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Want Superhero-Sized Arms? The 8-Week Ultimate Workout Plan Will Be Your Origin Story.

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Want Superhero-Sized Arms? The 8-Week Ultimate Workout Plan Will Be Your Origin Story.

JUST BECAUSE YOUR arms are made up of smaller muscles—mainly your biceps and triceps—doesn’t mean you can coast through a few lazy sets tacked onto training days and expect serious growth. If you want sleeves that stretch, you need to hit arms with the same intensity you bring any other type of workout. You need a solid, comprehensive plan.

That’s exactly what Men’s Health fitness director Ebenezer Samuel, C.S.C.S., had in mind when he built this program that can build superhero-sized arms while still considering for busy schedules. “This winds up being the perfect arm training program for the Men’s Health guy,” he says. This is the cornerstone of our Ultimate Arm Recomp plan, which will be your key to real muscle growth.

Samuel’s four-day program uses intensity techniques designed to push every set to the brink. Supersets, lengthened partials, pauses, drop sets—you’re going to feel every rep. You’ve never trained arms like this before. But give it six to eight weeks, and you just might see gains you’ve never had before, either.

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What You Need to Do to Build Superhero Arms

Walk 8,000-10,000 Steps Per Day

AS YOU’RE LIVING an active lifestyle, you should kind of trip and fall your way to eight to 10 thousand steps per day,” says Samuel. “If not, just try to get a little bit of extra activity in.” Walking more is the most measurable way to increase your NEAT (non-exercise activity thermogenesis). That is, how many calories you burn when not exercising. Increasing your NEAT can help you burn hundreds of additional calories per day without contributing to your fatigue.

Eat to Gain Muscle

“We want to make sure we’re not in a calorie deficit for this program,” Samuel explains. “We want to be in a slight surplus because you’re going to need those calories to grow muscle on your biceps and triceps.” For more information on how to eat, check out our guide here.

Lift Heavy and Focus On the Eccentric

“What this program is about is owning your form and owning the eccentric portion [or lowering phase] of every single contraction on your arm exercises,” Samuel says. “If you’re rocking and cheating your way through your form, then you’re not going to get those good squeezes and long eccentrics movements that can help grow arm muscle.”

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4 Key Arm Training Principles

Do Exercises With Multi-Joint Stimulus

“WHEN I’M BUILDING a general strength training program for you guys, I’m focusing on our big lifts,” Samuel says of exercises like rows, bench presses, and deadlifts. “We build our program around those multi-joint ideas because they’re good for calorie burn and they’re good for sending signals to our muscles to grow everything.”

The multi-joint movements (also called compound exercises) are, in this instance, programmed to help you preserve the muscle you already have so you can expend your energy growing your arms. Too many heavy lifts, he says, will leave you too physically and mentally fatigued to attack your arms with the intensity you need to make gains. For that reason, Samuel says you’ll pull back on these compound movements while on this specific program to make room for more arm exercises.

“What we still want to make sure to do is enough of those big lifts, so that we’re still sending signals to our larger muscle groups that we want to preserve the size we have,” Samuel says.

Split Workouts Into Push and Pull Motions

“I’ve had you do splits that were two upper days and two lower days, really crushing our legs and big lifts, but this split is a little different,” says Samuel, who is switching it up for this program.

This time around, you’ll stick with four training days: a push day, a pull day, a leg day, and an arm day. This set-up lets you accumulate more arm work into your week by pairing triceps with chest and biceps with back, in addition to a standalone arm workout. Your legs, chest, back, and shoulders will take a backseat during this program, with enough volume to maintain the muscle you already have in those areas.

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Utilize Techniques to Fight Through Fatigue

Your sets and reps for multi-joint lifts like deadlifts and bench presses will be straightforward: three sets for anywhere from six to 12 reps. Push those sets but remember that the goal of this program is to size-up your arms.

With that in mind, Samuel includes a series of intensity techniques to help you lift more weight for more reps to eke out as much muscle-building stimulus as possible.

Direct Arm Work Three Times Per Week

As mentioned above, Samuel set up this workout split to include three arm training days, with your triceps and biceps each getting two sessions per week.

“You can train arms often if you train them smart because, overall, you are working lighter loads,” Samuel says. “We’re going to push through and make sure we get as much direct arm work as we can over the course of this program.”


Your Superhero Arm Workout Plan

Warmup

KEEP YOUR WARMUP quick to get you in and out of the gym in about an hour. Do a one-minute-long set of jumping jacks, planks, and reverse lunges, “something to get your heart rate moving,” as Samuel puts it. Not included in the workouts below are the one to two “feeler sets” that you should do for your heavier lifts. For example, if you can dumbbell press 80 pounds, it’s wise to do a set of, say, six reps with 40 pounds and then another set of four reps with 60 pounds before hitting your working sets.

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How to Progress

Each week, you want to do more reps or more weight for pretty much every exercise, week to week. For example, say you do dumbbell skull crushers with 25 pounds for 10 reps during week 1. Next week, you’ll try for 11 reps, then 12 reps the week after, and so on. If you run this program for longer than four weeks, you’ll add five to 10 pounds to your lifts and repeat that weekly rep progression. If you make it to the top end of each prescribed rep range quickly, add more weight during next week’s session and try again.

Rest

A good general rule of thumb is to rest for 90 seconds to two minutes between sets of heavy compound movements, like the trap-bar deadlift and Bulgarian split squats, and 60 seconds between isolation movements.


DAY 1:

Back & Biceps

EZ-Bar Incline Row

SAMUEL SAYS: “I love starting with some sort of horizontal pull because it’s going to teach our shoulder blades to move correctly. Let’s say you have some sort of office job or you’re driving a lot, it’s going to offset that forward position and start to train our shoulder blades to come back.”

SETS AND REPS: 3 sets of 6 to 10 reps

HOW TO DO IT:

  • Sit on an incline bench facing forward, so you can rest your chest against the pad.
  • Use a supinated (or underhand) grip to grab the EZ bar. Engage your glutes and abs, then squeeze your shoulder blades to create tension.
  • Pull the weight up to the bench. Think about driving the EZ bar straight through the bench as quickly and explosively as possible.
  • Return the bar to the ground without allowing it to slam on the floor.
  • Pause between each rep to reset your position.

Chinup

SAMUEL SAYS: “Whether this is five reps or 10 reps, [the chin-up gets] that vertical pull in, and, two, the chin-up by itself is a really good way to start warming up our biceps and triceps. I want you to do three sets of max reps, and that last set should be so hard you can barely pull yourself up.”

SETS AND REPS: 3 sets of max reps

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HOW TO DO IT:

  • Get into a good hanging position with an underhand grip, squeezing your shoulders, abs, and glutes to maintain tension.
  • Drive your elbows into your hips to pull yourself up to the bar. Continue until your head is above the bar, pausing briefly at the top.
  • Lower back down until your elbows are extended, maintaining control of the position and keeping tension.

Preacher Curl

SAMUEL SAYS: “If you have access to a preacher bench, we can do this with an EZ-bar, which is the ideal way to do this. After you hit your eight to 10 reps, then we’re going to try and bang out two to three more reps of [lengthened partials]. When we’re in that stretched-out position, it’s a great way to grow muscle.” If you don’t have an exercise-specific bench, you can swap in an adjustable bench and dumbbells.

SETS AND REPS: 3 sets of 8 to 10 reps (plus partial reps)

HOW TO DO IT:

  • Begin by adjusting your seat to a position in which your chest is flush against the preacher pad with your armpits firmly wedged in, leaving little to no gap.
  • Grab the EZ bar. Another benefit of using the machine preacher curl is that it allows you the option of either using a tight grip or light contact with relaxed palms. Either style works.
  • Squeezing your shoulder blades and driving your lower body into the ground, begin curling the bar. Focus on rotating both pinkies toward the ceiling as you work toward a solid squeeze at the top of the rep.
  • Lower back to start position. That’s one rep.

Hammer Curl Rack Run

SAMUEL SAYS: “I want you to choose a relatively heavy weight, something you can curl for four to six reps. After you hit those four to six reps, you’re going to pick up something five pounds later and do as many reps as you can. Repeat that process all the way down until you’re down to, like, 10 pounds. If you’re starting with 40-pound dumbbells, only do four drops. If you’re starting with 25-pound dumbbells, try to go all the way down to 10 pounds.”

SETS AND REPS: 2 sets; 2 minutes rest between sets

HOW TO DO IT:

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  • Stand with your feet hip-width apart, holding a pair of dumbbells in a neutral grip (palms facing each other). Squeeze your shoulder blades, abs, and glutes to create full-body tension.
  • Curl the dumbbell up, moving only at the elbow joint. Keep your upper arms still and perpendicular to the floor. Squeeze your biceps at the top of the movement.
  • Avoid shifting your elbow forward to keep your shoulders out of the movement.
  • Lower the weight back down to the starting position under control.

DAY 2:

Chest & Triceps

Incline Dumbbell Press

SAMUEL SAYS: “This gives you a chance to go heavy, and we’re going to hit a large amount of our chest on this—our pec major, our upper pecs, our lower pecs.”

SETS AND REPS: 3 sets of 6 to 10 reps

HOW TO DO IT:

  • Set a bench to a 30- to 45-degree incline and sit back with a dumbbell in each hand.
  • Press the weights above your chest, keeping your wrists stacked over your elbows.
  • Lower until your elbows are just below bench level, then drive the dumbbells back up.

Super-Set: Cable Fly + Paused Pushup

SAMUEL SAYS: “We’re going to lead with the cable fly, ideally with your back supported. As soon as you get done with those cable flys, you’re dropping into pause push-ups to technical failure. I want a two-second pause in the bottom position of those push-ups, and I don’t care how many reps you get.”

SETS AND REPS: 3 sets of 10 to 12 reps + 3 sets to failure; rest 90 seconds between sets

HOW TO DO THE CABLE FLY:

  • Adjust the pulleys to chest height and attach D-handles.
  • Grab the handles with your elbows slightly bent and palms facing forward. Walk them around so you’re in front of the bench, and then plant your back firmly against the pad.
  • Press the handles forward until they meet in front of your chest
  • Slowly open your arms, allowing a deep stretch in your chest. Let your arms travel as far back as is comfortable for your shoulders.
  • Squeeze your chest and bring the handles back together.

HOW TO DO THE PUSHUP:

  • Drop to the floor immediately after your last rep with your palms flat, stacked directly below your shoulders.
  • Squeeze your shoulders, glutes, and core to create full-body tension. Your spine should form a straight line, keeping your eyes on the floor to maintain a neutral spine.
  • Bend your elbows to descend to the floor, stopping with your chest just above the ground. Your elbows should be at a 45 degree angle relative to the torso.
  • Press back up off the floor, raising up to the top position with your elbows fully extended.

Cable Overhead Extension

SAMUEL SAYS: “This is an exercise that’s going to give you a stretch at both the shoulder and elbow joint. The triceps has two main functions: it extends the elbow…it also brings our upper arm downward. We get to train both of those.”

SETS AND REPS: 3 sets of 6 to 8 reps + dropset to paused reps

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HOW TO DO IT:

  • Set up a bench to a 75-degree incline (likely the highest without the back support being fully vertical), and place it directly in front of a cable machine with a rope attachment. The cable should be anchored as close to the ground as possible.
  • Lie with your back against the bench, abs and glutes tight, arms perpendicular to the ground, and have a friend hand you the rope attachment with your hands directly over your shoulders. Grasp both its ends.
  • Slowly bend at the elbows, lowering the rope toward your shoulders. Bend your elbows as much as you possibly can, stretching your triceps. Don’t allow your elbows to flare as you do this.
  • Then straighten your arms (don’t flare your elbows here either!), squeezing your triceps.

Dumbbell Skull Crusher

SAMUEL SAYS: “What you’re going to do is 25 reps, but I want you doing this with a weight you think you can hit reasonably for 10 to 12 reps. Bang out as many reps as you can with good form. Once your form fails, sit up, rest for five deep breaths, and then lie back down and do as many reps as you can until you get 25 reps.”

SETS AND REPS: 2 sets of 25 reps; rest 2 minutes between sets

HOW TO DO IT:

  • Start by lying back on the bench. Don’t arch your back—drive your shoulder blades into the bench, squeeze your abs and glutes, and keep your feet flat on the floor.
  • Press the weight straight up above your chest, holding the dumbbells in a neutral position (palms facing each other). Your upper arms should be just past 90 degrees, at a 91 or 92 degree angle. Keep your wrists strong and a tight grip on the weight.
  • Lower the weights slowly down to an inch above your forehead, moving only at the elbows. Don’t allow your shoulders to shift forward; keep your upper arms still.
  • Drive the weight back up (again moving only at the elbows), squeezing your triceps at the top.

DAY 3:

Legs

Trap Bar Deadlift

SAMUEL SAYS: “Point blank: in any routine, the trap-bar deadlift is critical because it’s going to ensure we’re moving a heavy weight. You don’t need to think about setting PRs [personal records] in this block, but you do want to train this move heavy because it’s your one chance in this program to move heavy weight.”

SETS AND REPS: 3 sets of 6 to 8 reps; rest 90 seconds between sets

HOW TO DO IT:

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  • Position yourself inside the trap bar, with your shins aligned with (or just in front of) the center of the bar.
  • Push your butt back as far as possible, bend your knees, and reach down to grip the handles. Grip as tightly as possible.
  • Keep your head neutral, keeping your gaze fixed on something in front of you. Squeeze your shoulder blades to create tension, and turn the pits of your elbows forward, facing out.
  • Make sure your hips are lower than your shoulders, then prepare to initiate the lift.
  • Push your feet through the floor to stand straight up, squeezing your glutes at the top.
  • To finish the rep, push your butt back as far as you can, then bend your knees to set the weight down.

Dumbbell Bulgarian Split Squat

SAMUEL SAYS: “On these split squats, you don’t need to go crazy heavy, but I want you to challenge yourself. The last two reps should be relatively hard.”

SETS AND REPS: 3 sets of 8 to 10 reps

HOW TO DO IT:

  • Start on the floor in front of the bench (or whatever stable platform you have on hand).
  • Place one foot up onto the bench, then get into a position where your front foot is planted on the floor with a vertical shin (in relation to the ground). Your thigh should be parallel to the ground, forming a 90 degree angle at the knee.
  • Grab the weights off the floor.
  • Tighten your core and drive your ribcage in. Keep your neck neutral, looking straight ahead. Squeeze your shoulder blades to create tension.
  • Stand up, hinging forward slightly to avoid overextending your back.
  • Lower yourself down, working to keep your shin in that vertical position. Don’t allow your back knee to hit the ground; stop an inch from the floor if you can.
  • Squeeze your glutes hard to keep your knee in the proper position, then press your front foot off the floor to drive up.

Leg Press

SAMUEL SAYS: “You can do one set of this or two sets of this. This is as much about getting a little bit more calorie burn, and, again, moving a little bit of heavy weight. It’s about another thing, too: When it comes to training arms, one of the things we need to understand is how to push through fatigue. The leg press is a really good and safe way to understand, from a mental standpoint, how to push our limits.”

SETS AND REPS: 1 to 2 sets of 15 to 20 reps; rest 90 seconds between sets

HOW TO DO IT:

  • Get into a comfortable working position on the machine, with your shoulders and glutes squeezed and feet placed hip-width on the sled.
  • Press through the sled with your feet, maintaining tension in your torso. Release the sled from the safety lock, then control the weight down.
  • Watch your knees as you lower the weight, making sure you don’t allow them to cave in or track excessively outward.
  • Lower down as far as you can, maintaining upper body tension with your back flush against the pad. Don’t allow your butt to raise off the seat; if you shift you’ve gone too deep.
  • Press through the pad with both feet to raise the wait back up, extending your knees.

Kettlebell Swing

SAMUEL SAYS: “The kettlebell swing is doing one thing for us in this entire program. It’s the only time in this program where I’m asking you to be explosive, and just for longevity, we want to make sure we preserve a little bit of explosiveness in our program.”

SETS AND REPS: 3 rounds of 30 seconds on, 30 seconds off

HOW TO DO IT:

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  • Start standing with your feet slightly wider than hip-width apart, with the kettlebell on the ground in front of you.
  • Push you butt back, then lean over to grip the bell’s handle. Hold on tightly.
  • Squeeze your shoulder blades, then shift your arms to turn the pits of your elbows outward. Squeeze your abs to create tension. Keep your eyes on the floor to maintain a neutral spine.
  • “Hike” the weight back between your legs, keeping your knees slightly bent. Keep your arms straight.
  • Stand straight up, locking your knees, and aggressively squeeze your glutes to perform the swing. Keep your arms loose, like ropes connecting yourself to the kettlebell. Don’t aim for a certain point; allow the momentum to determine how high the bell goes.
  • Allow the weight to fall back down, back through your legs.

DAY 4:

Arms

Barbell Curl

SAMUEL SAYS: “Why do we like barbell curls? Because we’re going to be able to go very heavy on barbell curls compared to our other biceps exercise, and two, it’s making sure it hits both functions of our biceps [elbow flexion and supination]. Choose a weight that you can do for 10 to 12 reps. Bang out as many reps as you can. Put the bar down and rest for five deep breaths, and then you’re going to pick it up again and keep doing that until you’ve done 20 total reps.”

SETS AND REPS: 3 sets of 20 reps (rest-pause style); rest for 90 seconds between sets

HOW TO DO IT:

  • Stand with your feet about shoulder-width apart, holding the bar with a shoulder-width grip.
  • Squeeze your glutes, abs, and shoulder blades. Keep your torso tight.
  • Curl the weight up, moving only at the elbows.
  • Squeeze your biceps at the top for a split second, then lower the weight back down.

Cable Curl

SAMUEL SAYS: “There is one other function that does not get hit with the barbell curl: shoulder flexion. Our biceps play a small role in pulling our shoulder forward, and that role gets challenged in the cable curl.”

SETS AND REPS: 3 sets of 6 to 8 reps (plus partial reps)

HOW TO DO IT:

  • Grab the handle with one hand and take a step and a half away from the machine (or as far as you need to feel tension on the muscle).
  • Squeeze the abs and glutes for a solid base.
  • Create a slight angle with the elbow to where the cable feels like it’s pulling you back.
  • Ensure that your hips and shoulders are facing square in front—don’t allow the tension from the cable to twist your torso backwards.
  • Moving only at the elbow, curl your hand towards your shoulder.
  • As you lower back down, make sure the cable doesn’t pull your shoulder from its position. Think about keeping the upper arm in line with your torso.

Hammer Curl

SAMUEL SAYS: “Choose a weight that lets you get anywhere from eight to 12 reps, and then we’re going to do as many reps as you can. Then we’re going to put the dumbbells down, rest for a three-count, and then pick the dumbbells up again and do as many reps as you can. Keep repeating this until you can no longer complete two to three reps.” (If you want to see this technique in action, check out our Building Blocks video in which Samuel performs Myo Reps.)

SETS AND REPS: 1 set of myo reps

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HOW TO DO IT:

  • Stand with your feet hip-width apart, holding a pair of dumbbells in a neutral grip (palms facing each other). Squeeze your shoulder blades, abs, and glutes to create full-body tension.
  • Curl the dumbbell up, moving only at the elbow joint. Keep your upper arms still and perpendicular to the floor. Squeeze your biceps at the top of the movement.
  • Avoid shifting your elbow forward to keep your shoulders out of the movement.
  • Lower the weight back down to the starting position under control.

JM Press

SAMUEL SAYS: “The beauty of the JM press [which you can do with a barbell or dumbbells] is that it’s going to give us a really good loaded stretch on our triceps when we lower into the bottom position. Think about resting in that bottom position, feeling that stretch, and then pressing up.”

SETS AND REPS: 3 sets of 8 to 10 reps;

HOW TO DO IT:

  • Start by lying back on the bench. Drive your shoulder blades into the bench, squeeze your abs and glutes, and keep your feet flat on the floor.
  • Press the weight straight up above your chest, holding the dumbbells in a neutral position (palms facing each other). Your upper arms should be just past 90 degrees, at a 91 or 92 degree angle. Keep your wrists strong and a tight grip on the weights.
  • Lower the points of your elbows down to your ribcage so the top of each dumbbell touches your shoulders. Fight to prevent your elbows from flaring out.
  • Press back up to the starting position.

Incline Bench Skull Crusher

SAMUEL SAYS: “Why are we going for the incline skull crusher this time? One, so we get a slightly different angle than the exercises we’ve already hit. And two, in general…we’re going to get a little bit more stretch overall when we’re doing these skull crushers.”

SETS AND REPS: 3 sets of 8 to 10 paused reps;

HOW TO DO IT:

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  • Start by setting an adjustable bench to about a 15-degree angle.
  • Sit on the bench, driving your shoulder blades into the back pad, squeezing your abs and glutes, and keeping your feet flat on the floor.
  • Press the weight straight up above your chest, holding the dumbbells in a neutral position (palms facing each other). Your upper arms should be just past 90 degrees, at a 91 or 92 degree angle. Keep your wrists strong and a tight grip on the weight.
  • Lower the weights slowly down to an inch above your forehead, moving only at the elbows. Don’t allow your shoulders to shift forward; keep your upper arms still.
  • Drive the weight back up (again moving only at the elbows), squeezing your triceps at the top.

X Pressdown

SAMUEL SAYS: “The beauty of the X pressdown is that it’s a vertical triceps kickback that we can load more exclusively. I have this down for one set, but if you’re feeling like you want a little bit more triceps work…you can do this in two sets.”

SETS AND REPS: 1 to 2 sets of myo reps; rest 90 seconds between sets

HOW TO DO IT:

  • Stand in the center of a cable crossover machine, chest facing the machine. Reach across your body and grab the right handle with your left hand. Grab your left handle with the right hand (you can grab D-handles to do this move, but you may find it more comfortable to instead detach the handles and grab the ball at the end of the cable. You can also attach wrist straps and loop your wrists through those. Do what feels most comfortable).
  • Pull the cables down and toward your torso, keeping your elbows bent as you do. Pull down until your upper arms are in line with your torso, and squeeze your shoulder blades. This is the start.
  • Now straighten your arms, flexing your triceps hard and bringing your wrists in line with your elbows and shoulders. Slowly lower the weight back to the start, never letting your elbows drift forward.

Check out all of our arm-building videos in our Ultimate Arm Recomp Video Training Guide, available exclusively for MH MVP subscribers, here.

Lettermark

Andrew Gutman, NASM-CPT is a journalist with a decade of experience covering fitness and nutrition. His work has been published in Men’s Health, Men’s Journal, Muscle & Fitness, and Gear Patrol. Outside of writing, Andrew trains in Brazilian Jiu-Jitsu, helps coach his gym’s kickboxing team, and enjoys reading and cooking. 

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“Forget living longer, exercise can make life easier right now”—a 72-year-old fitness influencer and marathon runner shares two accessible ways to start moving

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“Forget living longer, exercise can make life easier right now”—a 72-year-old fitness influencer and marathon runner shares two accessible ways to start moving

Retirement is often a time when people slow down, but in Christine Hobson’s case, she’s speeding up. When her daughter persuaded her to join a running club so she wouldn’t get bored, she had no idea she’d get the fitness bug and run 125 marathons in total, visiting all seven continents.

And the 72-year-old former teacher has plans to run the North Pole marathon in 2027.

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Fitness

Why 21-15-9 Might be the Smartest Workout Format in Fitness – and How to Use it to Drive Muscle Growth

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Why 21-15-9 Might be the Smartest Workout Format in Fitness – and How to Use it to Drive Muscle Growth

CrossFit means a lot of things to a lot of people – because it’s made up of a lot of things.

Since the rise of the fitness giant, countless brands, events and training methods have sprung up around it – not claiming to be CrossFit, but looking suspiciously CrossFit-esque.

There are, however, a handful of things that are uniquely CrossFit: the ‘Girls’ benchmark workouts. The Hero WODs and, of course, its signature rep schemes.

Chief among them is ’21-15-9′.

The 21-15-9 rep scheme may just be the single most CrossFit thing in existence. But what exactly is it? Where did it come from? And why might it actually be better at building muscle in a hurry than its conditioning roots would have you believe?

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Let’s have a look.

What Is 21-15-9?

If you’ve never encountered it before, the format couldn’t be simpler. Choose two exercises (occasionally more) and perform 21 reps of each, then 15 reps of each, then nine reps of each, completing the entire workout as quickly as possible – with good form.

Probably the best-known example is ‘Fran’: 21 thrusters and pull-ups, followed by 15 of each, then nine. On paper it doesn’t look especially intimidating. In practice, it’s one of the most feared benchmark workouts in fitness.

Where Did it Come From?

Unlike many modern training methods, 21-15-9 didn’t come out of a study. It came from the gym floor.

CrossFit founder Greg Glassman has explained that the format emerged through years of coaching and experimentation in the 1990s. Rather than chasing a perfect sets-and-reps prescription, he was looking for a workout that allowed athletes to maintain a high power output from start to finish.

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The thinking is surprisingly elegant. You begin with 21 reps while fresh. By the time you reach the set of 15, your ability to produce force has already fallen. By the final nine, you’re significantly more fatigued – but the workload has dropped by almost the same amount.

Instead of grinding through increasingly miserable sets of the same length, the workout ‘meets you where you are’, reducing the work required as your capacity declines. The result is a workout that encourages you to keep moving instead of standing around trying to recover.

The numbers themselves are also remarkably practical. Forty-five total reps per movement provides plenty of training volume without turning the session into an endurance slog, while every set divides neatly into thirds if you need to break it up.

(Although I’ve got to be honest, I’m a 20-15-10-5 man myself, just for the sake of round numbers.)

Why Does it Work So Well?

Although there isn’t research showing that 21-15-9 is somehow the magic formula, there are obvious reasons why it consistently produces brutally effective workouts.

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Descending reps help maintain intensity. As fatigue accumulates, reducing the target allows movement quality, bar speed and overall work rate to stay higher than they would if you simply repeated the same number of reps over and over.

It also tends to land in a physiological sweet spot. Most 21-15-9 workouts take between three and eight minutes, depending on the movements and the athlete. That’s long enough to create a serious cardiovascular challenge while still requiring meaningful force production throughout. You’re taxing your anaerobic systems hard while relying on your aerobic system to help you recover just enough to keep going.

Finally, there’s the psychological trick. The hardest-looking part comes first. Once you’ve survived the opening 21, every remaining round appears more manageable. ‘Only 15 left.’ Then, ‘Just nine.’ In reality, you’re becoming more fatigued with every rep, but the shrinking target keeps you attacking the workout instead of pacing too conservatively.

Why it Might be Surprisingly Good for Building Muscle

Perhaps the biggest misconception about 21-15-9 is that it’s ‘just cardio with weights’.

Choose the right load and something interesting happens. Very few athletes complete every round unbroken. Instead, the workout naturally evolves into a series of short, broken sets separated by only a few seconds of rest.

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Your 21 might become 11-5-5. Your 15 becomes 8-4-3. Your final nine might stay unbroken – or become 5-4.

In effect, you’ve accidentally turned the workout into a form of rest-pause training.

Those brief pauses allow just enough recovery to squeeze out more high-quality repetitions before fatigue catches up again. By the latter stages of each mini-set, you’re repeatedly working very close to failure, recruiting the high-threshold motor units with the greatest potential for muscle growth.

It’s a similar principle to rest-pause training, myo-reps and cluster sets: all methods used to accumulate hypertrophy-friendly volume while keeping the load relatively heavy and the rest periods brutally short.

You’re basically speed-running a large number of hard, growth-stimulating reps in a very small window of time. Could this help explain why elite CrossFit athletes often carry an impressive amount of muscle despite spending relatively little time performing traditional bodybuilding splits?

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It’s certainly plausible, although the ‘elite’ part often selects for athletes with the greatest muscle-building potential.

Much of their training isn’t simply conditioning. It’s high-density resistance training performed under accumulating fatigue, with only fleeting recovery between efforts. In other words, they’re often doing something bodybuilders have deliberately programmed for decades: packing a lot of hard work into a very short period of time.

That’s not to say 21-15-9 is superior to a well-designed hypertrophy programme. If your sole goal is building muscle, there are more efficient ways to do it.

But if you’re looking for a workout that develops fitness, tests your mettle and still provides a meaningful stimulus for strength and size, it’s easy to see why this deceptively simple rep scheme has remained one of CrossFit’s defining fingerprints for more than 20 years.

Best Bodyweight 21-15-9 Workout: ‘JT’

If you’re looking for an interesting twist on the 21-15-9 format, look no further than Hero WOD ‘JT’, which concentrates the muscle-building potential of the format into a brutal upper-body workout.

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Created in honour of Petty Officer 1st Class Jeff Taylor, who was killed in Afghanistan in 2006, the workout strips away barbells altogether and relies solely on three bodyweight movements:

21-15-9 reps of:

Don’t let the lack of equipment fool you. The volume – 45 reps of each movement, 135 reps in total – combined with the descending rep scheme makes this a brutal upper-body test, hammering the shoulders, chest and triceps while demanding serious muscular endurance.

Better still, it perfectly demonstrates one of the biggest strengths of 21-15-9. As fatigue mounts and the sets naturally fragment, the workout begins to resemble one giant rest-pause set, allowing you to accumulate a huge number of hard, near-failure reps in less than 10 minutes.

If your goal is building an impressive upper body while developing serious work capacity, there are few bodyweight workouts that deliver quite so much bang for your buck, making ‘JT’ one of my personal favourites.

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If there’s one thing Kori Sampson knows, it’s how to optimise your body composition for performance. To tap into his knowledge as an elite athlete and coach, we asked him to create a 4-week plan to help you move faster, recover quicker and keep pushing when the fatigue sets in – all while improving your muscle-to-fat ratio.

Ready to build muscle, burn fat and come out the other side looking, feeling and performing better? Click here to get 14 days of free access to the plan via the Men’s Health app.


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Fitness

10 minutes of swimming might not sound worth it – but I tried it for 2 weeks and found the benefits of a quick dip

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10 minutes of swimming might not sound worth it – but I tried it for 2 weeks and found the benefits of a quick dip

The concept of ‘exercise snacking’ has never been more popular. Not only is it convenient and accessible, but there is solid scientific evidence that short bursts of physical activity can yield real benefits for our health. But can a swimming workout be an effective ‘exercise snack’?

A study published in the European Heart Journal found that just 15 to 20 minutes of vigorous physical activity a week (almost as low as two minutes a day) was enough to significantly lower the risk of heart disease, cancer and early death. The study defined vigorous activity as any exercise that leaves you out of breath and raises your heart rate, including swimming.

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