Muscular System

• Skeletal muscles which are consciously controlled (voluntary – “think then do”) are attached to 2 different bones across a joint
• One of the major functions of the muscular system is to produce movement
• This enables the human body to perform day to day tasks and to respond quickly to changes in the external environment e.g. changing direction in a game of sport
• Origin of a muscle is the attachment onto the bone that does not move when the muscle contracts
• Once a muscle contracts to move a bone, another muscle must contract to return the bone to its original position – muscles work in pairs to produce movement
• When a muscle contracts, it pulls on 1 of the 2 bones to which it is attached, creating movement
• Muscles have two attachment points onto the skeleton. Each attachment is on a different bone and across a joint
• To create movement e.g. walking, swimming, the Central Nerves System delivers a message from the brain to the relevant muscle to contract, resulting in a pulling force to be exerted on the bone which causes movement to occur
• The human body is made up of over 600 muscles, working together to provide both conscious and subconscious movements for the human body
• All muscles work across a joint and when contraction occurs, movement takes place altering the joint angle
• Insertion of a muscle is the attachment point at the distal end (further from midline of the body)
• Major muscles of the human body - Anterior


  • Deltoid
  • Biceps brachii
  • Flexors of the wrist & hand
  • Pectoralis major
  • Serratus anterior
  • Abdominals
  • Rectus abdominus
  • Internal & external obliques
  • Transverse abdominus
  • Quadriceps
  • Rectus femoris
  • Vastus lateralis
  • Vastus medialis
  • Vastus intermedius
  • Sartorius
  • Adductor longus
  • Tibialis Anterior
• Control of muscles involves the recruitment (size principle) and activation (all or nothing principle) of motor units in relation to force production
• Types of muscular actions include isoinertial, isometric, and isokinetic
• Major muscles of the human body - Posterior cont.


  • Trapezius
  • Triceps brachii
  • Rhomboids
  • Hamstrings
  • Soleus
  • Gluteus maximus
  • Erector spinae
  • Deltoid
  • Gastrocnemius
  • Biceps femoris
  • Semitendinosus
  • Semimembranosus
  • Latissimus dorsi
• Structure and functions of the muscular system include interactions of muscles and bones to produce movement in physical activity, sport, and exercise
• Movement Created


  • Trunk flexion
  • Shoulder adduction
  • Elbow extension
  • Hip flexion
  • Shoulder elevation
  • Trunk extension
  • Ankle (dorsi) flexion
  • Knee flexion
  • Hip adduction
• Agonists, antagonists, stabilizers, and the concept of reciprocal inhibition are important in muscle function
• Characteristics and functions of muscle fibers, including fiber arrangement and type (fast twitch and slow twitch)
• Major muscles of the human body - Posterior

  • Deltoid
  • Trapezius
  • Biceps brachii
  • Pectoralis major
  • Quadriceps
  • Tibialis anterior
  • Rectus abdominus
  • External obliques
  • Sartorius
  • Flexors of the wrist & hand
  • Serratus anterior
  • Adductor longus
  • Rectus femoris
  • Vastus lateralis
  • Vastus medialis
  • Vastus intermedius
• Striated appearance


  Fibers contain alternating light and dark bands that are perpendicular to the fibers
• Pennate fibers are short and attach at an angle to the central tendon that runs along the muscle length
• Muscles change in length to create movement
• Proteins actin and myosin "slide over" each other to change the length of the sarcomere depending on the type of contraction (eccentric vs concentric), known as the "Sliding Filament Theory"
• Muscle length increases in an eccentric contraction, and muscle length shortens in a concentric contraction
• Distinct types of skeletal muscle determined by color

  • Slow twitch fibers (red) – used for longer duration events, also referred to as Type I muscle fibers
  • Fast twitch fibers (white) – used for speed and power events, referred to as Type IIa and Type IIb muscle fibers
• Skeletal muscle


  Links 2 bones across its connecting joint, under voluntary control, and creates movement
• Myofibril length changes

  Myofibril is made up of many sarcomeres joined end to end
• Muscle length at rest has sarcomeres at normal length
• Muscle fibers are made up of many sarcomeres joined end to end
• Fast twitch muscle fibre type (Type 2B) is used for speed, strength, and power-based activities, fatigue very quickly, generate greater force and more powerful contractions
• Fusiform muscles

  • Spindle-shaped muscles with fibres running in the same direction as the tendon
  • Produce low force but have a large contractile range, i.e., they can shorten quickly, e.g., Biceps
• The pennation of the muscle allows for more fibres to be packed into the muscle
• Slow twitch muscle fibre type (Type 1) is referred to as "red" or "slow twitch" fibres, used for endurance activities, fatigue resistant, contract repeatedly for continuous activity, e.g., Marathon runner, Endurance cyclist
• Greater pennation


  More force the muscle is able to produce, therefore the muscle has more power
• Intermediate speed of contraction, moderate force of contraction, generate greater force and more powerful contractions compared to slow twitch fibres, possess some aerobic characteristics, e.g., speed endurance based activities like 400m, 800m run
• Fast twitch muscle fibre type (Type 2A) is suited to events requiring both aerobic and anaerobic elements
• Pennate fibres


  • Short fibres that attach at an angle to the central tendon
  • Unipennate - fascicles insert into only one side of the tendon, e.g., Extensor digitorum
  • Bipennate - fascicles insert into the tendon from opposite sides, e.g., Quadriceps
  • Multipennate - all fascicles insert into one larger tendon, e.g., Deltoid
• When muscles produce movement, they work in pairs
• Fast Twitch Muscle Fibers (Type 2B)

  • 100m sprint
  • 200m sprint
  • field events (throws/jumps)
  • 50m freestyle