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Mechanics of Pushing a Loaded Cart up an Incline

Mechanics of Pushing a Loaded Cart up an Incline. D. Gordon E. Robertson, Ph.D. Dianne Ellwood, B.Sc. Paul Johnson, B.Sc. Dany Lafontaine, B.Sc. School of Human Kinetics, University of Ottawa, Ottawa, CANADA Supported in part by Canada Post Corporation. Purpose.

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Mechanics of Pushing a Loaded Cart up an Incline

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  1. Mechanics of Pushing a Loaded Cart up an Incline D. Gordon E. Robertson, Ph.D. Dianne Ellwood, B.Sc. Paul Johnson, B.Sc. Dany Lafontaine, B.Sc. School of Human Kinetics, University of Ottawa, Ottawa, CANADA Supported in part by Canada Post Corporation

  2. Purpose • to determine the functional role of the three leg moments of force while subjects push a heavily loaded cart up a 10 deg incline • to test whether resultant forces at L5/S1 exceed 3400 N (NIOSH action limit)

  3. Methods • 10 female subjects • cart loaded to 100 kg • five steps to 10 deg inclined ramp • force plates for last two footfalls before ramp • cinefilm at 50 fps, forces at 200 Hz • inverse dynamics to obtain moments of force at three leg joints for both legs • computed work and power produced by moments of force

  4. Stick-figures of subject pushing loaded cart up incline. Force vectors are shown under two of the feet.

  5. Results • average velocity before ramp was 1.75 m/s • peak powers were similar in magnitude to those of walking but differed in pattern

  6. Force signatures of last two steps before ramp. Direction of motion is left to right. Note, second force is concentrated under ball of foot.

  7. Ankle powers • 8/10 subjects produced two or more bursts of work by the plantar flexors during second last step before ramp • 9/10 subjects produced two or more bursts of work by the plantar flexors during the last step before ramp

  8. Powers of the ankle, knee and hip moments 1000 Hip powers 500 0 Trial: CP02CH -500 I Ankle I Knee Knee powers I Hip 500 C Ankle C Knee Power (watts) C Hip 0 -500 Ankle powers 500 0 IFS CTO CFS ITO IFS CTO -500 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Time (seconds)

  9. Knee powers • 5/10 subjects produced bursts of positive work by the knee extensors during second last step • 9/10 subjects produced bursts of positive work by the knee extensors during last step

  10. Powers of the ankle, knee and hip moments 1000 Hip powers 500 0 Trial: CP06AU -500 I Ankle I Knee Knee powers I Hip 500 C Ankle C Knee Power (watts) C Hip 0 -500 Ankle powers 500 0 IFS CTO CFS ITO IFS CTO -500 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Time (seconds)

  11. Hip powers • hip extensors performed positive work during early part of stance • hip flexors performed negative work during latter part of stance • 6/10 subjects performed as described for second last step • 8/10 subjects performed as described for last step

  12. Powers of the ankle, knee and hip moments 1000 Hip powers 500 0 Trial: CP01TR -500 I Ankle I Knee Knee powers I Hip 500 C Ankle C Knee Power (watts) C Hip 0 -500 Ankle powers 500 0 IFS CTO CFS ITO IFS CTO -500 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Time (seconds)

  13. Conclusions • patterns of power production differed from those of walking • peak powers were similar in magnitude to those of walking • compressive forces at L5/S1 did NOT exceed NIOSH action limit (3400 N) • standard lifting model is not applicable to pushing

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