Effects of various types of lifting like stoop lifting, squat lifting, semi-squat lifting on the body and also when to use which type of lift to help prevent or minimize the risk of musculoskeletal injury.

1. Biomechanical Analysis
of Lifting
-Nidhi Chhabra

2. Lifting
• Lifting is an activity that is an essential part of
everyday life.
• Unfortunately, it has been implicated as a
contributing factor in the development of a
variety of musculoskeletal injuries, particularly
those that involve the lumbar spine.
• So, in order to know how much load is being
imposed on joints in day today life,
biomechanical analysis is important.

3. Characteristics of Lifting Tasks
• Lifting involves movement of an object from
one location to another location, generally
traversing both vertical and horizontal
distances.
• This, can be subdivided into three stages:
– Access
– Movement
– Placement

4. Lifting
Techniques
Stoop Lifting

5. Lifting
Techniques
Squat Lifting

6. Lifting
Techniques
Semi- squat Lifting

7. Squat Lifting v/s Stoop Lifting
Stoop lift
• Trunk flexion achieved by
thoracolumbar flexion and
there is no knee flexion.
• The extensor muscles are at
a disadvantage , because of
shorter moment arms in
this position, a change in
the line of pull and the
possibility of passive
insufficiency resulting from
elongated state of muscles.
Squat lift
• Spine remains as erect as
possible and trunk flexion
achieved primarily by hip
and knee flexion.
• The deep layer of erector
spinae is capable of
producing posterior shear,
which helps to offset
anterior shear that occurs
with trunk flexion, in case of
carrying additional load.

8. Squat Lifting v/s Stoop Lifting
Stoop lift
• Intradiskal pressure higher.
• Knee-High quadriceps
femoris group activity at the
beginning and at the end of
the lift.
• Moderate use of hamstrings
occurs in the middle third of
the lift.
Squat lift
• Intradiskal pressure
comparatively lower.
• Knee-The flexion moment
at the beginning of the lift
changes to an extension
moment.
• Medium to high activity of
vastus lateralis, less activity
of rectus femoris and low to
medium activity of biceps
femoris.

9. Squat Lifting v/s Stoop Lifting
Stoop lift
Phases
Muscles Beginning Middle End
Quads *** * ***
Hams * ** *
Squat lift
Phases
Muscles Beginning Middle End
Quads *** *** ***
Hams * * *
* = Low activity
** = Moderate activity
*** = High activity

10. Squat Lifting v/s Stoop Lifting
Stoop lift
• FRR in lumbar erector
spinae is evident and the
peak EMG response was
delayed towards the middle
of the lift. 1
• This FRR results in the
flexed spinal motion
segment resisting the flexor
moment by the posteriorly
placed passive structures.
Squat lift
• Earlier peak EMG
readings in erector spinae
were evident.1
1. McGorry et al 2001.

11. Squat Lifting v/s Stoop Lifting
Stoop lift
• The erector spinae in flexed
posture have changed line
of actions relative to the
motion segment and are
therefore less able to resist
the anterior shear forces
seen to cause damage to
the spine in full flexion.
Squat lift
• Contraction of erector
spinae muscles results in
the development of a
posterior shear force on the
superior vertebrae. This has
the potential effect of
reducing the effect of
anterior shear forces
generated by the weight of
the upper trunk and load.

12. Load

13. Stability of the load
• Keep the load close :
– Documented reduction in lumbar stress.
• Ensure the placement of a secure hand couple:
– Minimizes trunk instability during a lift involving asymmetric handling
and load shift.
• Use the lifting technique that is most applicable to the situation:
– Semi squat lift- This would be the ideal lift for heavy loads performed
on an occasional basis.
– Squat lift- To be used as an alternative to the semi-squat when space
is limited and load size does not allow for foot placement to the side
of the object to be lifted.
– Stoop lift- Lifting scenarios requiring light loads (20 pounds and
below) on a frequent basis are more efficiently managed using this
technique.

14. Stability of the Load
• When lifting on an uneven-sloped surface, face down the slope to
negotiate the lift.
• When lifting, do so as much as is possible in the sagittal plane.

15. Role of Intra-abdominal Pressure(IAP)
• An increase in IAP is frequently demonstrated during lifting tasks.
• Bartelink suggested that an increase in IAP decreases spinal
compressive loads by pushing it on the rib cage.
• McGill and Norman challenged this theory by arguing that the large
compressive loads caused by contraction of the abdominal muscles
negate any potential unloading effect and that a net increase in
compression through the lumbar spine would result from increased
IAP.
• Cholewicki et al suggested that the increase in IAP has more to do
with providing stability to the lumbar region and less to do with
generating extensor torque.
• Hodges et al suggested that an increase in IAP may in fact facilitate
an extensor torque if the IAP is generated through selective muscle
recruitment, in particular of the diaphragm, pelvic floor muscles
and transversus abdominis.

16. Manual lifting analysis
• NIOSH developed the Work Practices Guide for Manual Lifting
– the first comprehensive tool to assist in the process of risk factor identification
and subsequent ergonomic abatement to correct those factors identified as
being potential problems.
• Revised NIOSH lifting equation
RWL= LC x HM x VM x DM x AM x FM x CM
Here, RWL= Recommended Weight Limit
LC = Load Constant
HM = Horizontal Multiplier
VM = Vertical Multiplier
DM = Distance Multiplier
AM = Asymmetry Multiplier
FM = Frequency Multiplier
CM = Coupling Multiplier

17. Take home
message

18. References
• Joint structure and function (Fourth edition)- Pamela K. Levangie,
Cynthia C. Norkin
• Ergonomics for therapists
• Biomechanical Basis of Human Movement- Hamill, Joe
• Ergonomics in Sport and Physical Activity- Thomas Reilly
• Stoop or squat: a review of biomechanical studies on lifting
technique -Jaap H. van Dieen , Marco J.M. Hoozemans, Huub M.
Toussaint
• How to lift a box that is too large to fit between the knees -Idsart
Kingma, Gert S. Faber and Jaap H. van Diee
• Biomechanics of Lifting and Lower Back Pain- S.N. Robinovitch
• http://www.cdc.gov/niosh/