Here's what you need to know...

  1. There are three mechanisms of hypertrophy: mechanical tension, metabolic stress, and muscle damage. If you neglect any one of them, you're leaving a lot of growth on the table.
  2. Mechanical tension equates to muscular force. There's a "sweet spot" shy of the 1RM where mechanical tension is at its highest.
  3. For optimal metabolic stress ("the pump"), maintain constant tension on the muscles by reversing directions just short of lockout or just before bottoming out.
  4. To incur muscle damage, adjust volume according to your training split. Too much will leave you overly sore and unable to recover in time for the next workout.
  5. The most versatile lifts are those that can be manipulated to target each of the three mechanisms. The basic big lifts do the trick.
  6. Use all three of these mechanisms in a single workout, or cycle through them over the course of a week.

The 3 Ways to Grow Muscle

Ask the baddest dudes at your gym for advice on adding muscle and you'll probably get mixed responses.

"Just lift heavy," the powerlifters will tell you.

"Go for the pump," the bodybuilders will say.

"Do something different," the CrossFitters will advise.

There's a good deal of validity to each of these suggestions, but for optimal development you'll need a combination of all three.

In fact, a 2010 review paper by Brad Schoenfeld showed that there are three mechanisms of hypertrophy – mechanical tension, metabolic stress, and muscle damage – which line up neatly with the above maxims.

1 – Mechanical Tension: Go Heavy

Mechanical tension means good old-fashioned heavy lifting. You want to generate the largest muscle force possible through a full range of motion.

You might think that the heavier you lift, the more mechanical tension. That's true only to a certain extent. For example, a 2013 study by Pinto, et al. found that muscle activation in an isometric bench press task topped out at 90% of maximal voluntary contraction.

This finding suggests that most lifters have some "sweet spot" below the one-rep max for which mechanical tension on the targeted muscles is at its highest. Adding additional weight won't increase mechanical tension and may actually shift it away from the desired muscles and onto passive structures or other muscles.

So, the lifters in the study would be better off working at 90% of their max and not more, as they'll be able to perform more reps with the same or higher tension, thereby producing more time under maximum tension.

Finding the Sweet Spot

The sweet spot will vary from person to person and even from lift to lift. For an advanced lifter with favorable anthropometry and strict form on a particular lift, the sweet spot might be on the low end of the 3-8 rep range.

For a less experienced lifter whose form erodes as he goes heavy – or even an experienced lifter whose body proportions aren't ideal for a certain lift – the sweet spot may shift up to the 5-12 rep range.

Some lifts, like rows and hip thrusts, are better suited for slightly higher reps regardless of the lifter's limb lengths and technical prowess.

Hip Thrust

Pilot data has shown that some lifters' glute activation rises almost linearly along with load, whereas some lifters will max out their peak glute activation with as low as 50% of their 1RM.

With these lifters, further increases in load bring about increases in muscle activation in other synergistic muscles, but not the prime movers. However, a recent paper by Vigotsky et al. showed a fairly linear increase in hamstring activation with increasing loads in the good morning exercise, so it all depends on the movement.

How do you know where your unique sweet spot is for a particular movement? Use your intuition, and let technique be your guide. If your form goes to hell or you can't lock a weight out fully, then it's too heavy.

To maximize mechanical tension, strategic pauses can also be implemented, as in the bottom position of the bench press, right after lift-off in the deadlift, and at the end-range of the hip thrust.

Here are the parameters for mechanical tension:

Sets 3-8
Reps 3-8 or 5-12 (depending on the lifter and the lift)
Tempo 2/0/1/0, 2/0/1/3, or 2/3/1/0
Rest 2-3 minutes

Tempo indicate the amount of time in seconds allotted to the eccentric (negative), transition, concentric (lifting), and second transition phases.

2 – Metabolic Stress: Go for Pump and Burn

Metabolic stress is essentially training for the pump or a big burn.

The key is to keep constant tension on the muscles by maintaining a continuous cadence (no rest between reps) and reversing direction just short of lockout or just before bottoming out, depending on the exercise's strength curve.

This way, as blood gets pumped into the muscles by the arteries, the steady muscular contractions will prevent the veins from letting blood escape, resulting in high levels of metabolic stress and cell swelling.

To maintain constant tension on the muscles for exercises with descending or constant strength curves (exercises that get harder or stay the same throughout the concentric phase) like hip thrusts and inverted rows, reverse direction just prior to bottoming out.

For exercises with ascending strength curves (exercises that get easier throughout the concentric phase) such as squats and stiff-legged deadlifts, reverse direction just short of lockout, and add accommodating resistance in the form of bands or chains. For even higher levels of metabolic stress, incorporate strategic pauses in the bottom position of these lifts.

When training for the pump, take sets to momentary muscular failure for moderate to high reps with short rest periods in between.

A pump routine would look like this:

Sets 3-4
Reps 12-20+ (to momentary muscular failure)
Tempo 1/0/1/0 or 2/3/1/0
Rest less than 1 minute

Arnold Biceps

3 – Muscle Damage: Focus on the Negative

Muscle damage corresponds roughly with soreness. It's elicited by slow negatives, extended range of motion, and high tension in the stretched position of the muscle. Variety in exercise selection also does the trick.

Too much muscle damage can be cripplingly counterproductive, though, so training volume must be tuned according to your training split and frequency. If you utilize a body part split where you're working a muscle once a week, go to town with up to five sets of an exercise focused on muscle damage. After all, you have a whole week to recover.

In contrast, if your split requires you to work a muscle or movement multiple times per week, you simply can't afford to get that sore. If your muscles haven't healed by the time you go to train them again, your performance will undoubtedly be impaired.

In this case, to induce a lesser but still significant degree of muscle damage, you might perform as few as two sets of a particular exercise in order to be healed in time to train again in a couple of days.

A muscle damage routine would look like this:

Sets 2-5 (depending on training frequency)
Reps 8-12
Tempo 4/0/1/0
Rest 1-2 minutes

Small Tweaks on the Big Lifts

While certain lifts lend themselves better to one mechanism than the others, the most versatile movements are the ones for which each of the three mechanisms of hypertrophy can be selectively targeted with just a subtle tweak in how you do it.

Lo and behold, the basic big lifts – squat, deadlift, hip thrust, bench press, overhead press, pull-up, and row – are well suited for this very purpose.

Here's a breakdown of the modifications needed for each lift in order to evoke the various mechanisms of hypertrophy. Perform the exercise with the sets, reps, tempos, and additional instructions indicated below.

Regardless of the intended mechanism, perform all exercise variations with a direct focus on the targeted muscle. Never use so heavy a weight that you lose the mind-muscle connection.

Exercise Variation Sets Reps Tempo
Squat
Mechanical Tension Barbell Front Squat 3-8 3-8 2/0/1/0
Metabolic Stress Paused Barbell Front Squat
Reverse direction just short of lockout
3-4 8-12+ 2/3/1/0
Muscle Damage Deep Barbell Front Squat 2-5 8-12 4/0/1/0

Deadlift
Mechanical Tension Dead-Stop Barbell Deadlift 3-8 3-8 2/0/1/2
Metabolic Stress Touch-and-Go Barbell Deadlift
Reverse direction just short of lockout
3-4 12-20+ 1/0/1/0
Muscle Damage Dumbbell Stiff-Legged Deadlift 2-5 8-12 4/0/1/0

Hip Thrust
Mechanical Tension Paused Barbell Hip Thrust 3-5 5-12 2/0/1/3
Metabolic Stress Band or Barbell Hip Thrust
Reverse direction just above the floor
3-4 12-20+ 1/0/1/0
Muscle Damage Barbell Hip Thrust
Use a bench for increased ROM
2-5 8-12 4/0/1/0

Bench Press
Mechanical Tension Paused Barbell Bench Press 3-8 3-8 2/3/1/0
Metabolic Stress Touch-and-Go Barbell Bench Press
Reverse direction just short of lockout
3-4 12-20+ 1/0/1/0
Muscle Damage Dumbbell Bench Press
As large a ROM as comfortable
2-5 8-12 4/0/1/0

Overhead Press
Mechanical Tension Barbell Overhead Press 3-8 3-8 2/0/1/0
Metabolic Stress Barbell Overhead Press
Reverse direction just short of lockout
3-4 12-20+ 1/0/1/0
Muscle Damage Seated Dumbbell Arnold Press 2-5 8-12 4/0/1/0

Pull-Ups
Mechanical Tension Paused Weighted Pull-Up 3-8 3-8 2/0/1/3
Metabolic Stress Bodyweight or Band-Assisted Pull-Up
Reverse direction prior to bottoming out
3-4 12-20+ 1/0/1/0
Muscle Damage Sternum Pull-Up 2-5 8-12 4/0/1/0

Row
Mechanical Tension Pendlay Row 3-5 5-12 2/0/1/3
Metabolic Stress Kroc Row 3-4 12-20+ 1/0/1/0
Muscle Damage Suspension Trainer Inverted Row
Externally rotate the handles during the concentric phase
2-5 8-12 4/0/1/0

Planning Your Workouts

Don't leave growth on the table. You' re probably already doing most of the exercises above. All it takes is a small tweak in execution – be it a longer eccentric phase, the addition of strategic pauses, or an increase in reps – and big gains are yours for the taking.

Because the three mechanisms of hypertrophy feed off one another, it's best to follow a daily undulating or concurrent periodization scheme, as opposed to a linear model.

Undulating Periodization: Cycle through the three mechanisms over the course of a week: one day for mechanical tension, the next for metabolic stress, and the third for muscle damage.

Concurrent Periodization: Emphasize mechanical tension at the beginning of the workout or for the first few sets of an exercise. Then transition to metabolic stress and muscle damage later in the session or on the last couple of back-off sets of each movement.

Related:  More on mechanical tension

Related:  More on the Kroc Row and Pendlay Row