Myofibrillar Hypertrophy

Myofibrillar hypertrophy refers to an increase in the size and density of myofibrils, the contractile components of muscle fibers responsible for force production. Unlike other forms of hypertrophy that emphasize cellular volume, myofibrillar hypertrophy primarily enhances muscle strength and contractile efficiency.

What Is Myofibrillar Hypertrophy?

Myofibrillar hypertrophy is the adaptation characterized by an increase in the number and thickness of myofibrils within a muscle fiber.

Myofibrils are composed of repeating units called sarcomeres, which contain actin and myosin filaments. These structures are directly responsible for muscle contraction and force generation.

In simple terms:

More myofibrils = greater force potential
Denser contractile tissue = stronger muscle without excessive size increase

This type of hypertrophy is commonly associated with strength-focused resistance training.

How Myofibrillar Hypertrophy Influences Muscle Growth

Muscle hypertrophy occurs when training imposes sufficient stress to disrupt muscle homeostasis, triggering adaptive remodeling.
In the case of myofibrillar hypertrophy, the primary driver is mechanical tension.

Key mechanisms include:

High force production across muscle fibers
Recruitment of high-threshold motor units
Structural remodeling of contractile proteins

Unlike sarcoplasmic hypertrophy, which increases non-contractile components, myofibrillar hypertrophy improves the muscle’s ability to produce force per unit of size.

This makes it particularly relevant for athletes where strength-to-weight ratio is critical.

Practical Applications in Hypertrophy Training

To prioritize myofibrillar hypertrophy, training should emphasize high mechanical loading and performance progression.

Common training characteristics:

Moderate to heavy loads (typically >70% 1RM)
Lower to moderate repetition ranges
High intent to produce force
Progressive overload over time

While myofibrillar hypertrophy is often linked to strength training, it is not exclusive to powerlifters.
Bodybuilders, athletes, and recreational lifters all benefit from periods of training that target this adaptation.

Importantly, myofibrillar hypertrophy contributes to long-term hypertrophy sustainability by increasing the muscle’s capacity to handle higher volumes later on.

Common Mistakes and Misconceptions

“Myofibrillar hypertrophy doesn’t increase muscle size”

This is incorrect.
While size increases may appear slower compared to sarcoplasmic-focused training, myofibrillar hypertrophy still contributes to visible muscle growth.

“It only happens with very low reps”

There is no strict repetition cutoff.
Myofibrillar adaptations can occur across a wide range of rep schemes as long as mechanical tension is high.

“You must choose between myofibrillar and sarcoplasmic hypertrophy”

In reality, both adaptations occur simultaneously.
Training emphasis may shift the ratio, but complete separation is biologically unrealistic.

Interaction With Other Training Variables

Myofibrillar hypertrophy does not exist in isolation. Its development depends on how other training variables are managed.

Training Volume

Excessive volume without sufficient load progression may reduce the stimulus for myofibrillar growth.
Learn more in our guide on training volume for hypertrophy.

Training Intensity

Higher relative loads increase motor unit recruitment, a key factor in myofibrillar adaptations.
This relationship is explained further in training intensity for hypertrophy.

Rest Periods

Adequate rest between sets allows performance maintenance, which supports higher force output per set.
Short rest periods may compromise this stimulus.

Evidence-Based Summary

Myofibrillar hypertrophy increases the density and size of contractile muscle proteins
It is primarily driven by mechanical tension and force production
It contributes significantly to strength and long-term muscle development
It often develops alongside sarcoplasmic hypertrophy, not independently
Periods emphasizing myofibrillar adaptations can improve overall hypertrophy outcomes