long biomechanics final

statics

• branch of mechanics examining systems that are moving at a constant velocity or aren't moving

• forces are present but in equilibrium

dynamics

ranch of biomechanics which studies systems in which acceleration is present

kinetics

• examines the forces acting on a system to cause motion

• Ex: power

kinematics

• examines characteristics of motion from a spatial and temporal perspective without references to forces causing motion

• Ex: joint angles

qualitative analysis

observation of the movement being performed

quantitative analysis

measure and evaluate quantities related to space, time, motion, force, or energy

running velocity patterns

• lower running velocity = same stride rate and increased length

• higher running velocity = increased stride rate and same stride length

mechanical system

a body or portion of a body that is deliberately chosen by the analyst

2D methods of motion analysis

video or photography

3D methods of motion analysis

translated info from markers placed on the body to stick figures and volumetric models

motion capture

process of recording movement and translating that movement into a digital form that provides the position of an object in 3D space

examples of how motion analysis is useful in sports and performance

heel strike v. forefront strike, barefoot running and force production, baseball pitching mechanics

Newton's three laws of motion

inertia, acceleration, action-reaction

internal forces

forces that act within the object whose motion is being investigated

Newton's First Law of Motion

• an object at rest will remain at rest unless acted upon by a force

• higher running velocity = increased stride rate and same stride length

• larger body size = greater resistance to acceleration

inertia

an object's resistance to change in velocity

Newton's Second Law of Motion

F = ma

conservation of momentum

a system's momentum will remain constant unless acted upon by a force

momentum

p = mv

linear elastic collisions

• when two objects collide and bounce off each other, their combined momentum is conserved

• if one object is stationary, the momentum of the moving object will be completely transferred to the stationary object after collision

inelastic collision

2 objects collide and stay together and momentum is conserved

impulse

change in momentum

how to use impulse to increase momentum when throwing an object

generate a large force over long period of time

how to use impulse to decrease momentum when landing from a jump

increase time of landing to reduce impact force experienced by the body

why car crashes are dangerous

big changes of velocity in small amount of times results in large impact forces

why air bags save lives

increases the time over which the velocity changes resulting in smaller peak impact forces

Newton's Third Law of Motion

• for every action, there is an equal and opposite reaction

• contact/reaction forces come in pairs

how acceleration affects force balance

• no acceleration = balanced forces

• acceleration = unbalanced forces

relative angle

• angle at a joint formed between the longitudinal axes of adjacent body segments or joint angle

• straight fully extended position at a joint is 0 deg

body plane position

anatomical position

absolute angle

• angular orientation of a body segment with respect to a fixed line of reference

• reference lines are usually vertical or horizontal

angular displacement

change in angular position

• directed angular distance from initial

to final angular position

• vector equivalent of angular distance

• measured in degrees, radians or rotations

• angular displacement ⍬ = arc length/distance in

  degrees of radians over time

angular velocity

rate of change in angular position

angular displacement ⍬ = arc length/distance in

degrees of radians over time

angular velocity w = ⍙⍬/ ⍙ t

measured in units of rad/sec

tangential acceleration

• component of acceleration of angular motion directed along a tangent to the path of motion

• a = (v2-v1)/t

radial acceleration

• component of acceleration of motion directed toward the center of curvature

• represents change in direction

• a = v^2/t

movement speed

the ability of a person to move themselves or their limbs at a very rapid rate for relatively few repititions

reaction time

• time it takes from the detection of a stimulus to first movement

• can be trained with signal recognition or efficient execution of movements

signal recognition

try different scenarios to accommodate the body to quick processing and reaction to unpredictable stimulus

efficient execution of movement

training the same movement to make the movement efficient

determinants of speed

muscle composition, stride length and stride frequency, physiological demands, neural influences

how muscle composition affects speed

• each individual has different muscle composition/fiber types

• fast twitch fibers (type 2) produce peak power at high loads and velocities

• maximize FT fibers

how stride length and stride frequency affects speed

• increase stride length to move faster but there is a max length so compensate by increasing the number of steps taken

• stride length affected by size, joint flexibility

• stride frequency affected by muscle composition and neuromuscular development

intramuscular coordination

• individual fibers in your muscles contract and relax in sync

• produce more power without bigger muscles

strength and neural drive training

• maximize motor unit recruitment

• firing rates of nerves innervating muscles

• synchronization of motor units

intermuscular coordination

• ability of agonist, antagonist and synergist muscles to fully contribute to activity

• minimize antagonist coactivation

• maximize synergist contribution

more about repetition of movement)

how co-activation prevents injury

co-activation provides stability to the joint

best type of muscle for explosive strength

muscle with optimal balance in long angles in muscles that lengthen over a wider ROM and large pennation angles in muscles that need to produce large force over short ROM

Newton's 2nd Law angular equivalent

• increased torque = increase force generation

• reduce intertia = reduce limb mass

joint flexibility

description of the relative ranges of motion at a joint in different direction

range of motion (ROM)

• range through which bones of a joint can be moved

• measured in degrees

• anatomical position = 0

static flexibility

• ROM present when body segment is passively moved

• considered best indicator of tightness or laxity of a joint

dynamic flexibility

• ROM that can be achieved by actively moving a body segment

• need to be sufficient to allow normal daily movements

why stretching increases ROM

• unknown

• no evidence that stiffness is altered with stretching

factors contributing/affecting ROM

• structure or shape of the articulating bones or surrounding muscle or fatty tissue

• strength and tension of joint ligaments

• arrangement and tension of muscles

• disuse

active insufficiency

inability of a two joint muscle to produce force when joint position shortens the muscle to the point where it cannot contract

passive insufficiency

inability of a two joint muscle to be stretched sufficiently to allow a complete ROM at all joints it crosses

tenodesis effect

passive insufficiency of finger extensors occurs when the wrist is flexed, causing the fingers to extend

flexibility development

• stretching of soft tissue surrounding a joint

• increase in muscle-tendon unit length

stretching

action in which the muscle-tendon unit responds viscoelasticly

extensibility

• ability of a muscle to lengthen, directly related to the resistance of the tissues as it lengthens

• measured by stiffness

muscle spindles

• sense changes in muscle length

• ballistic stretch

golgi tendon organs

• sense changes in the tension generated by muscle contraction

• tension can be generated during muscle stretch

• stretch exceeds critical level => GTO inhibit any contraction or stretch => reduce tension to prevent injury

ballistic stretch

sense muscle is close to being overstretched => neurons fire sending signals to contract => reduce the limb extension

active stretching

• active tension development in the antagonist muscles

• Ex: actively stretch hamstrings, quadriceps contract

active stretching technique

• ballistic: repetitive bouncing movements at end of joint ROM

• dynamic: slow or fast movement of joint due to antagonist muscle contraction throughout ROM

• proprioceptive neuromuscular facilitation (PNF): reflex activation and inhibition of agonist and antagonist muscles

passive stretching

• produced by a force other than tension in the antagonist muscles

• can achieve a greater stretch

passive stretching technique

• static: passive movement of muscle to maximum ROM and hold position for 5-60 sec

• partner: passive movement maximized by external force and hold for extended time period

stress-relaxation response

• when tissues are held at constant length the force at that length (resistance to stretch) gradually declines

• may result in increased ROM immediately after static stretching

• creep

why changes in ROM after acute stretching are short lived

• muscle tendon unit has viscoelastic properties so the ROM is eventually reduced to its original set point

anatomical components affected by stretching

connective tissue, fascia, skeletal muscle, tendons, ligaments

most common inhibitors of joint's ROM

tight ligaments and muscles with limited extensibility

connective tissue and stretching

connective tissue of some joints has more elastic properties than others

fascia and stretching

• fascia surrounds muscle fibers

• limited stretching

• quickly resists movement

skeletal muscle and stretching

• can be stretched by external force

• sarcomeres slide apart

tendons and stretching

• stretch in order to transfer muscle contractions to bone

• store elastic energy when stretched

ligaments and stretching

some stretch to maintain joint stability

chronic static stretching and ROM

evident ROM increases with static stretching after 4-6 weeks

chronic dynamic stretching and ROM

not as effective in increasing long term ROM but increases joint movement through non-restricted ROM

proprioceptive neuromuscular facilitation (PNF) and stretching

PNF may be more effective at increase ROM than static stretching

causes of increased ROM after chronic stretching

• theory 1: increase in sarcomeres added in series

• theory 2: tolerance to stretch

acute static stretching on strength

reduced strength after static, ballistic, and PNF stretching due to decreased nerve firing and decreased contractile force development

chronic stretching and performance

• may have beneficial affects on performance

order in which a person should stretch

• warm up

• dynamic exercises

• performance

• static stretch and cool down

• adopt consistent stretching regimen on non-performance days

flexibility and temperature

local heating improves flexibility thus promoting tissue relaxation and compliance

flexibility and injury

• limited flexibility = increased risk of tearing or rupturing tissues

• excessive flexibility = prone to displacement injuries

• imbalance in flexibility = increase injury

• tight ligaments = increased incidence of lower body injury

• overstretched ligaments = less joint stability = increased incidence of injury

aging and flexibility

• growth spurt = reduced flexibility possible

• tendons and connective tissue shorten and calcification of cartilage = reduced ROM

• increased calcification and thinner cartilage = steady reduction flexibility

gender and flexibility

women are more flexible due to smaller bones, less musculature, and hormones

pros and cons of static passive stretching

• pros: increased ROM, simple technique

• disadvantage: reduced muscle strength, can cause injury

pros and cons of partner passive stretching

• pros: increased ROM, simple technique

• cons: requires external force

pros and cons of dynamic active stretching

• pros: beneficial effect for activities requiring muscle power

• cons: unknown

pros/cons of ballistic active stretching

• pro: increased ROM

• cons: reduced muscle strength, may cause injury

pros/cons of PNF active stretching

• pros: increased ROM (most effective stretching method)

• cons: reduced jump height, requires experience and practice

bipedal walking

• walking on two legs

• inherently unstable

requirements for bipedal walking

• control system (nervous system)

• motor generators to produce power and moments (muscles)

• system of levers to transmit motion (bones)

requirements for successful locomotion

progression, postural control, adaptation

progression in locomotion

• ensured through rhythmic and coordinated pattern of motion activations

• includes the ability to initiate and terminate locomotion

postural control in locomotion

establish and maintain appropriate posture, control dynamic stability by counteracting force of gravity and other expected or unexpected forces

adaptation in locomotion

• change speed and direction to meet the goals of the individual and the demands of the environment

• avoid obstacles, negotiate uneven terrain

gait cycle

• functional unit of normal walking is cyclic

• no true beginning or end

• consists of a single stride with 2 phases: stance and swing

stance phase

loading response, midstance, terminal stance, preswing