Ever hear of 21s? Not black jack—I’m talking fitness, son.

21s are a popular method used by top bodybuilders to shock their muscles into new growth by targeting specific ranges of motion (ROM) for a given movement. It’s a mix of partial and full reps within the same set to fully pump your muscles up.

For example, you do 7 reps in the top half of a movement, 7 reps in the bottom half, and then 7 full reps to get to 21 total reps. This strengthens weaknesses and forces your muscles to work harder for longer.

Though the rep-based approach for 21s works just fine, I personally prefer using the time-based alternative. For example, using the biceps curl, you do 20 seconds in the top half of the movement, 20 seconds in the bottom half, and full reps for 20 seconds.

Most trainees apply this muscle-maximizing method to curls to turn their biceps into baseballs. But you can apply it to a bunch of other exercises too, like squats, shoulder raises, pushups, and rows, to name a few.

And if you can do this with pullups, you’re a fitness freak show … in a good way.

You can also play around with the order that each range of motion is targeted to keep your body guessing.

In the beginning, I’d recommend starting with the most difficult range of motion when you’re most fresh. In the case of the pulling moves like the biceps curl and row, that would be the top half of the move. In the case of pushing moves like squats and pushups, that would be the bottom half of the move.

Keep in mind that your lower body has a greater proportion of slow twitch to fast twitch muscle fibers than your upper body. That means your legs inherently have more endurance than your arms.

That’s why I’ve created customized lower- and upper-body intensive routines for you to choose from. The lower-body workouts use longer work periods at each range of motion for extended time under tension.

Finally, be sure to load yourself on the lighter side in the beginning. For the upper body, I recommend using loads or exercise variations you can do at least 15 reps with. For the lower body, use loads or exercise variations you can do at least 20 reps with.

Lower-Body Multi-ROM Exercises

Each one of these lower-body exercises is performed for 2 straight minutes, broken down into 3 ranges of motion in the exact order outlined below.

After completing each 2-minute block, rest 1 to 2 minutes. That’s 1 round. Do 2 to 3 rounds on each side for unilateral moves and 3 to 5 total rounds for bilateral moves.

You can also shorten rest periods by moving onto the other non-competitive exercises before doing the next round. For example, go from calf raises to squats or alternate with one of the upper-body exercises below.

Try to get at least 10 to 12 reps every 40 seconds. If you can’t, then bump the loads down or use an easier exercise variation. If you’re consistently getting more than 12 reps, bump the loads up or use a harder exercise variation.

1. Bulgarian split squat

1. Bottom half of rep, 40 seconds
2. Top half of rep, 40 seconds
3. Full rep, 40 seconds

2. Extended ROM dumbell sumo deadlift

1. Bottom half of rep, 40 seconds
2. Top half of rep, 40 seconds
3. Full rep, 40 seconds

3. Extended ROM calf raise

1. Bottom half of rep, 40 seconds
2. Top half of rep, 40 seconds
3. Full rep, 40 seconds

4. Goblet squat

1. Bottom half of rep, 40 seconds
2. Top half of rep, 40 seconds
3. Full rep, 40 seconds

*To add an extra challenge, or “MetaBoost” to the goblet squat, add a miniband around your knees to make your hips work harder and improve your form.

Upper-Body Multi-ROM Exercises

Each one of these upper-body exercises is performed for 1 straight minute, broken down into three ranges of motion in the exact order outlined below.

After completing each 1-minute block, rest 1 to 2 minutes. That’s 1 round. Do 2 to 4 total rounds.

You can also shorten rest periods by moving onto the other non-competitive exercises before doing the next round. For example, go from rows to pushups.

Try to get at least 6 to 8 reps every 20 seconds. If you can’t, then bump the loads down or use an easier exercise variation. If you’re consistently getting more than 8 reps, bump the loads up or use a harder exercise variation.

1. Dumbbell T row*

1. Top half of rep, 20 seconds
2. Bottom half of rep, 20 seconds
3. Full rep, 20 seconds

2. Dumbbell extended ROM pushup*

1. Top half of rep, 20 seconds
2. Bottom half of rep, 20 seconds
3. Full rep, 20 seconds

3. Tall kneeling biceps curl*

1. Top half of rep, 20 seconds
2. Bottom half of rep, 20 seconds
3. Full rep, 20 seconds

4. Split kneeling lateral raise, left leg forward

1. Top half of rep, 20 seconds
2. Bottom half of rep, 20 seconds
3. Full rep, 20 seconds

5. Seated overhead triceps extension, right leg forward

1. Top half of rep, 20 seconds
2. Bottom half of rep, 20 seconds
3. Full rep, 20 seconds

*MetaBoost: Add fat-gripz to your dumbbells to improve arm activation and strengthen your grip.

Radically change your body and get seriously fit with the Bobby Maximus approach. Warning: it's the opposite of easy. But it works. Check it out.