↑ duration of erector spinae contraction. ↓ bicep femoris activity. Since this is a biarticular muscle, ↓ activity could result in less assistance in trunk extension. This could cause more work for the back. ↓ biceps femoris activity may cause more work at the low-back to compensate.
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↓ bicep femoris activity
↑ bicep brachii activity
Biceps brachii fatigue over time
Possible risk for low-back injury
1. Subject post-test comments.
- 7out of 8 subjects preferred the straight-shaft shovel.
- 5out of 7 subjects said they felt their upper arms hurt more
when using the bent-shaft shovel.
- 2of these 5 further stated that this lead them to use their
backs more to compensate because their arms were tired.
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 . 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.
2. Paired-samples t-test for iEMG and heart rate results.
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.
3. Muscle recruitment patterns (ensemble averages).
Fig. 1 – Bent-shaft (left) and straight-shaft (right) shovels
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).
Bent-shaft shovel use
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
Fig. 5 – Combined results and possible outcomes from bent-shaft shovel use
1. Canadian Tire. Snow removal: snow shovels. Retrieved 17 March 2009 from www.canadiantire.ca,
2. Huang C, Paquet V. Kinematic evaluation of two snow-shovel designs. Int J Industrial Ergon
3. McGorry RW et al. The effect of technique and shaft configuration in snow shoveling. Appl Ergon
Fig. 3 – EMG recorded from the anterior deltoid, biceps brachii, erector spinae, gluteus maximus, rectus femoris, and biceps femoris muscles (1000 gain, >110 CMRR)
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