Most first weeks fail for the same reason: they are too good. Six sessions, no bread, no beer, bed by ten. It is a fortnight of willpower dressed up as a plan, and when it collapses the man blames himself rather than the plan.

A first week that works looks almost disappointingly small. That is the point. You are not trying to lose weight this week. You are trying to prove to yourself that this version is repeatable in an ordinary week, including the bad days.

Before anything else, get your numbers

Five minutes, on day one, and it pays off for months. You cannot judge progress you never measured, and the thing that keeps men going in week six is being able to see that week one was worse.

• Waist, at navel height, breathing out normally, not sucking in.
• Chair rises, how many times you can stand from a dining chair in thirty seconds without hands.
• Weight, if you must, but treat it as the least interesting of the three.

Write all three down with the date. Photograph the page if you are likely to lose it.

The week itself

Four things. Not a schedule, a set of small commitments that fit around whatever your week actually looks like.

1. Two strength sessions, twenty minutes

Bodyweight is fine. Something that pushes, something that pulls, a squat, a hinge, a carry. Leave a day between them. End each set feeling you could have done two or three more.

2. A ten minute walk after your main meal, most days

Not a workout, and it does not need kit or a change of clothes. It is the single easiest habit to keep in a bad week, which is exactly why it is on the list.

3. Protein at every meal

Eggs, yoghurt, fish, meat, beans, whatever fits your life. You are not counting anything this week. You are simply making sure the protein is there, because it keeps you full and protects the muscle you are about to start building.

4. Improve one meal, not your whole diet

Pick the meal you eat most often and make one honest change to it. Not the perfect version. A better version you will still be eating in October.

What week one will actually feel like

Days one and two feel easy and slightly silly, like you should be doing more. Resist that. Days three and four you will be stiffer than you expected, and you will wonder whether you have done yourself an injury. You almost certainly have not, and it settles by the second week.

Somewhere around day five something will go wrong. A late finish, a family thing, a bad night's sleep. This is the important part of the week, because how you handle that is the entire difference between a programme that works and another false start.

The rule that matters more than any of the others

Miss one, never miss two. A missed session is an ordinary week. Two missed sessions in a row is how it quietly stops, and it stops without you ever deciding to stop.

You do not need to make it up, double the next one, or start again on Monday. Starting again on Monday is the trap that has probably cost you years. You just do the next one as planned.

What to do at the end of the week

• Do not re-measure. Seven days is noise. Leave the tape alone until week four.
• Ask one question: could I do exactly this again next week, on a normal week, without heroics? If yes, do exactly that. If no, make it smaller until the answer is yes.
• Write down what got in the way, in one line. That is your real plan for week two.

A first week you can repeat beats a first week that impresses you. Twelve repeatable weeks will change your waist, your strength and what you are willing to say yes to. Twelve impressive first weeks, one after another, will change nothing at all, and most men reading this have already run that experiment.

Alex Jordan · Over 50 and Healthy