21s Workouts To Help You Add More Muscle

Dumbbell biceps curl
(Image credit: Getty Images / Juan Algar)

When you first start resistance training it can be surprisingly easy to build muscle – it’ll feel gruelling, obviously, but you’ll pack on muscle quite quickly. However, after a time, muscle development can slow and while there can be many reasons for this, one of the most common is that your body has adapted and needs a different stimulus. If you suspect that’s the case, try these 21s workouts to see if they do the trick.

What are 21s? 

They’re workouts that use a weightlifting technique referred to as partial reps. You do 21 reps of an exercise, but use a light weight and do only the first half of the movement for a third of the reps, the second half of the movement for another third of the reps, then the entire movement for the final third of the reps. 

Take biceps curls as an example: lift the weights only halfway up and lower seven times, then start at the halfway point of the curl and do the top half seven times. Finally complete seven full reps for a total of 21 reps. You don’t rest at all during the sequence, which is why you need to pick a much lighter weight than usual.

What are the benefits of 21s?

The purpose of 21s is to place the targeted body part under a sustained and unusual load to maximise muscle fatigue. This puts 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 to help you lose body fat and also increase your muscular endurance

21s Workout Plan

We’ve got a three-workout-a-week plan to try. Here’s what you need to know.

Do each workout once a week, leaving one day’s rest between each session. Allow 45 minutes for each session, including the warm-up.

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

For the 21s exercises, choose a weight that’s 40% of what you can normally lift 10 times. 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 sets and two minutes between exercises.

Workout A: Shoulders And Arms 21s Workout

1 Dumbbell overhead press

Sets 3 Reps 21 (7, 7, 7) 

Target: shoulders 

To do a full rep, stand holding dumbbells above your shoulders, with your palms facing forwards, your upper arms pointing to the sides and a 90° bend in your elbows. Brace your core and, without tilting your hips forwards, extend your arms to raise the dumbbells. Lower under control. 

2 Dumbbell curl

Sets 3 Reps 21 (7, 7, 7) 

Target: biceps

To do a full rep, stand holding dumbbells in front of your thighs with your palms facing forwards. Keeping your back straight and your upper arms pinned to your body, bend your elbows to lift the dumbbells to your shoulders. Lower under control. 

3 Triceps press-down

Sets 3 Reps 21 (7, 7, 7) 

Target: triceps

Set up a cable machine by attaching the rope handle at head height. To do a full rep, stand holding the rope handles in line with your upper chest, with your upper arms pinned to your body and elbows bent. Keeping your upper arms still, move your forearms down until your arms are extended. Squeeze your triceps at the bottom of the move. Reverse the move under control.

4 Gym ball back extension

Sets 3 Reps 10 

Target: lower back, core

Lie belly-down on a gym ball and wedge your feet against a wall for stability. Raise your torso until your body forms a straight line, making sure you don’t overextend.

5 Triceps dip

Sets 2 Reps 10 

Target: triceps, chest, front shoulders

On dipping bars, hold your body in the air with your arms extended. Bend your elbows to lower as far as is comfortable, then press back up powerfully. Don’t roll your shoulders forwards during the move.

6 Chin-up

Sets 2 Reps 10 

Target: biceps, back

Grasp a pull-up bar using an underhand grip. Bend your elbows to lift your body until your chin is above the bar, then lower under control. Lower all the way down between reps.

Workout B: Legs And Abs 21s Workout

1 Cable crunch

Sets 3 Reps 21 (7, 7, 7) 

Target: abs

Set up a cable machine with the rope attachment at head height, kneel down and hold the handle in both hands by your head. To do a full rep, tense your abs and curl your shoulders down, keeping your hands in the same spot by your head. Pause at the bottom of the move, then rise slowly back to the start. Ensure you use your abs rather than your arms to move the weight.

2 Front squat

Sets 3 Reps 21 (7, 7, 7) 

Target: quads, hamstrings, glutes

Stand with your feet hip-width apart and a barbell resting on your chest and shoulders, with bent elbows pointing forwards and held as high as you can. To do a full rep, push your hips back and bend your knees to lower until your thighs are parallel to the floor. Keep your back upright and core braced throughout.

3 Aquaman

Sets 2 Reps 8 each side 

Target: lower back, core

Lie face down on the floor. Raise your arms and legs just off the floor. Raise your right arm and left leg, then lower to the starting position. Alternate sides with each rep. Keep your arms and legs off the floor between reps.

4 Gym ball crunch

Sets 2 Reps 10 

Target: abs

Rest your back on a gym ball with your feet firmly planted on the floor. Using your abs, lift your head and shoulders, then lower under control.

5 Dumbbell lunge

Sets 2 Reps 10 each side 

Target: quads, hamstrings, glutes

Holding dumbbells by your sides or shoulders, take a big step forwards and bend both knees to lower until your back knee is just off the floor. Push through your front foot to return to standing. Alternate sides with each rep.

6 Overhead squat

Sets 3 Reps 10 

Target: quads, hamstrings, glutes

Stand with your feet hip-width apart, holding an empty barbell above your head with arms extended and hands wider than shoulder-width apart. Squat as far as you can without letting your back arch forwards.

Workout C: Chest And Back 21s Workout

1 Straight-arm pull-down

Sets 3 Reps 21 (7, 7, 7) 

Target: lats

Set up a cable machine by attaching a straight-bar handle at head height. Step back from the machine until you can hold the handle at shoulder height with your arms extended and palms facing down. To do a full rep, pull the handle to your thighs, keeping your arms extended throughout. Reverse the movement under control.

2 Smith machine bench press

Sets 3 Reps 21 (7, 7, 7) 

Target: chest

Even though you are benching 40% of what you could shift for 10 reps, it’s wise to use a Smith machine (or a spotter) so you can bail out if needed. Position the bench so that the bar is above the lower half of your chest. Unhook the bar and hold it above your chest with your arms extended. To do a full rep, bend your elbows to lower the bar to your chest, then press the bar back up powerfully.

3 Reverse flye

Sets 3 Reps 10 

Target: middle back, rear shoulders 

Stand holding dumbbells in front of your thighs with your palms facing. Hinge forwards at your hips, letting your arms hang down and bending your knees and elbows slightly. Raise the weights to the sides without moving your torso. Maintain the slight bend in your elbows. Lower under control. 

4 Cable cross-over

Sets 2 Reps 10 

Target: chest

Set up a cable machine by attaching two D-handles to the highest points. Stand in the middle, holding the handles with your arms out to the sides. Adopt a split stance and lean forwards slightly, keeping a straight back. Brace your core and, with a slight bend in your elbows, bring the handles together in front of your chest. Return to the start under control.

5 Reverse-grip bent-over row

Sets 2 Reps 10 

Target: upper back, lats

Hold a barbell in front of you with an underhand grip, palms facing forwards. Hinge at the hips, maintaining a straight back, and let your arms hang down. Brace your core, then lift the barbell to your sternum, keeping your elbows close to your body. Lower under control.

6 Incline dumbbell overhead press

Sets 2 Reps 10 

Target: chest, triceps, front shoulders

Sit on an upright bench, holding dumbbells by your shoulders, with your elbows out to the sides and bent to 90°, and your palms facing forwards. Extend your arms to press the weights overhead, keeping the dumbbells in line with your shoulders. Lower the weights under control. 

Nick Hutchings worked for Men’s Fitness UK, which predated, and then shared a website with, Coach. Nick worked as digital editor from 2008 to 2011, head of content until 2014, and finally editor-in-chief until 2015.

With contributions from