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Ten minutes of work a day for 30 days. The duration never changes and everything else does. Ten exercises rotate through five different session formats, so a day that takes exactly as long as yesterday can feel nothing like it. Between them the exercises cover cardio, legs, core and upper body, which makes this one of the broadest challenges we have for the time it costs.

The five formats are:

• Two-exercise intervals: a pair of one-minute blocks for 4 or 5 sets with 1 to 2 minutes of rest.
• Three-exercise circuits: three 20-second blocks run together, 10 sets, a minute of rest between them.
• Circuit plus finisher: 7 sets of a shorter pairing, then a straight three-minute block of one exercise to close.
• Non-stop days: ten unbroken minutes of a single exercise, no sets and no rest.
• Four-exercise circuits: four 30-second blocks, 5 sets, two minutes of rest.

The ten minutes is working time. The rest between sets sits on top of it, so a 10-set day with a minute of rest takes about twenty minutes of your day and delivers ten minutes of effort. That distinction is what makes the calendar work.

The difficulty rating is 4 and the non-stop days and finisher days are what earn it. Ten unbroken minutes of punches is a long time for your shoulders, and a three-minute block of squats arriving after seven sets of anything is a hard finish. The circuits with rest are the manageable half.

How to do the exercises

Ten exercises run through this challenge.

• High Knees: run on the spot driving each knee to hip height, landing softly on the balls of your feet. Lower the knees as you tire rather than stopping. March steps are the no-impact version.
• Jumping Jacks: feet out and arms overhead, then back. Land soft with your knees bent. Step jacks remove the impact entirely.
• Squats: feet shoulder-width, hips back, thighs to near parallel, weight through your heels, knees tracking over your toes.
• Punches: jab and cross from a fighting stance, rotating your hips into each one and switching your lead foot halfway through. The Guide to Punching covers form.
• Sit-Ups: knees bent, feet flat, curl all the way up and lower with control. Do not pull on your head.
• Flutter Kicks: on your back, legs straight and lifted, small alternating kicks. Keep your lower back pressed to the floor - raise your legs higher if a gap opens up.
• Side Leg Raises: lying on your side, lift the top leg without letting your hips roll back. Half the time on each side.
• Climbers: from a plank, drive the knees in alternately. Keep your hips low and level and your shoulders over your wrists.
• Plank Jacks: from a plank, jump both feet out wide and back in. Hips stay level throughout.
• Shoulder Taps: from a plank, tap the opposite shoulder with each hand in turn. The job is stopping your hips rotating rather than the tap itself.

On circuit days the exercises run back to back with no break between them - the rest comes at the end of the set. On finisher days the three-minute block starts as soon as the last set ends. On non-stop days set a timer and keep moving for the full ten minutes, slowing the pace rather than stopping.

Adjust Difficulty

Make it easier: Use march steps and step jacks for the jumping days, which removes all the impact and every number still applies. On floor days, put your hands on a chair for the plank exercises and bend your knees on the flutter kicks. Drop two or three sets on the circuit days. Take longer rests. On non-stop days, allow yourself two short breaks and shrink them over the month. A reduced day keeps the streak going.

Make it harder: Cut the rest in half on every circuit day. Do the non-stop days at a pace you can only just hold rather than a comfortable one. Add a set to the circuits. Run the finisher days with no rest between the sets and the finisher. Doing two days in one session is the ceiling and by week four it is a genuine workout.

What to expect

The first week introduces four of the five formats and each one will feel different. The three-exercise circuits go quickly because nothing lasts more than 20 seconds. The non-stop day on day 3 is the shock - ten unbroken minutes of punching is far longer than it sounds and your shoulders will tell you so by minute four.

Expect soreness to move around your body rather than settling, since consecutive days rarely work the same thing. Expect the floor days to catch you out if your core is the weak link and the jumping days to find your calves. By the second week you will have a sense of which format suits you and which one you dread, and the dreaded one is the useful information. Around week three the recovery between sets improves noticeably, which is the clearest sign the conditioning is working. What you get from a month of this is broad general conditioning - cardio, core endurance and muscular stamina - for ten minutes a day, which is a good trade. What you do not get is strength or size, since nothing here is loaded.