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.
Inverse Dynamics AnalysisInverse Dynamics Analysis
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
Joint Power Produced By Joint TorquesJoint Power Produced By Joint Torques
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
Joint Power Produced By Joint TorquesJoint Power Produced By Joint Torques
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.
Joint Power Produced By Joint TorquesJoint Power Produced By Joint Torques
Knee power & torque in STAIR ASCENT.
Positive powers dominate by concentric contractions.
Torque and velocity in same direction.
Joint Power Produced By Joint TorquesJoint Power Produced By Joint Torques
Knee power & torque in STAIR DESCENT.
Negative powers dominate by eccentric contractions.
Torque and velocity in opposite directions.
Joint Power Produced By Joint TorquesJoint Power Produced By Joint Torques
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
Inverse Dynamics AnalysisInverse Dynamics Analysis
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.