Sports Biomechanics Final Exam

technique

the pattern and sequence of movements that athletes use to perform a sport skill

closed skill

when an athlete performs a skill in which the athlete determines when to begin and end the movement

closed skill examples

shooting a free throw, golf putt, target shooting, discus thrower, javelin

open skill

actions depend on what the opponent has done

open skill examples

playing soccer, wrestling, boxing

for eccentric force

R>F (ex: F < 60 units)

for concentric force

R<F (ex: F> 60 units)

basic law of force and motion

linear/angular kinematics, linear/angular kinetics. forces. laws of motion, center of mass, torque, moments of inertia

quantitative measures

description and measurement using numbers

qualitative data

describes the quality of movement

most common lever in the body

3rd class lever

planes of motion

transverse: longitudinal/polar axis

sagittal: medial-lateral axis

frontal: anterior/posterior axis

general motion

a mix of linear and angular motion

A _______ is the turning effect of a force

torque

only the _______ component of force will cause rotation

perpendicular

what three factors influence the amount of torque that will be produced?

force arm/resistance, force value/resistance, axis

what is the definition of a moment arm?

perpendicular distance from the force vector to the axis of rotation

force arm

how far applied force is from axis

resistance arm

how far resistance from the axis

what are the arrangements of the components of the first class lever

Force, Axis, Resistance (FAR)

which function of a simple machine does the first class lever favor?

balance forces, favor force production, and speed ROM

example of a first class lever in the body

neck

what are the arrangements of the components of the second class lever

axis, resistance, force (ARF)

which function of a simple machine does the second class lever favor

favors force production over speed/ROM

example of a second class lever in the body

calf raises

what are the arrangements of the components of the third class lever

axis, force, resistance (AFR)

which function of a simple machine does the third class lever favor

favors speed/ROM over force production

example of a third class lever in the body

bicep curl

what three components does the angle of pull represent?

line of pull/action, perpendicular component, compression force

biomechanics

application of mechanical principles to the study of biological systems

kinematics

describe the forces that create motion or are generated from moving

includes: ground reaction force, friction, torque, and internal muscle forces

linear motion

describes movement that occurs in a straight line

angular motion

rotation around an axis (rotating, spinning, swinging, circling, turning, rolling, pirouetting, somersaulting and twisting)

statics

describe motion that is in a constant state/things that are not changing

dynamics

motion that is undergoing change or varying

machine weight exercise

requires less stabilization and generally safer

free weights

requires more control (ex: dumbbells)

isometric resistance

maintaining constant joint position without change in muscle/tendon length

variable machine devices

exercise machines that adjust resistance through movement

non-weight resistance devices

focus on specific muscle with no added weight (ex: exercise bands)

validity

measures what its supposed to and is accurate

reliability

can be repeated and provides a consistent value

when an athlete performs a skill in which the athlete determines when to begin and end the movement, this is known as a __________ skill.

closed

in sports, mechanical principles can be primarily used to improve _______.

safety and performance

when a right-handed hitter swings a bat, what type of rotation occurs at the pelvis?

left transverse PG rotation

_______ is a term that refers to a structure toward the head (top) of the body

superior

a ________ is the turning effect of a force or a force that causes rotation

torque

the ______ class lever is the most common type of lever in the human body

third

in a ______ class lever, the force moment arm (FMA) is always longer than the resistance moment arm (RMA)

2nd

Which characteristic best explains why athletes with shorter limbs have an advantage in activities such as powerlifting and gymnastics?

these athletes have greater mechanical advantage because of smaller resistance arms; they require smaller muscle forces and joint torques to work against resistance

A basketball player is performing a leg extension hamstring curl. If there is a resistance arm (RA) of 8 units and resistance (weight) coming from a leg extension machine of 5.5 units. How much force would need to be produced to balance the torque?

44

Starting at a 90-degree angle, an athlete performs a biceps curl. The biceps muscle shortens to lift the external load and then extends to lower the external load back to the starting position. What type (s) of contraction is the biceps muscle undergoing during the whole range of motion?

both concentric and eccentric

The angle of pull at a given joint represents the _______________ component of force and produces a torque

perpendicular

True/False: Demonstrating good technique when introducing a new skill to an athlete is essential.

false

What type of injury is often associated with excessive inversion of the ankle?

lateral (low) ankle sprain

True/False: In sports, quantitative and qualitative assessments of technique are both effective ways to measure performance.

true

A coach uses a jump mat to estimate the vertical jump height of a volleyball player. The jump mat provides consistent measures over repeated trials, but the outcome measures drastically overestimate the volleyball player's actual jump height. The measures derived from the jump mat are _______________________.

reliable but not valid

What variable describes how fast or slow a person is moving in a specific direction?

validity

what is displacement?

change in position

what is distance?

the total amount of ground covered

what is speed?

scalar measure; indicated how fast an object is traveling; measured by dividing the length or distance travelled by the time

what is velocity?

change in position divided by time; direction and how fast the object is traveling

what is acceleration?

the rate at which velocity or speed changes

if a person has negative velocity and a negative acceleration, what does that indicate?

they are moving in a negative direction and are speeding up in that direction

X component of projectile motion

horizontal component (not affected by gravity) and velocity remains constant

Y component of projectile motion

vertical component (affected by gravity)

rules of projectile motion

• gravity influences only the vertical motion

• the horizontal and vertical motions are independent of each other

• the time to reach the peak is the same as the time to descend

what factors can influence flight path?

initial velocity, angle of projection, height of release, air resistance

first law of motion

inertia

an object at rest will stay at rest, an object that is moving will stay moving unless disturbed by an unbalanced force

second law of motion

acceleration

force equals mass times acceleration

third law of motion

action-reaction

for every action there is an equal and opposite reaction

whats momentum?

describes the quantity of motion that occurs

momentum equation

M=mv

what is inertia?

resistance to change in motion/stopping

inertia equation

mk²

mass

the amount matter that makes up something

body weight

gravity x body mass

what is impulse equal to?

change in momentum

impulse equation

F x change in time

soft landing

increases time of impact, reducing force and injury risk

hard landing

decreases time of impact and increases force and injury risk

When a person is absorbing force, such as during the landing or followthrough phase, should they try to absorb the force over a shorter or longer time period in order to reduce injury risk?

absorb the force over a longer period of time

phases of gait cycle

alternation between the stance phase (foot makes contact with ground) and swing phase (when foot is swinging through the air)

variables for improving running gait

stride length, stride rate, and ground reaction force

the three orthogonal planes that are used to describe angular motion of human movement

longitudinal, transverse, and frontal axes

transverse plane

rotations around the horizontal axis (ex: somersaults)

frontal plane

rotations around front-back axis (ex: cartwheels)

longitudinal plane

rotation occurs around the length of the body (ex: figure skating spin)

angular velocity

describes the rate of spin of an athlete or an object

what two quantities are needed to get linear velocity?

angular velocity and the radius

centripetal forces

this force pulls (or pushes) an object toward the axis of rotation to make it follow a curved, or circular, pathway

centrifugal forces

the inertia that makes objects want to move away from the axis

large moment of inertia

will resist changes in rotational motion but will be steady, however, it will be hard to accelerate and reduce speed quickly, it will be hard to stop and will also be slow moving

small moment of inertia

will respond to a change in rotational momentum more easily but be less steady. it will accelerate and reduce speed quickly and be fast moving - but it will be easier to stop

what are fundamental components for anything to rotate?

axis of rotation, force applied, objects mass

can gravity cause and initiate rotation or limit rotation?

limit rotation

which variable has the greatest impact on rotary inertia/moment of inertia?

radius of gyration

how can a sprinter use the concept of rotary inertia to increase her stride rate?

by reducing the radius of gyration or changing the k value

How can athletes use the mechanical principles for rotation to change their serves or passes in sports?

Tennis serve: adjusting grip and arm extension changes moment of inertia
Football pass: Spinning motion stabilizes trajectory
Volleyball spike: rotating arm generates angular momentum

what is the kinetic link principle?

movement pattern follows a sequence from the proximal segments to the distal segments