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The Rep Range That Builds the Most Muscle

When it comes to stacking on size, just how many times do you need to lift those weights in a given set? Here's an explainer.

Wanna start a fight? Walk into a room filled with strength coaches, personal trainers, and exercise physiologists, and ask how many reps per set you should be doing to build muscle. Then take cover.

High reps, medium reps, low reps—each approach has been touted as an ideal way to build muscle. Stalwarts in the exercise business argue with deep-rooted passion, but incontrovertible conclusions are rare, leaving the average Joe wondering: Okay, which range should I use to get bigger?

Here we build separate cases for high, medium and low reps and render a verdict on which is the best choice for increasing muscle mass. The weight room will now come to order.

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The Argument for High Reps (15 or More)

If you've ever tried a set of 15 or more reps, you know it can be difficult. If you're unaccustomed to training in this zone, you'll find your muscles fatigue quickly, and 40 pounds starts to feel more like 100 by the final rep.

Sets that stretch past 15 reps, though, have one major drawback: The amount of weight you can handle isn't heavy enough to recruit fast-twitch type-2 muscle fibers. So what, you ask? Simply put, type-2 fibers are where the potential for growth resides, and they respond only to heavy weights at least 75 percent of your one-rep max.

High-rep training is, however, an excellent means of increasing muscular endurance. If you're after sports-specific adaptations such as a throwing arm for softball that can hold out for more than half an inning or legs that will carry you to the finish line of a marathon high reps can help. But if size is paramount, high reps won't get it done, especially if the preponderance of your training lies in this zone.

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The Argument for Low Reps (5 or Less)

In weight training, one adage has stood the test of time: To get big, you have to get strong. Taking that to an extreme, many lifters adopt a powerlifting approach, coupling very heavy weights with low reps. Take a look around your gym, and you're likely to find an aspiring bodybuilder or two struggling through sets of squats or bench presses with weights at or near their one-rep maxes.

This method is a sure strength builder, and if you take a close look at any successful powerlifter, you'll notice the added mass in his frame. However, low-rep training has one significant shortcoming: Muscle-fiber stimulation, and thus growth, is correlated closely to the amount of time a muscle is under tension. Short, intense sets of 15 seconds or less will develop strength, but they simply aren't as effective in prodding a muscle to grow as sets of 30 to 60 seconds.

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The Argument for Moderate Reps (8–12)

The time-under-tension theory leads us to our third suspect: 8–12-rep sets. At a cadence of two seconds on the concentric (lifting) action and two seconds on the eccentric (lowering) movement, your set will end up right in the middle of the optimum 30- to 60-second range for a given set of exercise.

Why is that range critical? Because when the set lasts longer than a few seconds, the body is forced to rely on the glycolytic-energy system, which leads to the formation of lactic acid. You may think of lactic acid as a bad thing, since it's mistakenly associated with the muscle ache you feel days after a workout, but that soreness is actually a very fleeting reaction that's vital to new muscle-tissue production.

When lactic acid, or lactate, pools in large amounts, it induces a surge in anabolic hormone levels within the body, including the ultrapotent growth hormone and the big daddy of muscle-building, testosterone. These circulating hormones create a highly anabolic state within the body and if you're after more muscle, that's exactly the state you want to be in.

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The increased time under tension also leads to more muscle damage, imperative if you plan on getting larger any time soon. Theoretically, the longer a muscle is contracted, the greater the potential for damage to the tissue.

The moderate-rep range, when coupled with a challenging weight, will also bring about a much-desired condition: the muscle pump. That tight, full feeling under the skin, caused by blood pooling in the muscle, has value beyond its ego-expanding qualities. Studies have demonstrated that the physiological conditions which lead to a pump activate protein synthesis and limit protein breakdown. Thus, more of the protein you eat goes toward muscle construction instead of being burned off for energy. In a scientific twist of good fortune, the fast-twitch fibers appear to be the biggest beneficiaries of this phenomenon.

The Verdict

In the final analysis, substantial evidence argues that training in a moderate-rep range is the best way to build muscle mass. It increases hormone response, spares protein, and provides the necessary time under tension to spark muscle damage. These benefits work in unison to get you from pencil neck to powerhouse in no time.

But does this mean you should store your low-rep and high-rep regimens away in the closet, underneath your parachute pants and Thriller album? Certainly not. To make sure your body doesn't adapt to a particular regimen and stagnate, you need variety. Cycle periods of low-rep training and high-rep training into your overall program, while progressively trying to increase your strength and perfect your exercise form every time you lift.

Case closed.

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How to Put This to Work: A Periodization Planner

If your haphazard training has been producing mixed results for a while now, consider periodizing your training. Periodization is a system of training that organizes your workout into distinct cycles. Because each cycle has specific objectives, the number of reps for each varies sharply.
A typical periodization plan usually consists of three or four phases (depending on your goals):
Phase 1: Preparatory, consisting of extremely high volume (15 or more reps, three to five sets) and low resistance.
Phase 2: Hypertrophy, or growth, consisting of high volume (eight to 12 reps, three to five sets) and moderate resistance (50 percent to 75 percent of one-rep max).
Phase 3: Strength, consisting of moderate volume (five or six reps, three to five sets) and heavy resistance (80 percent to 88 percent of one-rep max).
Phase 4: Power, consisting of low volume (two to four reps, three to five sets) and very heavy resistance (90 percent to 95 percent of one-rep max).

To build the explosive strength necessary for competition, athletes frequently use Phase 4, the power phase. For the average Joe who's merely after more impressive weight-room results, Phases 1 through 3 are the way to go. Keep reading for a simple three-month periodization cycle that can be used by both gym novices and grizzled veterans.

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Get Bigger: The Sample Workout Program

Devote one month to each phase, gradually increasing resistance while decreasing the number of sets as the month progresses. After the completion of this three-month cycle, actively rest (run, hike, play basketball, etc.) for a week or two before hitting the weights hard again. In the interest of simplicity, we have not changed the exercises between cycles. Traditionally, however, the exercises do vary. Note how the number of repetitions changes per phase. This will maximize growth by engaging the greatest number of muscle-fiber types.

Preparatory Phase

Squat
Sets: 3-5
Reps: 15 or more

Hamstring Curl
Sets: 3-5
Reps: 15 or more

Bent-over row
Sets: 3-5
Reps: 15 or more

Bench press
Sets: 3-5
Reps: 15 or more

Triceps dip
Sets: 3-5
Reps: 15 or more

Barbell curl
Sets: 3-5
Reps: 15 or more

Hypertrophy Phase

Squat
Sets: 3-5
Reps: 8-12

Hamstring Curl
Sets: 3-5
Reps: 8-12

Bent-over row
Sets: 3-5
Reps: 8-12

Bench press
Sets: 3-5
Reps: 8-12

Triceps dip
Sets: 3-5
Reps: 8-12

Barbell curl
Sets: 3-5
Reps: 8-12

Strength Phase

Squat
Sets: 3-5
Reps: 5-6

Hamstring Curl
Sets: 3-5
Reps: 5-6

Bent-over row
Sets: 3-5
Reps: 5-6

Bench press
Sets: 3-5
Reps: 5-6

Triceps dip
Sets: 3-5
Reps: 5-6

Barbell curl
Sets: 3-5
Reps: 5-6

Rest and Recovery

Now for moves like the hamstring curl, which are single-joint exercises, meaning they work one major body part, new research, published in the Journal of Exercise Physiology, suggests there's a sweet spot for recovery. In the study, 10 trained men performed 3 sets of 10RM biceps curls and machine chest flyes. Each exercise was performed with a different rest period: 1, 2, and 4 minutes for recovery. The shorter rest periods (1 and 2 minutes) hurt the number of reps the guys could bang out early on in the workout; it also lowered training volume over multiple sets for both exercises—so keep this in mind! Longer rests may benefit you in the long run. 

For the rest of the moves, which are compound exercises, meaning they work more than one body part and muscle group, your target amount of rest will vary depending on your goal. Read this definitive guide, which can cater to the hypertrophy and strength phase above (and more).

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