ACSM CPT Chapter 3: Anatomy and Physiology

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Chapter Objectives:

  • Give an overview of the anatomical structures of the musculoskeletal system.
  • Give details regarding the underlying kinesiological principles of musculoskeletal movement.
  • Find the key terms used for describing the body’s position and movements.
  • Talk about specific structures, movement patterns, range of motion, muscles, and common injuries for all of the body’s major joints.

Describing Body Position and Joint movement

Anatomical Position

All professionals will use this universally accepted reference position when describing regions, the spatial relationships of the body, and body positions.

Anatomical position is described as the body being erect with your feet together and both of the upper limbs at the side with the palms of your hands facing to the front and thumbs facing away from the body with the fingers fully extended.

Planes of Motion and Axes of Rotation

The sagittal plane – divides the body, or the structure being talked about, into both right and left sides.

The frontal plane – divides the body, or structure being talked about, into the anterior and posterior portions. We also call it the coronal plane.

The transverse plane – divides the body, or structure being talked about, into the superior and inferior sections. We also call this plane the horizontal, axial and cross sectional plane. 

Activities and sports all require movements within all three planes.

Center of Gravity, Line of Gravity, and Postural Alignment

The center of gravity of something is the point where the force of the object’s weight is thought to act. This changes with movements and body positioning.

The line of gravity is the imaginary vertical line that goes through the center of gravity and is usually tested while the subject stands. It gives the proper definition of body alignment and posture.

Postural abnormalities should all be described from this ideal line of gravity.

Joint Movement

The spatial patterns of movement about our body often describe this. We relate it to terms of anatomical position. 

Musculoskeletal Anatomy

Bones, joints, and muscles are the three main anatomical structures of interest for the musculoskeletal system.

Skeletal System

This system consists of bones, periosteum, and cartilage tissues. The bones support soft tissues, act as important nutrient sources and blood constituents, protect internal organs, and serve as rigid movement levers.

We have 206 bones in the body, and 177 of those are responsible for voluntary movement. 

The axial skeleton consists of the skull, hyoid, ribs, vertebral column, and sternum.

The remaining bones, mostly the upper and lower limb bones, are known as the appendicular skeleton. 

The two primary types of bones are trabecular and cortical. Cortical, or compact, bone is arranged in what is called osteons and they contain few spaces. This is the main formation of the bone’s external parts, and most of the diaphysis is in long bones. The trabecular, AKA spongy, bone is a less dense bone. It is made of trabeculae, which are oriented to provide the best resistance to stress.

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We can also group bones by their shape of them. Here we have long, short, flat, and sesamoid bones.

Articular System

Joints are used for the articulations between bones, and when bones and ligaments are together, it is called the articular system. There are three classifications of joints. These are synarthrodial, which do not move. Amphiarthrodial, which move slightly and are held by ligaments and fibrocartilage, and diarthrodial, which are the most common and are movable easily.

Synovial Joints

This is the most common type of joint, called synovial or diarthrodial, that we have, and they have a fibrous articular capsule and a synovial membrane that encloses the joint cavity.

Synovial joints have five distinct features.

  • Enclosed in a fibrous joint capsule.
  • The joint capsule encloses the joint cavity.
  • The cavity is also lined with a synovial membrane.
  • Synovial fluid is within the joint cavity.
  • All of the articulating surfaces of the bone are covered with hyaline cartilage, which helps absorb shock and reduce friction.

Synovial membranes produce synovial fluid, providing constant movement lubrication to minimize friction. Ligaments also reinforce synovial joints sometimes. 

Joint Movements and Range of Motion

The movements that occur within joints are combinations of spinning, rolling, and sliding of joint surfaces. We have open and closed chain movements that we do. 

Open chain movements happen when distal segments of the joints move in space. This would be like leg extension exercises and the knee joint.

Closed chain movements happen when the distal segments of joints are fixed in one spot. One example is a standing barbell squat.

Movements of one joint will most likely influence the movements at the adjacent joints due to the many numbers of muscles and other soft tissues that cross multiple joints.

Hypermobile means that someone has more range of motion than is normal, and the opposite definition would be hypermobile. 

There are two types of movements for joints and ROM classifications. Active range of motion is the range that voluntary movements and the contraction of skeletal muscles can reach. Passive range of motion is the range of motion that can be reached externally.

Joint Stability

There are five factors of joint stability or a joint’s resistance to displacement.

  • The ligaments of the body facilitate normal movements and resist excessive movements.
  • Tendons and muscles spanning a joint will enhance stability.
  • The fascia contributes to the stability of a joint.
  • The atmospheric pressure creates a larger force outside of the joint than the internal pressure does form within the joint.
  • Bony structures are important joint stability contributors.

Muscular System

There are more than 600 skeletal muscles in the human body and 100 of them or so should be known by trainers.

Classification of Skeletal Muscles

  • Muscles have a parallel or a pennate arrangement of their fibers and are classified by these two.
  • Another way to classify muscles is by the number of joints that they act on.

How Muscles Produce Movement

The force produced by muscles is transferred into the tendons, and these pull on bones and other structures to which they are connected, like the skin. 

Since most of our muscles cross a joint, they pull one of the bones toward the other when they contract. 

Muscle Roles

All movements require muscles working together to move, never usually one muscle doing all of the work.

We typically classify muscles based on the role they have during movement. 

The prime mover of the movement is known as the agonist. This is the one responsible for the main action. So, the biceps in the bicep curl. 

The muscles that oppose the agonist and relax for the concentric contraction are the antagonist’s muscles. So, for a bicep curl, this would be the triceps.

Synergists are another type of muscle, and they are used to prevent movements that are not wanted and thus will help the agonists perform better. We can separate synergists into fixators and stabilizers.

Co-contraction is when we contract the agonist and the antagonist at the same time.

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Specific Joint Anatomy and Considerations

Upper Extremity


  • Structure – This is a multijoint structure providing a link between the thoracic cage and the upper extremity. This is a ball and socket joint. The shoulder is known for its high degree of mobility and resulting instability from that.
  • Bones – The shoulder bones are the humerus, scapula, and clavicle.
  • Ligaments and Bursae – The main ones are the coracohumeral ligament, the glenohumeral ligament, coracoacromial ligament, acromioclavicular ligament, coracoclavicular ligament, sternoclavicular ligament costoclavicular ligament, and the subacromial bursa.
  • Joints – The shoulder has four main joints: the glenohumeral, acromioclavicular, sternoclavicular, and scapulothoracic joint. 


The glenohumeral joint – moves in three planes. The scapulothoracic joint also has movement within all three planes.

Scapulohumeral Rhythm – The dual movement of the glenohumeral and scapulothoracic joints for full arm abduction is known as scapulohumeral rhythm.


The joint shoulder muscles move the arm directly, and the shoulder girdle muscles are used primarily to stabilize the scapula onto the thoracic cage. They are very important for keeping proper posture. The muscles in Figures 3.17 and 18 in the text are too numerous to list here, but we will list the muscles in each region.

  • Anterior – the pectoralis major, subscapularis, biceps brachii, and coracobrachialis.
  • Superior – the deltoid and the supraspinatus.
  • Rotator Cuff – The supraspinatus, infraspinatus, teres minor, and the subscapularis. We use the acronym of SITS.
  • Posterior – the infraspinatus and the teres minor.
  • Scapular – Pectorals major, serratus anterior, and the subclavius for the anterior shoulder girdle. The levator scapulae, rhomboid, and trapezius are for the posterior shoulder girdle. 
  • Inferior – the latissimus dorsi, teres major, and the long head of the triceps brachii.


Impingement syndrome is one of the most common nontraumatic causes of shoulder pains. It happens from approximating the acromion and the humerus’ greater tubercle. These entrap the rotator cuff tendons.

Thoracic outlet syndrome is another shoulder condition that results from muscle imbalances, poor posture, and bad biomechanics.

The shoulder is also very susceptible to traumatic injuries due to the joint’s lower stability and greater range of motion.


Structure – the elbow is an important joint for swinging, carrying, lifting, and almost every upper extremity exercise.

  • Bones – The elbow joint bones are the humerus, radius, and ulna.
  • Ligaments – There are three primary ligaments for the stabilization of the elbow. These are the ulnar collateral, radial collateral, and annular ligament.
  • Joints – This synovial compound joint comprises the humeroulnar and humeroradial joints.


The two joints of the elbow are hinge joints and they are used to flex and extend the elbow within the sagittal plane. 


Anterior – the muscles are the biceps brachii, the brachialis, and the brachioradialis. These are used for flexing the elbow.

Posterior – the main muscles are the triceps, brachial, and anconeus. These extend the elbow.


The elbow is very susceptible to overuse and repetitive motion injuries due to using them throughout most daily life tasks.

Wrist, Hand, and Fingers

Structure – These are required for most sports, work, and daily living activities through throwing, eating, typing, writing, lifting, and gripping tasks.

  • Bones – There are 29 bones in this region. 
  • Ligament – the radioulnar joint is supported by the ulnar collateral, radial collateral, dorsal radiocarpal, and volar radiocarpal ligaments.
  • Joints – the main wrist joint is called the radiocarpal joint.


The wrist allows flexion and extension in the sagittal plane.


Anterior – wrist flexor muscles

Posterior – wrist extensor muscles


Many dislocations, sprains, and fractures can occur from falling.

Carpel tunnel syndrome is another big issue that happens due to median nerve entrapment in the anterior side of the wrist.

Lower Extremity

Pelvis and Hip – This links the axial skeleton and lower body extremities. The region is responsible for assisting with shock absorption, stability, and motion, and the distribution of the body weight evenly to the lower extremities.

  • Bones – the sacrum and the innominate are the pelvic girdle bones. The innominate includes the fused ilium, ischium, and pubis, which are on both sides.
  • Ligaments – The anterior, posterior, and interosseus ligaments are used to bind the sacroiliac joint. Many intrinsic ligaments stabilize the hip joint, like the iliofemoral, pubofemoral, and ischiofemoral ligaments. 
  • Joints – The pubic symphysis, sacroiliac, and hip joint act as the main joints in this region.
  • Movements – The pelvic girdles have movement occurring in all three planes. The hip joint also does this.
  • Muscles
  • Pelvis – lumbar spine muscles, lower trunk, and hip muscles.
  • Hip
  • Anterior – the iliopsoas, pectineus, sartorius, rectus femoris, and the tensor fascia latae.
  • Medial – the gracilis, adductor longus, adductor brevis, and adductor magnus.
  • Posterior – glute max, min, and med, the six deep lateral rotators, and the hamstring muscles.
  • Injuries – These are very structurally strong areas, and since this is so, there are few traumatic injuries to this region. The soft tissues, however, may be injured often.


Structure – The largest joint in the human body due to the amount of weight that is present from the upper body and trunk partnered with the need for locomotion. 

  • Bones – The distal femur, proximal tibia, and patella.
  • Ligaments – There are the cruciate ligaments and collateral ligaments of the near.
  • Joints – The tibiofemoral and the patellofemoral joints.


The tibiofemoral joint allows flexion and extension in the sagittal plane. It can also move in the transverse plane when flexed. 


Anterior – The quadriceps, rectus femoris, and the three vasti muscles are the largest ones.

Posterior – The hamstrings, sartorius, gastrocnemius, popliteus, and the gracilis.


The knee is a frequently injured joint and is vulnerable to acute and repetitive injuries.

Sprains and tears of the ligaments are pretty common in the knee for athletes primarily.

The menisci are often injured.

Patellofemoral pain syndrome is common for young athletes and produces anterior knee pain for them.

Ankle and Foot

Structure – these are responsible for bearing the body’s weight and for ambulation. These need to function right due to being essential for most sports and daily activities.

  • Bones – there are 26 bones in the foot.
  • Ligaments – there are close to 100 ligaments in the ankle and the foot.
  • Joints – the ankle is a synovial hinge joint. There are many joints in the ankle and foot.


The foot joints allow for dorsiflexion and plantarflexion, pronation, and supination.


Anterior and Lateral – The dorsiflexion are the peroneus tertius, extensor digitorum longus, tibialis anterior, and extensor hallucis longus.

Superficial and Deep Posterior – these are the gastrocnemius, plantaris, and the soleus.

Injuries – due to bearing weight and virtually every activity involving moving this joint, this joint is most commonly injured. For sports, ankle sprains are the most common injury. 


Structure – This intricate structure plays the most important role in functional mechanics. It links the upper and lower extremities, enables trunk motion in three planes, and protects the spinal cord.

  • Bones – vertebrae make up the spinal column. We have 24 of them. The 12 thoracic vertebrae all have ribs attached to them. The spinal column also has the sacrum and the coccyx.
  • Ligaments – the anterior and posterior longitudinal ligaments and the ligamentum flavum are the main supporting spinal ligaments. 
  • Intervertebral Discs – these provide load bearing, stability, and shock absorption.
  • Joints – there are many motion segments in the spine, each with five articulations.


The spine can move in all of the planes, but this varies depending on the region of the spine being discussed.

Compound Trunk Extension – This movement is required of the hip joints, pelvis, and lumbar spine when lifting and bending.


The muscles exist in pairs on both sides.


Anterior – the sternocleidomastoid, scalenes, longus colli, and he longus capitis.

Posterior – the splenius, erector spinae, and suboccipital. 

Lateral – levator scapulae and the upper trapezius.


Anterior – The rectus abdominus, internal and external abdominal oblique, and the transverse abdominus.

Posterior – erector spinae, multifidus muscles, and the intrinsic rotators.

Lateral – quadratus lumborum and the psoas major and minor.


Cervical – This is the most mobile part of the spine, and the cervical muscle supporting the head is small. This makes it possible to injure this region easily. Sprains and strains are somewhat common but mostly happen in whiplash scenarios.

Lumbar – Lower back pain is the leading disability cause and the top reason for people visiting their doctors. Restorative exercise is often implemented for these lower back injuries and pains.

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Tyler Read - Certified Personal Trainer with PTPioneer

Tyler Read

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