In this article, we will explore the basic traits of skeletal muscles, their positions in the body, their attachments to bones, and how they facilitate joint movement. Additionally, we will delve into the ways in which muscles change shape during different movements. Tendons will also be introduced, focusing on their characteristics and how they affect surface form. This foundational knowledge will be expanded upon in subsequent chapters, which will explore muscle groups in different regions of the body.

The Importance of Muscles in Figure Drawing

Muscles, along with the subcutaneous layer of adipose (fatty) tissue, define the overall shape of the human figure, giving it structure, substance, and character. Drawing accurate surface forms that change in different poses can be challenging. Having an understanding of how muscles are positioned and how they stretch and compress during movement gives artists a valuable advantage by providing insight into what lies beneath the skin and how it influences what is visible on the surface.

Throughout history, figurative artists have recognized the value of studying the human muscular system. Masters like Michelangelo, Artemesia Gentileschi, Auguste Rodin, and Peter Paul Rubens possessed a deep understanding of anatomy and used that knowledge to enhance their artistic vision. Whether aiming for anatomical realism, dynamic visual effects through exaggeration, or expressive interpretations of the human form, learning about muscles opens up a world of artistic possibilities.

Exploring the Muscular System

Let’s start by examining the entire muscular system. The following illustrations depict male and female figures from anterior and posterior views.

Muscles are arranged within the body in two main layers: the superficial muscle layer (also known as externus or superficialis) and the deep muscle layer (also called internus or profundus). The superficial layer is more commonly studied by artists when learning about basic anatomical forms. However, aside from a few exceptions, the muscles in the deep layer do not significantly impact surface forms and are generally not visible. Some anatomy books refer to a middle layer, known as the intermediate layer, found in the lower arm, foot, and torso.

Categorizing muscles into groups helps in familiarizing oneself with their structure. Besides classifying muscles based on the layer they belong to, we can also group them in various other ways:

• By function or action (e.g., flexor group, extensor group, adductor group)
• By location in the body or by reference to other anatomical forms (e.g., gluteal group, abdominal group, pectoral group, scapula group, radial group, thenar group, peroneal group)
• By compartment, as muscles are separated into compartments by deep fascia called intermuscular septa (e.g., anterior compartment, posterior compartment, medial compartment)
• By colloquial (common) names (e.g., thumb group, inner thigh group, upper thigh group, hamstring group)

Certain muscles, like the sartorius muscle of the upper leg, do not fit into any specific category and assist in various movements while remaining independent.

Skeletal Muscles

In addition to these categories, muscles are classified into three basic types: cardiac muscle (found in the heart), smooth muscles (affiliated with tubular structures in the body, such as arteries, colon, bronchial tubes, and the iris of the eye), and skeletal muscles. Skeletal muscles, as the name suggests, attach to bones. They are of utmost interest to artists because they play a crucial role in creating bodily movements, and their shapes are often visible beneath the skin.

The primary function of skeletal muscles is to contract and shorten their muscle fibers, resulting in movement. To understand this process better, let’s examine their internal structure. Muscles consist of elongated muscle fibers (muscle cells) arranged in muscle fiber bundles called fascicles. Despite being parallel to each other, muscle fibers can have varying lengths and orientations, including short, long, circular, fan-shaped, or oblique positions along tendons.

The length of muscle fibers determines the range of movement, with longer fibers providing greater mobility and shorter fibers generating more power. Muscle architecture refers to the arrangement of muscle fibers and can be classified into several types: parallel, pennate, convergent/triangular, circular, spiral, and biventer.

Within each muscle fiber are rod-like strands called myofibrils, which extend throughout the entire length of the muscle fiber. The myofibrils contain units called sarcomeres, positioned end to end within them. Sarcomeres, in turn, contain microscopic threads called myofilaments, which are specialized for contraction. These myofilaments consist of two types of contractile proteins, myosin, and actin.

Contraction occurs when sarcomeres receive an electrical impulse from the central nervous system, causing the actin and myosin filaments to slide along each other. This sliding filament mechanism generates the dynamic force necessary for muscle contraction. As a muscle contracts, its fibers shorten towards the center, exerting a pulling force on the muscle attachments to bones and creating movement.

Muscle Attachments (Tendons)

In most cases, a muscle attaches to two or more bones, resulting in joint action when it contracts. The points at which muscles attach to bones are known as the origin and insertion sites. These sites are usually located on different bones to allow for movement. While the origin site remains relatively fixed during contraction, the insertion site moves as the muscle contracts.

Muscles do not directly attach to bones; instead, they connect via fibrous connective tissues called tendons. The tendon at the origin site is known as the tendon of origin or fixed attachment, while the tendon at the insertion site is called the tendon of insertion or mobile attachment. In some cases, a muscle may have multiple origins and a single insertion, or vice versa. The distinction between fixed and mobile attachments helps us understand the muscles’ roles in movement.

It’s worth noting that some anatomists use alternative terminology, replacing origin and insertion with proximal and distal attachments, respectively. This categorization focuses on the attachments’ position on the body rather than their role in movement. However, for consistency, we will continue with the traditional terms in this article.

Understanding muscle attachments can greatly benefit artists striving for realism by ensuring accurate depictions of how tendons connect to bones within specific regions of the body. One example is the sternocleidomastoid muscle’s tendon of insertion into the upper part of the sternum, which becomes prominent when the head is rotated. Depicting tendons accurately is essential for capturing the overall dynamics of a particular body region. While the precise location of muscle attachments may vary slightly, approximating their placement is crucial for portraying anatomical accuracy.

It’s important to note that facial muscles often behave differently from skeletal muscles in the rest of the body. Facial muscles, apart from those controlling the mandible (lower jaw), do not move bones but rather soft-tissue structures, allowing for the creation of facial expressions. Although their attachments differ, the principles of muscle contraction and tension still play a role. Understanding these distinctions can aid artists in capturing the subtleties and nuances of facial expressions.

Tendon Landmarks

Tendons come in various shapes, including cord-like forms, flat wide sheaths, and thin flat strips. Many tendons are obscured by the subcutaneous layer of adipose tissue, but certain cord-like tendons do occasionally become visible when the associated muscle contracts, bringing the tendon closer to the skin. Representing these tendons in figure studies can add a sense of dynamic tension, but care must be taken to avoid making them overly prominent. For instance, when depicting multiple tendons, varying their prominence by subtly suggesting some while emphasizing others prevents them from appearing rigid or unnatural.

Flat fibrous structures are known as tendons, while wider sheets of fibrous material are called aponeuroses. Aponeuroses serve as broad flat sheaths that cover larger areas for muscle attachment. They can be observed in muscles like the latissimus dorsi and external oblique in the torso and abdominal regions. The following illustrations show the basic locations of tendons and aponeuroses on the surface forms of the front torso and arms, back torso and arms, and legs. Additionally, key bony landmarks and triangular surface-form characteristics are provided.

Specific Tendons

Let’s examine a few specific tendons that can be visible on the surface form in certain poses:

Tendons of the Sternocleidomastoid Muscle of the Neck

The tendons of the sternal portions of the sternocleidomastoid (SCM) muscle attach to the manubrium of the sternum, with the suprasternal notch (pit of the neck) located between them. When the head rotates sideways, one of these tendons becomes prominently visible on the surface, as shown in the following portrait study.

Tendons of the Dorsal Side of the Hand

The tendons of the extensor digitorum muscle of the lower arm insert into the four fingers. They are most visible on the surface when the fingers are forcefully spread apart. In relaxed hand positions, the tendons may still be discernible depending on the hand’s posture and lighting conditions.

Tendons of the Anterior Region of the Lower Arm

The tendons of the flexor muscles of the lower arm are typically visible on the surface when the hand clenches into a fist. When the hand is relaxed, detecting these tendons becomes more challenging.

Tendons of the Hamstring Muscles

The tendons of the hamstring muscles attach on both sides of the popliteal fossa (the back of the knee). When the knee bends, these tendons become more visible on the surface. The tendon of the biceps femoris muscle, which lies on the outer side of the upper leg, is particularly prominent. It attaches to the head of the fibula bone, located on the outer side of the lower leg.

The Achilles Tendon

The Achilles tendon, named after the Greek mythology warrior, attaches the gastrocnemius and soleus muscles of the lower leg to the heel bone (calcaneus). It appears on the surface as a thick, ropelike structure. The Achilles tendon is particularly visible and pronounced in the following study of feet.

Tendons of the Dorsal Side of the Foot

The tendons of the extensor digitorum longus muscle of the lower leg insert into the lesser toes. When the toes are forcefully spread apart, these tendons become very apparent. The extensor hallucis longus, responsible for extending the big toe, has a prominent tendon that becomes noticeable when the toe points upward.

It’s important to emphasize that the visibility and prominence of tendons can vary depending on factors such as muscle tension, posture, and lighting conditions. Artists should aim for a natural, organic representation, avoiding excessive emphasis that could result in a stiff or unrealistic appearance.

Muscle Contraction: Dynamic and Static

Muscle contraction refers to the generation of tension within muscle fibers, leading to movement or stabilization. There are two primary categories of muscle contraction: dynamic (isotonic) and static (isometric).

Dynamic Muscle Contraction

Dynamic muscle contraction occurs when a muscle changes length during a specific movement, either by shortening (concentric contraction) or lengthening (eccentric contraction) its muscle fibers.

In concentric contraction, muscle fibers shorten towards their centers, generating tension that pulls a bone and causes movement at a joint. This is typically observed in the “up phase” of a movement, like lifting a barbell.

In eccentric contraction, muscle fibers lengthen from a contracted state and return to their resting length. This type of contraction is usually associated with the “down phase” of a movement, such as lowering a barbell. During eccentric contraction, muscle fibers relax in a controlled manner, resisting the force of gravity and preventing rapid descent. Although the fibers lengthen, tension is maintained within the muscle.

When depicting active poses, it is essential to identify muscles that are in a state of compression or stretching. Visual cues include compact muscle shapes, muscles pressing against each other, stretched muscles, and tendons protruding close to the surface due to muscle tension.

Static Muscle Contraction

Static contraction, also known as isometric contraction, occurs when a muscle increases tension within its fibers without changing length. This type of contraction stabilizes joints or maintains posture by holding bones in place. It prevents unwanted movements while allowing agonist and synergist muscles to act efficiently. Models in figure studies often engage in static contraction to sustain poses without shifting their weight.

Different Roles of Muscles

During a particular movement, multiple muscles near a joint contribute. Each muscle may play different roles at different times, depending on the specific movement or sequence of movements. Generally, muscles fulfill four different roles: agonist (prime mover), antagonist, synergist (assistor), and stabilizer (fixator).

The agonist, or prime mover, is primarily responsible for activating a bone or body part during a specific movement. When the agonist muscle contracts, it becomes more compact, initiating the desired movement. In opposition to the agonist, the antagonist muscle stretches its fibers to yield to the contraction of the agonist. This relationship can be observed in the flexion and extension of the lower arm at the elbow joint.

Synergist muscles, also known as assistors, provide additional pull near the prime mover’s tendon of insertion. They assist the prime mover and help prevent unwanted movements during a specific action.

Stabilizer muscles, or fixators, hold a bone firmly in place, typically the bone where the prime mover originates. Their contraction prevents unwanted movement, allowing the agonist and synergist muscles to function more efficiently. Stabilizer muscles contract isometrically, maintaining the bone’s position without lengthening or shortening.

The Influence of Force on Anatomical Forms

Force refers to the energy that generates, modifies, or restrains movement within the body. There are two primary types of force: internal force, created within the body, and external force, exerted from outside the body. Internal forces result from muscle contractions, which generate tension and facilitate movement. Soft tissues such as tendons, ligaments, the subcutaneous layer, and the skin are also influenced by these internal forces and can change shape accordingly.

The effect of force on anatomical forms includes compression, stretching, bending, and twisting. These actions may occur individually or in combination, depending on the type of movement. When drawing figures in active poses, artists should observe how force dynamically impacts the forms and lines of the body, infusing them with energy and vitality.

External forces, such as gravity, also significantly affect the body. Gravity constantly pulls the body and its components towards the center of the earth. Muscles contract isometrically to counteract this force and maintain an upright posture. Additionally, external forces can arise from environmental factors like wind or physical impact with objects. They can influence the body alongside internal forces, and their interplay is often depicted by artists in various forms of movement.

Conclusion

Understanding the characteristics of muscles and tendons provides artists with a solid foundation for figure drawing. By grasping the basic traits, positions, and movements of muscles, artists gain the ability to depict surface forms accurately and capture the dynamics of the human figure. Incorporating the principles of E-E-A-T and YMYL in one’s artistic practice ensures both expertise and credibility in portraying the complexity and beauty of the human body.