Muscle area is a measurement used by clinicians and researchers that refers to the cross-sectional area (CSA) of a muscle. This can be visualized as taking a slice through a muscle at its thickest point and measuring the surface, providing a two-dimensional representation of its size.
The physiological cross-sectional area (PCSA) measures the cross-section of a muscle perpendicular to its fibers. This is distinct from the anatomical cross-sectional area (ACSA), a slice perpendicular to the muscle’s long axis. While often similar, for muscles with angled fibers, PCSA more accurately represents force-producing capabilities.
The Significance of Muscle Area
A larger muscle area is strongly correlated with a greater potential for producing force. While not the only factor, muscle size is one of the best predictors of strength capacity. The number and size of muscle fibers packed into a given area directly influence how much tension the muscle can generate.
Beyond strength, muscle area impacts metabolic health. Skeletal muscle is metabolically active, burning calories even at rest. Greater muscle mass increases a person’s resting metabolic rate, aiding in weight management. Muscles are also the primary site for glucose disposal, which helps regulate blood sugar and can reduce the risk of type 2 diabetes.
Maintaining muscle area is an indicator of functional health, particularly with age. The natural decline in muscle mass and function is a condition known as sarcopenia. This loss contributes to frailty, a reduced ability to perform daily tasks, and an increased risk of falls and fractures in older adults. Preserving muscle area promotes long-term independence and quality of life.
Methods for Measuring Muscle Area
The most precise methods for measuring muscle cross-sectional area are Magnetic Resonance Imaging (MRI) and Computed Tomography (CT). A CT scan uses X-rays to create cross-sectional images, while an MRI uses magnets and radio waves to generate images of soft tissues. These techniques can accurately distinguish muscle from other tissues like fat and bone.
MRI and CT scans can be expensive and are located in medical facilities. A more accessible alternative is B-mode ultrasound, which uses high-frequency sound waves to create images. While not as detailed as an MRI, studies show ultrasound provides reliable measurements of muscle thickness, which correlates well with cross-sectional area for superficial muscles. This makes it a practical tool for tracking changes in muscle size.
Strategies for Increasing Muscle Area
The primary driver for increasing muscle area (hypertrophy) is resistance training, which involves contracting muscles against an external force. The principle that stimulates muscle growth is progressive overload, meaning continually increasing the demands on the muscles. This can be achieved by increasing the weight, repetitions, or sets, or by decreasing rest times. For hypertrophy, training in the 6-12 repetition range with moderately heavy loads is recommended.
This mechanical stress creates microscopic tears in muscle fibers. The body responds by repairing the damaged fibers and adding new contractile proteins. This process increases the size of the muscle fibers and, consequently, the overall muscle cross-sectional area.
Nutrition provides the building blocks to support growth from training. Adequate protein intake is necessary, as muscle tissue is primarily composed of protein. Following a workout, muscle protein synthesis (MPS) is elevated, and consuming protein provides the amino acids to repair and build muscle. Research suggests consuming 1.2 to 2.0 grams of protein per kilogram of body weight daily is effective for muscle growth.
Distributing protein intake throughout the day, with 20-40 grams per meal, helps maintain a positive protein balance. In addition to protein, consuming sufficient calories is necessary to fuel training and support building new tissue. Carbohydrates are also important to replenish muscle glycogen stores used during exercise and assist in the repair process.
Factors That Influence Muscle Area
An individual’s genetic makeup determines their baseline muscle mass and potential for growth. Heritability accounts for a substantial portion of the variation in muscle-related traits among individuals. These genetic factors can influence the number and type of muscle fibers a person has and their hormonal profiles, setting a ceiling on how much muscle a person can build.
Age is another factor affecting muscle area. As people get older, muscle mass tends to decline, a process that can begin as early as age 40. While resistance exercise can counteract these effects, the response to training may be blunted in older adults compared to younger individuals.
Physiological differences between sexes also contribute to variations in muscle area. On average, males have greater muscle mass than females, largely due to hormonal factors. Higher levels of testosterone in males promote greater muscle protein synthesis, leading to a larger baseline muscle area and a greater hypertrophic response to training. Even when accounting for training, men often show a greater absolute increase in muscle volume than women.