Muscle Fibers: Principles of Hypertrophy

Author: Nikita Rungta,

Visiting Faculty, INFS


Key Points:

  • Muscle fiber is an important component because muscles are made of numerous muscle fibers. There are two kinds of muscle fibers and training each one is equally important
  • Muscle can be developed with the help of resistance training which provides a number of benefits including increased muscle size, fat loss, etc.
  • Progressive lifting, Muscle damage, and Muscle stress helps in building lean muscle mass and reduce fat

Keywords: Muscle, fiber, Type, hypertrophy, contraction

  1. Introduction to muscle mechanics

Skeletal Muscle is one of three major muscle types, the others being cardiac muscle and smooth muscle. It is a form of striated muscle tissue which is under the willful command of the somatic nervous system. A skeletal muscle refers to multiple bundles of cells called muscle fibers (fascicles). Muscle fibers are the cells or essential building block of the muscle. There are various kinds of muscle fiber, each intended for a particular sort of muscle movement. Some muscle fibers are useful for an endurance workout, other work best for the short blasts of strength workouts. Muscles are made of numerous individual muscle fibers. Muscle fibers are long, barrel-shaped cells giving skeletal muscles their striped or striated appearance. They are also in charge of muscle contraction.

      There are two kinds of muscle fibers 

(A)Slow-twitch fibers also called ST or Type I fibers. ST fibers have a slow contraction time, but a high resistance to fatigue. These muscle fibers use aerobic respiration for energy. This provides for their high level of endurance. Slow-twitch muscles are used for aerobic activities requiring a low exertion level over a long period of time. A person uses slow-twitch muscles for activities such as sitting or walking.

(B) Fast-twitch fibers, also called FT or Type II fibers, have a quick contraction time but are quick to fatigue. These muscle fibers use anaerobic respiration for energy and are used for anaerobic activities requiring a high-force, such as sprinting or jumping. There are three different types of fast-twitch muscles:

  • Type IIa muscle fiber has a moderately fast contraction time and a relative long resistance to fatigue
  • Type IIx muscle fiber has a fast contraction time and a moderate resistance to fatigue
  • Type IIb muscle fibers have a very fast contraction time but tire very quickly.

Each muscle fiber is a single cell which constitutes:


  • Sarcolemma – it is the membrane surrounding the muscle fiber.
  • Nuclei – the brain of the cell, controlling its function.
  • Myofibrils – it contains the proteins that produce the contraction force. These myofibrils are packed with proteins and energy sources to support muscle contraction.
  • Sarcomeres – these are the basic contractile unit of the muscle.
  • Mitochondria – this provides chemical energy to the cell, supporting all cellular activity. Together these components form the muscle fiber cell and provide for muscle contraction.

2. Lifting weights

Resistance training is a form of exercise that requires the use of resistance to increase muscle size and strength. Well known equipment used are weights, dumbbells, and barbells. During resistance training exercise muscle fibers are broken down and in the days following the workout the fibers repair and grow stronger to meet the demands that have been placed on it. Therefore rest days are as important as the exercise itself. In fact, it acts as a medicine for reversing many diseases

What happens when you lift weights?

You get bigger and stronger – As we know, resistance training results in an increase in the muscle size (and consequently strength) and this can occur primarily in two ways: 27658388_10212702176884164_1277478070_n (1)Hypertrophy – Muscle hypertrophy involves an increase in the size of skeletal muscle through a growth in the size of its component cells. Two factors contribute to hypertrophy: sarcoplasmic hypertrophy, which focuses more on increased muscle glycogen storage; and myofibrillar hypertrophy, which focuses more on increased myofibril size

Hyperplasia – It is an increase in the number of muscle fibers due to some type of stimulus. In most discussions that stimulus is exercise. Specifically, resistance exercise. However, it’s unclear if hyperplasia actually occurs in adults but some studies have suggested that long-term strength training might actually result in hyperplasia. 

Your mind gets better – Resistance training results in a number of central nervous system adaptions as well. When a force is applied to a muscle, a signal is transmitted that activates the muscle cells. When a person performs resistance training, the number and intensity of signals that are transmitted to that muscle are increased until the muscle gets tired. The two neurological factors that govern muscle force are motor unit recruitment and rate coding. The former is simply the size of the muscle force created by the muscle contraction for a given task. During resistance training, the muscles grow more tired with each repetition of a given movement pattern, and, as a result, the rate coding becomes impaired and the firing sequence becomes less and less precise.

Laws of Building Muscle

  1. Progressive Overload – This refers to increasing tension levels in the muscle fibers over time. Effective ways to do this progressively are by either increasing the amount of weight that a person lifts or by increasing the number of reps done in a particular set or by increasing the number of sets done. The human body adapts to the changes that it is made to follow and unless we force it to stress, it won’t change. This helps in gaining strength and power over a shorter period of time.
  2. Muscle Damage – This refers to the actual damage caused to the muscle fibers by high levels of tension. This damage necessitates repair, and if the body is provided with proper nutrition and rest, it will adapt the muscle fibers and help to deal in a better manner with future stimuli.
  3. Metabolic Stress – This refers to pushing muscle fibers to their metabolic limits through the repetition of actions to muscular failure. This helps to increase the size of the muscle fiber and contributes to lean body mass and also helps in reduction of body fat percentage. Such a lifting strategy helps people of all age groups including senior citizens.
  4. Muscle Memory – The body and the mind are always being challenged. When doing new or varying exercises, neural circuits are being formed and strengthened. This is because while new movements stress the muscles in a new way, they are also connected to the spine and brain, which have to learn the movements as well. The neural circuits formed are a large part of the workout. They are the reaction to a movement you want the muscle to do, while the muscle simply moves the load.


According to Heymsfield, 30 to 40 percent of a healthy person’s body mass is made up of skeletal muscle. It is important for each individual to maintain this and to try to increase it and simultaneously reduce fat. This can be effectively attained if a person follows resistance training regime diligently and keeps progressing it over a period of time. Such an exercise pattern helps to increase muscle size as well increase the number of cells, helps reduce body fat levels, fights against lifestyle disorders and makes a person fit. With resistance training, equal emphasis should be placed on nutrition, rest and recovery so that maximum benefits can be attained.


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