by Christian Thibaudeau
Mechanical and Metabolic Stress for Muscle Growth
Not all muscles respond the same way to lifting. So why train every muscle group with the same methods? Do this instead.
Designing a training program can be daunting when there are a ton of methods to choose from. It’s hard picking among all the cool techniques and loading schemes.
But not all muscles respond the same way to various training methods. If you apply the same methods universally to each muscle group, you’ll end up with less than optimal results.
Why? Some will point out the fiber dominance of each muscle (not all muscles have the same ratio of fast twitch to slow twitch fibers), and there might be some truth to that. But it has more to do with where the tension is in the range of motion, which makes some methods more effective than others.
For example, slow eccentrics/negatives work great on movements like presses, but they won’t be optimal for pulling exercises. For pulling, stato-dynamic methods, including holds at the peak contraction, will be more effective.
Let’s look at some of my favorite methods for chest, shoulders, and biceps. But first, a reminder about the two main hypertrophy pathways. Understanding them will show you why some methods are better than others for different muscles.
Hypertrophy Pathway 1: Mechanical Stress
Here we’re talking mostly about muscle fiber damage and mTOR activation. Essentially, causing some micro-trauma to your muscle fibers and activating mTOR will get your body to rebuild the muscle tissue, adding more protein to the fibers to make them more resilient to future damage. This also makes the muscle fibers, thus the muscle itself, bigger and stronger.
Muscle damage occurs when a muscle fiber is being lengthened/stretched while it’s producing tension. The more tension there is and the more you’re stretching a fiber, the greater the damage will be.
This means three things. First, you need to have a full range of motion. Second, the amount of intramuscular tension (force) has to be higher, so you need fairly heavy weights. And third, the tension needs to still be present when the muscle fibers are lengthened.
Hypertrophy Pathway 2: Metabolic Stress
You can also stimulate growth by increasing the level of local growth factors: anabolic hormones released within the muscles. This is maximized by accumulating a lot of lactate inside the muscle as well as having the muscle lacking oxygen.
To meet those two conditions, you need a fairly long set duration (at least 30 seconds and up to 70) and a constant tension (releasing muscle tension will allow some lactate to get out and some oxygen to get in).
With that out of the way, here’s a kick-ass growth method for pecs, delts, and arm flexors.
Pecs: The 6-12-25 Method
Pectorals have a fairly high ratio of fast-twitch fibers – around 60 percent – and they can easily be stretched under load. This makes both the mechanical stress and muscle damage methods very effective.
On several chest exercises (presses, cable flyes, crossovers, pec deck, dips) you can also keep a high tension on the muscle fibers for most of the range of motion.
You also have options where including a hold at the peak contraction will be effective. As such, the pecs are one of the easiest muscles to train since they’ll respond well to most training methods.
Both mechanical and metabolic stress methods will work equally well. That’s why one of my favorite methods for the pecs is the 6-12-25 method by Charles Poliquin. It uses both the mechanical and metabolic stress pathways.
It consists of a triple set (three exercises done in a row with minimal rest) for the same muscle group. First you go heavy for 6 reps on one exercise, then you do an intermediate rep range (12 reps) with another, and the last exercise you do high reps (25).
It would look something like this:
A1. Dumbbell Bench
Do the eccentric or lowering phase fairly slowly (around 3 seconds). Exaggerate the stretch in the bottom by lifting the chest up and pulling the weights down. Do 6 reps.
A2. Dumbbell Flyes
Don’t go all the way up because there’s no tension at the top. Go from the full stretch to around three-fourths of the way up. Exaggerate the stretch and hold the bottom position for 1-2 seconds per rep. Do 12 reps.
A3. Cable Crossover
Do your reps with an isokinetic method: control both the way down and the way up, then squeeze at the peak contraction for a second or two. Do 25 reps.
Delts: The Gironda 8 x 8 Method
When using pressing exercises to develop the shoulders, you’re focusing mostly on the anterior portion of the delts – a portion already heavily stimulated by any form of bench pressing, dumbbell flyes, or pec decks.
There’s likely no real reason to emphasize the anterior delts. And while you CAN include overhead pressing in your plan, for optimal shoulder development you’ll need some direct work for the medial portion: lateral raises.
But here’s the thing: it’s very hard to make lateral raises effective. All forms of lateral raise are inappropriate with methods focusing on creating muscle damage (fairly heavy weights for 5-10 reps).
Why? Because muscle damage is created when you stretch/lengthen the muscle fibers while they’re producing a lot of tension. During lateral/front raises there’s no tension when the fibers are at their most elongated, thus very little potential for muscle damage.
So you must rely on the metabolic pathway which means going for the burn, bro. Or more accurately, going for the accumulation of lactate and hydrogen ions that will lead to the release of growth factors.
Here’s another thing: the bottom third of the lateral raise is essentially tension-less, or has a very low level of tension. So when “going for the burn,” that relaxation point allows some of these metabolites to exit the muscle, making it harder to accumulate enough to get the growth factor release.
Also, you can easily create just enough momentum in that bottom third (without even realizing it) to reduce tension for most of the range of motion.
That’s why it’s hard to make the standard lateral raise effective. But there are ways to improve it. Here’s how to do your reps:
- Don’t bring your arms all the way down. Stop before your reach that bottom third range to keep tension on the delts.
- Perform the concentric/lifting portion fairly slowly (2 seconds up). Focus on flexing the delts, not moving the weight up.
- Think about pushing the weights away from your side as far as possible. The fact that they go up is a side effect of pushing away. Keep your arms straight, no elbow bend.
- Lift the weights until your hands are in line with the shoulder joint and hold that position for a second.
- Lower the weight under control (2 seconds) and stop before your reach the bottom third.
Yes, the weights you’ll use will be lighter. That’s fine. The metabolic pathway isn’t about lifting heavy or even increasing weight. It’s about accumulating as many metabolites as possible. The more it burns, the more effective it is.
Use all those tips and do the Gironda 8x8 with lateral raises. You’ll do 8 sets of 8 reps with a load you’d be able to lift around 12 times. Take very short rest periods between sets. Gironda recommended 15-30 seconds. (At least shoot for 45 seconds until you’re better conditioned.)
You can also adjust the rest periods during the exercise. For example, you can start with 15 seconds of rest between sets. If by set 4 you don’t think 15 seconds will be enough, and that you’d fail to get 8 reps on your next set, you can rest up to 30 seconds.
Basically, you want to get your 8 sets of 8 with the same weight with as little rest between sets as possible. Get all your reps in while getting a nasty pump. If it doesn’t burn like crazy by set 3, you aren’t doing it right!
Biceps: Mechanical Drop Set Method
Most biceps exercises suck for maximizing muscle damage because, in typical curls, you don’t really reach a stretched position… unless you’re doing curls on an incline bench and really pulling your arms back. But with most free-weight curling exercises, there’s much less tension in the lengthened position.
So, biceps are best trained using the metabolic stress pathway. Mechanical drop sets are a great way to do it. This method consists of combining three variations of the same exercise as a superset. You use the same weight for all variations.
Start with the weakest variation and finish with the strongest. When you can no longer get reps in the first variation, you’ll still be able to get a few in the second movement, then a few more on the third exercise.
It’s similar to a drop set, but instead of dropping the weight, you “drop” to an easier exercise.
Here are a few combos to try:
Combo 1
- A1. Lean-away curl
- A2. Standing curl
- A3. Lean forward curl
Combo 2
- A1. Reverse curl on EZ-bar
- A2. Wide-grip curl on EZ-bar
- A3. Narrow-grip curl on EZ-bar
Combo 3
- A1. Barbell curl, back and triceps on wall
- A2. Barbell curl, back on wall (allowed to move arms)
- A3. Slightly cheated barbell curl
Use a weight you can get 8-12 reps with on the first exercise. Go close to failure on the first two exercises and all the way to failure on the last.
Brachialis: 1.5 Reps Method
If you want big arms, developing the brachialis is a must. This muscle sits underneath the biceps and it’ll thicken up your arms and increase your biceps peak. If you’re lean enough, it’s the golf-ball-like muscle that’ll pop out on the side of your arm.
Here are four characteristics regarding the brachialis and training:
- It’s more active when using a neutral (hammer) grip.
- It responds better to slow contractions. It’s more slow-twitch dominant.
- It responds well to spending more time in the peak contraction since it’s involved in maintaining your arm flexed under load.
- It’s hard to stretch under load, so heavy loading won’t work very well to develop it. We must rely more on the metabolic pathway (longer time under load and constant tension).
For those reasons, my favorite way to develop the brachialis is the 1.5 rep method performed at the top of the range. This means doing the top half of the movement twice on each rep.
Curl the weight all the way up. Bring it down halfway, curl it back up, lower it all the way down. That’s ONE rep.
- Select a hammer curl variation, rope or dumbbells.
- Perform the reps under control, slowly and with constant speed. This is even more important for the half-rep portion.
- Focus on keeping the muscles flexed for every inch of every rep.
Your reps will look like this:
- Curl the weight all the way up in around 2 seconds.
- Bring the weight halfway down slowly.
- Curl it back up, flexing the muscle as hard as you can.
- Bring the weight all the way down in around 2 seconds.
Do 8-10 reps this way.
