The human body is highly evolved, over thousands of years our bodies evolved to stand upright with a skeletal system that allows us to run; jump, swim, walk, and perform intricate detailed work with our hands. Fitness instructors and personal trainers need to know about the physiology; structures, and functions of the skeletal system. It is also important for fitness instructors and personal trainers to be aware of the effects of exercise and the effects of a sedentary lifestyle on the skeletal system.

The skeletal system consists of bone; ligament, and cartilage. Bone is formed by calcified connective tissue, the skeletal system contains 206 bones.

Functions of the Skeletal System


The skeletal system provides a framework for the body to give it shape.

Attachment sites

Ligaments attach bones to muscles.


Vital organs are protected by the skeletal system, the brain is protected by the skull, and the lungs and heart are protected by the rib cage.


Long bones produce red blood cells, granular white blood cells, and platelets within the red bone marrow.


Bones act as bio-mechanical levers that muscles can pull on to produce movement also known as locomotion.


Bones store several minerals including calcium and phosphorus, these are released when they are required. Triglycerides are also stored in the adipocytes of the yellow bone marrow.

Axial & Appendicular Skeleton

The skeletal system can be divided into two parts, the axial skeleton that acts as the anchor points and includes the skull; spine, and ribs. The appendicular skeleton includes everything that hangs off the axial skeleton and includes; the upper and lower limbs, the pelvic and shoulder girdles.

Classifications of Bone

Long bones

Are used to produce movement.

Short bones

Act as shock absorbers spreading the load from walking; jumping, movement and impact.

Flat bones

Protect vital organs, and act as attachment sites for muscles to produce movement.

Irregular bones

Provide shape and protection.

Sesamoid bones

Found in specific joints to improve leverage and protect the joint.


Structure of a Long Bone


The head of the bone.


The shaft of the bone.

Hyaline Cartilage

Covers the ends of bones; prevents bone rubbing against bone, and absorbs shock.


Protective layer covering bone where there is no hyaline cartilage. Ligaments and tendons s attach to the periosteum.

Compact Bone

Provides strength to hollow parts of the bone, specifically the shaft.

Cancellous Bone

Found specifically in the epiphysis, spongy in structure giving bone elastic strength to absorb shock. Red marrow is stored here, producing red blood cells; platelets, and most white blood cells.

Medullary cavity

The hollow tube in the middle of compact bone, the cavity stores yellow bone marrow where some white blood cells are produced.

Yellow Marrow

Stores fat (Triglycerides) and produces some whote blood cells.

Red Marrow

Producing red blood cells, platelets, and most white blood cells.

Bone Formation

The bones of embyros begin life as cartilage, making them soft. Ossification is the process that uses calcium to create bone as the child grows. As bone ages it loses its strength and density. In severe cases in the older adult this is known as osteoporosis. Bones contain important cells, two of which include osteoblasts, cells that help form bone, and osteoclasts, cells that help break down old bone. Osteocytes are another cell contained by bone. Osteocytes are mature osteoblasts that no longer form new bone. Osteoblasts are the cells that transport calcium from blood to be deposited into cartilage, it is this process of the gradual build up of calcium and mineral deposits that creates bone.

Note: Osteoblasts and Osteoclasts are continually performing their jobs, creating new bone and reabsorbing old bone cells. Ossification is completed between the ages of 18-30 years old. Bone formation is affected by four factors; nutrition, physical activity, exposure to sunlight, and hormonal secretions.

Important: Skin has the ability to produce vitamin D when exposed to ultraviolet light or sunlight. The radiation produces and activates vitamin D in the body. Vitamin D must be present in the body for calcium to be absorbed in the small intestine. With the absence of vitamin D, calcium is not sufficiently absorbed, causing bones to be weak and brittle.

The Spine

In a developing foetus the spin is one curve, as it matures the spin develops four natural curves; two convex and two concave. The greatest range of movement occurs in the cervical and lumbar regions. The spine has specific roles and can be divided into 5 sections.


  • Smallest of the vertabrae.
  • Support the head and neck.
  • Top vertebrae (atlas) allows the head to nod.
  • Second vertabrae (axis) allows the head to rotate.


  • Ribs are attached to the thoracic vertebrae, making a protective “cage”
  • Allows slight bending movement at each joint to the left, the right, forward, and backwards.

Lumbar – Largest of the vertebrae. – Large range of movement allowing movement forwards; backwards, left and right. – Prone to injury.


  • All 5 sacral vertebrae are fused together.
  • Make a strong base and transport force from the lower body to the upper body.


  • All 4 vertebrae are fused and have no special functions. The coccyx is the remainder of a “tail” as the human body has evolved to an upright position.

Vertebral Disks

Cartilage discs that sit between the vertebrae. They are round in diameter and flat on the top and bottom. Also known as intervertebral discs. Each disc forms a “fibrocartilaginous joint with the vertebrae to allow slight movement; act as a ligament to hold vertebrae together, protects spinal nerves, and act as a shock absorber. Each disc has a strong outer layer called the annulus fibrosus and a softer, gel like centre called the nucleus pulposus

Neutral Spine

Fitness instructors and personal trainers coaching any exercise should include information about neutral spine. Neutral spine aligns the vertebrae into a position where minimal stress is placed on ligaments, vertebral joints and discs. Neutral spin also teaches the abdominal and hip muscles to hold the body in this neutral position. This will also reduce the possibility of lower back pain. We teach how to hold neutral spine on out fitness instructor courses and level 2 gym courses. It is important to teach this in health and fitness to promote good posture, reduce the chance of injuries, and prevent non functional development of the musculoskeletal system.

Common Postural Abnormalities

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  • Lordosis – An excessive curvature of the lumbar spine.
  • Kyphosis – An excessive curvature of the thoracic spine.
  • Scoliosis – A lateral deviation of the spine.

Pregnancy will cause the spine to change its lordotic curve, increasing the curve. The extra weight of the body lengthens and weakens the abdominal muscles and changes the angle of the hip. The hip is anteriorly tilted causing the lumbar spine to increase its curve.

Following birth the mother may develop scoliosis from holding the baby on their hip. A natural lifestyle habit that can cause a slight lateral deviation of the spine.

Connective Tissue

Connective tissue surrounds; connects, and stabilises joints. Connective tissue is not stimulated by the nervous system and is non contractile. Connective tissue can be divided into three main categories:

  • Cartilage
  • Ligaments
  • Tendons


There are three types of cartilage, each having its own function:

Hyaline (articular) cartilage

  • The most common type Tough, smooth, thin and bluey white in colour.
  • Covers the end of bones to form joints.
  • Found in synovial and cartilaginous joints.
  • Becomes slippery when lubricated with synovial fluid.
  • Reduces friction to allow optimal joint movement.

Elastic Cartilage

  • Similar to hyaline cartilage in its structure.
  • Has more fibres than hyaline cartilage.
  • Most of the fibres are elastin giving this cartilage the ability to spring back into shape.
  • Found specifically in the ear, eustachian, the epiglottis, nose, and all other places that require maintenance of a specific shape.


  • Thicker and stronger than both elastic and hyaline cartilage.
  • Limited distribution in the body.
  • Forms various shapes according to its role.
  • Acts like a shock absorber in cartilaginous joints.

Characteristics of Cartilage

  • Dense
  • Tough
  • Fibrous
  • Withstands compression
  • Can be work or torn
  • Very durable
  • No blood supply
  • Limited ability to repair itself
  • Dependant on regular activity for health
  • Ligaments

Ligaments Have Four Main Functions:

  • Connect bone to bone.
  • Enhance joint stability.
  • Guide joint motion.
  • Prevent excessive movement in joints.

Characteristics of Ligaments

  • Tough, white, non elastic fibrous tissue.
  • Attach bone to bone in all joint to provide stability.
  • Withstand tension.
  • String together in a strap like formation.
  • Allow normal movement and prevent unwanted movement.
  • Prolonged tension can damage the fibres.


Tendons are similar to ligaments but play a slightly different role. Tendon functions include:

  • Attach muscle to bone.
  • Transmit the force produced from muscles.

Note: Healing from injury is limited for connective tissue due to poor blood supply. When cartilage is damaged it may require surgical removal to prevent further damage. Tendons, if ruptured may also require surgical reattachment to bone.

Classifications of Joints

There are three types of joint, defined by the range of movement available at the type of joint.


Immovable and interlocking bones such as the skull.


Slightly moveable joints, bones brought together by ligaments e.g. the vertabrae.

Synovial (freely moveable)

The most common of the joints, characterised by:

  • End of bones covered with hyaline cartilage.
  • Stabilised by ligaments.
  • Surrounded by a fibrous capsule.
  • Capsulse lined by synovial membrane that secretes synovial fluid to lubricate the joint.

Synovial Joints

There are 6 types of synovial Joints.

  • Gliding joints
  • Pivot Joints
  • Ball & Socket Joints
  • Hinge Joints
  • Saddle Joints
  • Ellipsoid Joints

Effects of Exercise on the Skeletal System

Exercise has long and short term effects on the physiological state of the skeletal system.

Short Term

  • Increased synovial fluid production

Much like a car engine having oil, as the engine heats, the oil becomes thinner and slippy. As joints heat up synovial fluid becomes slippery and the synovial membrane secretes synovial fluid to manage increased activity levels and range of movement to prevent damage to the joint. It is important to effectively warm up joints with low impact movement to start, building to higher intensities and impacts towards a main workout.

Warm up is a key component of a workout and has stages to take the body through, preparing for the main activity. Warm up should never be overlooked in a workout. There are a number of ways to warm up. Level 2 fitness instructors learn a warm up protocol that allows them to choose specific standardised exercises to learn how to deliver a warm up. Personal Trainers use this protocol and can then become more inventive, the level 3 personal trainer course is a level up from the fitness instructor course. Due to increased knowledge of anatomy and physiology, a greater range of exercises can be used as part of the workouts they design.

Long Term Effects of Exercise

Weight bearing exercise can have positive benefits for the skeletal system that include:

  • Increased bone density
  • Stronger ligaments

Bearing your own body weight or resistance training can achieve these benefits, stimulating osteoblasts to transport and convert calcium into bone cells, strengthening bones to cope with the demands of exercise. Contrastingly, a sedentary lifestyle does not require strong or dense bones. This will result in the skeletal system being weaker and more frail. The human body is very clever and will adapt to the environment so that it does not waste energy maintaining a physiological state that is not necessary. Reversibility, a principle of fitness training, explains why muscular and cardiovascular endurance performance can return to starting levels after prolonged lay off from exercise.

Want to learn more about the skeletal system? We have a range of fitness courses available to help you start your fitness career. Already studying with us? Refer back to your online fitness course material or your level 2 course and level 3 course manual.

PT Skills is a UK provider of fitness training courses. We deliver classroom, and online courses for fitness instructors and personal trainers. If you are looking to become a fitness instructor or personal trainer, or looking to add additional qualifications to your level 2 gym or level 3 personal trainer qualification. We have a range of level 2 CPD awards you can add to your coaching qualifications. The awards we deliver include instructing kettlebellscircuits, and suspended movement training.

Our fitness instructor course; personal trainer course, and level 2 awards are delivered by blended learning, providing our learners with the ability to study fitness courses while working; completing other studies, or maintaining family commitments. This applies to all of our level 2 courses and level 3 courses

For more information about our gym courses, please contact our enrolment team or request a call back.