Moment Power and Work of the
Ankle, Knee and Hip during Three
Bimanual Lifting Techniques
Maria Nicolaou, B.Sc.*
D. Gordon E. Robertson. Ph.D.**
*Department of Physical Education
McGill University, Montreal
**School of Human Kinetics,
University of Ottawa, Ottawa
Introduction
• Manual materials handling (MMH) and
manual lifting in particular are consistently
linked to a high occurrence of occupational
injuries.
• Injuries to the lower back and low back pain
have been associated with the postures
adopted throughout the lifting movement.
• The issue of a single, safe, energy efficient
lifting style is of great importance because of
its effect on individuals from different levels
of industry (employees and employers).
Introduction (cont’d)
• Past research has produced inconsistent
results and has led to the creation of many
opposing ideologies.
Purpose
• To examine the powers produced
• To calculate the total work done by
examining the moments at the ankle, knee
and hip while performing three bimanual
lifting techniques.
Techniques:
– Leg-lift (squat)
– Back-lift (stoop)
– Free-style (the position spontaneously
assumed by an individual when not
instructed specifically)
Hypothesis
• The lifting technique most likely to reduce
the moments at the L5/S1 discs is that which
is spontaneously adopted by the individual.
Rationale
• The human body acts as a coordinated
system which gathers sensory information to
produce movement.
• During unsupervised lifting individuals
spontaneously adopt postures that are the
least stressful for them.
• This position decreases the compressive
forces acting on the lumbosacral region
reducing the chances of injury during lift.
Methods
• Six males, age 19-24, with no history of back
pain.
• Reflective markers were placed at the
shoulder, hip, knee, ankle, heel, ball and toes.
• Verbal instructions and a demonstration
were given followed by a warm-up and
practice trials.
• Participants assumed a parallel foot stance
with both feet on one force platform (40 cm)
• Participants were required to lift a 25 lbs.
crate placed 30 cm away from their toes.
Testing Setup
25 lbs.
Force platforms
Methods (cont’d)
• The lift began from a vertical standing
position, using the predetermined technique
the participants lifted the 25 lbs. crate from
the force platform to a tabletop.
• Bioware software and two force platforms
(Kistler) were used for force acquisition.
• Forces were sampled at 200 Hz with 4 s
allowed for each lift.
• Trials were videotaped using one camera in
the sagittal view and sampled at 60 Hz.
Methods (cont’d)
• Ariel Performance Analysis System (APAS)
digitized the video data.
• Biomech and BioProc Analysis Systems
(University of Ottawa) were used for data
analysis.
• A two-dimensional linked-segment model
was used to calculate the net moments of
force at each joint using inverse dynamics
(Winter, 1979) from which the work and
powers were computed.
Results
• Average peak hip
moments of force for the
three lifting styles.
350
• Signficant difference
between leg-lift and
back-lift only.
Hip Moments (Nm)
300
250
200
150
100
50
0
Leg-lift
Freestyle
Lifting Style
Back-lift
Ankle Angular Velocity,
Moment and Power
•Plantar flexors perform
negative work throughout.
•Low angular velocity and
power.
•The ankle moment contributes
very little to the total work done
during each lift:
10.
Dorsiflexing
0.
-10.
Trial: DAR11BAC
Plantar flexing
Ang. vel.
Net moment
Power
Dorsiflexor
100.
0.
-100.
Plantar flexor
Concentric
1000.
0.
Leg-lift: 6.38%
-1000.
Eccentric
Back-lift: 6.84%
-2000.
Free-style: 6.98%
0.0
0.5
1.0
1.5
2.0
Time (s)
2.5
3.0
3.5
Knee Angular Velocity,
Moment and Power
• Low angular velocity and
power.
•Knee contributions to the total
work done:
10.
Extending
0.
-10.
Trial: JP3FREE
Flexing
Ang. vel.
Net moment
Power
Extensor
100.
0.
-100.
Flexor
Leg-lift: 29.18%
Concentric
1000.
Back-lift: 7.52%
0.
Free-style: 10.8%
-1000.
Eccentric
-2000.
0.0
0.5
1.0
1.5
Time (s)
2.0
2.5
3.0
Hip Angular Velocity,
Moment and Power
(Leg-lift)
• Highest moments of force and
powers
• Initially perform negative work
then positive work
• Hip contribution to the total
work done:
Leg-lift: 56.1%
10.
Flexing
0.
-10.
Trial: KEN4LEG
Extending
Ang. vel.
Net moment
Power
Flexor
100.
0.
-100.
Extensor
Concentric
1000.
0.
-1000.
Eccentric
Back-lift: 70.8%
-2000.
Free-style lift: 73.5%
0.0
0.5
1.0
1.5
Time (s)
2.0
2.5
3.0
Hip Angular Velocity,
Moment and Power
(Back-lift)
• Significantly lower peak hip
moments than the leg-lift
10.
Flexing
0.
-10.
Trial: JP8BACK
Extending
Ang. vel.
Net moment
Power
Flexor
100.
0.
-100.
Extensor
Concentric
1000.
0.
-1000.
Eccentric
-2000.
0.0
0.5
1.0
1.5
Time (s)
2.0
2.5
3.0
Hip Angular Velocity,
Moment and Power
(Free-style)
• Peak moments were
intermediate between back-lift
and leg-lift
10.
Flexing
0.
-10.
Trial: DAR5FREE
Extending
Ang. vel.
Net moment
Power
Flexor
100.
0.
-100.
Extensor
Concentric
1000.
0.
-1000.
Eccentric
-2000.
0.0
0.5
1.0
1.5
Time (s)
2.0
2.5
3.0
Discussion
• Inverse dynamics: hip moments contribute
the most during lifting. This is extremely
important because the hip musculature acts
directly on the lower back.
• One-way analysis of variance: significant
difference in peak hip extensor moments
P=0.02
• Post-hoc (Scheffé): showed a significant
difference between leg-lift and back-lift
• Back-lifts had lowest peak moments and
therefore were the safest lifting technique
Discussion (cont’d)
• This contradicts previous research findings
which state that the back-lift is the least
effective in reducing the moments on L5/S1
(Anderson and Chaffin, 1986).
• These results may be due to the restricted
size of the force platform (40 cm) because the
leg-lift and free-style lift require a broader
base for proper execution.
• Larger moments of force at the hip during
the leg-lift and free-style lift may be due to
having to lift the crate in front of knees.
Conclusions
1. The hip extensor muscles create the highest
moments during the lifting of the loads from
the floor.
2. The hip extensor muscles perform most of
the work during the lifting of loads from the
floor.
3. In situations where a wide base is not
possible the back-lift is the most effective
technique in reducing the moments of force
about the hip during the lifting of loads from
the floor.
References
Anderson, C.K., and Chaffin, D.B., (1986)
Applied Ergonomics, 17(1): 2-8.
Winter, D.A., (1979) Biomechanics of
Human Movement. New York: John Wiley
and Sons.