Two Types of Hypertrophy For Muscle Growth
Hypertrophy is an increase and growth of muscle cells. Hypertrophy refers to an increase in muscular size achieved through exercise. There are two types of muscular hypertrophy:
- Myofibrillar: growth of muscle contraction parts
- Sarcoplasmic (SH): increased muscle glycogen storage
Skeletal muscles connect to the bones by tendons and are responsible for movement. Bundles of muscle fibres, known as myocytes, make up the skeletal muscles. Each myocyte contains myofibrils that allow the muscles to contract.

Sarcoplasmic Hypertrophy (SH)
The muscles contain sarcoplasmic fluid, an energy resource that surrounds the myofibrils. This fluid includes Adenosine Triphosphate, Glycogen, Creatine Phosphate, and water. During high-volume metabolic-stress-style Resistance Training (RT), more fluid moves to the muscles to provide energy. Sarcoplasmic hypertrophy refers to the increase in the volume of this fluid. It can make muscles appear more prominent, but it does not necessarily lead to an increase in strength.
During this more metabolic-stress training, the volume of the sarcoplasmic fluid in the muscle cells increases, making the muscle volume larger. However, during sarcoplasmic hypertrophy, the size of the fibres does not grow; it is just the fluid.
The illustration below and above shows the Myofibrils as red dots within the muscle fibre and the sarcoplasm as white fluid around them. The sarcoplasm fluid has increased around the myofibrils within the muscle fibre, making the muscle cell larger. Still, the Myofibrils do not grow in size or quantity.

Sarcoplasmic hypertrophy involves the growth of the sarcoplasm and non-contractile proteins (α-actinin, Desmin, dystrophin, Myosins, nebulin, titin, and vinculin) that do not directly contribute to muscular force production. Filament area density decreases while cross-sectional area increases without a significant increase in strength.
Typically, for Sarcoplasmic hypertrophy to occur, resistance training (RT) needs to be higher in volume in terms of the repetitions performed per set (12+ repetitions), the number of sets (3-5 sets), shorter rest intervals (30-60 seconds), and the use of Metabolic Stress Training, also known as Pump Training. These protocols create an environment of sustained tension and metabolic stress within muscles. This stress triggers a cascade of physiological responses that contribute to Sarcoplasmic hypertrophy.
Applying more advanced training principles, such as drop sets, supersets, and cluster sets, or implementing Blood Flow Restriction (BFR) training can increase the rate of Sarcoplasmic hypertrophy.
BFR training is particularly effective for sarcoplasmic hypertrophy as it’s a form of metabolic stress-induced hypertrophy. This training limits blood flow to the working muscles, creating a Hypoxic environment (a reduced tension level or oxygen deprivation). Thus, it intensifies the accumulation of metabolic byproducts such as hydrogen and Lactate. Therefore, enhancing muscular fatigue and cellular signalling pathways related to muscle growth leads to increased sarcoplasmic volume, creating a hypertrophic response.
Myofibrillar Hypertrophy (MH)
The above illustrations of hypertrophy show that the Myofibrils are the red dots within the muscle fibre/Cell, and the sarcoplasm is the white fluid around the myofibrils within the muscle fibre. During Myofibrillar Hypertrophy, the number of contractile units within the muscle (called Sarcomeres) increases in number, size, and strength. The Sarcomeres comprise actin, Myosin, Troponin, and Tropomyosin. They are responsible for muscular contraction based on the process outlined in the Sliding Filament Theory also known as Cross Bridge Theory.
Myofibrils are bundles of Sarcomeres, and Myofibrillar Hypertrophy occurs when these sarcomeres split and grow. This process increases the density and strength of the muscles, allowing them to contract and relax more effectively. Myofibril Hypertrophy happens mostly at Low repetitions with higher loads, commonly ranging from 1 to 6 repetitions per set and above 80% of One Rep Max (1RM). Lower reps with heavier loads lead to MH and an increase in the strength of the muscle fibre contractile units.
Three Mechanisms of Hypertrophy

The conventional hypertrophy model emphasises three significant factors: Mechanical Tension, Metabolic Stress, and Muscle Damage. The generalised ‘Gym Bro-Science’ is Hypertrophy, which is the process by which lifting weights creates microscopic tears, also known as ‘Damage’, in the muscle fibres; the body responds by using the nutrients we consume to repair this damage.
The body fuses the fibres that repair the damaged muscles and grow new muscle tissue. This is the reaction to the stimulus of the weight training (also known as resistance training).
Is this Gym Bro-Science wrong, then? Yes and No. This form of hypertrophy is called Mechanical Trauma (Muscle Damage) and is only one of the three principles of Hypertrophy.
However, the Gym Bro Scientists peddle the narrative that hypertrophy is limited to this—why? It’s easy to simplify the complexity of hypertrophy to their audience: lift weight, damage muscle, repair and rebuild, and come back bigger and stronger. It's simple. Therefore, let’s talk about the first principle of hypertrophy: Mechanical Trauma.
The illustration below outlines the main training variables for each of the Three Mechanisms:

Mechanical Tension: Mechanical stress on the muscle fibres during resistance training
Muscle Damage: Micro-tears and damage to the muscles from the mechanical stress on the muscles
Metabolic Stress: This stress results from the buildup of metabolites during intense resistance training, the most noticeable metabolite being Hydrogen ions.
Mechanical Tension
Mechanical tension hypertrophy is generated using heavier loads (heavy weights) and exercises performed with a ‘Full Range of Motion’ for a period of time. It involves lifting heavier weights and greater mass to create muscle tension with loads between 70-90% of your One-Rep Maximum (1RM).
The rep range should be between 3 and 8 repetitions per set for advanced lifters. For less experienced lifters whose form erodes when lifting heavier loads, it's best to stay between 5 and 10 repetitions per working set. Progressively overloading weight is the most common method used in resistance training to create mechanical tension, whether using a linear, non-linear, or periodised approach.
Studies show that lifting heavier loads leads to a higher protein synthesis response to training than lifters who use lighter loads. Another approach to mechanical tension is that lifting heavier loads is not the desired option—lifting lighter weights to failure. Studies show that lifting lighter, manageable weights to complete failure is just as effective at inducing hypertrophy as lifting heavier weights.
Due to the high levels of resistance and intensity, whether you're using heavier loads or training to complete failure, it’s essential to take sufficient rest intervals longer than the other two principles of hypertrophy, generally between 3 and 5 minutes after each set.
However, the optimal strategy in training is to rotate both methods in your training program to create optimal amounts of tension on the muscle, forcing it to respond to muscle growth. The key points for mechanical tension training
- Full range of motion
- Heavier loads for lower repetitions with longer recovery
- Lighter loads but to total failure
- 3-5-minute rest intervals between sets
2. Metabolic Stress (Cellular Swelling)
This is training for The Pump or ‘The Burn’. Arnold Schwarzenegger was a big believer in and implementer of this form of training during the Golden Era of bodybuilding. This type of training for hypertrophy requires constant tension on the muscles (eliminating any resting between repetitions) with lighter loads performing each set to momentary failure and beyond using techniques such as cluster sets, drop sets or partial repetitions and short rest periods between sets and exercises.
Metabolic stress or cellular swelling is caused by blood pumping into the muscles by the arteries. Steady muscular contractions prevent the veins from letting blood escape, resulting in high levels of metabolic stress and cell swelling, giving that sensation of a pump and burn.
Metabolic Stress hypertrophy occurs when muscles continually contract and relax, creating a blood-pooling effect called cellular swelling. This, in turn, results in restricted blood flow to the muscle (occlusion) and a lack of oxygenated blood to fuel the muscle (Hypoxia) during the continual contractions.
This significantly builds up metabolites like Lactate, Hydrogen ions, and Inorganic Phosphate. The resulting metabolic stress placed on the muscles has an anabolic effect, leading to molecular signalling and an increasing hormonal response by the body. This build-up creates a hostile environment within the muscle, triggering an adaptive response that leads to muscle growth.
The technique to achieve the pump is placing mechanical tension with lower loads/lighter weight for medium to high repetitions, reps performed at a slower tempo with under one-minute rest between sets and/or exercises. This creates the pump, which is the signal of metabolic stress.
Key training points for Metabolic Stress:
Short rest intervals under 60 seconds
Light to medium weight is used as a load
Higher repetitions: 12-25 reps per set
3-4 sets
Slow tempo
Mind-to-muscle connection
Apply advanced training protocols such as drop sets, cluster sets, supersets and pre-fatigue training.
3. Muscle Damage
Muscle damage results from intensive exercise, typically resistance training, which focuses on loading force using mechanical tension onto the muscle fibres. This usually focuses on the eccentric portion of the lift (negative/lowering portion), subsequently causing microscopic tears (or microtrauma) to the muscle. However, both concentric and isometric repetitions performed with proper technique and control cause muscle damage, not just the eccentric portion of a repetition.

This leads to the initiation of a repair process that includes a complex series of events within the body, such as an inflammatory response and protein synthesis, which leads to an increase in muscle.
This process happens post-training. Instead of rebuilding what was before, the body rebuilds the muscles to grow bigger and stronger, making them better adapted to future exposure to stress and more resistant to future loads.
It is said that eccentric training, referred to as Negative Training, is particularly effective in stimulating hypertrophy.
This is because the muscles are more potent in eccentric contraction than isometric or Concentrated contraction, meaning one can lower a heavier weight than one can hold. You can hold a heavier weight than you can lift, so your muscles can generate maximum force under eccentric conditions.
The familiar sensation from muscle damage is ‘D.O.M.S’, known as delayed-onset muscle soreness. This soreness is often experienced in the days following a training session and is a vivid manifestation of muscle damage.
Muscle damage is the most prominent theory about the cause of hypertrophy. It was the first theory about the science of muscle growth, from which the classic expression in bodybuilding comes: “Break a muscle down and build it up stronger and bigger.”
Key training points for Muscle Damage:
2-3 sets
8-12 repetitions per set
Tempo: 2/1/4/0 (the 4-6 second eccentric is determined based on how many repetitions and sets are performed)
60-90 second rest between sets
Focus more on the eccentric portion of the lift, but don’t neglect the concentric or isometric portion.
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