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 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) 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. 0.00.10.20.30.40.50.60.70.80.91.0 Time (seconds) -500 0 500 -500 0 500 -500 0 500 1000 Power (watts) Powers of the ankle, knee and hip moments Trial: CP02CH I Ankle I Knee I Hip C Ankle C Knee C Hip IFS CTO CFS ITO IFS CTO Hip powers Knee powers Ankle powers

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. 0.00.10.20.30.40.50.60.70.80.91.0 Time (seconds) -500 0 500 -500 0 500 -500 0 500 1000 Power (watts) Powers of the ankle, knee and hip moments Trial: CP06AU I Ankle I Knee I Hip C Ankle C Knee C Hip IFS CTO CFS ITO IFS CTO Hip powers Knee powers Ankle powers

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. 0.00.10.20.30.40.50.60.70.80.91.0 Time (seconds) -500 0 500 -500 0 500 -500 0 500 1000 Power (watts) Powers of the ankle, knee and hip moments Trial: CP01TR I Ankle I Knee I Hip C Ankle C Knee C Hip IFS CTO CFS ITO IFS CTO Hip powers Knee powers Ankle powers

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