Victor Forge
It was previously believed that muscle nuclei are lost when muscles shrink or atrophy due to disuse, disease, injury, or paralysis. However, recent studies using modern techniques have challenged this notion, suggesting that muscle nuclei gained during training are retained even during muscle atrophy or breakdown. This phenomenon, known as muscle memory, has implications for muscle regrowth, public health, and anti-doping efforts in sports. The discovery that muscle nuclei may persist raises questions about the role of these residual nuclei in muscle retraining and the potential for banking muscle growth potential to prevent age-related frailty.
| Characteristics | Values |
|---|---|
| Muscle nuclei lost during atrophy | No, nuclei are not lost during atrophy, but are retained during severe atrophy |
| Muscle nuclei lost by cell death | No, nuclei are lost by cell death, but not the actual muscle nuclei |
| Muscle nuclei added during muscle growth | Yes, muscle nuclei are added during muscle growth to support the enhanced synthetic demands of larger muscle cells |
| Muscle nuclei lost during muscle shrinkage | No, muscle nuclei are not lost during muscle shrinkage |
| Muscle nuclei and muscle memory | Muscle nuclei are retained during muscle shrinkage, and allow for faster growth when muscles are retrained, suggesting that muscle has a "memory" |
| Muscle nuclei and steroid use | Steroid use increases muscle nuclei, which are retained after steroids are withdrawn, and can go undetected |
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What You'll Learn
Muscle nuclei are not lost from atrophying muscle fibres
Muscle fibres are the largest cells in the human body, and a single muscle fibre can contain thousands of nuclei. Historically, scientists believed that a single nucleus regulates a limited cell volume and that the ratio between the nucleus and cell volume was constant, termed a "nuclear domain". This led to the assumption that when a muscle shrinks or "atrophies" due to disuse or disease, the number of nuclei decreases.
However, modern research has challenged this idea, suggesting that muscle nuclei are not lost from atrophying muscle fibres. Studies in mice and rats have shown that nuclei gained by muscles during training are maintained even when muscles shrink due to disuse or start to break down. These residual nuclei allow for faster growth when muscles are retrained, indicating that muscle fibres may have a memory of their previous strength.
For example, in one study, mice were given testosterone, leading to increased muscle mass and muscle nuclei. After the testosterone was withdrawn, the muscles returned to their normal size, but the extra nuclei remained. When the mice were then subjected to an intense fitness regimen, the nuclei-rich muscles exposed to previous testosterone treatment grew significantly more than untreated muscles.
This phenomenon has also been observed in rats, where nuclei gained by muscle after training were maintained during long periods of detraining. When training was resumed, these nuclei helped the muscle to regrow more effectively.
The discovery that muscle nuclei are not lost from atrophying muscle fibres has important implications for public health and sports. It suggests that muscle growth potential can be "banked" in our teens to prevent frailty in old age and that athletes may be able to benefit from using steroids to grow their muscles without fear of detection.
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Nuclei gained during training persist during atrophy
Muscle cells are the largest cells in the human body and contain thousands of nuclei to support their large volume. Nuclei are the control centres of each cell and, as well as housing DNA, coordinate a range of cell activities, including their growth. It was previously believed that muscle nuclei are lost when muscles shrink due to disuse or disease. However, modern lab techniques have shown that nuclei gained during training persist even when muscle cells shrink due to disuse or start to break down. These residual nuclei, called 'myonuclei', allow more and faster growth when muscles are retrained. This phenomenon is called "muscle memory".
The idea of muscle memory challenges the old adage "use it or lose it", which suggests that if you stop using your muscles, they will shrink and lose their nuclei. While it is true that muscles do shrink from lack of use, recent studies have shown that the nuclei gained by muscle after training are maintained during long periods of not training. These nuclei then help the muscle to regrow more effectively when training is resumed. This explains why people who get back into training after a break find it easier to gain muscle compared to newbies.
The retention of nuclei after muscle atrophy was first observed in mice studies. Mice that were given testosterone acquired new myonuclei that persisted long after the steroid use ended. When the muscles of these mice were then loaded to mimic weight training, the extra nuclei helped the muscles grow faster and bigger than untreated mice. Similar results were observed in studies on rats, rodents and insects.
The discovery of muscle memory has important implications for public health and sports. For instance, it suggests that individuals may benefit from strength training at an early age when the ability to create myonuclei is higher. It also has implications for anti-doping efforts in sports, as athletes may be able to benefit from using steroids to grow their muscles without the fear of detection.
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Muscle memory
When we learn a new movement or skill, we go through the cognitive stage, where our movements are slow and inefficient, and there is high activation in the prefrontal cortex, the brain's thinking region. As we practice and repeat the movement, we progress to the associative stage, where our movements become more fluid and consistent. Eventually, with enough practice, we reach the autonomous stage, where our performance is smooth and accurate, and our brain's main activity has switched to the basal ganglia, the region involved with automatic functioning.
The basal ganglia play a crucial role in memory and learning, particularly in stimulus-response associations and the formation of habits. The connections between the basal ganglia and the primary motor area are strengthened through practice, suggesting their importance in the motor memory consolidation process. While the exact mechanism of motor memory consolidation is still controversial, it is believed that there is a redistribution of information across the brain from encoding to consolidation.
In terms of muscle mass, muscle memory refers to the ability to regain muscle mass in previously trained muscles. When we gain muscle mass through strength training, our muscles can retain the extra nuclei that helped them grow even if we stop training and lose some muscle mass. These residual nuclei allow for faster regrowth when we resume training, which is why it is generally easier to regain muscle mass than to build it from scratch.
While muscle memory is real, it is important to note that the term encompasses two different concepts: neurological muscle memory and physiological muscle memory. Neurological muscle memory is related to the recall of learned activities and the formation of strong neural pathways, while physiological muscle memory is tied to the regrowth of actual muscle tissue. Understanding both aspects of muscle memory can be beneficial for anyone looking to establish or reboot a fitness routine.
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Muscle nuclei and steroid use
A muscle fibre consists of just one cell, but many nuclei. Muscle growth is accompanied by the addition of new nuclei from stem cells to help meet the enhanced synthetic demands of larger muscle cells. As a muscle cell grows, it needs more nuclei to support that extra volume.
Research in rodents and insects has demonstrated that nuclei are not lost from atrophying muscle fibres and can even remain after muscle death. Similarly, research in rats found that nuclei gained by muscle after training were maintained during long periods of not training. These nuclei then helped the muscle to regrow more effectively when training was resumed.
In studies on mice, it was found that when muscles grow in response to steroid use, they also gain nuclei, which are retained when muscles have returned to their normal size after steroid withdrawal. When the muscles of these mice were then loaded to mimic weight training, the extra nuclei helped muscles grow faster and much bigger than muscles in normal mice. This means that athletes can benefit from using steroids to grow their muscles without the fear of detection.
The World Anti-Doping Association bans steroid use because they cause large increases in muscle size which in some sports may be advantageous. However, steroids or their byproducts can be detected in urine and blood samples for a short period of time, and the benefits of steroid use on muscle growth may last long after traces in urine and blood have vanished.
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Muscle nuclei and ageing
The loss of skeletal muscle mass and strength is a well-known effect of ageing. This loss of muscle mass and function is termed sarcopenia. Muscle mass decreases approximately 3–8% per decade after the age of 30, and this rate of decline is even higher after the age of 60. The mechanisms underlying this phenomenon are multifactorial and not yet fully understood. However, changes in the cell nucleus structure and function have been considered among the possible contributing causes.
Skeletal muscle fibres are the largest cells in the human body, and they contain thousands of individual nuclei to support their large volume. These nuclei are the control centres of each cell, coordinating a range of cell activities, including their growth. During muscle growth, new nuclei are added from stem cells to meet the enhanced synthetic demands of larger muscle cells. It was previously assumed that when a muscle shrinks or atrophies due to disuse or disease, it gets rid of the extra nuclei as they are no longer necessary. However, modern research techniques have shown that these nuclei gained during muscle training persist even when muscle cells shrink or start to break down. These residual nuclei, called myonuclei, allow for faster growth when muscles are retrained, indicating that we can "bank" muscle growth potential in our teens to prevent frailty in old age.
Research in rats has supported this idea, finding that nuclei gained by muscle after training were maintained during long periods of not training. When the rats resumed training, the nuclei helped the muscle to regrow more effectively. This provides evidence for muscle "memory", which could explain why people who return to training after a break find it easier to gain muscle compared to beginners.
At the cellular level, specific age-related alterations in skeletal muscle include a reduction in muscle cell number, muscle twitch time and twitch force, sarcoplasmic reticulum volume, and calcium pumping capacity. Sarcomere spacing becomes disorganized, muscle nuclei become centralized along the muscle fibre, the plasma membrane of the muscle becomes less excitable, and there is increased fat accumulation within and around the muscle cells. Additionally, there is a decrease in the number of satellite cells, which are responsible for muscle growth and repair, contributing to muscle mass loss. Furthermore, telomeres, which are specialized nucleoprotein caps located at the ends of eukaryotic chromosomes, undergo erosion during each round of cell division, resulting in the loss of telomere length during ageing. This telomere shortening impairs tissue renewal, contributing to sarcopenia. However, physical activity can limit telomere shortening in skeletal muscle, highlighting the importance of exercise in mitigating age-related muscle loss.
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Frequently asked questions
No, muscle nuclei are not lost when a muscle shrinks or atrophies due to disuse, disease, injury, or paralysis.
Modern cell-type-specific dyes and genetic markers have shown that the dying nuclei detected in atrophied muscles were inflammatory and other cells, not muscle nuclei.
Muscle nuclei are the control centres of each cell, housing DNA and coordinating a range of cell activities, including growth. They also allow muscles to grow faster and bigger.
The presence of residual muscle nuclei allows for more and faster growth when muscles are retrained, suggesting that we can "'bank' muscle growth potential in our teens to prevent frailty in old age".
