at home and, most importantly, pay daily attention to the residual level of tension in your torso.

This breastbone lift with straight leg specifically targets your lower abs in conjunction with the other ab muscles. Lie face up, one knee bent, sliding the same foot away from your bottom so toes lift off the floor; extend the other leg on the floor. With hands at the side of your head, lift the head, so you feel your abs contracting - this is your start position. Now lift your torso two inches, leading from the breastbone. Hold for four counts and lower back to start position. Try 12-16, then swap legs and repeat. For readers new to abs exercises, keep both knees bent, then progress to straight-leg version.

For 24/7 tone, pull in abs to about 75% tension throughout the day. Some of my clients visualise wearing a bikini; others imagine trying to slip their fingers inside their belts.

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