Meet Your Muscles

Last updated on October 15, 2022

This key to building a great physique is to know your anatomy. After all, building lean muscle is all about adapting the anatomy. Muscular proportion and symmetry about when you choose the best exercises; it doesn’t happen by chance. As Arnold Schwarzenegger put it in Pumping Iron, you need to treat your body like a piece of clay that you sculpt to perfection.

Getting to know your anatomy allows you to take the guesswork out of building your body. As a result your training will be far more productive. In this article, we peel back the skin to reveal the muscles that you will be working as you sculpt your lean physique.

The Key Muscles

There are six key muscle groups that need to be trained in order to develop your entire body. They are:

  • Chest
  • Shoulders
  • Back
  • Arms
  • Legs
  • Abdominals


The chest, or pectoralis major, is a fan-shaped muscle that has two anatomic sections, or heads. The upper clavicular head originates on the collarbone and the lower sternal head ridges on the sternum, or breastbone. These two heads pass outward across the chest wall and merge into a single tendon that attaches to the humerus bone of the upper arm.

When your chest muscle contracts, movement takes place at the shoulder joints. The main function of the muscle is to adduct, flex and internally rotate the arm. This moves the arm forward and across the chest, as when you are doing a bear hug action.

To read more on our preferred chest exercises please read our article on effective chest exercises.


The shoulder is a ball and socket joint between the humerus bone of the upper arm and the scapula bone, or shoulder blade. There are six key movements that occur at the shoulder:

  • Flexion
  • Extension
  • Abduction
  • Adduction
  • Internal rotation
  • External rotation

The muscle that covers the shoulder joint is called the deltoid. It has three separate sections, or heads. Each head moves the arm in a different direction. They each have separate origin points and merge into a single tendon that attaches to the humerus bone.

The three deltoid heads are:

  • Anterior (front) deltoid
  • Medial (side) deltoid
  • Posterior (rear) deltoid this

The anterior deltoid in front attaches to the clavicle and raises the arm forward. The medial deltoid at the side attaches to the acromion and lifts the arm outward. The posterior deltoid head attaches to the scapula and moves the arm backward.

Read more on our chosen shoulder exercises for men and shoulder exercises for women on this site.


The back is made up of several layers of muscle that stack upon each other like a sandwich. For bodybuilding purposes it can be divided into three sections, each representing a triangular segment of a quilted blanket. Those three sections are:

Upper Back

The upper back is made up of a large triangular shaped muscle called the trapezius, or traps. This muscle originates along the upper spine from the skull down to the last rib. The upper fibers of the trapezius attach to the outer tip of the shoulder on the clavicle, acromion and scapula. The lower fibers attach to the scapula, or shoulder blade.

The upper traps provide support to the shoulders and are used to shrug the shoulders. The lower traps retract the scapula and pull the shoulders backward.

Middle Back

The major muscle of the middle back is the latissimus dorsi. This is a fan-shaped muscle that originates on the lower half of the spinal column in the rear ridge of the pelvic bone. It then moves up the back to converge into a band-like tendon that attaches to the upper humerus, right alongside the pectoralis major.

The function of the lats is to pull the upper arm downward and backward toward the hipbone. It also pulls the arm in against the side of the body.

Lower Back

The lower back is made off of the erector spinae muscles that run alongside the entire length of the spinal column. In the lumbar region, the erector spinae splits into three columns. These three muscles are the pillars of strength in the lower back that keep the spine straight and extend the torso, arching the spine backward.

To learn more about our key back exercises check out our article.


The main muscles of the arms are the biceps, triceps and forearms.


As its name suggests, the biceps is a two headed muscle. The short head attaches to the coracoid process, and the long-head arises from above the glenoid of the shoulder joint. The muscle passes down alongside the humerus and attaches about 1 ½ inches below the elbow joint onto a tuberosity on the inside of the radius bone.

The job of the biceps is to flex the elbow joint, raising the hand towards the face. The biceps is also capable of supination of the forearm. This involves rotating the hand so the palm faces upward.


The triceps is a three headed muscle group on the back of the upper arm. The three heads are known as:

  • Long head
  • Lateral (outer) head
  • Medial (inner) head

The long head arises from beneath the glenoid fossa of the shoulder joint.

The lateral head originates on the outer part of the humerus.

The medial head originates on the rear surface of the humerus.

All three heads fuse together at their lower ends to form a single tendon that attaches behind the elbow joint onto the ulna bone.

The main function of the triceps is to cause extension at the elbow. This moves the hand away from the face. The triceps is the only muscle that straightens the elbow joint. All three heads of the triceps muscle cross the elbow joint, but the long-head is the only one that crosses beneath the shoulder joint.


The forearms are a mass of 20 different muscles. They have two different compartments. These are the flexor group on the palm side, and the tensor group on the reverse side. The fleshy muscle portion of nearly all of these muscles are located on the upper two thirds of the forearm.

The functions of the forearm muscles are supination  and pronation of the hand.

For our arm guide for men and women read our article here.


We can divide the font of the leg into the quadriceps and the calves. The upper leg has a single bone – the femur. The lower leg consists of two bones – the tibia, on the big toe side, and the fibula, on the little toe side.

The knee is a hinge joint at the junction of the femur and the tibia and fibula. The knee joint performs the two movements of flexion and extension. During knee flexion, the lower leg bends toward the back of the thigh. During knee extension, the lower leg moves away from the thigh so the leg straightens.


The quadricep muscle is made up of four separate heads:

  • Rectus femoris originating on the front of the pelvic bone
  • Vastus medialis originating on the inner edge of the femur
  • Vastus lateralis originating on the outer edge of the femur
  • Vastus intermedialis originating on the front surface of the femur

The four heads merge together to attack onto the patella, or knee cap. They then insert via a single tendon onto the tibia, just below the knee joint.

The main function of the quadriceps is to extend the knee and straighten the leg.


The hamstrings sit at the back of the upper leg. This is a group of three muscle heads. All of them originate on the pelvis. The biceps femoris passes behind the outer aspect of the thigh to attach at the head of the fibula bone, just below the knee. The semimembranosus and semitendinosus pass together behind the inner aspect of the thigh, attaching to the upper tibia bone.

All three hamstring heads span both the knee and the hip joints. As a result, they cause flexion of the knee and extension of the hip.


The gluteus maximus originates on the pelvic bone and passes down behind the hip joint to attach on the upper femur. It covers the butt and is the largest and most powerful muscle in the body. Its function is hip extension.


The calves are made up of two muscles:

  • Gastrocnemius
  • Soleus

The gastrocnemius, or gastro, is the visible part of the calves. It has two heads on the rear of the femur bone, immediately above the knee joint. The soleus originates on the rear of the tibia and lies under the gastrocnemius.

The calf muscles cause plantar flexion of the ankle, as when standing on tiptoes. The gastro is the prime mover when the leg is straight, while the soleus becomes more active when the knee bends.

Our homepage would provide you with are articles for our preferred leg workouts.


The abdominal wall has two separate anatomical parts. The front wall consists of one muscle – the rectus abdominis, or abs. The abs originate on the lower margin of the rib cage and sternum and pass vertically downward to attach on the pubic bone.

The two rectus abdominis muscles (one on each side) are encased in a sheath of fascia that forms the central demarcation down the middle of the abs. Fascia divisions in the muscle are responsible for the six pack appearance.

The function of the abs is to cause flexion of the trunk to bend the torso forward toward the legs.

The side abdominal wall is made up of three layered of muscle:

  • External obliques, passing obliquely down from the ribcage to the pelvic bone
  • Internal obliques, passing obliquely upward from the pelvic bone to the ribs
  • Transversus abdominis, lying horizontally cross the abdominal wall

For our best abdominal workouts check out our abs workouts article.


Now that you have a working knowledge of the anatomy of your body’s muscles, you will be able to select the exercises that best work them through their full range of motion. In our next article, we’ll investigate how to choose the best program to meet your lean muscle building goals.

Steve Theunissen has qualified from the International Sports Sciences Association (ISSA) and is a certified Personal Trainer and Nutritionist. He has over 30 years experience in fitness and nutrition and currently working with famous fitness professionals. He is currently living in New Zealand with is wife and daughter.

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