If you ask most people what muscles are for, the answer is usually simple: movement. Muscles help us run, lift, jump, and carry the shopping bags in from the car. But muscles are far more complex and fascinating than that. They are living, metabolically active tissue that influence everything from metabolism and posture to blood sugar control, bone health, and longevity.
In fact, muscle is one of the most important tissues in the human body when it comes to long-term health. It plays a critical role in how our bodies use energy, how strong and mobile we remain as we age, and even how resilient we are to illness.
Understanding what muscles are made of, what they actually do, and how nutrition affects them can help us look after this essential tissue properly. Even more importantly, modern technology now allows us to measure muscle mass accurately, giving us a much clearer picture of our health than body weight alone.
This is where a DEXA Scan becomes incredibly useful.
Let’s take a deeper look at the science behind muscles, their functions, and some fascinating facts you may not know.
What Are Our Muscles Made Of?
At their core, muscles are made up of specialised cells designed to contract and generate force. These cells are called muscle fibres, and they are quite different from the typical cells found elsewhere in the body.
Muscle fibres are long, cylindrical structures that can run the entire length of a muscle. Unlike most cells, they contain multiple nuclei and are packed with contractile machinery that allows them to shorten and create movement.
Inside each muscle fibre are structures called myofibrils. These are made up of repeating units known as sarcomeres, which are the smallest functional units responsible for muscle contraction.
Within each sarcomere are two key proteins:
Actin, a thin filament
Myosin, a thick filament with small “heads”
When muscles contract, the myosin heads pull on the actin filaments, causing the sarcomere to shorten. When thousands of these tiny contractions happen simultaneously, the entire muscle shortens and produces force.
This microscopic sliding mechanism is what allows you to perform everything from lifting weights to blinking your eyes.
Muscles Are Mostly Water
One of the lesser-known facts about muscle tissue is that it is made up largely of water. Approximately 75% of muscle tissue is water, which is why hydration plays a major role in muscle performance and recovery.
Water is essential for:
nutrient transport
cellular communication
energy production
waste removal
muscle contraction itself
Even mild dehydration can affect muscle performance and increase fatigue during exercise.
Protein: The Building Blocks of Muscle
Muscle tissue is rich in protein, which forms the structural and functional components of muscle fibres. These proteins are constantly being broken down and rebuilt in a process known as protein turnover.
Dietary protein provides the amino acids required for:
repairing damaged muscle fibres
building new muscle tissue
maintaining lean mass
supporting recovery after exercise
Without adequate protein intake, the body may struggle to maintain muscle mass, especially during weight loss or periods of intense training.
This is one of the reasons why nutrition is such a crucial component of muscle health.
The Three Types of Muscle in the Human Body
The human body contains three distinct types of muscle tissue, each with its own specialised role.
Skeletal Muscle
Skeletal muscles are the ones most people think of when discussing fitness and strength. These muscles attach to bones via tendons and allow voluntary movement.
Examples include the biceps, quadriceps, hamstrings, and gluteal muscles.
Skeletal muscle is the tissue that grows in response to resistance training and plays a significant role in metabolism and physical performance.
Cardiac Muscle
Cardiac muscle exists only in the heart. It is incredibly resilient and designed to contract continuously throughout life without fatigue.
Unlike skeletal muscle, cardiac muscle works involuntarily and is controlled by the autonomic nervous system.
Your heart beats roughly 100,000 times every day, pumping blood and oxygen throughout the body.
Smooth Muscle
Smooth muscle is found in the walls of internal organs and blood vessels.
Examples include muscles in:
the digestive tract
the bladder
blood vessels
the uterus
These muscles perform automatic functions such as moving food through the digestive system and regulating blood pressure.
The Many Functions of Muscles
While movement is the most obvious role of muscles, their responsibilities go far beyond helping us walk or lift objects.
Movement and Strength
Muscles contract to produce movement by pulling on bones. This is how we perform everyday activities like climbing stairs, picking up objects, or even maintaining facial expressions.
Without muscles, the skeleton would simply be a rigid structure incapable of movement.
Posture and Stability
Many muscles work continuously at low levels to keep us upright and stable. These include the muscles that support the spine, core, and hips.
Poor muscle strength in these areas can contribute to back pain and poor posture.
Metabolic Health
Muscle tissue is metabolically active, meaning it plays an important role in how the body uses energy.
Muscle helps regulate:
blood sugar levels
insulin sensitivity
energy expenditure
In fact, muscle is one of the largest sites for glucose storage in the body.
Higher muscle mass is often associated with better metabolic health and a reduced risk of conditions such as Type 2 Diabetes.
Temperature Regulation
Muscle contractions generate heat, which helps regulate body temperature.
When you shiver, your muscles rapidly contract to produce heat and warm the body.
In fact, muscles generate a large proportion of the body’s heat during cold conditions.
Circulation
Muscles also help move blood through the body.
The calf muscles, for example, act as a “secondary pump,” helping push blood back toward the heart when you walk or move your legs.
This is one reason why regular movement is important for circulation and cardiovascular health.
Muscle Fibre Types: Fast vs Slow
Not all muscle fibres are the same. In fact, skeletal muscles contain a mix of different fibre types, each designed for specific types of activity.
Type I fibres (slow-twitch) are built for endurance. They contract slowly but can keep working for long periods without fatigue. These fibres are heavily used during activities like long-distance running or cycling.
Type II fibres (fast-twitch) are designed for power and speed. They produce greater force but fatigue more quickly. These fibres are used during explosive movements like sprinting, jumping, or lifting heavy weights.
Most people have a mix of both fibre types, although genetics can influence the ratio.
Training can also influence how these fibres behave. Endurance training tends to develop slow-twitch capacity, while resistance training stimulates fast-twitch fibres and muscle growth.
How Muscles Grow: The Science of Hypertrophy
Muscles grow through a process called hypertrophy, which occurs when muscle fibres repair and adapt after being challenged by resistance training.
During strength training, tiny amounts of damage occur within muscle fibres. This damage signals the body to repair and strengthen the muscle, making it slightly thicker and stronger than before.
For hypertrophy to occur, three main factors are important:
Mechanical tension from lifting weights
Adequate protein intake
Sufficient recovery
Without proper nutrition and recovery, the body cannot fully repair and build stronger muscle tissue.
Muscle Loss and Ageing
Unfortunately, muscle mass does not remain constant throughout life.
After the age of around 30, adults can begin to lose muscle mass gradually if they are not engaging in regular resistance training or consuming adequate protein.
This process is known as Sarcopenia.
Loss of muscle mass can lead to:
reduced strength
slower metabolism
increased risk of falls
reduced mobility
poorer metabolic health
Maintaining muscle mass is therefore one of the most important factors in healthy ageing.
Fascinating Facts About Muscles
Muscles are full of surprises, and there are many interesting facts that highlight just how incredible this tissue is.
The human body contains over 600 skeletal muscles, working together to produce movement and stability.
The gluteus maximus is the largest muscle in the body and is responsible for powerful movements like climbing and sprinting.
The masseter, located in the jaw, is one of the strongest muscles relative to its size and allows us to chew food efficiently.
The fastest muscles in the body control eye movement, allowing us to change focus almost instantly.
Another fascinating feature of muscle tissue is muscle memory. Even after long periods without training, muscles can regain size and strength more quickly because muscle cells retain additional nuclei gained during previous training.
Nutrition and Muscle Health
Nutrition plays a central role in maintaining and building muscle tissue.
Without the right nutrients, muscles cannot repair, grow, or function optimally.
Protein Intake
Protein provides the amino acids needed for muscle repair and growth.
Good sources of protein include:
lean meat
fish
eggs
dairy products
legumes
tofu and plant-based alternatives
Adequate protein intake is particularly important for people who exercise regularly or are trying to maintain muscle mass while losing fat.
Energy Balance
Muscle growth also requires sufficient energy. Extremely low-calorie diets can lead to the loss of lean tissue alongside fat.
This is why aggressive dieting can sometimes result in people becoming “skinny fat,” where body weight decreases but muscle mass is lost as well.
Maintaining muscle during weight loss is crucial for preserving metabolic health and physical strength.
Micronutrients
Several vitamins and minerals support muscle function and recovery, including:
vitamin D
magnesium
potassium
iron
A balanced diet that includes a variety of whole foods helps ensure the body has the nutrients required for healthy muscle function.
Why Measuring Muscle Matters
Most people rely on scales or BMI to assess their health or fitness progress. However, these measurements do not distinguish between fat, muscle, and bone.
Two people with the same body weight can have very different body compositions.
This is where body composition testing becomes valuable.
A DEXA Scan is considered one of the most accurate ways to measure:
lean muscle mass
body fat percentage
visceral fat
bone density
By analysing these components separately, a DEXA scan provides a much clearer understanding of your body.
For example, someone losing weight might discover they are losing muscle rather than fat, which could signal the need for dietary or training adjustments.
Tracking Muscle Changes Over Time
One of the biggest advantages of body composition testing is the ability to track changes over time.
Many people focus only on weight loss, but this can be misleading. If you lose weight quickly through extreme dieting, some of that loss may come from muscle rather than fat.
Tracking lean mass with a DEXA Scan allows individuals to ensure they are protecting muscle while reducing body fat.
This insight can help guide:
nutrition strategies
training programmes
recovery planning
long-term health goals
For athletes and fitness enthusiasts, it can also reveal whether strength training programmes are effectively increasing muscle mass.
Muscle, Longevity and Future Health
Increasingly, research suggests that muscle mass is strongly linked with longevity and long-term health.
Higher levels of lean muscle are associated with:
improved metabolic health
better balance and mobility
lower risk of chronic disease
improved quality of life with age
Maintaining muscle mass is not just about aesthetics or athletic performance. It is one of the most important investments we can make in our future health.
The Bottom Line
Muscles are extraordinary tissues made from specialised fibres, proteins, water, and connective structures designed to generate movement and maintain stability.
They do far more than help us move. Muscles regulate metabolism, support posture, assist circulation, and help control blood sugar levels. They are also vital for maintaining independence and mobility as we age.
Nutrition plays a critical role in supporting muscle health, providing the protein, energy, and micronutrients required for repair and growth.
But understanding muscle health goes beyond simply exercising and eating well. Knowing how much muscle you have, and how it changes over time, can provide powerful insights into your overall health.
This is where a DEXA Scan can make a real difference. By measuring lean mass, fat mass, and bone density accurately, it allows you to see what is really happening inside your body.
Because when it comes to long-term health, strength, and longevity, muscle is one of the most valuable tissues we have.