Published on March 18, 2014
Neuromuscular Function: I. The Motor Unit:
II. The Structure of Muscle Tissue:
III. The Role of Neurotransmitters in stimulating skeletal muscle contraction: A. Acetylcholine (Ach): increases the post- synaptic membrane’s permeability to sodium and potassium ions spreading the impulse over the entire muscle fiber.
B. Cholinesterase: enzyme that breaks down Ach repolarizing the muscle fiber to await another nerve impulse.
IV. Skeletal Muscle Contraction:
A. The sliding filament theory: Steps of a muscle contraction: *Ca++ are released by the sarcoplasmic reticulum. *Ca++ binds to troponin preventing the blocking action of tropomyosin.
Sliding filament cont. *myosin heads can now attach to active sites on the actin filament. *myosin heads pulls on the actin filament, decreasing the width of the sarcomere Z- lines get closer. *myosin head releases the actin when a new ATP is formed.
Explain what is happening in an eccentric, concentric, and isometric contraction in relation to the sliding filament theory?
V. Types of Muscle Fibers: A. Slow Twitch: (type 1) *smaller in diameter *reddish color *use aerobic resp. for ATP supply *contain more mitochondria *fire slowly, but take long to fatigue.
B. Fast Twitch: used for short explosive movements, stop and go sports. Type IIA: *large diameter *white in color *less mitochondria *uses both anaerobic and aerobic energy transfer Type IIB: *same physical characteristics as Type IIA, but strictly uses the glycolytic anaerobic system.
Joint and Movement Type A. Types of Joint Movement: 1. Abduction: movement away from the body’s center. 2. Adduction: movement towards the body’s center.
3. Circumduction: making circular movements. 4. Dorsiflexion: movement of the ankle elevating the sole. (digging in the heel) 5. Plantar flexion: extending the ankle and elevating the heel. (standing on tiptoes)
6. Elevation: occurs when a structure moves in a superior (towards head) manner. Ex. Closing your mouth/elevating the shoulders. 7. Depression: movement is inferior (towards feet). Ex. opening your mouth/lowering the shoulders
8. Extension: movement that increases the angle between articulating elements opening the joint. 9. Flexion: decreases the angle between articulating elements and closes the joint.
10. Pronation: rotating the palm down. 11. Supination: rotating the palm up. 12. Rotation: turning the body around a longitudinal axis.
13. Inversion: when the ankle rolls outward. 14. Eversion: ankle roles inward.
B. Types of Muscle Contraction: 1. Isotonic: describes concentric and eccentric muscle actions. a. Concentric: muscle is shortened during contraction. b. Eccentric: muscle is contracting while lengthening.
2. Isometric: muscle generates force without changing length. Ex. Hand grip and plank position. 3. Isokinetic: the speed of movement is fixed and the resistance varies with the force exerted. *requires special equipment!
C. Reciprocal Inhibition: describes muscles on one side of a joint relaxing while the other side is contracting. (antagonistic pairs) 1. Agonist: muscle that causes the movement. 2. Antagonist: muscle that works opposite the agonist to return the joint to its initial position.
D. Delayed Onset Muscle Soreness: (DOMS) The pain and stiffness felt in muscles several hours to days after unaccustomed or strenuous exercise. *brought on by eccentric contractions of the muscle causing pressure at the nerve endings.
Biomechanics: the science concerned with the internal and external forces acting on the human body and the effects they produce on the body. a. Force: a pushing or pulling action that causes a change of state (rest/motion) of a body. *proportional to mass x acceleration *measured in Newtons (N)
Types of Motion • Translation: Motion along a path – results in a change of location examples: Position, Velocity, Net force • Rotational: Rigid of a body about an axis – Orientation of the axis, Angular position, – Rotational motion occurs when an object spins • Deformation: motion inside of an object like tension, buckling, bending, stretching, twisting, compression, or expansion.,
Measuring Movement • Measurement with size and direction is known as a vector • Measurement with only size is a scalar
Newton’s Laws of Motion in Sport 1. First Law: a body in motion/rest will remain in motion/rest in a straight line unless acted upon by another force. Also known as inertia.
2. Second Law: the rate of change of momentum of a body is proportional to the force causing it and the change takes place in the direction in which the force acts. (F= M A)
Law of Acceleration • The acceleration of an object is in the direction of the net force. If you push or pull an object in a particular direction, it accelerates in that direction. • The acceleration has a magnitude directly proportional to the magnitude of the net force. If you push twice as hard (and no other forces are present), the acceleration is twice as big. • The magnitude of the acceleration is inversely proportional to the mass of the object. That is, the larger the mass, the smaller the acceleration for a given net force (which is just as you’d expect from inertia).
3. Third Law: For every action there is an equal and opposite reaction. (every force involves the interaction of two objects)
b. Speed: describes the rate at which a body moves from one location to another. *Distance/Time. *speed is described in terms of magnitude (amount) which makes it a scalar quantity.
c. Distance vs. Displacement 1. Distance: (scalar) the length of a path a body or object follows 2. Displacement: (vector) body or object changes its position from on place to another i.e. how far the body or object has moved horizontally, vertically and laterally.
d. Velocity: the rate at which a body moves from one location to another with both magnitude (speed) and direction making it a vector quantity. *Displacement/Time
e. Acceleration: is defined as the rate at which velocity changes over time and the ability to change ones speed from either a static position or a moving state. • Final velocity – initial velocity/time
f. Momentum: is a vector describing a “quantity of motion” and is the product of mass and velocity. *an athlete can increase their momentum by either increasing their mass or velocity.
g. Impulse: the effect of force over time. Calculated as the product of force and time.
Speed and Acceleration Lab • Moment of Inertia – How difficult a body or object is to rotate about an axis • More mass further away from the axis gives a great moment of inertia and makes it more difficult to rotate • Example
h. Center of mass: the point at which the body is balanced in all directions. *a change in body position can change the position of the center of mass within or outside the body. *Different for individuals *depends on age, gender and position of limbs during athletics
a. Conservation of Momentum: momentum is neither gained or lost within a closed system. Total momentum before a collision equals the total momentum after.
b. Angular Momentum: a measurement of an objects tendency to continue to spin. It is the product of angular velocity and moment of inertia. 1. Moment of inertia: the distance from the rotational axis. 2. Angular velocity: the number of revolutions per minute.
The Fosbury Flop! *notice how the center of gravity is located outside the jumper’s body.
Examples of the center of gravity outside the body.
Center of Mass • Center of mass and center of gravity are effectively the same for the human body • Point where the body is evenly distributed • The "center of mass AN IMAGINARY point on the body at which all the individual forces acting on the body if applied would produce the same effect IF THAT IMAGINARY POINT WAS CONNECTED RIGIDLY TO EVERY OTHER POINT ON THE BODY“ Hula hoop
Used to measure movement through calculations.
What technique works better? Video
Torque (moment) • Force applied to an object that is free to rotate around an axis, but the force does not act through the axis • Depends on: – The size of the force – The direction of the force – How far it is applied from the axis of rotation
Torque • In the golf swing, power comes from good rotation, but how is this rotation achieved? • You need resistance, or a foundation from which the rotation happens. • This foundation is your hips. (rotate back slightly). • Relieving tension and reducing the swing power (rotate too much)
Torque • In sports usually torque is usually created with implements • But in humans the way muscles are anatomically arranged relative to the joints play a large part in determining how much torque can be created around each joint. • Relates to levers (bones rotating about axes such as the joints.
Linear Momentum and Linear Impulse • Linear momentum is a property an object has due to its movement (p=mv) • Linear impulse is force multiplied by the time it acts for (J=Ft) (vector)
Impulse-momentum relationship • Important when understanding changes of motion • Linear impulse is the change in linear momentum (starting block 0-15) • i.e. the size and direction of the change in momentum of a body or object depend on the force (muscles) applied to it and the time for which that force acts.
Impulse-momentum relationship • The task in many sport skills is to cause a large change in the velocity of something. In throwing events, the ball (or shot, discus, javelin, or Frisbee) has no velocity at the beginning of the throw, and the task is to give it a fast velocity by the end of the throw. We want to increase its momentum.
Impulse-momentum relationship • Similarly, in striking events, the racket (or bat, fist, club, or stick) has no velocity at the beginning of the swing, and the task is to give the implement a fast velocity just before its impact. Our bodies may be the objects whose momentum we want to increase in jumping events and other activities.
Impulse-momentum relationship • Techniques used may be explained in part by the impulse–momentum relationship. • A large change in velocity is produced by a large average net force acting over a long time interval • Limits on the forces humans are capable of producing, many sport techniques involve increasing the duration of force application.
Throwing Exercise • When was the largest impulse created? • Why? • Ball’s momentum changed, and the ball left your hand with the fastest velocity. • The large impulse was the result of a relatively large average force being exerted on the ball for a relatively long time.
Throwing • Smallest impulse? • The ball’s momentum didn’t change very much, and the ball left your hand with the slowest velocity. • The small impulse=relatively small average force being exerted on the ball for a relatively short time.
Angular Momentum • Measures the amount of rotation a body or object has • Vector • Angular effect of a force that does not act through the axes of a freely rotating body or object
• Newton's three laws of motion relate how forces change motion they are applied into daily activities and all sports.
Application • How does our body move? • Muscles play different roles in different stages of movement depending on their contraction type and requirements of the action
Levers: a rigid rod, a fulcrum (axis), a resistance force and an effort force. Resistance arm- distance from resistance acts from fulcrum. Effort arm- distance the effort acts from the fulcrum 1. First Class Lever: The fulcrum lies between the effort and load. Rare in humans. Ex. Triceps extension and neck providing the effort force to overcome resistance force of weight of head.
2. Second Class Lever: effort force and resistance force on the same side of the fulcrum. Effort arm longer than resistance i.e. the effort froce is further away from fulcrum Ex. Standing heel raise. Very rare
3. Third Class Levers: effort and resistance forces on the same side of fulcrum but effort arm is smaller than the resistance arm i.e. the effort force is closer to the fulcrum. Ex. Biceps curl swinging a bat. A small movement of the lever near the fulcrum is magnified by the length of the leaver. Lever moves through a greater angle, and with greater angular velocity. Thus, advantage is in range of motion and speed.
Types of Levers
Projectile Motion 1. Projectile: an object that has been dropped, thrown vertically upwards or thrown at an angle following a parabolic path and is subject to the forces of gravity.
Projectile motion • An object that is thrown into the air or dropped and is acted upon by only the forces of gravity, air resistance, and lift • Analyses how objects move when thrown into the air or dropped from a height • Propelling force occurs only when the object or body is in contact with the thing that starts the motion. (hand, ground or racket)
Projectile Motion • As soon as the contact is lost the force no longer exists and the object or body keeps moving only due to newton's first law of motion.
Factors Affecting Projectile Motion a. Projection Speed: most important factor in determining how far the object will go because the range is dependent on the square of the project speed.
b. Projection Angle: important for range but more important accuracy. Examples in sports???
c. Height of Release: the greater the height of release the greater the distance.
The Bernoulli Principle: States that as the velocity of a fluid increases, the pressure exerted by that fluid decreases. Photo Video
Why do golf balls have dimples?
Drag • As air moves past a sphere, two types of drag are developed. • The first is drag due to friction and second separation of the airflow behind the golf ball. • As the air loses its ability to stick close to the ball (known as the boundary layer), it separates from the ball and creates lots of little eddies (swirling of a fluid) that basically try to pull the ball backwards.
Why does a dimpled ball help delay airflow separation? • Dimples create very small amounts of turbulence near the ball's surface that actually add energy to the air in the boundary layer. • More energy means more sticking power which means the airflow separation occurs later. • Later the separation decreases the force trying to pull the ball backwards and allowing the ball to fly further.
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