IB Sports Midterm

Motor Units- functional groupings of muscle fibers and their corresponding motor neurons that contract together (contract based on all-or-none principle)

All-or-none principle- the principle stating that a motor unit will either fully contract or not contract at all when stimulated 

  • ensures that muscle contractions are efficient and coordinated, preventing partial contractions that could lead to instability

ATP Metabolism- ATP is required for muscle contraction, particularly during cross-bridge cycling and myosin release

Acetylcholine- a neurotransmitter that stimulates skeletal muscle contraction at the neuromuscular junction

  • primary neurotransmitter 

  • release of acetylcholine is essential for the excitation-contraction 

Hypertrophy- increase in muscle size that can enhance force production and alter motor unit recruitment patterns

Atrophy- decrease in muscle size that can negatively affect force production and motor unit recruitment 

Isometric- muscle generates force without changing length, crucial for maintaining posture (no movement)

Isotonic Concentric- muscle shortens while generating tension, as seen in lifting weights 

Isotonic Eccentric- muscle lengthens under tension, important for controlled movements like lowering weights 

Isokinetic- muscle controls at a constant speed, often used in rehabilitation settings

Agonist- the primary muscle responsible for a specific movement (prime movement)

Antagonist- the muscle that opposes the action of the agonist 

Synergist- a muscle that assists the agonist in producing a movement 

Fixator- stabilizes the bone or body part from which the agonist muscle originates

Bicep Curl-

Agonist: Biceps Brachii

Antagonist: Triceps Brachii

Synergist: Brachialis 

Fixator: Rotator Cuff

Type I (slow-twitch)- 

  • small motor neuron diameter

  • low force production, high fatigue resistance

  • used for endurance and low-intensity activities 

Type IIa (fast oxidative)-

  • medium motor neuron diameter 

  • moderate force production and fatigue resistance 

  • used for moderate-intensity, sustained activities 

Type IIx (fast glycolytic)-

  • large motor neuron diameter

  • high force production, low fatigue resistance 

  • recruited for maximal, short-duration efforts 

Sliding Filament Theory Step 1- a muscle contraction starts in the brain, where a signal is sent to the motor neuron. The combination of the motor neuron and the skeletal muscle fibers make up a motor unit.

Sliding Filament Theory Step 2- the impulse travels into the transverse tubules where it causes calcium to be released from the sarcoplasmic reticulum

Sliding Filament Theory Step 3- calcium binds to the troponin in the actin causing a change in the tropomyosin and cause it to change shape so that it can interact with myosin

Sliding Filament Theory Step 4- the change in shape allows myosin heads to form cross-bridges between the actin and myosin

Sliding Filament Theory Step 5- energy from ATP is used to create a “power stroke” between the two filaments. The actin filament slides inward and shortens, or contracts, the whole muscle 

First-Class Lever- The fulcrum is between the effort and the load

  • MA: occurs when the effort arm is longer than the load arm

Second-Class Lever- the load is between the fulcrum and the effort 

  • MA: the effort arm is always longer than the load arm

Third-Class Lever- the effort is between the fulcrum and the load 

  • MA: effort arm is always shorter than the load arm 

Mechanical Advantage- the effort arm is longer than the load arm, so less force is required to move the load 

Mechanical Advantage of 1st Class- can be less than, greater than, or equal to 1

Mechanical Advantage of 2nd Class- always greater than 1

Mechanical Advantage of 3rd Class- always less than 1

Mechanical Advantage Equation (meters)- length of effort arm/length of load arm 

Mechanical Advantage Equation (newtons)- magnitude of load (R)/magnitude of effort (E)

Fulcrum- the fixed point around which the lever rotates. In the body, this is typically a joint

Effort (force)- the force applied to the lever to create movement. In the body, this is provided by muscle contraction

Load (resistance)- the weight or resistance being moved. This can be part of the body, an object being held, or an external force

First Class- Effort-Fulcrum-Load

Second Class- Effort-Load-Fulcrum

Third Class- Fulcrum-Effort-Load

First Class Lever - acim (neck/head)-

Fulcrum: where the skull meets the first vertebra 

Load: Mandible, frontal cranium

Effort: the neck and back muscles, such as trapezius

MA: during neck extension, the effort arm is longer, and less muscle force is needed to lift a heavier load (>1)

Second Class Lever - Push-up-

Fulcrum: toes

Load: body weight 

Effort: arms and chest 

MA: greater than one because the distance from the fulcrum (your toes) to the effort (your hands) is greater than the distance from the fulcrum to the center of mass (your hips)

Third Class Lever - Flexion of the elbow-

Fulcrum: elbow joint 

Load: forearm and any weight held by the hand

Effort: bicep 

MA: less than 1 

Newton’s First Law- An object will stay at rest or in uniform in a straight line unless a net force acts upon it (inertia)

Newton’s Second Law- the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (force, mass, and acceleration)

Newton’s Third Law- for every action, there is an equal and opposite reaction (action-reaction)

Speed- how fast an object moves (distance/time) and has no direction 

Velocity- both speed and direction

Acceleration- the rate of change of velocity 

Force- a push or pull that can change the motion or shape of an object

Resultant Force- the vector sum of all forces acting on an object 

  • Determines: whether an object accelerates and its direction of motion

  • If the resultant force is zero, velocity stays constant (Newton's 1st Law)

Stability- the ability of an object to maintain balance when forces act upon th

Increases when:

  • Centre of mass is lower

  • Base of support is wider

  • Greater mass

Summing Joint Forces-

  • Muscle force

  • Joint reaction force

  • External forces

Inertia- the resistance of an object to changes in its motion, dependent on mass

Impulse- force x time

Momentum- the quantity of motion of an object, equal to mass x velocity 

Principle of Impulse Direction- the direction of impulse determines the direction of motion

Angular Motion- occurs when a force acts at a distance from the centre of mass

  • called an eccentric force, creates torque 

  • torque causes rotation

Angular Momentum- the quantity of rotational motion, equal to moment of inertia angular velocity 

Angular Velocity- the rate of change of angular displacement, or how fast an object rotates