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Hyperplasia is the increase in the number of muscle fibres, which results in an increase in muscle strength. It is one of the two mechanisms that allow the increase of muscle mass, the other being hypertrophy, which is the increase in the thickness of muscle fibres. Hyperplasia has been observed in several animal species, including birds, mice, cats, and fish. However, the occurrence of hyperplasia in humans is still a subject of debate due to limited evidence. While some studies suggest that bodybuilders exhibit hyperplasia, others attribute muscle growth in humans primarily to hypertrophy.
| Characteristics | Values |
|---|---|
| Definition | Hyperplasia is the increase in the number of muscle fibers. |
| Visuals | Hyperplasia and hypertrophy would look very similar aesthetically. |
| Occurrence in Humans | There is a lack of evidence and ongoing debate about the occurrence of hyperplasia in humans. |
| Occurrence in Animals | There is evidence of hyperplasia in birds, mice, cats, and fish. |
| Models for Study | Three models used to study hyperplasia are compensatory hypertrophy, stretch, and exercise. |
| Muscle Enlargement | Muscle enlargement can be attributed to hypertrophy or hyperplasia. |
| Muscle Strength | An increase in the number of muscle fibers leads to increased muscle strength. |
| Training | Progressive overload, strength training, and resistance training are associated with muscle hypertrophy. |
| Genetics | Individual genetics account for a significant portion of variance in existing muscle mass. |
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What You'll Learn
Hyperplasia vs. hypertrophy
Muscle growth can occur through two primary mechanisms: hypertrophy and hyperplasia. Hypertrophy refers to an increase in the size of individual muscle fibres, which can be achieved by increasing the size of contractile proteins or the fluid and enzyme content of the muscle cell. This can lead to an increase in the strength or function of the tissue. On the other hand, hyperplasia is the increase in the number of muscle fibres, which can occur through muscle fibre division or splitting. This can also lead to an increase in the overall size of the muscle.
While hypertrophy is a well-established mechanism of muscle growth, the existence of hyperplasia in humans is more controversial. Research over the past 40 years has shown that hypertrophy is the predominant mechanism for increasing muscle size. Hyperplasia may exist in humans, but it likely contributes very little to absolute muscle growth. Human evidence for hyperplasia is lacking, although there is some evidence of its occurrence in birds, mice, cats, and fish.
One way to distinguish between hypertrophy and hyperplasia is by measuring muscle fibre number. For example, in a study comparing the left and right tibialis anterior muscles in young men, it was found that the non-dominant side had a greater cross-sectional area than the dominant side, despite similar single muscle fibre size. This suggests that the difference in overall size was due to an increased number of muscle fibres, indicating hyperplasia.
Another way to distinguish between the two mechanisms is by understanding the triggers for each. Hypertrophy is typically associated with increased stress on the muscle, such as lifting weights. Hyperplasia, on the other hand, can be triggered by compensatory or hormonal mechanisms. Compensatory hyperplasia occurs in organs that regenerate, such as the skin, intestines, liver, and bone marrow. Hormonal hyperplasia occurs in organs regulated by hormones, such as those in the endocrine and reproductive systems.
In summary, hypertrophy and hyperplasia are two distinct mechanisms of muscle growth. Hypertrophy refers to the increase in size of individual muscle fibres, while hyperplasia refers to the increase in the number of muscle fibres. While hypertrophy is the predominant mechanism, hyperplasia may also contribute to muscle growth, especially in other organisms besides humans. Further research is needed to fully understand the role of hyperplasia in human muscle growth.
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Hyperplasia in animals
Hyperplasia is the increase in the number of muscle fibres, which increases the total cross-sectional area of a muscle. Hypertrophy, on the other hand, is the increase in the diameter of a muscle fibre. Hyperplasia can occur in other tissues of the body, and uncontrolled cellular proliferation is associated with tumour growth.
While evidence of hyperplasia in humans is lacking, there is evidence of hyperplasia occurring in animals. Studies have shown that hyperplasia occurs in birds, mice, cats, and fish. For example, hyperplasia was observed in birds that had weights hung from their wings for extended periods. Cats performing resistance training also exhibited hyperplasia. In addition, mice experienced hyperplasia after scientists reduced their levels of myostatin, a protein associated with limiting muscle growth. Fish underwent hyperplasia during adolescence.
In adult animals, skeletal muscle enlargement has been primarily ascribed to changes in fibre cross-sectional area (i.e. fibre hypertrophy). However, recent evidence strongly suggests that fibre hyperplasia contributes to muscle mass increases in adult animals. Scientists have used three models—compensatory hypertrophy, stretch, and exercise—to study the cellular mechanisms of muscle enlargement, and each of these models has provided direct and indirect evidence supporting muscle fibre hyperplasia. Direct counts of muscle fibres have shown that exercise and stretch overload result in significant increases in fibre number.
Hyperplasia can also occur in other parts of an animal's body. For example, gingival hyperplasia is a condition in dogs where there is abnormal growth of gum tissue due to an increase in the number of cells within the gums. It is most commonly observed in Boxer Dogs, followed by Bulldogs and Cocker Spaniels. Nodular hyperplasia is another form of hyperplasia that occurs in dogs as a benign, age-related mass lesion in the liver.
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Hyperplasia in humans
Muscle growth, or hypertrophy, is an increase in the size of individual muscle fibres. Hyperplasia, on the other hand, is an increase in the number of muscle fibres. Research over the past 40 years has shown that hypertrophy is the predominant mechanism for increasing muscle size. Hyperplasia in humans may exist but is still very controversial. If it does occur, it likely contributes very little (less than 5%) to absolute muscle growth.
Hyperplasia has been observed in animals, with evidence suggesting it contributes to muscle mass increases in adult animals. For example, muscle fibre hyperplasia has been observed in cats following weight-lifting exercises. In humans, evidence of muscle fibre division or splitting was provided in the nineteenth century, and more recently from fibres obtained from regenerating muscle, and from muscle which has undergone stress-induced growth. However, these observations in humans are open to methodological criticism.
Skeletal muscle enlargement in adult animals has been primarily ascribed to changes in fibre cross-sectional area (i.e. hypertrophy). However, recent evidence suggests that hyperplasia may also contribute to muscle mass increases in adult animals and possibly in humans. For example, muscle fibre hyperplasia has been observed in powerlifters, suggesting that hyperplasia may occur in humans as a result of extreme loading.
To increase muscle size, the muscle must be stimulated with an anabolic stimulus, such as resistance exercise. The amount of resistance used in a lift is related to the associated neural activation, with heavier resistance producing higher neural activation voltages. High voltage is needed to activate high-threshold motor units, and this also exposes low-threshold motor units to the neural stimulus. A well-designed resistance exercise program of sufficient volume and high intensity is the most prolific stimulus for muscle growth.
Everyday dietary patterns, including nutrient intake, sleep, and a healthy lifestyle, all contribute to the effectiveness of muscle repair and growth. The body needs carbohydrates, protein, and fat to repair and remodel muscle.
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Resistance training
Muscle hyperplasia is the increase in the number of muscle fibres. This is distinct from hypertrophy, which is the increase in the diameter of a muscle fibre. Hyperplasia can occur in other tissues of the body, and uncontrolled cellular proliferation is associated with tumour growth.
Evidence of muscle hyperplasia has been observed in birds, mice, cats, and fish. In one study, cats performing resistance training exhibited hyperplasia. However, human evidence is lacking, and it is unclear if hyperplasia occurs in humans during a controlled resistance training protocol.
There are various advanced resistance training techniques that can be used to maximise hypertrophy, such as agonist–antagonist, upper–lower body supersets, drop and cluster sets, and sarcoplasma stimulating training. Progressive resistance training can also be used to improve muscle strength and morphology in individuals with cerebral palsy.
While resistance training is a well-studied method for increasing muscle hypertrophy, the evidence for muscle hyperplasia is less clear. Some studies have compared bodybuilders to sedentary individuals to determine if hyperplasia contributes to extreme muscle growth. While bodybuilders were found to have more muscle fibres, it is challenging to distinguish hypertrophy from hyperplasia in humans. Further experiments are needed to substantiate hyperplasia in humans.
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Muscle overload
Hyperplasia in muscles refers to the increase in the number of muscle fibres. This is distinct from hypertrophy, which is an increase in the diameter of a muscle fibre. Hyperplasia can occur in other tissues in the body, and uncontrolled cellular proliferation is associated with tumour growth.
While hyperplasia in humans is not fully proven, there is some evidence to suggest it does occur. A study of the tibialis anterior muscle in young men found that the non-dominant side had a greater cross-sectional area than the dominant side, but the single muscle fibre size was similar. This suggests that the difference in size was due to an increase in fibre number, or hyperplasia.
There is also evidence of hyperplasia occurring in birds, mice, cats, and fish. In mice, hyperplasia was induced by reducing levels of myostatin, a protein that limits muscle growth. In fish, hyperplasia occurred during adolescent growth. In birds, hyperplasia was induced by hanging weights from their wings for extended periods. In cats, hyperplasia was observed after resistance training.
Progressive overload is a training regimen that can be used to increase muscle mass and strength. It involves gradually increasing the intensity or difficulty of workouts over time. This can be achieved by increasing the weight, the number of repetitions, or the length of workouts. For example, in the first month of strength training, one might perform 10 repetitions at one weight, and then the next month, perform 12 repetitions at the same weight.
The goal of progressive overload is to maximise results by regularly challenging the body. By strategically stressing the muscles, strength gains can be maximised while minimising the risk of injury. It is important to follow a plan to ensure that increases in weight or intensity are gradual, and to listen to your body to avoid injury or burnout.
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Frequently asked questions
Hyperplasia in muscles refers to an increase in the number of muscle fibres. This is different from hypertrophy, which is an increase in the thickness of muscle fibres.
It is currently unclear whether hyperplasia occurs in humans. Some studies have found evidence of hyperplasia in humans, while other studies dispute these findings.
Hyperplasia has been observed in birds, mice, cats, and fish. In mice, hyperplasia was induced by reducing levels of myostatin, a protein that limits muscle growth. In fish, hyperplasia occurred naturally during adolescence.
Hyperplasia can lead to increased muscle strength due to the higher number of muscle fibres. This can be beneficial for competitive bodybuilding and strength sports such as powerlifting and weightlifting.
