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EMG COMPARISON OF TWO TYPES

OF SNOW SHOVELS

INTRODUCTION

HYPOTHESES & OBJECTIVES

METHODS

RESULTS

DISCUSSION & CONCLUSION

1Ryan Lewinson, 1D. Gordon E. Robertson & 2Gholamreza Rouhi1School of Human Kinetics, 2Department of Mechanical

Engineering, University of Ottawa, ON, Canada

REFERENCES

Snow shoveling is necessary in many areas of the world and has resulted in back pain and/or cardiac sudden arrest; even for healthy people. The bent-shaft shovel is “designed to help reduce fatigue and back pain” by allowing the individual to maintain a more upright posture [1]. For snow shoveling, only kinematic research exists [2,3]; electromyographic activity has not yet been reported. EMGs may help identify which shovel design is best suited for the reduction of low back pain.

1. The objectives of this study:• Identify muscle recruitment patterns

for snow shoveling.

• Compare the electromyographic (EMG) activity between straight-shaft and bent-shaft shovels (Fig. 1).

2. The hypotheses were:• The bent-shaft shovel induces higher EMG activity in the erector

spinae and biceps brachii muscles due to a larger moment of force (Fig. 2).

• The most efficient shovel in terms of EMG activity will also reduce heart rate.

Fig. 2 – A larger moment is produced when using the bent-shaft shovel because the bent shaft makes it difficult to keep the load close to the body, thus increasing the moment arm. d1>d2

• Eight subjects (5M, 3F) shoveled continuously outdoors for 2 minutes; one trial with each shovel (Fig. 1), in random order.

Fig. 1 – Bent-shaft (left) and straight-shaft (right) shovels

1. Subject post-test comments.- 7 out of 8 subjects preferred the straight-shaft shovel.- 5 out of 7 subjects said they felt their upper arms hurt more

when using the bent-shaft shovel. - 2 of these 5 further stated that this lead them to use their

backs more to compensate because their arms were tired.

2. Paired-samples t-test for iEMG and heart rate results.

iEMG HR

Anterior Deltoid

Biceps Brachii

Erector Spinae

Gluteus Maximus

Rectus Femoris

Biceps Femoris

Heart Rate(/min)

Mean diff. 1.0659 4.23 0.57 -0.651 -0.66 -0.959 9.75

S.D. 2.60 3.76 1.660 0.800 1.340 1.0317 17.25

p-value 0.284 0.015* 0.365 0.055 0.206 0.034* 0.154* Statistically significant at α=0.05

Table 1 - Mean difference values were obtained by calculating the difference in iEMG between shovel designs recorded for each subject, then calculating the means across subjects. Positive mean differences indicate that the bent-shaft shovel induced larger amounts of muscular activity, while negative values indicate the straight-shaft shovel induced more EMG activity.

• EMGs were recorded and integrated over time. Heart rate and lead knee angle were recorded (Fig. 3).

• iEMG differences were calculated (bent – straight).

• Differences compared by a paired-samples t-test (α=0.05).

• One subject’s EMGs were ensemble averaged.

Fig. 3 – EMG recorded from the anterior deltoid, biceps brachii, erector spinae, gluteus maximus, rectus femoris, and biceps femoris muscles (1000 gain, >110 CMRR)

1. Canadian Tire. Snow removal: snow shovels. Retrieved 17 March 2009 from www.canadiantire.ca, 2009.2. Huang C, Paquet V. Kinematic evaluation of two snow-shovel designs. Int J Industrial Ergon 29:319-330, 2002.3. McGorry RW et al. The effect of technique and shaft configuration in snow shoveling. Appl Ergon 34:225-231, 2003.

↑ duration of erector spinae contraction

↓ biceps femoris activity may cause more work at the low-back to compensate.

↓ bicep femoris activitySince this is a biarticular

muscle, ↓ activity could result in less assistance in trunk extension. This could cause more work for the back.

Biceps brachii fatigue over time

↑ bicep brachii activity

Could be a result of the increased moment of force, as hypothesized.

Could also be a compensation for increased work at the back caused by ↓ bicep femoris activity.

Possible risk for low-back injury

Fig. 5 – Combined results and possible outcomes from bent-shaft shovel use

Fig. 4 – Knee angle begins and ends at its lowest (or bent-over) position. In the bent-shaft condition, erector spinae activation duration was longer than in the straight-shaft condition before maximum knee angle (standing position) was reached (46% cycle vs. 28% cycle).

3. Muscle recruitment patterns (ensemble averages).

• Bent-shaft shovel did not reduce low-back activity as marketed.

• Longer trials needed to allow biceps to fatigue.

• Use both types of shovels and take frequent breaks while shoveling.◦ Balance muscular workload◦ Allow HR to recover

Bent-shaft shovel use

For more information, please email dger@uottawa.ca