Biomechanics Exam 4

Springboard Diving Phases

Approach- only for forward and reverse Hurdle- movements to raise/lower COM before takeoff Takeoff- final depression and recoil of board Flight Entry

Windup Phase

Combined with stride helps to optimally position body Duration: initial movement of contralateral leg --> elevation of same leg to highest point/separation of throwing hand from glove COM over back leg

Muscle Activity Sequence

Contract the hip muscles first, we don't have to rely on the ankle to cause that initial movement. Using ankle muscles first wastes the energy by not being in a proper position.

Landing Graphs

F1 and F2 represent the two peaks/impulses

Acceleration lower body

Lead leg: -hip flexion and knee extension Trunk -peak anterior tilt -max angular velocity at ball release

Passive Landing

No additional muscle activation can occur in response to sudden impact forces

6 o'clock to 3 o'clock

Shoulder IR Ipsilateral trunk rotation Muscle activity -Peak infraspinatus and supraspinatus to stabilize humeral head

3 o'clock to 12 o'clock

Shoulder at 180° of flexion Shoulder ER Muscle activity -Peak posterior deltoid -Infraspinatus and teres minor to ER the shoulder

Gait Phases

Stance (60%) -Initial contact -Loading response -Mid-stance -Terminal stance -Pre-swing Swing (40%) -Initial swing -Mid-swing -Terminal swing

Delivery

Stride foot contact to ball release Acceleration of arm and ball forward

Softball Wind-mill pitch

Wind-up Stride -6-3 -3-12 Delivery -12-9 -9-release Follow-through

Follow through

body moves forward with arm until motion has ceased Horizontal adduction: 60 degrees

Double Limb Stance

both feet on the ground, only occurs when walking

Loading response (landing)

dependent on the elasticity of the tissue as rate of loading increases, so does stiffness to absorb more force/unit deformation

Distance Jumped is dependent on time in air

determined by vertical velocity at takeoff 9 step produces greatest horizontal distance

Late Cocking Duration

end of stride --> max shoulder ER

Centripetal Force

force going around a circular path with the force acting back toward the middle Max speed at which we can walk and maintain circular path of COM is limited by gravity and limb length Mom waking and child running next to her, leg length difference Speed does not necessarily mean someone is walking or running Froude number > 1 = running

Terminal Stance (30-50%)

forward propulsion Hip 20 degree extension, adductor longus peak contraction in order to pull leg back into midline Knee 5 degree flexion, biceps femoris Ankle 10 degree dosriflexed, eccentrically contracted to dosriflex then concentrically contract in order to plnatar flex for propulsion -Peroneals longus contracts and flexes the first digit, makes the food create a dome (rigid object) to propulse us forward. -helps us conserve energy

Long Jump

maximize horizontal distance between takeoff and landing positions Contributors to distance jumped -displacement of COM (most important factor) -Lean of the body at takeoff and landing, forward at takeoff and backward at landing

Spring Board Diving

takeoff phase most critical, board provides reaction force to diver pressing down on board, lifting up off board as board is depressed it stores elastic energy max potential energy at bottom

long Jump and vGRF

vGRF does not pass directly thru the COM at takeoff, jumper experiences angular momentum during flight phase Rotate arms and legs to generate momentum and control Length of approach to jump must be adequate to obtain 10 m/s horizontal velocity at beginning of takeoff

Optimal Takeoff Angle (Long Jump)

45 degrees Requires horizontal and vertical velocity of COM to be similar Actual takeoff angle -20° when running -29° when standing

Baseball vs Softball

Both exploit the stretch-contract cycle Pec major is primary power generator

Active Landing

Eccentric muscle activity generated to resist LE flexion Goal: bring body's motion to zero

Mid-Swing (75-85%)

Foot clearance, forward propulsion of limb Hip 25 degree flexion, biceps femoris Knee 25 flexion, biceps femoris, gracilis Ankle Neutral, tibialis anterior, EDL EHL

Loading response (0-15%)

shock absorption Hip 20 degree flexion, max contract glut max. Knee flex 15 degrees, vastus lateralis contracts to slow down so we dont excessivley flex Ankle 5 degrees plantar flexed

Stride (windmill)

stride foot toe-off to contact ER of pivot foot

Follow-through (softball)

59% of body weight is the force applied at shoulder Ball release until end of motion

Vertical Jump Muscles

Approximately 21% of work done to extend knee comes from hip extensors Nearly 25% of work done to PF ankle comes from knee Glutes and hamstrings - hip extensors Plantar flexor ankle comes from knee - quads

Leg Spring Stiffness During running continued

As grf travels up through the body, its position to the knee depends on how much of a moment is happening Knee is also more flexed therefore the quads have to generate more force to have to counteract the knee versus our hips do not Weak Quads = Pic A - not able to go into flexion so forces will isolate into joint Relationship of GRF as it goes thru each joint is going to equate to how much each muscle has to counteract

Muscle Activity

Braking Impulse Propulsion impulse Trunk Stabilization Toe-off Foot Strike

Energy Flucuations during Walking

COM is at max height during mid-stance Thus, Ep is at max While Ek is at min Recover ~65% mechanical energy Greatest for intermediate walking speeds Running only ~5% As pendulum swings up potential energy is at highest point and kinetic energy is at lowest point and COM is highest

Factors influencing vGRF attenuation

Cushioning material in footwear -Conflicting evidence whether it attenuates forces or not -May even increase impact forces Surface properties -Peak impact forces do not vary substantially with different surfaces -Believed that kinematics of landing override adaptation to surface Muscles -Eccentric muscle activity dampens impact -Additional muscle activation cannot occur during passive phase of landing, so muscle activity must occur before ground contact -muscle activation before landing -quads demonstrate more pre-activation when jump follows landing Elastic Energy -Recall performance differences in countermovement vs. squat jump -Likely related to storage of energy during eccentric muscle loading associated with countermovement jump Fatigue -Likely reduces ability to absorb energy of impact

Early Cocking/Stride

Duration: end of windup --> lead foot contacts ground Purpose: increase distance over which linear and angular trunk motions occur Stance leg: glut max firing to maintain slight extension Pelvis Trunk: obliques contract to limit lumbar hyperextension Shoulder:External rotation caused by supraspinatus, infraspinatus, and teres minor Scapula retracted and upwardly rotated

Leg Spring Stiffness during running

Eccentrically contract muscles in order to prevent falling or slamming the ground, slow ourselves down During second half of GRF we concentrically contract our muscles in order to propulse forward

Acceleration duration

End of late cocking -> ball release

GRF and Speed

Faster I am moving my GRF is increased, due to COM acceleration going to up and down, the greater rate of change results in a greater grf. If contact time decreases but stride length stays the same then GRF will increase due to foot moving faster

Energy Cost

Faster we run, more energy we consume -Mainly due to increase in intensity of muscle activity required to run faster Muscle activity during locomotion serves to -Support BW -Generate propulsive impulse Magnitude of vGRF > hGRF -More energy expended to support BW -Magnitude of vGRF major determinant of metabolic cost of running

GRF

Force the ground exerts back onto the body Foot must be in contact with ground to have a reaction force The faster the COM is moving or changing velocity will have a change in GRF

Pitching Injuries

Greatest potential for pec major during delivery Posterior shoulder muscles may be injured during deceleration Elbow ligaments may be injured during acceleration

Spring Board diving angular momentum

Impulse during recoil determines magnitude and direction of angular momentum during flight phase (To perform forward somersault, impulse must produce angular momentum pointing inward) Does not change during flight phase Only force acting on diver is gravity Angular momentum of individual segments can change Faster the recoil the high up you will go

Wind-Up

Initial movement until toe-off of the stride foot/arm hits 6 o'clock position Weight shifts from stride foot to pivot foot Shoulder moves from extension to flexion

Countermovement Jump

Lengthening -> shortening Lengthen the muscle first to open actin binding sites Golgi tendon organs Believed that lengthening contraction increases contraction force prior to push-off

Leg Spring Stiffness

Load a tendon we actually lengthen it and compress/shortening the muscle As it shortens that's the spring rebounding Stiffness of our leg increases in order to propulse more Leg Stiffness is going to change with the surface, overall stiffness is going to be constant More stiff surface = less stiff leg

9 o'clock to ball release

Maximum pelvic rotation Peak elbow extension velocity (570 °/s) Muscle activity -Peak pec major and serratus anterior -Subscapularis, posterior deltoid

Energy Fluctuations

Most work done during locomotion is to displace COM vertically and forward Energy to perform this work comes from Ek and Ep of COM Work = Force x Distance Comes from both our kinetic energy and potential energy

Jumping

Movement that causes the COM to project upward and the feet to leave the ground

Landing Phases

Passive - your muscles aren't activating because there is no resistnace Active - muscles begin to activate when COM is no longer going downward you have landed begins with ground contact

12 o'clock to 9 o'clock

Peak adduction and IR torque at shoulder Muscle activity -Pec major and subscapularis to IR shoulder -Serratus anterior, teres minor, posterior deltoid

Late Cocking Lower Body

Pelvis reaches peak rotation Trunk continues to rotate and tilt anterolaterally Lead knee extends

Improving Vertical Jump

Power clean and snatch Hang clean Plyometrics Max intensity Jumps: Squats Heel Raises Squats lower the velocity of our exercise and improve the endurance component of muscle

Mid-Stance (15-30%)

Prepare for Forward propulsion VGRF straight up, no angle to it Ankle 5 degrees dorsiflexion, foot is mobile Hip 0 degrees

Terminal Swing (85-100%)

Prepare limb for next heel strike, prep body for landing Hip 20 degree flexion, biceps femoris, semimembranosus Knee 0-5 degree flexion, biceps femoris, Semimembranosus, Semitendinosus Ankle neutral, tibialis anterior, EDL, EHL

Landing

Rapid dorsiflexion accompanied by knee and hip flexion Purpose: Reduce amount of body mass involved in initial collision with ground Allow LE to absorb energy of impact and prepare for subsequent propulsive movement Reduce forces acting on body by increasing distance that COM travels while these forces act on body

Mechanical energy transfer

Rectus femoris, hip flexion and knee extension - causes the antagonist action Because of this we are able to have the net muscle length

Running vs. Walking GRF

Running is higher than walking because our limb represents a rigid strut during walking but a spring mechanisms during running Also has to do with the speed of running Blip occurs during heel strike

running pendulum

Running: COM Lowest point at mid-stance COM Highest point at flight phase

Acceleration Upper Body

Scapula Protracts Trunk rotates and tilts Shoulder horizontally adducts, internally rotates (faster this occurs greater ball velocity is) Elbow flexes then extends Wrist Flexes

Late Cocking Upper Body

Scapula retracts and tilts upward Elbow Flexes (max valgus torque) Should abducts and externally rotates -Greater ER allows accelerating forces to act over longer distance, allowing greater prestretch and elastic energy transfer to ball during acceleration

Early Cocking/Strike Lead Foot

Should land in line with stance foot, pointing forward or with slight internal rotation If lands too closed (across body), have to throw across body If lands too open, see overrotation of pelvis

inverted pendulum

Walking: COM Lowest point at heel strike and mid-swing COM Highest point during mid-stance when COM is at highest point, VGRF is at its lowest point

Walking GRF

Why is there a double hump during walking -loading limb relaxing limb and loading limb again -during walking our limb is more of a rigid structure vs running were its more spring like Knee is slightly flexes so it doesn't deal with the forces as well that's why its evenly distributed during walking

Deceleration Duration

ball release --> max shoulder internal rotation and elbow extension most violent phase of throwing

Vertical Jump

depends on amplitude and timing of muscle activity in the legs Countermovement Jump - where u move in the opposite direction of your angle Squat jump - start squatted and jump up as high as u can Countermovement results in a higher jump

Flight Phase

during running where both feet are off the ground

Initial Swing (60-75%)

foot clearance Hip 15 degree flexion, Iliacus, Gracilis, Sartorious Knee 60 degree flexion, Biceps femoris, Gracilis, Sartorius Ankle 5 degree plantar flexion, EDL EHL

Stride

foot strike of one foot to next foot strike of same foot

Initial Contact

foot strikes the ground Hip 20 degrees flexion, glut med prevents hips from swinging, maximal contraction Knee 5 degree flexion, hamstring, decelerate and stablize pelvis and knee ankle 0 degrees, tibialis anterior peak activation, stabilize foot

Step

lasts from foot strike of one foot, to foot strike of other foot step is half of a stride

Walk-Run Transition

occurs around 2 m/s

Pre-Swing (50-60%)

rapid knee flexion, transfer of weight to contralateral limb Hip 10 degree extension, rectus femoris max contracted Knee 40 degree flexion, rectus femoris Ankle 15 degree plantar flexion, Soleus | Tibialis anterior