2. 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

3. 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).

4. Introduction (cont’d) Past research has produced inconsistent results and has led to the creation of many opposing ideologies.

5. 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)

6. Hypothesis The lifting technique most likely to reduce the moments at the L5/S1 discs is that which is spontaneously adopted by the individual.

7. 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.

8. 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.

9. Testing Setup 25 lbs. Force platforms

10. 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.

11. 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.

12. Results Average peak hip moments of force for the three lifting styles. Signficant difference between leg-lift and back-lift only.

13. 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: Leg-lift: 6.38% Back-lift: 6.84% Free-style: 6.98% 0.00.51.01.52.02.53.03.5 Time (s) -2000. -1000. 0. 1000. -100. 0. 100. -10. 0. 10. Power (W) Moment (N.m) Angular vel. (/s) Trial: DAR11BAC Ang. vel. Net moment Power Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric

14. Knee Angular Velocity, Moment and Power Low angular velocity and power. Knee contributions to the total work done: Leg-lift: 29.18% Back-lift: 7.52% Free-style: 10.8% 0.00.51.01.52.02.53.0 Time (s) -2000. -1000. 0. 1000. -100. 0. 100. -10. 0. 10. Power (W) Moment (N.m) Angular vel. (/s) Trial: JP3FREE Ang. vel. Net moment Power Extending Flexing Extensor Flexor Concentric Eccentric

15. 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% Back-lift: 70.8% Free-style lift: 73.5% 0.00.51.01.52.02.53.0 Time (s) -2000. -1000. 0. 1000. -100. 0. 100. -10. 0. 10. Power (W) Moment (N.m) Angular vel. (/s) Trial: KEN4LEG Ang. vel. Net moment Power Flexing Extending Flexor Extensor Concentric Eccentric

16. Hip Angular Velocity, Moment and Power (Back-lift) Significantly lower peak hip moments than the leg-lift 0.00.51.01.52.02.53.0 Time (s) -2000. -1000. 0. 1000. -100. 0. 100. -10. 0. 10. Power (W) Moment (N.m) Angular vel. (/s) Trial: JP8BACK Ang. vel. Net moment Power Flexing Extending Flexor Extensor Concentric Eccentric

17. Hip Angular Velocity, Moment and Power (Free-style) Peak moments were intermediate between back-lift and leg-lift 0.00.51.01.52.02.53.0 Time (s) -2000. -1000. 0. 1000. -100. 0. 100. -10. 0. 10. Power (W) Moment (N.m) Angular vel. (/s) Trial: DAR5FREE Ang. vel. Net moment Power Flexing Extending Flexor Extensor Concentric Eccentric

18. 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

19. 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.

20. 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.

21. 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.