I can get to the gym only twice a week, for 40 minutes a go. How do I get the most out of my sessions? I currently do 20 minutes' CV work and 20 on the resistance machines.

Adopt an interval-style training approach to cardiovascular work. This involves varying the pace of your exercise; it's more challenging, but gets you fitter quicker as the body adapts best to being challenged at different intensities. Do 25 minutes on the treadmill (jogging stimulates bone density, and is one of the simplest, most effective ways to burn calories), including a warm-up and cool-down. For resistance exercise, maximise results by doing compound exercises, such as lunges and squats with knee lifts. Remember to pull your tummy in; this helps posture and gives a secret abdominal workout throughout.

Drop abdominal work in the gym and do four minutes of ab work every morning before you get dressed. For upper-body compound exercises, make-over the traditional tricep dip on a chair by letting go with one hand after you have done one tricep dip and reaching up over your head, feeling a stretch right through the side of your body. Repeat with the other arm.

Make-over regular press-ups, too, by starting in a standing position, then bending over so your hands are by your feet and walking your hands out away from your body. To make this easier, rest knees on the floor and complete one press-up, before walking hands back into feet and standing up. These two exercises create tone for your back, abdominals and arms, as well as building in a stretch and boosting upper body bone density.

For flexibility work, finish with modified yoga postures, which will help the blood circulate any waste products, and also stretch your thighs, back, arms and torso. Try to vary your programme once every six weeks to keep your body in optimum fitness.

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