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Cardio without the impact. Both exercises in this challenge keep one foot on the floor at all times, which means no jumping, no jarring and almost no noise - it works in a flat with neighbours below, at an early hour, or with knees and ankles that object to the usual options. Thirty days, no equipment and standing room only. It is aimed at beginners and equally useful as something to keep going alongside harder training.

Two day types alternate. Odd days pair step jacks with side jacks across 4 sets, run back to back with no rest, and climb from 10 reps to 24. Even days are a total number of step jacks spread across your whole day, climbing from 50 to 120. The two modes are what makes daily cardio sustainable for a month - one builds the ability to keep going without rest, the other builds volume without fatigue.

How to do the exercises

Two exercises run through this challenge: step jacks and side jacks.

• Step Jacks: stand with your feet together and your arms at your sides. Step one foot out to the side as your arms raise overhead, then step back in as the arms come down, and repeat on the other side. Same pattern as a jumping jack with one foot always on the floor. Keep the movement light and the rhythm steady rather than racing. Counted in total, alternating sides.
• Side Jacks: stand with your feet apart and one hand on your hip. Reach the opposite arm up and over your head while bending sideways at the waist, then return upright and repeat on the other side. This is a lateral movement rather than a jumping one, and the value is in the side bend as much as the arm. Keep the bend in the frontal plane rather than letting your torso rotate forward. Counted in total, alternating sides.

The "throughout the day" days

Even days give you a step jack total with no sets and no session. Spread it across your day in whatever chunks suit you - twenty every time you get up from your desk, thirty while the kettle boils. This is the grease the groove method: frequent small doses build capacity and movement quality with almost no fatigue, which is what allows the concentrated days to keep working.

Adjust Difficulty

Make it easier: On the no-rest days, take 30 seconds between sets and shorten that rest week by week until you reach the no-rest version. Slow the pace right down - these are low-impact exercises and there is no benefit to rushing them. Make the side bend smaller. On the spread days, use smaller chunks more often. Cutting to 3 sets on a hard day always beats missing it.

Make it harder: Speed up on the concentrated days and treat the four sets as continuous work rather than four separate efforts. Swap step jacks for jumping jacks if impact is not a problem for you, which raises the intensity considerably without changing the structure. Reach further on the side jacks so the bend is deeper. Adding a fifth set is the last step, and on the spread days you can do the total in fewer, larger blocks.

What to expect

The no-rest instruction is what gives the odd days their bite. Four rounds of two exercises with nothing in between will get your heart rate up more than the low rep counts suggest, and by the fourth set you will notice your breathing. The spread days barely register while you are doing them and add up to real volume across a month. Expect the side jacks to reach your obliques in a way that surprises people expecting pure cardio. What thirty days of this builds is a modest improvement in conditioning and a body that has spent a month moving every single day - which for anyone starting from very little is the more valuable of the two.