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Muscle is a soft tissue that allows the body to create movement through contraction. It is composed of muscle fibres, which are made up of proteins. These proteins include actin and myosin, which are contractile proteins that interact to cause movement. Other muscle proteins include troponin and tropomyosin, which are regulatory proteins. Myoglobin is another protein present in muscle, which stores oxygen transported to the muscle via the blood by haemoglobin. While protein is essential for building and maintaining muscle mass, it is important to note that consuming too much can lead to weight gain.
| Characteristics | Values |
|---|---|
| Muscle composition | About 40% of the body weight of a healthy human adult weighing about 70 kg (150 pounds) is muscle, which is composed of about 20% muscle protein. |
| Muscle protein types | Myofibrillar, regulatory, sarcoplasmic, stromal, actin, myosin, tropomyosin, troponin, fibrinogen, and more. |
| Muscle protein functions | Muscle contraction, tissue growth and repair, immune function, energy production, and more. |
| Muscle protein synthesis (MPS) | MPS is triggered for only a finite period, even with increased protein intake. It is the driving force behind adaptive responses to exercise and is stimulated by protein ingestion and resistance exercise. |
| Recommended protein intake | The minimum RDA for protein is 0.8 g per kg of body weight per day. For building muscle mass, the recommended intake is 1.4–2.0 g/kg/d and may go up to >3.0 g/kg/d. |
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What You'll Learn
Muscle protein synthesis (MPS) is triggered by exercise and protein intake
Muscle protein synthesis (MPS) is a crucial process in the body's adaptive response to exercise and nutrition. MPS refers to the synthesis of myofibrillar proteins, which are the most abundant proteins in muscle tissue. These proteins, such as actin and myosin, are essential for muscle contraction and play a key role in skeletal muscle development and function.
MPS occurs at a rapid rate during growth and slows significantly after the age of 20. In healthy, recreationally active individuals, skeletal muscle proteins have a daily turnover rate of approximately 1.2%. This means that muscle protein breakdown (MPB) and MPS are in a constant state of dynamic equilibrium, with MPS exceeding MPB when the body is in a fed state.
Exercise, particularly resistance exercise, is a potent trigger for MPS. The anabolic effect of exercise lasts for at least 24 hours, and its impact on MPS can be further enhanced by strategic protein intake. Consuming protein before or after resistance exercise creates a synergistic effect, maximizing the stimulation of MPS. For individuals engaging in exercise, a daily protein intake of 1.4-2.0 g/kg body weight/day is generally sufficient for maintaining or building muscle mass.
The relationship between diet and protein balance is complex. While increased protein intake can stimulate MPS, this effect is limited as the body can only utilize a finite amount of essential amino acids (EAAs). Any excess EAAs are broken down and excreted by the liver. Therefore, the timing and composition of nutritional intake are crucial considerations for optimizing MPS and muscle adaptation to exercise.
Additionally, biological factors such as DNA and sex, along with training variables, can influence the MPS response and subsequent muscle hypertrophy. While the exact mechanisms regulating MPS remain to be fully elucidated, it is clear that MPS is a dynamic and multifaceted process that is integral to the body's response to exercise and nutrition.
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Myofibrillar proteins are the most abundant proteins in muscle
Muscle proteins are the most abundant type of protein in the human body. They make up about 20% of the total body weight of a healthy human adult, which equates to around 5 to 6 kilograms.
Myofibrillar proteins are the most abundant type of muscle protein. They are composed of myosin and actin, which are the thick and thin filaments that give muscle its striated appearance. These two proteins are responsible for a muscle's ability to contract and relax. Myosin constitutes around 35% of the total protein volume of skeletal muscles, while actin is the most abundant protein in most eukaryotic cells.
Myofibrillar proteins are long fibril proteins that are organised into repeated sections called sarcomeres. These sarcomeres contract by sliding the thick and thin filaments along each other. The sarcomere structures give skeletal muscle its striated appearance and are readily visible under an electron microscope.
The number of myofibrils in a muscle ranges from 50 per myocyte in a fetus's muscles to about 2000 per myocyte in the muscles of an untrained adult. The growth in girth of muscle fibres occurs when these myofibrils split, which can be stimulated by stress on the sarcomere.
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Muscle is composed of 20% protein
Muscle is composed of about 20% protein. The human body contains about 5 to 6 kilograms (11 to 13 pounds) of muscle protein.
Proteins are the most important component of striated skeletal muscle. The total amount of muscle proteins in humans exceeds that of any other protein. About 40% of the body weight of a healthy human adult weighing about 70 kilograms (150 pounds) is muscle.
Muscle proteins can be divided into myofibrillar, regulatory, sarcoplasmic, and stromal proteins. Myofibrillar proteins are the most abundant proteins in muscle and directly impact the muscle's ability to contract and relax. Actin and myosin are the most common myofibrillar proteins, with actin being the most abundant protein in most eukaryotic cells. Myosin constitutes about 35% of the total protein volume of skeletal muscles. Actin and myosin combine to form actomyosin, a complex molecule that causes muscle contraction.
Regulatory proteins, such as troponin and tropomyosin, help regulate muscle force by controlling the intracellular concentration of calcium. Sarcoplasmic proteins, including hemoglobin and myoglobin, contribute to the red color of muscle and play a role in oxygen transport and metabolism. Stromal proteins, including collagen, form the connective tissue framework within which the myofibrillar proteins function.
To build and maintain muscle mass, it is recommended that physically active individuals consume a daily protein intake in the range of 1.4–2.0 g protein/kg body weight/day. Higher protein intakes of >3.0 g/kg/d may promote loss of fat mass and have positive effects on body composition in resistance-trained individuals.
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Animal protein is better for muscle gain than plant-based protein
Animal protein is often considered superior to plant-based protein for muscle gain due to its complete amino acid profile and better digestibility. Animal protein sources, such as meat, provide a more concentrated amount of protein, making it easier to meet the required daily intake. Additionally, animal protein is higher in the amino acid leucine, which is crucial for stimulating new muscle growth and aiding in recovery after exercise.
However, it is important to note that recent studies have challenged this notion. Some research suggests that a well-planned vegan diet can lead to equal muscle gains when compared to an omnivorous diet, even when coupled with resistance training. This indicates that it is possible to build muscle effectively through a plant-based protein intake.
Nevertheless, the digestibility of animal protein remains a key advantage. Plant-based proteins are typically bound with fiber, which can hinder absorption as the body struggles to break down fiber efficiently. This means that the body may not fully utilize all the protein consumed from plant sources.
Furthermore, animal protein has been shown to have a favoring effect on lean mass, especially in younger adults. This was evident in a study where younger adults under 50 years of age demonstrated a significant increase in peak torque during leg/knee extension when consuming animal protein. While both animal and plant-based proteins can lead to strength gains, animal protein may offer a more efficient pathway to muscle growth, particularly for those under 50.
In conclusion, while it is possible to build muscle mass with either animal or plant-based protein sources, animal protein tends to be more beneficial for muscle gain due to its higher leucine content, better digestibility, and positive impact on lean mass, especially for younger individuals. However, it is worth noting that a well-planned vegan diet that includes complete plant protein sources can also support effective muscle growth.
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Protein is essential for building and maintaining muscle mass
Muscle proteins are the most important component of striated skeletal muscle. Muscle fibres are composed of myofibrils, which are made up of proteins including actin, myosin, and several others. Actin and myosin are contractile proteins, and their filaments are oriented parallel to each other and to the long axis of the muscle. During contraction, the S filaments (which link the actin filaments) shorten, causing the actin filaments to slide towards each other and past the myosin filaments, resulting in muscle shortening.
Myofibrillar proteins are the most abundant proteins in muscle, and actin, myosin, and tropomyosin are the best-characterised of these. Myosin is a hexameric molecule consisting of four light chains and two heavy chains. It is insoluble in water and highly viscous, and it combines easily with actin. Actin, in turn, interacts with various other myofibrillar proteins. Tropomyosin is a fibrous protein that is found on thin filaments in all muscles and in many non-muscle tissues.
The amount of protein required to build muscle depends on weight, activity level, and age. It is important to note that eating too much protein may pose health risks. Athletes should consider focusing on whole food sources of protein that contain all of the essential amino acids (EAAs). Pre-sleep casein protein intake (30–40 g) provides increases in overnight muscle protein synthesis and metabolic rate without influencing lipolysis.
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Frequently asked questions
About 40% of the body weight of a healthy human adult weighing about 70 kilograms (150 pounds) is muscle, which is composed of about 20% muscle protein. Thus, the human body contains about 5 to 6 kilograms (11 to 13 pounds) of muscle protein.
Actin, myosin, and tropomyosin are some of the most common muscle proteins.
There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle.
Protein is essential for building and maintaining muscle mass. When a person eats protein, it is broken down into amino acids, which are used for tissue growth and repair. To build muscle, one must consume more protein than what is broken down, as the body can break down muscle to provide itself with amino acids if there is a deficiency.
Lean meat, fish, beans, nuts, and legumes are good sources of protein for muscle building. Plant-based proteins can also be good sources of protein, but they may need to be combined with other foods to get all the essential amino acids.
