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A Biomechanical Analysis of Lifting


Dani C

on 25 March 2013

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Transcript of A Biomechanical Analysis of Lifting

A Biomechanical Analysis of Lifting Introduction Kinematics Kinetics Muscle Activation Profiles Danielle Carnegie
Miguel Reyes
Mary Geneau
Jessica Ho Importance of Lifting Lifting children or grand children

Picking up the laundry basket, or groceries from the ground

Manual material handling
at work Influencing Factors Participant-Dependent Factors
Lifting technique
Lifting experience
Task-Dependent Factors
Load Magnitude
Load Size and Stability
Lift Origin and Destination
Lifting Speed
Lifting Frequency Lower back pain is associated with poor lifting technique

Chronic lower back pain affects many daily life activities

LBP accounts for 18% of all injuries in Canada; more than 21 million

7% are left with permanent disability

Every year U.S. spends $50 billion on back-pain-related care and disability compensation Epidemiology Variation in Techniques Lift Analysis The safe and controlled movement of an external (anteriorly located) load in a vertical direction

Generate sufficient Mechanical Energy

Balance and coordination of entire body with external load

Transfer Energy Effectively NIOSH follows a static 2D model – underestimates loading on lumbar spine because it ignores muscle force above that which is required to hold a weight statically

Dynamic 3D biomechanical model
Accounts for linear accelerations of load AND angular accelerations of the body segments therefore more accurate representation of compressive forces present

Linked para sagittal lifting model
i.e., five-linked parasagittal lifting model
5 selected joints - major inputs for estimation of spinal loading and joint moments
•Elbow, shoulder, hip, knee, ankle System Model Phases of Lifting 1. Initial Unweighted phase During countermovement 2. Lift - Weighted Phase Acceleration of load to chest level

Function: generate large extension moment to overcome the inertia and bring load closer to Center of Gravity (CoG) of body to maintain balance

Low trunk velocity
•so as to decrease the dynamic effect of the load and body weight
•load is at furthest point from CoM
•an increased magnitude here combined with significant load may overcome tissue tolerance 3. Unweighted Phase Coming to a stop in upright position
Neutral spine Lifting can be accomplished using a variety of techniques

Each producing various amounts of stress on body 4. Carrying - Weighted Phase Acceleration of load from chest to destination

Function: bring load to highest position to provide load landing clearance

Increase trunk velocity
•Trunk erect therefore more stable
•While force capabilities are decreased with increased velocity, final stages of lifting are associated with a smaller moment arm since load is closer to CoM 5. Additional Phase Lowering Motion Profiles Application Problem Calculating Compressive Force Forces being transmitted through the low back can be estimated by calculating the moment and forces created by the weight of the load being lifted and the weight of the upper body

Moment of Force = (Force) X (Distance)


Moment = (Weight of load) X (Distance from COM of load to COM Lifter) A person is bending over to lift a load out of a bin. They are bending at approx. 40 degrees from horizontal, and the load weighs 65N. The person must reach 40cm in front of the lumbar spine to grasp the load and lift it. The center of mass of the upper body lies 26.4 cm anterior of the lumbar spine. The weight of the upper body is 400N (about half of total body weight)
Moment from weight of load = (65N) x (0.4m) = 26Nm
Moment from weight of upper body = (400N) x (.264m) = 105.6Nm
Total Moment (clockwise) = 79.6Nm To start to lift the load, this moment (clockwise) has to be counterbalanced by counterclockwise moment. The counterclockwise moment is generated by contraction of the erector spinae muscles (about 5cm behind the lumbar spine)
Calculate the counterclockwise moment
Moment (counterclockwise) = (force generated by erector spinae muscles) x (5cm) Remember: if the person is stooped and holding the load in a static posture at the start of the lift, the clockwise moment must equal the counterclockwise moment (or the person would fall over), therefore the counterclockwise moment must also be 79.6Nm
79.6Nm = (force generated by erector spinae muscles) x (0.05m)
(79.6Nm)/(0.05m) = force generated by erector spinae muscles)
1592Nm = force generated by erector spinae muscles Total compressive force is equal to the sum of the clockwise and counterclockwise moments (1671.6Nm in this case) Trunk Displacement The Spine Natural shape of the spine creates 3 balanced curves
Lordotic cervical region
Kyphotic thoracic region
Lordotic lumbar region Spine transfers loads from head and trunk to pelvis

Lifting changes the alignment of Center of Mass Each vertebral attachment has 3 planes of motion (6 DoF) All moments and force about the spine must be equilibrated by internal forces Asymmetry Strength dominant (Kicking Leg)
Coordination Dominant (Non Kicking Leg)

Creates positive and negative moments (affecting balance)

Causes and increase sagittal angle of trunk at which peak accelerations occur
moment arm of the load at peak acceleration
resultant compressive forces

Increases the number of peaks (# of changes in acceleration)
Coactivation Optimization Trunk Velocity
Too High
decrease force production capabilities
increase in co-activation = higher compressive loads
Too Low
more peaks in acceleration profile
longer duration of spinal loading Acceleration
Too High
potential to overcome tissue tolerance
increases joint moments, spinal loading, mechanical work
Too Early
large trunk angle - change in curvature of spine = weakest position Displacement
Greater trunk angle = increased spinal loading
Box location too far = Shifts COM and lifting kinematics Lift B Active and Passive Tissues The largest muscle groups in the body are used to complete a squat lift

Synergistic and complementary actions of muscle are required to complete a lift

Transfer of energy through isotonic “stiff” muscle and passive tissues is a large component in the completion of a lift

Each segment in the kinetic chain must be able to exert enough force and/or torque to compensate for the external loads and demands of a movement, including gravity and the lifted object

Muscle fibers: recruitment and sliding filament theory

Tissues can be described by their toughness, ductility, and strength
Which determine stress and strain qualities of the tissues Joints and Muscles Ankle
•Strain on the Achilles tendon from activation of the gastrocnemius
•Activation of the plantar flexors Knee
•Biceps femorus Hamstrings flex knee
•Moderate knee bend is optimal Hip
•Gluteus Maximus extends hip
•Biceps Femorus extends hip
but also contradictorily flexes leg at knee
•Hip Extensors should contribute most to the lift
Back and Trunk Neck, shoulder, elbow, wrist
Posture and stability is important
Protraction and retraction of scapula
Elevation from trapezius, levator spcapulae
Deltoids, biceps brachii, triceps
Forearm and wrist muscles and tissues involved with grip and lift of object SPINE
Lumbar Spine most stress during lift
Erector Spinae
Extensor of the spine
High concentric activation with stoop
High isotonic activation in squat lift
Compression of lumbar spine
Abdominal Obliques
Rectus abdominis
Latissmus Dorsi Spine Cont'd
Proper alignment necessary for spinal health
Pressure on intervertebral disks
Compressive force from the load, weight of the upper body, spinal extensors acting on the spine
Instruct people to keep objects close to the body while lifting. ****Keeping the object close to the fulcrum shortens its moment arm and therefore minimizes the compressive force exerted by the spinal extensors Stress on the passive tissues – cartilage
Poisson’s ratio: tendency for compressed objects (vertebral disks) to have transvers and axial strains References Abdoli-E, M., Agnew, M. J., & Stevenson, J. M. (2006). An on-body personal lift augmentation device (PLAD) reduces EMG amplitude of erectorn spinae during lifting tasks. Clinical Biomechanics, 21(5), 456-465. doi: 10.1016/j.clinbiomech.2005.12.021

Abdulrahman, A. (2003). Biomechancis of lifting. The Saudi Journal of Sports Medicine. 7 (2) 68-76

Cornell University (2013). Lifting Mechanics. http://ergo.human.cornell.edu/dea3250notes/lifting.html

Burgess-Limerick, R. (2003). Squat, stoop, or something in between? International Journal of Industrial Ergonomics, 31(3), 143-148.

Chang, C., Hsiang S., (2013). Generating Optimal Motion Patterns for Para-Sagittal Lifting Tasks. Proceedings of the Human Factors and Ergonomics Society Annual Meeting. 44. 292 Cresswell, A. G., & Thorstensson, A. (1994). Changes in intra-abdominal pressure, trunk muscle activation and force during isokinetic lifting and lowering. European Journal of Applied Physiology and Occupational Physiology, 68(4), 315-321.

Hsiang, S., Ayoub, M. (1994) Development of methodology in biomechanical simulation of manual lifting. International Journal of Industrial Ergonomics. 13. 271-288

Hsiang, S., Chang, C., McGorry, R., (1999). Development of a set of equations describing joint trajectories during para-sagittal lifting. Journal of Biomechanics. 32, 871-876

Hwang, S., Kim, Y., & Kim, Y. (2009). Lower extremity joint kinetics and lumbar curvature during squat and stoop lifting. BMC Musculoskeletal Disorders, 10(1),15. Maines, M., Reiser, R. (2005). Ground reaction force bilateral asymmetries during submaximal sagittal plane lifting from the floor. International Journal of Industrial Ergonomics. 36. 109-117

Maki, B. E., & McIlroy, W. E. (1997, 05; 2013/3). The role of limb movements in maintaining upright stance: The change-in-support strategy.77, 488+.

MARRAS, W. S., & DAVIS, K. G. (1998). Spine loading during asymmetric lifting using one versus two hands. Ergonomics, 41(6), 817-834. doi: 10.1080/001401398186667

Mirka, G., Marras, W., (1990). Lumbar Motion Response to a Constant Load Velocity Lift. The Journal of Human Factors and Ergonomics Society. 32. 493 Troup, J. D. G., Leskinen, T. P. J., Stalhammar, H. R., & Kuorinka, I. A. A. (1983). A comparison of intraabdominal pressure increases, hip torque, and lumbar vertebral compression in different lifting techniques. Human Factors: The Journal of the Human Factors and Ergonomics Society, 25(5), 517-525.

Van Dieën, J. H., Hoozemans, M. J., & Toussaint, H. M. (1999). Stoop or squat: a review of biomechanical studies on lifting technique. Clinical Biomechanics, 14(10), 685-696.

Xu, X., Hsiang. M., Mirka. G., (2008) Coordination indices between lifting kinematics and kinetics. International Journal of Industrial Ergonomics. 38. 1062-1066 Moments Power Newtonian Mechanics Ground Reaction Forces Consider: effect of hand position and foot placement on GRF Law of Inertia
to lift a load body must generate enough force to overcome inertia Law of Acceleration
to move an object to its destination you must cause it to accelerate
think of differences in acceleration depending on lift technique/goal Law of Reaction
to make an object accelerate quickly requires more force generation and therefore greater ground reaction forces Lumbar Moments
Needed to overcome weight of load and weight of upper body
increase in weight or distance of load from COM results in increased moment of force
think of implications for spinal compression Support Moments
flexion at hip, knee and ankle joints can work to absorb movement M = f x d Load Moment = (weight of load) x (distance of load from COM) Balance
Torque at Heel > 0 = Tipping over Backward
Torque at Ball > 0 = Tipping over Forward Dependent on the muscular force production capabilities and velocity of lift (duration of lift) Impulse Momentum In order to change the momentum of the object, an external force (generated by the lifter) must be applied Consider Impulse
appropriate force generation and duration of lift are required to generate enough impulse to move load Function: to place load on preset surface without throwing the load or hitting the surface
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