Exss 3850 10 summer angular kinetics

EXSS 3850 Introduction to BiomechanicsEXSS 3850 Introduction to Biomechanics

Angular Kinetics – Angular Kinetics – Torques Causing Torques Causing Rotational MovementRotational Movement

Paul DeVita, Ph.D. Biomechanics Laboratory East Carolina University Greenville, North Carolina

Angular KineticsAngular Kinetics

Angular kinetics is the study of torques and their rotational effects on masses.

Weight creates an external torque around the ankle causing the person to rotate clockwise.

Muscle force creates and internal torque around the elbow joint axis causing the forearm to rotate towards flexion.

Lever arm between force vector and axis in red

A little secret: we have studied angular A little secret: we have studied angular kinetics throughout the semesterkinetics throughout the semester

1) Muscle Contractions – 3rd class levers

2) Muscle co-contraction – developing opposing torques with muscles

Angular Kinetics and Co-contractionAngular Kinetics and Co-contraction

Simultaneous contraction of muscles on both sides of a joint

Agonist muscle must overcome external load and load from co-contracting, antagonist muscle

E.g. Biceps Brachii in elbow flexionTriceps

torqueBiceps torque

Angular Kinetics:Angular Kinetics:Biceps Torque with Co-contractionBiceps Torque with Co-contraction

Ext. force, lever arm = 40 N, 0.30 m Ext. torque = F * dist.= 40 N * 0.30m = 12 Nm

Triceps force = 400 N Triceps lever arm = 0.02 m Triceps torque = 8 Nm

Total Extensor torque = Ext. torque + Triceps torque =

12 Nm + 8 Nm = 20 Nm

Biceps force

External force (40 N)

Triceps force

Angular Kinetics:Angular Kinetics:Biceps Torque with Co-contractionBiceps Torque with Co-contraction

Ext. torque = 20 NmBiceps force = ? N Biceps lever arm = 0.02 m Biceps torque > 20 Nm: Slow lift = 25 Nm

25 Nm = Biceps force * 0.02 m

Biceps force = 1250 N

Biceps force

External force (40 N)

Triceps force

Angular Kinetics: Angular Kinetics: Force – Velocity RelationshipForce – Velocity Relationship

Concentric:Concentric:

Knee joint velocity and muscle torque during the stance phase of running. Torque (and muscle force) are highest in midstance when the joint stops moving (zero velocity). Muscle shortening velocity is low at this time.

Angular KineticsAngular Kinetics

The study of torques and their rotational effects on masses

Torque – the turning effect of a force exerted at a distance to an axisEffects – positive and negative angular accelerations, stabilize objectMasses – the object under consideration – a whole human or animal, a

body segment, IN ALL CASES THE MASS IS A LEVER (a rigid object)

TorqueTorque

Torque is a vector – direction is either: 1) clockwise or counterclockwise 2) anatomical – flexor or extensor, adductor or abductor

Torque measured in Newton * meters: 1 Nm = 1 kg m/s2 * 1 m = 1 kg m2/s2

1 Nm of torque is a small amount for human biomechanics: elbow torque in biceps curl with 25 lbs (~100N) = 30 Nm knee torque in running = 250 Nm

Torque Trumps ForceTorque Trumps Force

While forces create linear movement, their primary musculoskeletal effect is their application of torques onto our body segments.

Torques rotate our segments to produce coordinated human movement.

External forces create external torques on body segments

Humans exert muscle torques onto their body segments in response to these external torques

Torque = Force * Distance = 22 N * 0 m = 0 Nm

Dumbbell Weight

The external force is identical but its musculoskeletal effect is much different.

The external force now creates a large torque and thus a large muscle response.

Torque = Force * Distance = 22 N * 0.8 m

= 18 Nm

Thus the primary musculoskeletal load from both external and muscles sources is TORQUE.

Dumbbell Weight

Distance (Moment Arm)

Muscle Torque Response

Torque Trumps ForceTorque Trumps Force

Newton’s Laws of Angular MotionNewton’s Laws of Angular MotionI. Law of Angular Inertia – An object will remain stationary or

rotate with constant angular velocity until an external torque is applied to the object

Rotational Inertia – resistance

Rotational Inertia = Moment of Inertia = I = mr2

Rotational resistance depends on objects mass and length

Long, massive objects are hard to rotate –

Why does tight rope walker carry long pole?

(see next slide)

Newton’s Laws of Angular MotionNewton’s Laws of Angular Motion

Why? To live, of course!

In this case living involves not falling off the wire.

The pole provides a support brace – it resists rotation due to its mass but mostly due to its length.

As the person falls slightly to one side, he torques the pole around its center. The pole resists this torque due to its large Moment of Inertia and it applies a reaction torque back on the person to stabilize him.

Moment of InertiaMoment of Inertia

Most important application of Moment of Inertia:

Moment of Inertia for individual body segments – the amount of resistance to a change in rotation within each segment.

Affects the rotational motion caused by muscle torques.

Larger people – more mass and longer segments – have larger segment I values (7’ Basketballers)

Moment of InertiaMoment of Inertia

Moments of Inertia are low for most people and most body segments except trunk. Trunk offers some resistance to rotation. Related to Low Back injuries.

Moments of Inertia (kgm2) Segment Women Men

Trunk 0.8484 1.0809

Arm 0.0081 0.0114

Forearm 0.0039 0.0060

Thigh 0.1646 0.1995

Shank 0.0397 0.0369

Newton’s Laws of MotionNewton’s Laws of Motion

III. Law of Angular Reaction – When one object applies a torque on a second object, the second object applies an equal and opposite torque onto the first object

“equal and opposite” – equal magnitude and opposite direction

Evident in joint or muscle torques

Law of Angular ReactionLaw of Angular Reaction

Muscles operate as springs which have equal and opposite torques on each lever (i.e. body segment). The, “muscle spring,” rotates each segment in the opposite directionWhy does only forearm rotate

then in biceps curl?

Law of Angular Reaction – Inverse Law of Angular Reaction – Inverse Dynamics & Muscle TorquesDynamics & Muscle Torques

Gastroc-Soleus force Gastroc-soleus force creates a

clockwise torque on foot (blue arrow) and a counterclockwise torque on leg (red arrow) = ankle joint plantarflexion.

Exactly like the spring on the skin calipers torques each arm in the opposite direction

Newton’s Laws of MotionNewton’s Laws of Motion

II. Law of Angular Acceleration – a torque will accelerate an object in the direction of the torque, at a rate inversely proportional to the moment of inertia of the object:

T = I Torque – the rotational effect of a force applied at a

distance to an axis

Two Equations for TorqueTwo Equations for Torque

T = I T = F d

I = mr2

F

d

=

Kinematic – Kinetic Equivalents

I = F d

Two Calculation Techniques for TorqueTwo Calculation Techniques for Torque

1) What is the lever arm dist? Biceps attached 3 cm from elbow joint.

= 60°

Forearm

Arm

Biceps force = 4,000 N

0.03 m

Sin 60° = d1/0.03 d1=0.026 T = 4000 N (0.026 m)

= 104 Nm

d1

4,000 N

Use length triangle

60°

Two Calculation Techniques For TorqueTwo Calculation Techniques For Torque2) What is the amount of force

perpendicular to lever (the rotational effect of the muscle force)?

= 60°

Forearm

Arm

Biceps force = 4,000 N

0.03 m

Cos 30° = F1/4000 F1=3464 N T = 3464 N (0.03 m)

= 104 Nm

F1

4,000 N

Use force triangle

= 30°

Law of Angular Acceleration & and Law of Angular Acceleration & and Angular Impulse-MomentumAngular Impulse-Momentum

Law of Angular Acceleration restated:

T = I * T = I * (f – i)/time

T * time = I * (f – i) - angular impulse-momentum equation

T * time = angular impulse = area under torque-time curve = total effect of the accumulated or applied torque; measured in Nms = kgm/s2 * m *s = kgm2/s

Angular Impulse Changes Angular Momentum

Angular Impulse in Movement AnalysesAngular Impulse in Movement Analyses

Use area under torque-time curve to assess the total effect of a muscle torque

Area sensitive to magnitude and temporal changes

Brace did not change angular impulse in ACL group

ACL group had more angular impulse at the hip and less at the knee compared to healthy group

0.26 0.23 * 0.17 Nms/kg

0.13 0.14 * 0.33 Nms/kg

Law of Angular Acceleration Law of Angular Acceleration and Inverse Dynamicsand Inverse Dynamics

Inverse Dynamics – an analysis that calculates unknown torques inside the human body. These are the muscle torques that combine to create skillful human movement.

Torques at joints produced by all muscles crossing the joints.

Inverse Dynamics AnalysisInverse Dynamics Analysis

Inverse Dynamics – combines position and acceleration data from kineamatic motion analysis and force data from force platforms or other force sensors to calculate internal torques. Most commonly used in

locomotion but also in cycling and other activities.

Joint Torques During WalkingJoint Torques During Walking

Joint torques show neuromuscular contributions to movement.

Support torque is sum of 3 joint torques and is exactly like GRF.

Subject walking up the ramp.

Video to produce position and acceleration data. Force plate to measure the known external forces.

See analysis on next few slides and on board.


White line is force plate. Curves are vertical and ant-post GRFs.

Data used in the I.D. analysis in next few slides:

Masses and moment of inertias:

Subject: 70 kg Foot: 1.7 kg, 0.0023 kgm2 Leg: 3.44 kg, 0.0044 kgm2

Accelerations:

Foot vertical: 2.47 m/s2 Foot horizontal: 4.70 m/s2

Foot rotational: -52.5 rad/s2

Leg vertical: 1.30 m/s2 Leg horizontal: 9.23 m/s2

Leg rotational: -10.3 rad/s2

Av – large & down: the body weight plus inertial force of accelerating body mass upward push down on the foot.

The upward GRF is larger than the downward ankle reaction force – THUS THE FOOT AND PERSON MOVE UPWARD.

Ankle Joint ForcesAnkle Joint Forces

Vertical Ankle Joint Reaction Force (JRF)

Av: Fv = mav

GRFv – mg + Av = mav

975 – (1.07) (9.81) + Av = (1.07) (2.47)

Av = -961 N

Foot

Ankle

-961 N Av

mg

Note: Weight applied at the center

of mass

GRFv = 975 N

Vertical Direction:

Ah – small and backward: the foot pushes the body forward & the body pushes back on the foot at the ankle.

The forward GRF is larger than the backward ankle reaction force – THUS THE FOOT AND PERSON MOVE FORWARD.

Ankle Joint ForcesAnkle Joint Forces

Horizontal Ankle Joint Reaction Force (JRF)

Ah: Fh = mah

GRFh + Ah = mah

162 + Ah = (1.07) (4.7)

Ah = -157 N

GRFh = 162 N

Foot

Ankle

-157 NAh

Horizontal Direction:

Each force causes a torque in particular direction – in this case all Each force causes a torque in particular direction – in this case all external force-torques in counterclockwise (dorsiflexor) directionexternal force-torques in counterclockwise (dorsiflexor) direction

FBD for Ankle Joint TorqueFBD for Ankle Joint Torque

Fy = 162 N

Fz = 975 N

Foot

Met head (0.572,0.011)

Az =- 961 N

Ay = -157 N

Ankle

Unknown Ankle Torque

Fz lever arm

Fy lever arm

Az lever arm

Ay lever arm

Ankle Joint Torque

T = I

975(0.055) + 162(0.061) + 961(0.045) + 157(0.047) + Ma = (0.0023)(-52.5)

Ma = (0.0023)(-52.5) - 975(0.055) - 162(0.061) - 961(0.045) - 157(0.047)

Ma = -114 Nm

Fy = 162 N

Fz = 975 N

Foot CoM (0.516,0.072)

mgFoot

Met head (0.572,0.011)

Az =- 961 N

Fy = -157 N

Ankle

Unknown Ankle Torque

Ankle Joint TorqueAnkle Joint Torque

Ankle Joint Torque:large and negative –

strong push off required by ankle plantarflexors to

propel forward and up the ramp.

CM (0.517,0.072)

(0.472, 0.119)

T = I

975(0.055) + 162(0.061) + 961(0.045) + 157(0.047) + Ma = (0.0023)(-52.5)

Ankle Joint Torque ComponentsAnkle Joint Torque Components

Vertical GRF torque = 54 Nm

Horizontal GRF torque = 10 Nm

Vertical Ankle JRF torque = 43 Nm

Horizontal Ankle JRF torque = 7 Nm

Inertial torque = 0.1 Nm

Vertical torque = 119 Nm

Horizontal torque = 20 Nm

Nearly all muscle torque due to the muscle response to external loads on the body segment

(more on this issue a few slides down)

Knee Joint ForcesKnee Joint Forces

Vertical Knee Joint Reaction Force (JRF)

Kv: Fv = mav

Av – mg + Kv = mav

961 – (3.44) (9.81) + Kv = (3.44) (1.30)

Kv = -922 N

Av = 961 N

Leg

Knee

Kv

Kv – large & down: the body weight plus inertial force of accelerating body mass upward push down on the knee

The upward ankle force is larger than the downward knee force – THUS THE LEG AND PERSON MOVE UPWARD.

Ankle

Note: Ankle JRFs reversed onto leg (the

law of reaction)

mg

-922 N

Vertical Direction:

Knee Joint ForcesKnee Joint Forces

Horizontal Knee Joint Reaction Force (JRF)

Kh: Fh = mah

Ay + Kh = mah

157 + Kh = (3.44) (9.23)

Kh = -125 N

Ah = 157N

Leg

Knee

Kh – small and backward: the leg pushes the body forward & the body pushes back on the leg at the knee.

The forward ankle force is larger than the backward knee force – THUS THE LEG AND PERSON MOVE FORWARD.

Ankle

Note: Ankle JRFs reversed onto leg (the

law of reaction)

Kh

-125 N Horizontal Direction:

Knee Joint Torque

T = I

-961(0.112) + 157(0.205) - 922(0.085) + 125(0.155) + 114 +Mk = (0.0044)(-10.3)

Mk = (0.0044)(-10.3) + 961(0.112) -157(0.205) + 922(0.085) - 125(0.155) -114

Mk = 20.4 Nm

Knee Joint TorqueKnee Joint Torque

CM (0.584,0.324)

Ax = 157N

Ay = 961 N

Leg

Knee

-922 N Ky

Ankle

-125 N

(0.472, 0.119)

(0. 669, 0.479)Mk

Trq. = 114 Nm

Knee joint torque low and positive (extensor) in direction. Walking uphill had larger ankle vs. knee extensor torques.

Some (i.e. horizontal) external joint forces torqued the leg in the desired direction – aided & so reduced muscle effort.

Old adults have larger hip torques and lower knee torques.

Shows altered motor strategy with age.

Joint Torques in Old & Young AdultsJoint Torques in Old & Young AdultsLevel Walking Stair Ascent

Several Muscles Combine to Produce Several Muscles Combine to Produce Torque at Each JointTorque at Each Joint

These muscles create the torques at each joint. Each muscle torque is the combined effect of all the extensor and flexor muscles at each joint. For example, an extensor knee torque occurs when the quadriceps produce more extensor torque than the flexor torque produced by the hamstrings and gastrocnemius. The co-activating muscles have an overall extensor effect in this case.

Joint Torques in Obese and Lean AdultsJoint Torques in Obese and Lean Adults

1) Hip torques equal

2) Obese less knee torque at slow speed and same torque at same speed as lean

3) Obese more ankle torque at both speeds

Obese

Lean

Inverse Dynamic AnalysisInverse Dynamic Analysis

Inverse dynamic analysis calculates unknown joint torques inside the human body (also called muscle torques).

Torques at joints produced by all muscles crossing the joints and show how each muscle group contributes to a particular movement.

Joint torques are interpreted as the motor pattern of a movement – they show the neurological strategy used in a movement

Avg lever arm = 0.25 m

Avg Muscle torque = 10 Nm

40 N

While torque is not work, it can do work: Work = Torque *

= angular displacement = 0.78 rad

Work = 10 Nm * 0.80 rad = 8.0 J

(check with linear calculation:

Work=mgh: 40 N(hf) – 40 N(hi)= 8.0 J

hf – hi = 0.20 m)

Work Done By A TorqueWork Done By A Torque

Elbow joint angular velocity, torque and power

Power = Torque *

Positive power – concentric contraction, positive work, increase energy

Negative power – eccentric contraction, negative work, decrease energy

Joint Power Produced By Joint TorquesJoint Power Produced By Joint Torques

Calculate work from power curve:

Work is area under the power curve or a portion of the curve:

Power = Watts = T/s = Nm/s = kgm2/s2 / s = kgm2/s3 * s (for area) = kgm/s2 * m = force * distance = WORK


Knee power, torque, and angular velocity during stance phase of running.

Knee flexes during brief flexor torque then longer extensor torque – low positive power & work then large negative power & work

Knee extends during long extensor torque then shorter flexor torque – large positive power & work then low negative power & work


Knee power, torque, and angular velocity during stance phase of running.

Peak torque at zero velocity – at maximum knee flexion, maximum quadriceps stretch – muscle force maximized early in movement.

Peak power at mid levels of torque and velocity – both torque and velocity contribute to power – muscle work maximized in middle of movements.


Knee power & torque in STAIR ASCENT.

Positive powers dominate by concentric contractions.

Torque and velocity in same direction.


Knee power & torque in STAIR DESCENT.

Negative powers dominate by eccentric contractions.

Torque and velocity in opposite directions.


Positive work equal between groups in ascent.

Work Done By Joint TorquesWork Done By Joint Torques

0.00

0.50

1.00

1.50

2.00

Total Hip Knee Ankle

Wo

rk (

J/kg

)

Old

Young

**

* P < .05

*

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

Total Hip Knee Ankle

Wo

rk (

J/k

g)

Old

Young

*

* P < .05*

Negative work not equal between groups in descent.

Joint torques during stair descent

Old adults have larger hip torque and this torque performs more work: 0.41 vs. 0.24 J / kg

Young adults have larger knee torque and this torque performs more work: 0.81 vs. 0.56 J / kg

Positive work – concentric contraction – increase energy

Work Done By A TorqueWork Done By A Torque

Angular Kinetics SummaryAngular Kinetics Summary

Torque

Torque

TorqueTorque is more important in terms of loads on the body and loads produced by muscles than is weight.

Torque causes all human rotations – external torques from various weights and forces (e.g. GRF) and internal torques from muscles combine to move animals around the environment.

Five Years From Now…Five Years From Now…

Please come back and visit me in five years to tell me how much you understand about biomechanics.

Extra SlidesExtra Slides

Rotational Inertial TorquesRotational Inertial Torques

Inertial torques are caused by angular acceleration of body segment

Solid line – joint or muscle torque in running

Dashed line – inertial torque due to mass and length of body segments

Inertial torques are very small – body segments offer little resistance to rotation - swing phase rotations are easy.

Joint torques and powers and muscle activity


We have done this analysis during the semester.

We will do the analysis on the front board.

No – We Have New Slides With the Analysis

Muscle Work is Larger While Running Muscle Work is Larger While Running Up vs. Down an Inclined SurfaceUp vs. Down an Inclined Surface

Paul DeVita, Erin Bushey,

Patrick Rider, Allison Gruber,

Joseph Helseth, & Paul Zalewski

Biomechanics LaboratoryBiomechanics Laboratory

Department of Exercise and Sport Department of Exercise and Sport ScienceScience

East Carolina UniversityEast Carolina University

Greenville, NC, USAGreenville, NC, USA

Mechanical Energy Changes in Mechanical Energy Changes in Ascending and Descending GaitsAscending and Descending Gaits

Ascent: Total energy increases by Ascent: Total energy increases by adding PE to the body. Performed adding PE to the body. Performed by shortening contractions in by shortening contractions in skeletal muscles that generate skeletal muscles that generate energy.energy.

Descent: Total energy decreases by Descent: Total energy decreases by removing PE energy from the body. removing PE energy from the body. Attributed to lengthening Attributed to lengthening contractions in skeletal muscles contractions in skeletal muscles that dissipate energy.that dissipate energy.

Laursen et al, Appl Ergon., 2000

En

erg

y (J

)

Joint Powers in Ascending and Descending StairsJoint Powers in Ascending and Descending Stairs

McFadyen & Winter, J Biomechanics, 1988McFadyen & Winter, J Biomechanics, 1988

Joint Work in Stairway GaitJoint Work in Stairway Gait

Stair Ascent Stair Descent

Work from joint powers during stair descent was lower than stair ascent despite identical magnitude changes in PE.

Joint Powers While Ascending Joint Powers While Ascending and Descending Inclinesand Descending Inclines

Riener et al, Riener et al, Gait & Posture, 2002Gait & Posture, 2002

Ascent: 2.33 J /kgAscent: 2.33 J /kgDescent: -2.01 J/kgDescent: -2.01 J/kg

Joint Work During Ascent and Joint Work During Ascent and Descent Walking on InclinesDescent Walking on Inclines

Descent work Descent work was 30% less was 30% less than ascent than ascent work in all work in all subjects.subjects.

* p < .001

HypothesisHypothesis

We hypothesize a generalized We hypothesize a generalized biomechanical principle that lower biomechanical principle that lower extremity muscles dissipate less extremity muscles dissipate less mechanical energy in gait tasks that lower mechanical energy in gait tasks that lower the center of mass compared to the the center of mass compared to the mechanical energy they produce in gait mechanical energy they produce in gait tasks that raise the center of mass. tasks that raise the center of mass.

PurposePurpose

The purpose of this study was to The purpose of this study was to compare work produced by lower compare work produced by lower extremity joint powers while running extremity joint powers while running up and down a surface inclined 10up and down a surface inclined 10 and and while running on a level surface.while running on a level surface.

Our secondary purpose was to compare Our secondary purpose was to compare the total joint work in these the total joint work in these movements with the change in total movements with the change in total body energy.body energy.

Methods, Briefly….Methods, Briefly….

Subjects: 18 healthy males and females, age: 23 yr, Subjects: 18 healthy males and females, age: 23 yr, mass: 71 kg. mass: 71 kg.

Running velocity was constrained at 3.35 m/s (8 min/mile Running velocity was constrained at 3.35 m/s (8 min/mile pace)pace)

3-dimensional lower extremity joint powers and work were calculated 3-dimensional lower extremity joint powers and work were calculated through inverse dynamics. This work quantified muscular contributions through inverse dynamics. This work quantified muscular contributions to energy changes through the entire stride (termed: Joint Work). to energy changes through the entire stride (termed: Joint Work).

Total work per stride was calculated from the change in subject’s total Total work per stride was calculated from the change in subject’s total energy over the complete gait cycle in each gait (termed: d Energy)energy over the complete gait cycle in each gait (termed: d Energy)

One way ANOVA on 3 levels of incline with repeated measures and a few One way ANOVA on 3 levels of incline with repeated measures and a few specific t-tests, p<.05specific t-tests, p<.05

I love I love biomechanibiomechani

cs, don’t cs, don’t you?you?

Do We have Any Idea What We Are Doing?Do We have Any Idea What We Are Doing?

Elbow & Shoulder Power

-18.00

-12.00

-6.00

0.00

6.00

12.00

18.00

0.00 0.42 0.83 1.25 1.67 2.08

Time (s)

Pow

er (W

)

Elbow

Shoulder

Negative and positive joint work were identical in Negative and positive joint work were identical in shoulder ab- and ad-duction and both were shoulder ab- and ad-duction and both were equal to change in energy.equal to change in energy.

Negative and positive joint work were identical in Negative and positive joint work were identical in the slow squat exercise and both were slightly the slow squat exercise and both were slightly less (i.e. 95%) of the change in energy.less (i.e. 95%) of the change in energy.

Do We have Any Idea What We Are Doing, Part 2?Do We have Any Idea What We Are Doing, Part 2?

Ankle, Knee & Hip Powers

-300

-200

-100

0

100

200

300

400

0.00 0.42 0.83 1.25

Time (s)

Pow

er (W

)

Ankle

Knee

Hip

Sagittal Plane Sagittal Plane Joint PowersJoint Powers

Hip - biased towards positive power & work in all gaits

Knee – biased towards negative power & work in all gaits

Ankle – both negative and positive power & work phases

Po

we

r (W

)

-500

500

HipHip

KneeKnee

AnkleAnkle

Descent

Level

Ascent

Po

we

r (W

)

-500

500P

ow

er

(W)

-500

500

SwingSwing StanceStance

Po

we

r (W

)

-500

500

Frontal Plane Frontal Plane Joint PowersJoint Powers

Significant power and work in the frontal plane

Po

we

r (W

)

-500

500

HiHipp

KneeKnee

AnklAnklee

Descent

Level

Ascent

Po

we

r (W

)

-500

500

SwingSwing StanceStance

-250

-200

-150

-100

-50

0

50

100

150

200

250

Descent Level Ascent

Wo

rk (

J)

Joint Workd Energy

Joint Work & d Energy in Three GaitsJoint Work & d Energy in Three Gaits

Joint work:Joint work:

Descent = -108 JDescent = -108 J

Level = Level = 22 J 22 J

Ascent = 159 JAscent = 159 J

d Energy:d Energy:

Descent = -163 JDescent = -163 J

Level = Level = 12 J 12 J

Ascent = 178 JAscent = 178 J

* Joint Work ≠ d Energy, * Joint Work ≠ d Energy, p<.001p<.001

*

*

*

Stance Phase Kinematics and Stance Phase Kinematics and Resultant GRFsResultant GRFs

We propose that the fundamental We propose that the fundamental mechanism causing these results mechanism causing these results is the rate of acceleration in each is the rate of acceleration in each movement.movement.

Muscles, through their lengthening Muscles, through their lengthening contractions, dominate energy contractions, dominate energy dissipation in movements with dissipation in movements with low accelerations and velocities.low accelerations and velocities.

As the rate of acceleration increases As the rate of acceleration increases other non-muscular tissues other non-muscular tissues contribute to energy dissipation.contribute to energy dissipation.

0

400

800

1200

1600

0.00 0.05 0.10 0.16 0.21

Time (s)

Fo

rce

(N

)

Ascent

Descent

AscentAscent DescentDescent

Source of Mechanical Energy GenerationSource of Mechanical Energy Generation

Actin

Myosin

Power Stroke

Sources of Mechanical Energy DissipationSources of Mechanical Energy Dissipation

Art K: “The Jiggle Effect,” or “Mystery Work”

SummarySummary

The concept of directly comparing joint work The concept of directly comparing joint work through joint powers and change in total through joint powers and change in total body energy is reasonable based on the body energy is reasonable based on the shoulder and squat tests.shoulder and squat tests.

Joint work was 33% lower in descent vs. Joint work was 33% lower in descent vs. ascent running (-108 vs. 159 J per stride, ascent running (-108 vs. 159 J per stride, p<.001). p<.001).

SummarySummary

Ascent joint work was 11% less than the total Ascent joint work was 11% less than the total work done to raise the subjects’ masses work done to raise the subjects’ masses

(159 vs. 178 J per stride, p>.001) (159 vs. 178 J per stride, p>.001)

Descent joint work was 34% less than the total Descent joint work was 34% less than the total work done to lower the subjects’ masses work done to lower the subjects’ masses

(-108 vs. -163 J per stride, p<.001). (-108 vs. -163 J per stride, p<.001).

SummarySummary

Level running had small bias towards positive Level running had small bias towards positive joint work suggesting an equivalent result: joint work suggesting an equivalent result: muscles do more positive then negative work muscles do more positive then negative work in locomotion.in locomotion.

Results may also partially explain the higher Results may also partially explain the higher metabolic cost in ascending vs. descending metabolic cost in ascending vs. descending gaits (i.e. more muscle effort) in addition to gaits (i.e. more muscle effort) in addition to the decreased efficiency of shortening the decreased efficiency of shortening contractions used in ascent.contractions used in ascent.

ConclusionsConclusions

Data supported the hypothesized biomechanical Data supported the hypothesized biomechanical principle that lower extremity muscles principle that lower extremity muscles dissipate less mechanical energy in gait tasks dissipate less mechanical energy in gait tasks that lower the center of mass compared to the that lower the center of mass compared to the mechanical energy they produce in gait tasks mechanical energy they produce in gait tasks that raise the center of mass. that raise the center of mass.

Exss 3850 10 summer angular kinetics

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