Do You Need To Lift Heavy To Build Muscle Mass

One of the most commonly debated topics in gyms around the world is whether lifting heavy is the only way to build muscle.

According to this well-established theory, as you train you must progressively add more resistance to effectively promote muscle growth.

Otherwise, you will remain small and weak. 

That old-time concept, known as the principle of progressive overload, remains prevalent even to this day and according to exercise physiology is partly true [2, 3].

The basic premise of this theory is that according to the law of “stress and adaptation”, if the next training session does not exceed the previous training stimulus, no positive physiological changes will manifest.

This notion of “lift heavy to grow big” also supports that the greater the resistance/stimulus applied to a muscle, the more muscle fibers get destroyed, thereby the more muscle growth is achieved.

However, as with most things that look good in theory, in real life this phenomenon is not completely accurate.

There are many other parameters also contributing to muscular development.

According to the classic hypertrophy model, there are 3 major factors necessary for increasing muscle mass [4]:

1) Mechanical tension (physical force applied to muscle fibers)

2) Metabolic stress (overproduction of metabolic byproducts in muscle cells, such as creatine kinase, reactive oxygen species, ADP, chloride, potassium, hydrogen ions, lactic acid and inorganic phosphates)

3) Muscle damage (microscopic damage on muscle fibers and/or connective tissue inside and around the muscle)

The commonly-established principle of progressive overload mainly refers to the first major factor, that is progressive mechanical tension.

As you see, however, there are also other mechanisms by which muscle growth is facilitated.

Applying some of the below modifications in your training routine can safely and effectively increase your gains without the need to increase your loads:

A) Performing exercises with slow reps, perfect form, and no cheating (increased time under tension which equates to more metabolic stress)

B) Altering the number of sets, repetitions and rest times (potentially increased metabolic stress and muscle damage)

C) Adding in more exercises (increased training volume and variety which provokes both more metabolic stress and muscle damage)

D) Adopting a fundamentally different training protocol (i.e., body part split to full-body training)

From a physiological point of view, there is actually no real, direct relationship between muscle strength and muscle size.

Yes, muscle strength affects (to an extent) how much muscle you carry, but it is not the sole determinant.

A good real life example showcasing this is Olympic weightlifters.

A lightweight Olympic weightlifter may weigh only 61 kg but be able to Snatch 140 kg or Clean and Jerk 160 kg- a ridiculous amount of weight compared to his body weight and muscle size. 

Another example is bodybuilders.

If someone observes how they train, even during their off-season (loading period), he may very well notice that they typically go for lighter weights despite their hulky appearance.

Despite that, they are able to achieve the astounding musculatures they present on the competition stage.

It goes without saying that exogenous anabolic hormones are a big component of bodybuilding and that these substances have been shown in multiple instances to significantly increase muscle growth and strength.

However, anabolic steroid hormone administration alone can not make a person look super muscular without corresponding training and adequate protein and caloric intake [5].

Lifting heavy and chasing strength will not sabotage someone’s muscle-building efforts and can often offer great benefits when it comes to increasing muscle size, but there is another way that includes lighter weights as well.

In some instances, like when musculoskeletal injuries are present, it’s actually necessary for someone to include other muscle hypertrophy approaches in his training routine.

Nonetheless, to further elucidate this topic we need to dig into the anatomy and physiology of skeletal muscles.

There is no rule saying that you can’t get big without lifting heavy.

Muscle Tissue Consists of 3 Types of Fibers

Skeletal muscles, like all organs, are made up of cells.

In this case, we are talking muscle cells or muscle fibers which themselves are consisted of protein bundles, called myofibrils.

Myofibrils are similarly made up of long proteins called actin, myosin, and titin, along with other protein structures holding them together.

Muscle fibers may be assigned to 3 different identity classifications, with characteristic movement rates, response to neural inputs, and metabolic types [6].

These 3 taxonomies include : 

1) Type I (Slow-twitch muscle fibers): They are the first ones to get activated when we do something simple, like lifting a glass of water.

They work predominantly during endurance exercises, like swimming, cycling, marathon or distance running.

They require the presence of oxygen in order to produce energy (aerobic metabolism).

2) Type IIa (Fast-twitch muscle fibers): A mix between Type I and Type IIb.

They are mainly active during anaerobic exercises, like weight lifting.

They produce energy with or without the presence of oxygen (aerobic and anaerobic metabolism).

3) Type IIb or IIx (Fast-twitch muscle fibers): They partake in very explosive physical movements, like sprinting, powerlifting, jumping, and strength training.

They don’t require oxygen to produce energy (anaerobic metabolism).

Type IType IIaType IIb (or Type IIx)
Slow and weak contractionsFast and strong contractionsVery fast and strong contractions
Cost-effectiveNot so cost-effectiveNot cost-effective
Low power outputHigh power outputVery high power output
Resistant to fatigueMedium resistant to fatigueNot resistant to fatigue
Rich in mitochondria, myoglobin, and aerobic enzymes Rich in glycolytic enzymes and poor in mitochondria  Rich in glycolytic enzymes and very poor in mitochondria  
Rich blood supply (a lot of capillaries)Medium blood supply Small blood supply
Oxidative metabolismOxidative and glycolytic metabolismGlycolytic metabolism
Muscle Fiber Types and Characteristics
muscle fiber typology

NOTE: One common aspect of training for muscle mass and muscle strength is that in both cases the focus is on Type IIa and IIb fibers, since both are 50% more amenable to hypertrophy than type I [10].

What Determines The Fiber Type Composition of Each Muscle

Each muscle contains a specific percentage of muscle fibers due to evolutionary reasons [7].

The human body is a cost-effective, survival bio-machine that always wants to spend the least amount of energy for any activity, including movement.

Therefore, it has adapted through time to function in this manner.

A good example of this is our core muscles, like the abdominal complex or the erector spinae, which are muscles that work constantly to support and stabilize the whole body.

These muscles need to be very rich in Type I fibers, because Type I fibers require the least energy, get easily activated and fatigue slowly, thereby increasing our chance of survival [8, 9]

The muscle fiber type composition of any muscle is mainly dictated by our genetics and determines how strong and powerful that muscle will be [11].

A person may be born with very strong legs, being able to squat 300 pounds like it’s nothing, while another individual may struggle to squat his own bodyweight even once.

Put simply, inherited genetic characteristics are a big contributor to strength, as some people are gifted with more type II than type I fibers.

These individuals are predetermined from birth to excel in anaerobic type activities, like sprints and weight-lifting.

Proper training can change that muscle fiber type percentage, also know as contractile phenotype, to an extent, even though science hasn’t still grasped exactly how this conversion works.

Speculations about the effects of neurotrophic factors, motor neuron electrical activity, or specific hormonal stimulation have been made [12].

If someone trains in a way that his body eventually has to change its muscle fiber typology in order to adapt (and consequently survive), then it will do so.

That’s because the body is always thinking in terms of survival.

Someone who runs marathons on a regular basis, essentially “commands” his muscles to change, by transforming some type IIa fibers to type I.

It’s worth noting that muscle fibers can change “type”, but most likely cannot increase in number (hyperplasia).

Hyperplasia represents an increase in the number of muscle fibers, whereas hypertrophy involves an increase in muscle fiber size.

Most scientific papers showcase that hyperplasia can occur only with exogenous administration of human growth hormone (HGH or myostatin inhibitors (like GDF-8), or via gene doping, and it requires the partaking of myosatellite cells (undifferentiated muscle cells) [13, 14].

Myosatellite cells are muscle stem cells that act as a reserve, proliferating in cases of muscle injury.

Their function includes aiding the muscle tissue regeneration process when necessary.

Formation of a nucleate skeletal muscle fiber

The muscle fiber type composition is mainly dictated by our genetics and determines how strong and powerful a muscle is.

Can you Build Muscle Strength Without Building Muscle Mass

Techically, yes and no.

Increasing your muscle mass, also known as muscle hypertrophy, is the enlargement of muscle fibers, and can be divided into two categories.

Each category produces different results with regards to visual appearance and performance.

Sarcoplasmic Hypertrophy (Muscle Mass)

The first one, called sarcoplasmic hypertrophy, results from an increase in the volume of the sarcoplasmic fluid inside the muscle cell.

Muscle cells, like every type of cell, have cytoplasm- a thick solution that fills the cell inside the cell membrane.

When the volume of that fluid/solution is increased, we have sarcoplasmic hypertrophy.

The cytoplasm of muscle cells is called sarcoplasm.

The cytoplasm is a colloidal fluid enclosed inside the cellular membrane, consisted of 90% water and 10% mixture of organic & inorganic compounds, such as various salts, proteins, fats, and nucleic acids.

This type of hypertrophy can be facilitated with zero or very little increases in strength, and it is the kind of muscle growth bodybuilders focus their efforts on, since it creates an inflated and “pumped” muscular appearance.

Sarcoplasmic hypertrophy essentially results from the retention of water, glycogen, nitrogen, creatine and other micronutrients, inducing cell swelling.

It shall be deemed an artificial type of muscular development, since you are essentially trying to make muscle cells appear bigger by increasing their fluid content.

In sarcoplasmic hypertrophy, there is a small or no increase in the thickness and number of myofibrils, the contractile and structural proteins of muscle cells, namely, actin and myosin. 

Myofibrillar Hypertrophy (Muscle Strength)

The second type, called myofibrillar hypertrophy, is the one powerlifters and Olympic weightlifters focus on, and includes an increase in the size, number, and density of myofibrils (the contractile proteins of muscle fibers).

People who direct their efforts solely on myofibrillar hypertrophy look smaller than people focusing on sarcoplasmic hypertrophy, but are stronger, more functional, and more athletic.

This type of muscular development can be achieved by putting muscles under extreme mechanical stress, which forces them to adapt in order to withstand bigger loads in the future.

As a response to this, muscles end up much stronger and slightly larger.

The Nervous System is a Big Contributor to Muscle Strength But Not So Much To Muscle Mass

Why are some people extremely strong, but don’t look very muscular?

They have a very efficient nervous system!

The nervous system regulates every single movement performed by the body.

When someone begins to train, he notices that “size” comes a bit later than expected.

What happens first is an increase in strength [16].

In the beginning, the body is being accustomed to the increased neuromechanical stress that receives through exercise by developing previously inactive as well as new neuromuscular junctions [15]

Neuromuscular junctions are chemical synapses or “bridges” between the nervous and muscular system.

Through them, action potentials generated by the brain are transmitted, reaching the muscles and causing them to contract.

Any changes happening on them can impair or improve muscle contractility, and thus muscle strength.

In plain words, what happens initially when someone starts to lift weights is the creation of new communication channels between the brain and muscles, improving neuromuscular efficiency and high force production.

In practice, this translates to increased muscle strength after 2 or 3 workouts, but increased muscle size after 2 or 3 months!

That’s the first big difference between these two training adaptations.

Some people may also have the tendency to gain strength at a much faster rate than others, not solely due to a more rapid increase in their lean body mass, but due to superior neuromuscular efficiency.

Superior neuromuscular efficiency means 1) More neuromuscular junctions 2) Better electrical signal transmission (no interceptions across the neural signal transduction pathways) 3) Stronger and more frequent action potentials coming from the brain. 

Sarcoplasmic Hypertrophy Protocols Build Muscle Mass

In general, a training protocol for maximizing muscle mass (sarcoplasmic hypertrophy) consists of 6-12 reps, 60-85% 1RM (1 rep max), 3-6 sets per exercise and 60-120 secs. rest between sets.

Training frequency should range from 3 to 6 times per week and the training duration should last 60-70 minutes.

Even though there are no clinical studies on the exact time, after about the 60-minutes mark there is a significant spike in blood cortisol levels, which is an anti-inflammatory and catabolic (muscle eating) hormone.

Prolonged periods of high-intensity exercise can deplete glycogen stores from the liver and muscles, inducing a big increase in cortisol, which stimulates proteolysis (the breaking down of proteins) [17].

Concerning exercise selection, for optimal results you should focus on compound, multi-joint lifts, like the deadlift, squat, military press, and bench press.

Multi-joint exercises are more beneficial than single-joint/isolation exercises, such as leg extensions, because they engage multiple muscle groups at a time.

Multi-joint exercises will make you stronger, increase your maximal oxygen consumption (VO2max), strengthen your bones and joints (osteogenic effect), help you burn more calories, mimic real-life movement patterns (making you more functional), and address muscle imbalances [18, 19, 20, 21].

Myofibrillar Hypertrophy Protocols Build Muscle Strength

If your main focus is to maximize strength, then 1-6 reps, 85-100% 1 RM (1 rep max), 3-4 sets per exercise, and 2-5 minutes rest should be the foundation of your training routine.

Training duration, again, should be preferably around 60 minutes, and training frequency around 3-4 times per week.

Heavy weights tend to build powerful, thick and dense muscles, but overwork the joints, wearing you out quickly and reducing your “gym lifespan”.

A critical thing to also take into consideration, if you go the “heavy route”, is to allow your CNS (Central Nervous System) to recharge every now and then.

That means not to lift heavy all the time, because your Central Nervous System (CNS) will get fatigued.

CNS over-taxation is a very misunderstood concept in the fitness world, and some people falsely consider it to be a myth [22].

From an exercise physiology perspective, CNS fatigue refers to a reduced ability of muscles to contract, either maximally or submaximally, and occurs because:

1) The neurons innervating the muscles (motor neurons) receive and thereby transfer weaker electrical signals, resulting in reduced muscular electrical stimulation and force production.

2) The motor neurons themselves resist incoming signals from the brain, leading to reduced electrical transmission to muscles, who respond by producing less force.

3) The motor neurons receive a “command” from the motor centers of the brain’s cortex to halt their function [1].

If you want to experience CNS fatigue you may just go and perform heavy deadlifts after a night of no sleep.

Even if your caloric intake is perfect, you will still notice that you are weaker than usual.

Sleep is the primary method your body uses to heal and rebuild your CNS (Central Nervous System).

It achieves that by cleaning up cellular debris and creating new neurons (neurogenesis) in your brain [23].

Prolonged fasting also carries that benefit [24].


While muscle strength and muscle mass do not have a direct one-to-one relationship, there is a definite correlation between the two.

The biggest contributors to muscle strength (myofibrillar hypertrophy) are muscle fiber typology and the state of the nervous system.

On the contrary, muscle mass (sarcoplasmic hypertrophy) is primarily dictated by the size (volume) of muscle fibers.

When the aim is to get thick and strong, heavy loads with periodical tapering to restore CNS function appears to be a great strategy [25].

If the goal is to exhibit the distinctive “pumped and veiny” look, then lighter weights with higher reps, volume and frequency is the way to go [26]

Optimally, someone should look as strong as he actually is, so mixing sarcoplasmic and myofibrillar hypertrophy principles in your routine seems to be the best of both worlds.

PS. If you haven’t already, you may check out our Recommendations List for high-quality supplements, health products and services you can trust. There is probably nothing health-related you won’t find there + special discount codes are waiting for you.

You May Also Like

About George Kelly




This content is for informational and educational purposes only. It is not intended to provide medical advice or to take the place of such advice or treatment from a personal physician. All readers/viewers of this content are advised to consult their doctors or qualified health professionals regarding specific health questions. Neither Metabolic Body nor the publisher of this content takes responsibility for possible health consequences of any person or persons reading or following the information in this educational content. All viewers of this content, especially those taking prescription or over-the-counter medications, should consult their physicians before beginning any nutrition, supplement or lifestyle program.