I am 54, des­per­ately unfit and quite over­weight. I have just bought a tread­mill so I can exer­cise at least four times a week, along with a healthy diet. Could you give me some guidelines on how to pro­gress and whether I should be jog­ging after a spe­cific length of time, and if so, for how long?

You say you are “des­per­ately” unfit, so you should make haste slowly. You might also want to check out your under­ly­ing health with your GP before you get too intense with the exer­cise, espe­cially if you have any exist­ing med­ical con­di­tions. Ask for blood pres­sure and cho­les­terol checks if you’ve not had these for a while. Having inves­ted in the tread­mill, ensure you avoid injur­ies by also invest­ing in well-​fitting, sup­port­ive train­ing shoes.

If walk­ing for 20 minutes at 4.6mph doesn’t leave you gasp­ing, that’s prob­ably a good start­ing point. Spend the first couple of weeks walk­ing at this speed, con­cen­trat­ing on tech­nique: walk upright without hold­ing on to the sides, head bal­anced, chin par­al­lel to the ground, shoulders back and relaxed, a slight pulling in of your lower stom­ach and a “heel-​toe” walk­ing action: hit the ground with the heel and walk through your foot, push­ing off gently with your toes. Rather than exhaust your­self at this stage, do your workout every day, not just four times a week — it still adds up to more work and more cal­or­ies burnt.

From there, build up gradu­ally. First, add in a small incline of about 2 per cent. Next, increase your walk time, by one to two minutes each week, until you reach 30 minutes.

When that is com­fort­able, start to push up the speed (by, for instance 0.2mph each fort­night) – very soon you will be forced to change your walk­ing style to a power walk: bent elbows, long strides and a really strong pick-​up on your toes so you can roll through your feet effi­ciently.

Power walk­ing is ener­getic: a very effect­ive heart and lung workout. You can burn as many cal­or­ies as you would jog­ging, but with a far less pun­ish­ing impact on your back, hips, knees and ankles. Make the walk even more intens­ive by going uphill (but avoid this if you have low back prob­lems). Gradually increase the incline to 5 per cent, then try some “inter­vals”, play­ing around with speed and incline to cre­ate short bursts of harder work fol­lowed by easier “recov­ery” sec­tions.

A very reli­able way to test if you are work­ing at the right level is to ask your­self: “How hard am I work­ing right now?” and give an answer from 0 (asleep in bed) to 10 (as hard as I can ima­gine). Aim to work at levels of 4 (“some­what heavy”) to 7 (“very heavy”) out of 10. But always start the tread­mill slowly, tak­ing 2 to 3 minutes to creep up the val­ues to the tar­get level for that day’s workout. Reverse the pro­cess at the end so your heart rate can gradu­ally return to nor­mal. Drink plenty of water before and after.