Here's what you need to know...

Progressive overload is essential, but heavier weights alone won't build the biggest muscles. To signal hypertrophy, you must manage two things: mechanical tension and metabolic stress. To utilize both mechanisms for growth, rotate lifts, incorporate variety, and get strong in low, medium, and higher-rep ranges.

We all want bigger muscles, and to build bigger muscles we need to get stronger – much stronger. Gaining strength through progressive overload ensures that we continue to place more tension on the muscles over time, forcing them to adapt by growing larger. Heavier weights equals greater tension, which equals bigger muscles. Got it? Great!

However, heavier weights alone will not build the biggest muscles. Powerlifters lift heavier weight than bodybuilders, thereby placing greater tension on their musculature compared to bodybuilders. Yet despite this greater tension, bodybuilders are still bigger. If tension were the be-all-end-all, powerlifters would out-muscle bodybuilders.

We can't say it's just the drugs – both types of lifters take anabolic steroids. Natural bodybuilders are still bigger than natural powerlifters, and when powerlifters want to build more muscle, they borrow methodology from bodybuilders by employing higher-rep assistance lifts with shorter rest times in between sets.

2 Mechanisms for Muscle

There are two primary mechanisms to gaining muscle:

Mechanical tension Metabolic stress

To many lifters, these mechanisms make good sense as it jibes with personal experience. However, to many others, the list is a bit abstract. Let's talk about these mechanisms in plain and simple language.

Mechanical Tension

Sometimes when you're lifting heavy weights, you might feel like a muscle is about to rip off a bone. This is mechanical tension. If you place tension on a muscle by stretching it passively (without letting it contract), the source of tension is called passive elastic tension.

If you place tension on a muscle by flexing it as hard as possible through an isometric contraction, the source of tension is known as active tension .

When you lift weights through a full range of motion, the muscles are placed under a combination of passive and active tension because they're being stretched while being activated.

Research shows that dynamic movements are superior to both stretching and isometrics for hypertrophic gains, so tension alone won't deliver maximum muscle growth. Tension through a full range of motion is what builds maximum muscle.

Furthermore, time under tension (TUT) is another important factor to consider. Performing one maximal contraction once every two weeks will not yield maximal hypertrophic gains – it's just not enough of a stimulus to optimize anabolic processes. The muscles need ample signaling to grow larger.

Metabolic Stress

Think about the feeling you get when you know you're really targeting a muscle – that burning sensation you elicit and the pump that you achieve. These are two mechanisms that fall under the umbrella of metabolic stress .

Metabolic stress is brought about by several factors, including:

The occlusion of veins by persistent muscle contractions, which prevents blood from escaping.

The hypoxia or lack of oxygen supply in the muscles due to the trapping of blood.

The build-up of metabolic byproducts such as lactate and the increased hormonal surge.

The cell swelling or "pump" of the muscles, also due to the pooling of blood.

These factors aid in building muscle and are synergistic with tension and progressive overload. These factors also help explain why Kaatsu (occlusion) training is highly effective at inducing hypertrophy despite the lower levels of muscle tension, at least when compared to traditional resistance training.

Signaling Muscle Growth

This part will be a bit sciencey, but stick with me. Mechanical tension and metabolic stress are interrelated and signal hypertrophic responses through multiple pathways.

For example, a high magnitude of active tension at longer muscle lengths creates the greatest hypertrophy effect. In other words, tension has the greatest effect when muscle is stretched while being activated.

Here's another example. High tension through a full ROM is very effective at producing metabolic stress due to the prolonged muscle contractions that occludes the veins, which leaves no time for blood to escape the muscles and ultimately causes the pump effect.

A pump actually places the myocytes under tension due to a swelling effect exerted on the muscle cell membranes, which is theorized to lead to greater muscle growth due to the perceived threat on the cells' ultrastructures.

So constant tension and greater TUT are very effective at inducing metabolic stress, assuming muscle activation is high enough to occlude the veins.

Both mechanisms can increase satellite cell (muscle stem cells) activation as well as activation of the important mTOR pathway. As you can see, the two mechanisms are highly interrelated.

Practical Applications

Many coaches argue that progressive overload through low-rep training on the basic barbell lifts is sufficient for building maximal hypertrophy. The reason this advice is so effective is because many individuals don't quite grasp the importance of gaining strength for muscle growth.

However, low-rep training alone is not sufficient for maximal gains. There are many neural (non-hypertrophic) mechanisms through which a muscle can grow stronger without getting larger. This is a key facet of powerlifting, whereby lifters learn how to maximize strength by way of gains in nervous system efficiency and coordination.

If your goal is to build maximum muscle, you don't want to rely solely on neural improvements for strength gains – you want your hypertrophic gains to mimic your strength gains.

Therefore, be sure to rotate lifts, incorporate variety, and get strong in low, medium, and higher-rep ranges.

Pick the Right Tool for the Job

Some exercises are better than others at eliciting a pump and some exercises are better than others at creating tension in a muscle or a particular subdivision of a muscle.

In general, performing squats, deadlifts, hip thrusts, bench presses, military presses, chin-ups, and rows will ensure that you're maximizing mechanical tension across the various muscle groups.

However, one exercise alone will not maximize tension on the entire spectrum of fibers within a muscle. Exercises such as incline presses, dips, curls, shrugs, delt raises, leg presses, and glute-ham raises can and should be employed for maximum muscle growth since they target unique fibers compared to the big basic movements.

Furthermore, variations of the big lifts such as front squats, sumo deadlifts, close-grip bench presses, and pull-ups can and should be performed as well.

Movements that either place constant tension on a muscle or place the greatest tension on a muscle at shorter muscle lengths (in a contracted position) are best suited for creating a pump.

For this reason, exercises like the pec deck, pullover machine, leg extension, leg curl, back extension, barbell glute bridge, lateral raise, concentration curl, and rope triceps extension are valuable. When done for medium to high reps with short rest periods and multiple sets, they can produce a skin-splitting pump.

Movements that place the greatest tension at long muscle lengths (in a stretched position) are best suited for creating mechanical tension for hypertrophy. For this reason, exercises like chest flies, pullovers, lunges, Romanian deadlifts, good mornings, incline dumbbell curls, and overhead cable triceps extensions are valuable.

However, there's a fine line between optimal training loads and creating excessive damage in the muscle.

Damage is overrated and can easily do more harm than good if it interferes with strength gains and training frequency. Feeling a bit of soreness the following day or two is fine, but barely being able to sit down, or feeling like a muscle is going to pull from a simple activity, is overkill.

As the saying goes, stimulate, don't annihilate.

Action Plan

Noted gym scholar Ronnie Coleman said it best: Everybody wanna be a bodybuilder, but nobody wanna lift no heavy-ass weight.

Getting a pump and feeling the burn are easy, but getting stronger year in and year out is hard work. Setting PR's requires focus, determination, and consistency.

For this reason, reserve most of your mental energy for getting stronger. After you've warmed up and have begun your training session, start off with your heavy compound movements and try to set PR's. Rest fully in between sets and psyche yourself up appropriately.

After the heavy work is done, it's time to have some fun. Choose some targeted movements and seek the pump and burn. Don't work yourself up too much mentally, just bust out some medium to high rep sets with short rest periods. Don't be overly concerned with setting PR's during pump work. Focus on feeling the targeted muscle taking on the brunt of the work and fully fatiguing the fibers.

The majority of your mental energy should be focused on gaining strength through the big basics such as squats, deadlifts, hip thrusts, bench press, and chin-ups. However, some of your mental energy should be focused on muscle activation and inducing metabolic stress.

Becoming freakishly strong at the big basics through a variety of rep ranges might be the source of 80% of your hypertrophy gains over time, but if strength alone is your sole endeavor, you'll likely leave 20% of room on the table for maximum muscularity. The increased satellite fusion, hypoxia, occlusion, and cell swelling that accompanies pump and burn type training provide the icing on the cake, and this adds up over time.

Sticking to solely heavy work or solely high-rep work won't build the optimal physique. You need the best of both styles of training if you want to reach your maximum muscular potential.

Summary

For making maximum gains, muscles don't just respond to tension, they also need metabolic stress. So bust out your heavy work first during your workouts then switch to lighter movements and focus on inducing metabolic stress.