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Beginner's Guide to Musculature

Learn the how and why of resistance training with this walkthrough of all the major muscle groups involved in training, how they work, and which exercises can be used to train them.

Beginner's Guide to Musculature
Written By Jim Stoppani, PhD
Updated September 27, 2023

Obviously, we use our muscles on a daily basis. But when it comes to strengthening them, increasing their size, and conditioning them to endure more exertion for longer, exercise and weight training in particular are the path to improved musculature. In order to know how your muscles function during exercise, it’s important to understand their basic structure and function.

On the largest scale, skeletal muscle tissue is divided up into muscle groups with which most people are familiar. The pectoral muscles, for example, are the muscles of the chest, responsible for pressing movements like the bench press and push-ups. These large bundles of muscle tissue are connected to the bones of the body by tendons. Contraction of the muscles pulls on the connected bones, which facilitates movement of those bones. 

Muscle tissue is composed of bundles of what are known as fascicles, which are themselves bundles of individual muscle fibers. 

Muscle fibers, also called myocytes, are the unique cells of the body that make movement possible. Each muscle fiber contains multiple nuclei, the number of which is increased by muscle protein synthesis induced by exercise. This is one way in which muscles are thought to grow.

These muscle cells are filled with a fluid called sarcoplasm which, in addition to providing a medium through which the muscle cell’s exchange of nutrients and other bodily chemicals can travel, contains glycogen—stored glucose which the muscle tissue uses for the production of energy—as well as myoglobin, which stores oxygen also used in energy production inside the muscle.

Within these specialized cells are bundles of myofibrils, which are where muscle contraction actually takes place.

Myofibrils inside the muscle cells are composed of sarcomeres—long tubes of proteins that interact with each other to make muscle contraction possible. Many different protein strands make up each sarcomere, and each muscle cell may contain hundreds of thousands of sarcomeres. The most important protein strands or filaments are myosin and actin. During the concentric portion of a movement, myosin and actin attach to each other, shortening the sarcomere. This shortening, performed by thousands of myofibrils, contracts the overall muscle tissue of which they are a part. 

During the eccentric or negative portion of a movement, the sarcomeres must lengthen again. The myosin filaments release the actin filaments to make this possible. When muscle is lengthened while still under stress, as with heavy weight training, the actin is torn from the myosin. This damage and its subsequent repair are part of the process through which muscle mass is developed. 

Chest 

The chest refers primarily to the muscle group known as the pectoralis major. This consists of the upper pectoralis major and lower pectoralis major. The pectoralis muscles perform movements such as horizontal adduction of the upper arms, as in the dumbbell flye. 

Basic, multi-joint exercises for the chest involve pressing movements, such as the bench press, incline dumbbell press, and push-up. Isolation exercises for the chest are flye-like exercises that involve movement of the arms without any change occurring at the elbow joint. Examples of isolation exercises for the chest include the dumbbell flye, cable crossover, and pec deck. 

The upper and lower sections of the chest are hit differently by the various chest exercises. Therefore, the first order of importance when it comes to chest training is to ensure that you include exercises that target the upper, middle, and lower pectoralis. 

Chest Muscle Structure

  • Pectoralis Major – The largest muscle in the pectoral group, the pectoralis major connects the sternum (breastbone) and clavicle (collarbone) to the humerus (upper arm bone) and anterior deltoid (front of the shoulder) 
  • Pectoralis Minor – This narrow strip of muscle lies beneath the pectoralis major, running from the rib cage to the scapula (shoulder blade) 
  • Serratus Anterior – Connecting the rib cage to the scapula, the serratus lies along the side of the ribcage
  • Subclavius – Attached to the first rib and clavicle, this muscle forms the front of the axilla (armpit)

Chest Muscle Function

  • Pectoralis Major – Responsible for flexion of the shoulder joint, enabling adduction (inward movement), extension (forward movement), and internal rotation of the humerus 
  • Pectoralis Minor – Stabilizes and depresses (pulls downward) the scapula
  • Serratus Anterior – Pulls the scapula forward when the arm is extended in front of and away from the body
  • Subclavius – Contracts to pull the shoulder downward and forward

Common Chest Exercises

Back

Back refers to the muscles that make up the backside of the torso. Although the term back refers mostly to the large latissimus dorsi muscles, or lats, that run from the upper arms all the way down to the buttocks, it can also include the teres major, the rhomboids, and even the middle and lower portions of the trapezius, because these muscles are often involved in performing exercises that are considered back exercises. 

The two major types of lat exercises are the pulling exercises, which include pull-ups and pulldowns, and rowing exercises, which include bent-over barbell rows, T-bar rows, and seated cable rows.

Pull-up and pulldown exercises tend to concentrate more on the upper and outer lats as well as the teres major. Rowing exercises tend to concentrate more on the middle and lower lats as well as the rhomboids and middle trapezius muscles. Other types of lat exercises are the pullover and straight-arm pulldown. 

The term back also refers to the musculature of the low back. The muscles in the lower back are those that support the spinal column and allow it to extend back, such as when you recline in a chair. These are deeper muscle fibers such as the spinal erectors, which include the longissimus thoracis, iliocostalis lumborum, and spinalis thoracis. Exercises that train the low back are back extension exercises and good mornings.

Back Muscle Structure

  • Latissimus Dorsi – Latin for “broadest muscle of the back”, spans from the vertebrae of the spine and iliac crest, or top of the hip bone, to the humerus (upper arm bone) 
  • Rhomboids – Lying underneath the trapezius muscles, the rhomboids are attached to the spine and scapula (shoulder blade)
  • Teres Major – Located above the lats and connected to the scapula and humerus
  • Teres Minor – A rotator cuff muscle, the teres minor spans from the scapula to both the upper portion of the humerus as well as the shoulder joint
  • Erector Spinae – A series of muscle fibers and tendons that run the length of the back from origin points at the base of the spine and pelvis (hip bone) up to various vertebrae and ribs

Back Muscle Function

  • Latissimus Dorsi – Responsible for extension, vertical adduction (inward movement), and horizontal abduction (outward movement) of the humerus
  • Rhomboids – Retract the scapula
  • Teres Major – Plays a part in the extension and internal rotation of the humerus
  • Teres Minor – Work with the rear deltoid (shoulder muscle) to externally rotate the humerus
  • Erector Spinae – Postural muscles responsible for stabilizing, straightening, and rotating the back

Common Back Exercises

Shoulders

The shoulders refer to the deltoid muscles found on top of the upper arm. The deltoid is composed of three heads that originate on different points of the shoulder girdle but all converge on one common tendon that inserts on the humerus. The three heads are the anterior deltoid (front head), the middle deltoid, and the posterior deltoid (rear head). 

Although these three heads work together to lift the upper arm at the shoulder joint, such as during the lateral raise, each head is stressed differently by different exercises. That is why it is important to structure shoulder workouts around basic multi-joint movements such as the shoulder press that hit all three heads, as well as isolation exercises such as front raise for the anterior head, lateral raise or upright row for the middle head, and rear deltoid raise for the posterior head. 

Shoulder Muscle Structure

  • Anterior Deltoid – Begins at the clavicle (collarbone) as well as the pectoralis major (upper chest muscle), converging at the humerus (upper arm bone) with the other deltoid heads
  • Lateral Deltoid – Spans from the acromion of the scapula (shoulder blade) to the convergence point mentioned above
  • Posterior Deltoid – Attaches to the convergence point of the humerus from what is known as the spine of the scapula, at the top of the shoulder blade
  • Rotator Cuff – Composed of the supraspinatus, infraspinatus, subscapularis, as well as the teres minor as mentioned above, these muscles connect the scapula to the humerus

Shoulder Muscle Function

  • Anterior Deltoid – Works in tandem with the pectoralis major to perform pressing movements, and with the subscapularis to perform internal humeral rotation
  • Lateral Deltoid – Responsible for abduction, or movement of the arm away from the body, as well as overhead pressing movements
  • Posterior Deltoid – Cooperates with the latissimus dorsi (back muscles) to extend the arm backward
  • Rotator Cuff – As the name implies, these muscles assist in the rotation of the humerus

Common Shoulder Exercises

Biceps

Biceps refers to two muscle heads that run down the front of the upper arm that are called the biceps brachii. The two heads are the long head (or outer head) and the short head (or inner head). The major difference between them is where each muscle attaches on the scapula. The tendon of the long head attaches farther back on the scapula than the short head. This is why they are referred to as long head and short head. Both biceps heads converge into one tendon near the elbow, and this attaches to the radius to cause flexion of the elbow when the muscles contract, such as when curling a dumbbell. 

To flex the elbow, the biceps brachii receives help from the assistance muscle called the brachialis. This muscle lies underneath the biceps muscles and starts at the humerus and attaches to the ulna. The bulk of this muscle is lower than the bulk of the biceps muscle, which allows it to offer the most help during the first 30 degrees of elbow flexion. The brachialis is also strongly involved in elbow flexion when the hands maintain an overhand grip on the bar. The brachioradialis, although considered a forearm muscle, also helps at the initiation of elbow flexion when the hand is in a neutral position, such as during hammer curls. 

Biceps Muscle Structure

  • Biceps Brachii – Both the long head and short head of the biceps attach to the scapula (shoulder blade). The long head’s origin is called the supraglenoid tubercle of the scapula, while the short head begins at the coracoid process, located at the front of the scapula. Both converge into a single mass that ends at the radius, one of the forearm bones
  • Brachialis – Runs from the midpoint of the humerus (upper arm bone) to the ulna (forearm bone)
  • Brachioradialis – Technically a forearm muscle, connects the lower end of the humerus to the end of the radius, near the wrist 

Biceps Muscle Function

  • Biceps Brachii – Responsible for flexion of the arm at the elbow joint, supination (outward rotation) of the farm, and assisting the deltoids (shoulder muscles) in flexing the shoulder joint to move the arm upward when the arm is supinated, palms facing forward
  • Brachialis – Contracts to flex the elbow joint, particularly in the first portion of the movement from a starting position of a straightened arm
  • Brachioradialis – Assists in the flexion of the elbow joint, especially when the forearm is pronated, or rotated inward so that palms are down 

Common Biceps Exercises

Triceps

The triceps consist of three muscle heads that are on the back of the upper arm. The three heads of the triceps are the lateral head, long head, and medial head. Each head has a distinct attachment on the upper end, but they all meet at one common tendon that crosses the elbow and attaches on the ulna. Contracting the triceps results in extension at the elbow, such as the motion the arm makes when hammering.

The two types of triceps exercises are compound movements and isolation movements. Compound triceps exercises involve extension at the elbow and movement at the shoulder. These include close-grip bench presses and dips. Isolation triceps exercises involve just extension at the elbow with no other joint movement, such as dumbbell kickbacks.

Although every triceps exercise hits all three heads to some degree, certain ones are better than others at stressing the different heads because of the biomechanics involved. Because the long head of the triceps attaches to the scapula, it is more strongly contracted during exercises where the arms are brought overhead or in front of the body. This is because that action stretches the long head. Muscles contract the strongest when they are stretched to their longest length. Therefore, exercises that are done overhead such as overhead extensions best stress the long head of the triceps. 

Exercises that place the arms in front of the body, such as lying triceps extensions also hit the long head to some degree. Extensions that are done with the arms at the sides of the torso while holding a neutral or overhand grip—such as triceps pressdowns and dumbbell kickbacks—best target the lateral triceps head. The same exercises done with an underhand grip seem to stress the medial head.

Triceps Muscle Structure

  • Triceps Brachii – The three heads of the triceps converge at the same point, the olecranon of the radius, more commonly called the elbow. Both the lateral and medial heads originate from the back of the humerus, or upper arm bone. The long head starts at the scapula, or shoulder blade
  • Anconeus – Lies beneath the triceps brachii, originating at the middle of the humerus (upper arm bone) and ending at the olecranon as well as the radius (forearm bone)

Triceps Muscle Function

  • Triceps Brachii – Responsible for extension of the arm at the elbow, which straightens the arm, as well as participates in pressing movements that extend the arm away from the body
  • Anconeus – Assists in extension of the arm

Common Triceps Exercises

Abdominals

Abdominals refer to four muscles that are on the midsection, informally called abs by most bodybuilders. These include the rectus abdominis, the external obliques, the internal obliques, and the transverse abdominis. The best abdominal program uses exercises that target all four areas of the abdominal region—upper abs, lower abs, internal and external obliques, and the transverse abdominis. 

The upper abs are best targeted with crunch exercises that involve flexing the upper spine forward by bringing the shoulders toward the hips, such as the standard crunch. The lower abdominals are best trained with exercises that involve flexing the lower spin forward by bringing the knees toward the chest, such as hanging knee raises. 

Both the internal and external obliques are best targeted by exercises that flex the spine laterally to the left and right, such as oblique crunches. They also are targeted with exercises that involve flexing the spin forward and rotating it to the left or right, such as with crossover crunches. 

The deep transverse abdominis is best trained with core exercises that fore the flexing of the transverse abdominis, pulling the navel in toward the spine to stabilize the spine and pelvis. 

Abdominal Muscle Structure

  • Rectus Abdominis – The surface-level abdominal muscles that compose the visible abs, this pair of muscles run from the front of the pelvis (hip bone) to the ribs and sternum (breastbone), divided by a vertical line of connective tissue called the linea alba
  • Internal and External Obliques – The side muscles of the abdomen, they originate from several of the lower ribs and connect to the illia, or tops of the hip bone, on either side. The internal obliques lie beneath the external
  • Transverse Abdominis – Lies beneath the rectus abdominis and obliques, similarly connecting the bones of the rib cage to those of the pelvis

Abdominal Muscle Function

  • Rectus Abdominis – Performs flexion of the spine, bringing the rib cage toward the pelvis or vice versa. Important to posture and stability
  • Internal and External Obliques – Responsible for stabilization of the spine, compression of the abdomen as when bracing for a lift, as well as rotation of the trunk and lateral flexion of the spine, as when bending to the side
  • Transverse Abdominis – Primarily responsible for stabilization and compression

Common Abdominal Exercises

Quadriceps

The quadriceps are the four muscles that make up the front of the thigh. The vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris all originate from different attachment points on the thigh and hip bone, but they all converge on one common tendon to perform knee extension, such as when you kick a ball. 

Because the rectus femoris originates on the hip bone, not the femur (thigh bone) as with the other three quadriceps muscles, it also is involved in hip flexion, such as when you lift your knee up. 

Although all four muscles work together to straighten the knee, certain exercises are better for targeting specific parts of the quad. For instance, the leg extension best targets the rectus femoris muscle. However, doing leg extensions with the toes turned in places more stress on the outer quad (vastus lateralis), and doing leg extensions with the toes pointed out better targets the inner quads (vastus medialis). 

The leg press hits all four quad muscles, but research shows that the emphasis is on the medialis muscle. Conversely, the hack squat tends to place more emphasis on the outer quads. Squats and lunges, however, hit the four quadriceps muscles fairly evenly, along with the leg adductors, hamstrings, gluteus maximus, and other muscles. 

Quadriceps Muscle Structure

  • Rectus Femoris – Originates at the ilium, or largest portion of the hip bone, and connects to the tibia, one of the two bones of the lower leg
  • Vastus Lateralis – The outermost of the three muscles underlying the rectus femoris, it connects the femur, or thigh bone, to the tibia
  • Vastus Intermedius – Lies between the vastus lateralis and vastus medialis and runs from the femur to the tibia
  • Vastus Medialis – The innermost of the three muscles underlying the rectus femoris, it also connects at the femur and tibia

Quadriceps Muscle Function

  • Rectus Femoris – Responsible for flexion of the leg at the hip, as well as extension of the lower leg at the knee
  • Vastus Lateralis – Extends the leg
  • Vastus Intermedius – Extends the leg
  • Vastus Medialis – Extends the leg

Common Quadriceps Exercises

Hamstrings and Glutes

The hamstrings are the muscles on the back of the thigh. The gluteus maximus, also referred to as the glutes, are the large buttock muscles. The glutes are involved in extending the legs back, as when standing up from a seated position, and kicking the legs back behind the body. The hamstrings are composed of the biceps femoris, the semitendinosus, and the semimembranosus. Collectively the hamstring muscles not only flex the knee, as when you bend your knee, but they also work in conjunction with the glutes to extend the legs at the hips.

Although compound quadriceps exercises like the squat, hack squat, lunge, and step-up are traditionally considered quadriceps exercises, they also largely involve the glutes and the hamstring muscles. For this reason, most bodybuilders perform fewer hamstring exercises than quadriceps exercises.

Even though the hamstrings involve different muscles that work together to perform leg flexion and hip extension, specific exercises target each muscle. The Romanian Deadlift hits the entire hamstring fairly evenly along with the glutes because of the hip extension involved in the exercise. The biceps femoris is better targeted with lying and standing leg curls. The semitendinosus and semimembranosus, on the other hand, are better targeted with seated leg curls. Therefore, a thorough hamstring workout should include one exercise that involves hip extension and knee flexion. 

Hamstring and Glute Muscle Structure

  • Biceps Femoris – Begins at the ischium of the pelvis, also called the “sitting bones” at the rear of the pelvis, or hip bone, and connects to the fibula, one of the two bones of the lower leg
  • Semitendinosus – Connects the ischium to the tibia, the other bone of the lower leg
  • Semimembranosus – Also runs from the ischium to the tibia
  • Gluteus Maximus – Attached to several points including the sacrum (lower spine), coccyx (tailbone), and pelvis

Hamstring and Glute Muscle Function

  • Biceps Femoris – Responsible for extension of the hip, or rearward movement of the leg, as well as flexion of the knee, and outward rotation of the lower leg
  • Semitendinosus – Extends the hip, assists in flexion of the knee, and rotates the lower leg inward
  • Semimembranosus – Performs the same function as the semitendinosus, extending the hip, flexing the knee, and rotating the lower leg inward
  • Gluteus Maximus – Contracts to move the leg rearward, as well as straightening of the trunk or upper body, as when returning to an upright position after stooping. Stabilizes the upper body when standing

Common Hamstring and Glute Exercises

Calves

Calves refer to two separate muscles on the lower leg. These muscles are the gastrocnemius, a muscle shaped like an upside-down heart, and the soleus, a muscle that lies underneath the gastrocnemius. Both muscles perform extension at the ankle, such as when you stand up on your toes.

Certain exercises are better than others at targeting the two calf muscles. Standing calf raises, or any calf raise that involves a fairly straight knee, is better at focusing the stress to the gastrocnemius. The soleus, on the other hand, is better targeted with seated calf raises or any calf raise that is performed with the knee bent to about 90 degrees.

The best way to train calves is to include one or two exercises that target the gastrocnemius muscle and one exercise that targets the soleus muscle. Most bodybuilders train their calves after thighs. Some also include a second or third workout of the calves if they do not train legs twice a week. The reason for this is that the calves, particularly the soleus, are made up of  a slightly higher percentage of slow-twitch muscle fibers. These muscle fibers have a high-endurance capacity and recover more quickly than fast-twitch muscle fibers. This Is also the reason that many bodybuilders train their calves with very high reps (20-30 per set). However, the best way to train calves is with the use of a periodized program that cycles the number of reps performed. 

Calf Muscle Structure

  • Gastrocnemius – Begins at the base of the femur (thigh bone) and connects to the heel bone via the Achilles tendon
  • Soleus – Runs from the back of the tibia, one of the lower leg bones, and also connects to the heel

Calf Muscle Function

  • Gastrocnemius – Responsible for flexion of the ankle and overall stabilization
  • Soleus – Also responsible for flexion of the ankle and stabilization

Common Calf Exercises

  • Standing Calf Raise
  • Seated Calf Raise
  • Leg Press Calf Raise

Trapezius

The trapezius is the large diamond-shaped muscle on the upper back, often referred to as traps. This muscle has upper, middle, and lower portions that all perform different movements. The upper trapezius primarily lifts and rotates the shoulder blades upward as when shrugging the shoulders, such as during dumbbell shrugs. The middle trapezius primarily pulls the shoulder blades together, such as during face pulls. The lower trapezius rotates the shoulder blades downward, such as when lifting a barbell overhead with straight arms like during the snatch.  

Trapezius training can be paired with shoulders or back. Most bodybuilders train the traps after shoulders, because their primary interest is in developing the upper portion of the traps. The upper traps are involved in most deltoid exercises. Therefore, they are sufficiently warmed up after training shoulders. 

However, because it is technically a back muscle and assists during many back exercises, upper traps are often trained with back. Most lifters typically pick one or two exercises for trap workouts and perform three to eight sets. If both a barbell and a dumbbell trap exercise are done in the same workout, the barbell exercise is typically done first. 

Trapezius Muscle Structure

  • Superior Trapezius – The upper trap muscle connects to several bones in the neck and the base of the skull, leading down to the clavicle (collarbone)
  • Transverse Trapezius – The middle trap muscle, runs from vertebrae in the neck and upper back to the scapula (shoulder blade)
  • Inferior Trapezius – The lower traps originate from the spine in the middle of the back and extend upward to the bottom of the scapula

Trapezius Muscle Function

  • Superior Trapezius – Responsible for upward movement of the scapula (shoulder blade) and shoulders. Also assists in overhead movements
  • Transverse Trapezius – Retracts the scapulae, pulling them toward the spine
  • Inferior Trapezius – Depress the scapulae, pulling them downward

Common Trapezius Exercises

  • Barbell Shrug
  • Dumbbell Shrug
  • Prone Incline Dumbbell Shrug
  • Straight-Arm Dip
  • Y-Raise

Forearms

The forearms are the muscles that make up the entire lower arm. Though you do not need to familiarize yourself with all the different forearm muscles, you should recognize the difference in those referred to as the wrist flexor group and those referred to as the wrist extensor group. 

The wrist flexor group is composed of forearm muscles that perform wrist flexion—the movement of the palms toward the inner forearm, such as during a wrist curl. The wrist extensors, on the other hand, are involved in performing wrist extension—moving the back of the hand toward the back of the forearm, such as when you twist the throttle on a motorcycle.

It is wise to train the forearms after the biceps because they are used so strongly during all biceps exercises. Typically, choosing one wrist curl or flexion exercise and one reverse wrist curl or extension exercise is sufficient for working the forearm muscles after biceps, especially if reverse-grip or hammer-grip curls were performed. 

If grip strength is a limiting factor on back and biceps exercises, including a specific grip exercise may be warranted. The grip exercise should be done before the wrist curl and reverse wrist curl exercises. If training with a whole-body, upper- and lower-body, or two-day split, you may consider skipping specific forearm work and relying on the fact that the forearm muscles are used during back and biceps exercises. 

Forearm Muscle Structure

  • Flexors – Composed of a number of muscles including the Palmaris Longus, Flexor Carpi Radialis, Flexor Carpi Ulnaris, and Flexor Digitorum Superficialis, these muscles primarily run from the lower end of the humerus (upper arm bone), as well as the ulna and radius (forearm bones) to various locations on the palm side of the wrist, hand, and fingers 
  • Extensors – A grouping of muscles that include the Extensor Carpi Radialis Longus and Brevis, Extensor Carpi Ulnaris, Extensor Digiti Minimi, these muscles connect the ulna and radius to the back of the wrist, hand, and fingers

Forearm Muscle Function

  • Flexors – Responsible for flexion of the wrist, palm, and fingers, such as moving the hand toward the inside of the forearm and closing of the hand into a fist, as well as pronation (inward rotation) of the forearm
  • Extensors – Responsible for extension of the wrist, palm, and fingers, such as moving the back of the hand upward toward the back of the forearm and opening of the hand, as well as supination (outward rotation) of the forearm

Common Forearm Exercises

  • Wrist Curl
  • Reverse Wrist Curl
  • Reverse-Grip Curl
  • Hammer Curl
  • Farmer’s Carry

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