ACSM CPT Chapter 3: Anatomy and Physiology
ACSM CPT Chapter 3: Anatomy and Physiology

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Chapter Objectives:

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

Describing Body Position and Joint movement

Anatomical Position

This is the universally accepted reference position that all professionals will use when describing regions and the spatial relationships of the body, as well as 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 our 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 – this divides the body, or the structure being talked about, into both right and left sides.

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

The transverse plane – this divides the body, or structure being talked about, into the superior and inferior sections. We also call this plane the horizontal, axial, and the 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 on it where the force of weight of the object 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 it usually is tested while the subject is standing. It gives the proper definition of body alignment and posture.

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

Joint Movement

This is often described by the spatial patterns of movement in relation to our body. 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 levers for movements.

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 bones that remain, 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 formations of the external parts of bone, as well as most of the diaphysis in long bones. The trabecular, AKA spongy, bone is a less dense bone. It is made of trabeculae, and they are oriented so they can provide the best resistance to stress.

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

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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.
  • Joint capsule encloses the joint cavity.
  • The cavity is also line with synovial membrane.
  • Synovial fluid is within the joint cavity.
  • All of the articulating surfaces of bone are covered with hyaline cartilages and these help for the absorption of shock and reduction of friction.

Synovial membranes produce synovial fluid, and these provide lubrication constantly for movements in order to minimize the friction that occurs. 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 are ones that 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 sift tissues that cross multiple joints.

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

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

Joint Stability

There are five factors of joint stability, or the resistance a joint has to displacement.

  • The ligaments of the body facilitate normal movements and resist movements that are excessive.
  • Tendons and muscles spanning a joint will enhance stability.
  • The fascia contribute to 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

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

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

Muscle Roles

All movements require muscles working together to produce movement, 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 must relax for the concentric contraction are the antagonist 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.

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.

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  • Bones – The bones of the shoulder are the humerus, scapula, and the 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 – There are four main joints of the shoulder: the glenohumeral, acromioclavicular, sternoclavicular, and the 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 abduction of the arm is known as scapulohumeral rhythm.


The muscles of the shoulder joint move the arm directly and the muscles of the shoulder girdle are used primarily to stabilize the scapula onto the thoracic cage, and they are very important for keeping proper posture. The muscles are listed within figure3.17 and 18 in the text and are too numerous to list here, but we will list what muscles are 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, rhomboids and trapezius 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 for shoulder pains. It happens from approximation of 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 less stability and greater range of motion provided by the joint.


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

  • Bones – The humerus, radius, and ulna are the bones of the elbow joint.
  • Ligaments – There are three primary ligaments for stabilization of the elbow. These are the ulnar collateral, radial collateral, and the annular ligament.
  • Joints – This compound synovial joint is composed of 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 brachii, and the anconeus. These extend the elbow.


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

Wrist, Hand, and Fingers

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

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


There are many dislocations, sprains, and fractures that 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 is the link between the axial skeleton and the lower body extremities. The region is responsible for assistance 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 bones of the pelvic girdle. The innominate includes the fused ilium, ischium, and the pubis that 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 the ischiofemoral ligaments. 
  • Joints – The pubic symphysis, sacroiliac, and hip joint act as the main joints in this region.
  • Movements – The pelvic girdles has 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 the 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 weight of the body 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 of the ankle and the foot.
  • Joints – the ankle is a synovial hinge joint. There are many joints in the ankle and foot.


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


Anterior and Lateral – The dorsiflexors are the peroneus tertius, extensor digitorum longus, tibialis anterior, and the 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 is an intricate structure that plays the most important role in functional mechanics. It is used to link the upper and lower extremities, enable motion of the trunk in three planes, and protect 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 and each motion segment has five articulations.


The spine is able to 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 doing 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 that support the head are small. This makes it possible to easily injure this region. 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.

ACSM CPT Chapter 3: Anatomy and Physiology 1
ACSM CPT Chapter 3: Anatomy and Physiology 2
ACSM CPT Chapter 3: Anatomy and Physiology 3

Tyler Read

Tyler Read, BSc, CPT. Tyler holds a B.S. in Kinesiology from Sonoma State University and is a certified personal trainer (CPT) with NASM (National Academy of sports medicine), and has over 15 years of experience working as a personal trainer. He is a published author of running start, and a frequent contributing author on Healthline and Eat this, not that.

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