I go to the gym six times a week, walk to and from work, and watch what I eat. But I have reached a standstill. I've been told to shake up my workout, but have no idea how to do so.

You sound pretty fit, but also stuck in a rut. I want to give you something back - some time! For the next six weeks, try cutting back your cardio sessions to three to four a week with these three 30-minute treadmill programmes that use a concept called the rate of perceived exertion.

RPE is a simple concept by which you rate on a scale of 1 to 10 your aerobic exercise intensity. RPE 1-2 is very easy, 3 easy, 4 moderately easy, 5 moderate (you should feel slightly out of breath), 6 moderately hard (if chatting, it should be sporadic), 7 difficult (to talk requires a lot of effort), 8 very difficult (talking would require maximum effort) and 9-10 is peak effort (no talking possible). Start and end each workout with a five-minute warm-up and cool-down of RPE 3-4. Depending on your fitness, this will mean brisk walking or light jogging with some leg stretches.

For your Double Blast session, do five minutes at RPE 5, eight at RPE 7-8, two at RPE 4, eight at RPE 7-8, two at RPE 4 and five minutes at RPE 5.

For your High-intensity Hills session: five minutes at RPE 5 with treadmill flat, five at RPE 8 with treadmill on incline. Repeat twice, then 10 minutes at RPE 5 with treadmill flat.

The Steady Climb session involves five minutes at RPE 5, five at RPE 6, 10 at RPE 7, five at RPE 6 and five minutes at RPE 5. After week three, add five minutes to each workout's hardest segment.

These are challenging but the payoff is greater fitness in shorter workouts. Complement with one Astanga yoga session a week and you should find you have got off that plateau and gained more free time.

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