If preventing middle-age spread is important to you, then as well as HIIT you need to do some resistance training, to keep up your strength.
It really is a case of use it or lose it, as muscle bulk typically declines by three per cent each decade after the age of 30.
The great thing about having muscles is that they burn calories even when you are sleeping, so having extra muscle stores can prevent excess flabby bits.
Resistance training will also help control blood sugar levels and, particularly in post-menopausal women, improve bone density.
It is also an effective way of improving mood. A study from the University of South Carolina found that women who did resistance training twice a week saw an impressive reduction in anxiety levels in just six weeks.
Lie face-down with the palms of your hands directly beneath your shoulders and the balls of your feet touching the ground.
Keep your body straight – your head in line with your back – and raise yourself up using your arms.
Lower your body to the floor until your elbows form a 90-degree angle and then push up again. Repeat.
If you find this too hard, perform the exercise with your knees on the ground until you are strong enough to do the full thing.
2. Abdominal crunches
Lie on your back with your knees bent and feet flat on the floor and your hands positioned by your sides or lightly at the sides of your head.
Curl up your upper body without lifting your lower back off the floor.
Make sure your chin is tucked in towards your chest. Push back up without bending your back, and repeat.
3. Tricep dips
Stand with your back to a chair; place your palms on the seat behind you, bending your knees at right angles, hips straight.
Bend your elbows to 90 degrees to lower your body so that your bottom descends halfway to the floor. Push yourself back up using only your arms, and repeat.
Stand with feet shoulder-width apart and hands placed lightly on opposite shoulders.
Bend from the hips, keeping the weight in your heels. Make sure your back is straight.
Keep bending until your legs are at a 90-degree angle – imagine you are preparing to sit in a chair.
Push back up without bending your back, and repeat.
5. The Plank
Lie on the floor and then raise yourself on to your forearms and toes so that your body forms a straight line from head to toe.
Make sure your mid-section doesn’t rise or drop. Squeeze your buttocks and hold the position for as long as possible. The first few times you try this you probably won’t manage
6. Bicep curls
These are the only exercise I do that requires equipment: dumbbells. But you could start by using tins of beans or bottles of water.
Hold the dumbbells down by your side, palms facing away from you.
With your back straight, use your biceps to lift the dumbbells until they are shoulder height.
Without pausing, lower them slowly back down, and repeat. Resist the urge to drop the weights.