Partial reps or 21s are a weightlifting technique that you do with 40 per cent of the weight you can lift ten times. Take biceps curls as an example: lift the weights only halfway up seven times, then lift them to highest point of the move and do the top half of the curl six times. Finally complete seven full reps back-to-back without any rest for a total of 21 reps.

The purpose of 21s is to place the targeted body part under a sustained and unusual load to maximise muscle fatigue. This places enough microtears in the fast-twitch muscle fibres to ensure continued growth, which may have faltered after repetitive training. By increasing the time under tension and duration of the set they also burn more calories. 

Doing a workout that utilises partial reps has a number of benefits. Firstly, it will kick-start muscle growth and hit your body from a new angle. It will also burn more calories to strip body fat from your muscles, giving you better definition and also increase your strength endurance. 

We've come up with a comprehensive 21s workout – you'll find it in the navigation bar to the right of this text. Here's how to do it to get the best effect:

Allow 45 minutes for each session, including the warm up.

Do workouts A, B and C once a week, leaving one day’s rest between each session.

For the 21s choose a weight that’s 40 per cent of what you can normally lift ten times. 

Start by doing five minutes of cardio on a piece of cardio equipment, then do four sets of whole bodyweight exercises, such as star jumps and burpees. 

For the partial reps take one second to lift the weight and one second to lower. Take two to three seconds to lower for full reps.

Rest for 60 seconds between each set and two minutes between each exercise.