1.1a skeletal and muscular systems

• the skeleton

  the skeleton is a shaping framework for the body which gives protection for internal organs, is the site for blood cell production and is a mineral store. for human movement the skeleton provides attachments for the muscular system and acts as levers and pivot points required to create movement
• types of bones

  • flat bones such as the sternum, ribs, cranium and pelvis protect internal organs but also act as suitable sites for muscular attachment
  • long bones such as the femur, humerus, radius, tibia and phalanges act as levers for movement and act as sites for blood cell production

  there are also irregular bones such as the vertebrae, which protects the spinal cord, short bones such as the carpals and tarsals, which bear weight well, and sesamoid bones such as the patella, which ease joint movement and resist compression
• joint

  an area of the body where two or more bones articulate to create human movement
• features of a synovial joint- ligament

  structure- a tough band of slightly elastic connective tissue

  function- connects bone to bone and stabilises joints during movement
• features of a synovial joint- synovial fluid

  structure- lubricating liquid contained within the joint cavity

  function- reduces friction and nourishes articular cartilage
• features of a synovial joint- articular cartilage

  structure- smooth tissue which covers the surface of articulating bones

  function- absorbs shock and allows friction free movement
• features of a synovial joint- joint capsule

  structure- a fibrous sac with an inner synovial membrane

  function- encloses and strengthens the joint secreting synovial fluid
• features of a synovial membrane- bursa

  structure- a closed, fluid filled sac found where tendons rub over bones

  function- reduces friction between tendons and bones
• the joint type and shape of articulating bones will allow a specific range of motion at a joint: from the large range of motion at the ball and socket joint of the shoulder to the limited range of motion at the hinge joint of the ankle
• the three planes of movement

  1. the sagittal plane lies vertically. it divides the body into left and right parts from the medial (midline) to the lateral (outside)
  2. the frontal plane lies vertically. it divides the body into anterior (front) and posterior (back)
  3. the transverse plane lies horizontally. it divides the body into superior (upper) and inferior (lower) parts
• types of synovial joint

  • hinge joint- elbow, knee and ankle joints
  • pivot joint- radio-ulnar joint
  • condyloid joint- the wrist joint
  • ball and socket joint- hip and shoulder joint
• flexion and extension

  flexion and extension occur in the sagittal plane and are types of movement which change the angle between articulating bones at a joint

  • flexion decreases the joint angle, usually to the front of the body
  • extension increases the joint angle, usually to the back of the body

  flexion and extension can occur at the wrist when performing wrist curls, at the elbow when performing bicep curls, at the shoulder when performing basketball jump shots, at the hip when performing high kicks and at the knee when performing leg curls
• dorsi-flexion and plantar flexion

  plantar and dorsi-flexion occur in the sagittal plane and are unique to the ankle joint

  • dorsi-flexion decreases the joint angle bringing the toes closer to the tibia, for example when preparing to the perform a jump shot in basketball
  • plantar flexion increases the joint angle moving the toes further away from the tibia, for example when taking off in the high jump
• abduction and adduction

  abduction and adduction occur in the frontal plane and move an articulating bone at a joint away or closer to the midline of the body

  • abduction of a joint moves the articulating bone away from the midline of the body
  • adduction of a joint moves the articulating bone closer to the midline of the body

  for example, when performing lateral raises, in the upwards phase the humerus moves further from the midline as abduction occurs at the shoulder joint. in the downwards phase, the humerus moves closer to the midline as adduction occurs at the shoulder joint
• horizontal extension and horizontal flexion

  horizontal extension and horizontal extension occur in the transverse plane and occur when a limb is parallel to the ground and the articulating bone at a joint moves further away from or closer to the midline of the body

  • horizontal extension of a joint moves the articulating bone away from the midline of the body
  • horizontal flexion of a joint moves the articulating bone closer to the midline of the body

  these movements occur at the shoulder when performing a discus throw and at the hip when performing "open and close the gate" during warm ups
• rotation

  rotation occurs in the transverse plane. it occurs at the shoulder and hip joints when an articulating bone turns about its longitudinal axis, often referred to as a screwdriver action.

  rotation towards the body is medial and rotation away from the body is lateral

  for example, when performing a tennis forehand groundstroke with topspin, the humerus rotates at the shoulder joint laterally in the preparation phase and medially in the execution phase to sweep the racket over the top of the ball
• the muscular system

  each muscle is composed of many fibres encased in connective tissue forming tendons at either end. tendons attach muscle to bone and transmit the pull force created by the muscle to move the bones they are attached to. the points of attachment are termed "origin" and "insertion"

  • origin- the point of muscular attachment to a stationary bone which stays relatively fixed during muscular contraction
  • insertion- the point of muscular attachment to a moveable bone which gets closer to the origin during muscular contraction
• antagonistic muscle action

  paired muscle action as the agonist shortens to create the movement the antagonist lengthens to coordinate the movement

  1. agonist: a muscle responsible for creating movement at a joint. also known as the prime mover
  2. antagonist: a muscle that opposes the agonist providing a resistance for co-ordinated movement
  3. fixator: a muscle that stabilises one part of a body while another causes movement
• isotonic muscle contraction

  isotonic muscle contraction is when a muscle changes length during its contraction.

  • concentric muscle contraction is when the muscle shortens producing tension. this produces the force to pull two bones closer together, causing joint movement. e.g., the biceps brachii during the upwards phase of a bicep curl
  • eccentric muscle contraction is when the muscle lengthens producing tension. this resists forces such as gravity to control joint movement e.g., the biceps brachii during the downwards phase of a bicep curl
• isometric muscle contraction

  isometric muscle contraction is when a muscle contracts but does not change length. e.g., the biceps brachii holding a free weight in the hand still. the muscle will create tension by pulling on the tendon attachments but no movement is created. posture is maintained by muscles contracting isometrically
• delayed onset muscle soreness

  pain and stiffness felt in the muscle which peaks 24-72 hours after exercise, associated with eccentric muscle contractions
• ankle joint

  joint type: hinge joint

  articulating bones: tibia, fibula and talus

  movement: sagittal plane

  agonist muscles:

  • dorsi flexion- tibialis anterior
  • plantar flexion- gastrocnemius and soleus
• knee joint

  joint type: hinge joint

  articulating bones: femur and tibia

  movement: sagittal

  agonist muscles:

  • flexion- biceps femoris, semitendinosus and semimembranosus
  • extension- rectus femoris, vastus lateralis, vastus intermedius and vastus medialis
• hip joint

  joint type: ball and socket joint

  articulating bones: pelvic girdle and femur

  sagittal plane agonist muscles:

  • flexion- iliopsoas
  • extension- gluteus maximus

  frontal plane agonistic muscles:

  • adduction- adductor longus, brevis and magnus
  • abduction- gluteus Medius and minimus

  transverse plane agonist muscles:

  • medial rotation- gluteus medius and minimus
  • lateral rotation- gluteus maximus
• shoulder joint

  joint type: ball and socket joint

  articulating bones: humerus and scapula

  sagittal plane agonist muscles:

  • flexion- anterior deltoid
  • extension- posterior deltoid

  frontal plane agonist muscles:

  • adduction- latissimus dorsi
  • abduction- middle deltoid

  transverse plane agonist muscles:

  • horizontal flexion- pectoralis major
  • horizontal extension- posterior deltoid and teres minor
  • medial rotation- teres major and subscapularis
  • lateral rotation- teres minor and infraspinatous
• elbow joint

  joint type: hinge joint

  articulating bones: humerus, radius and ulna

  movement: sagittal plane

  agonist muscles:

  • flexion- biceps brachii
  • extension- triceps brachii
• wrist joint

  joint type: condyloid joint

  articulating bones: radius, ulna and carpals

  movement: sagittal plane

  agonist muscles:

  • flexion- wrist flexors
  • extension- wrist extensors
• AO3: the more mobile a joint, the more stability is compromised and injury becomes a risk. exercise is important for joint stability. the type of activity is also important:

  • regular aerobic and resistance based activities strengthen ligaments, tendons and muscles. elasticity is maintained and articular cartilage is nourished and thickened, protecting the joint during use.
  • contact and high impact sports like rugby can lead to sprains, strains, ligament damage and dislocation. ligaments are elastic but can become plastic as if they are overstretched, will not return to their original length.
• the role of a motor unit

  1. nerve impulse is initiated in the motor neurone of the body
  2. nerve impulse conducted down the axon of the motor neurone by a nerve action potential to the synaptic cleft
  3. neurotransmitter called acetylcholine is secreted into the synaptic cleft to conduct the nerve impulse across the gap
  4. if the electrical charge is above the threshold, the muscle fibre will contract
  5. this happens in an "all or none" fashion
• Motor neurone


  A nerve cell which conducts a nerve impulse to a group of muscle fibres
• Motor unit

  A motor neurone and the muscle fibres stimulated by its axon
• Action potential

  Positive electrical charge inside the nerve and muscle cells which conducts the nerve impulse down the neurone and into the muscle fibre
• Neurotransmitter

  A chemical produced and secreted by a neurone which transmits the nerve impulse across the synaptic cleft to the muscle fibre
• All-or-none-law


  Depending on whether the stimulus is above a threshold, all muscles will give a complete contraction or no contraction at all
• the strength of contraction of a muscle is dependent on the number of motor units recruited by the brain. the greater the number of motor units recruited, the greater the strength of the force of contraction. the motor neurones stimulate one of three types of muscle fibres with differing structures and functions.

  any one muscle contains three types of fibre. depending on genetics, the percentage of each fibre held will naturally suit an athlete to a specific type of event
• slow oxidative muscle fibres are structurally designed to store oxygen in myoglobin and process oxygen in the mitochondria, which allow them to work aerobically. they produce a small amount of force but resist fatigue for a long period of time.

  the gastrocnemius of a long distance runner may have around 70% of slow oxidative fibres, optimising performance in low intensity, long duration events
• fast oxidative glycolytic muscle fibres are structurally designed to produce a large amount of force quickly; however, they also have the capacity to resist fatigue.

  high intensity activities lasting several minutes, such as the 800m, will see athletes with a high percentage of fast oxidative glycolytic fibres
• fast glycolytic muscle fibre are structurally designed to work anaerobically, with large stores of phosphocreatine for rapid energy production and the largest amount of force. however, they fatigue quickly so are dominant in very high intensity activities that last a short duration.

  the gastrocnemius of a sprinter may have around 70% of fast glycolytic fibres
• phosphocreatine (PC)

  a high energy compound stored in the muscle cell used as fuel for very high intensity energy production (ATP-PC system)
• mitochondria

  a structure in the sarcoplasm responsible for aerobic energy production