Semester

Summer

Date of Graduation

2011

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Ashish D Nimbarte

Abstract

Pushing and pulling of carts are found to be associated with low back pain and shoulder complaints. It is currently unclear as to how the dynamic pushing and pulling tasks performed under different task conditions (e.g. weight, walkway gradient, direction of force application) affect the musculoskeletal loading of low back and shoulder joints. Therefore, the objective in this study was to evaluate dynamic pushing and pulling tasks to quantify their effects on the 3D musculoskeletal loading of low back and shoulder joints. Twelve male participants performed cart pushing pulling tasks along a 5° and 10° ramp by carrying loads of 20, 30, and 40 kg, respectively. An eight-camera optical motion analysis system configured with two force plates was used for kinematic and kinetic data collection. The experimental data was modeled using Anybody musculoskeletal modeling system. A biomechanical model consisting of a two wheeled cart and a full-body human model (34 bones and over 750 muscle fascicles) was formulated in the AnyBody modeling system. The model was validated by comparing the predicted reaction forces on the cart wheels with the actual forces recorded experimentally using ground reaction force platforms. A high correlation between the actual and predicted data (average = 0.919) was observed. The results of this study show that as the cart weight increased, so did the low back and shoulder joint loads. A walkway gradient of 10° on average produced larger low back and shoulder joint forces than a gradient of 5°. Uphill pushing caused higher mechanical load on the low back and shoulder joints than the downhill pulling. The magnitude of peak lateral shear forces at the L5S1 joint was negligible (< 150 N). The largest peak compression force observed in this study (3222 N) was below the recommended NIOSH limit of 3400 N. The peak anterior-posterior shear forces during uphill pushing at 30 kg and 40 kg weight conditions on a gradient of 10° were 553 N and 806 N, respectively. These values exceed the tolerance limit of 500 N, suggesting that the anterior-posterior shear loading at the L5S1 joint should be considered when assessing the risk of musculoskeletal disorders due to pushing and pulling activities.;For the shoulder joints, the peak forces at the sternoclavicular joint were small (< 220 N) in all situations. At the glenohumeral joint, the peak distraction, compression and anterior-posterior shear forces were 1357 N, 858 N, and 618 N, respectively, during uphill pushing at 40 kg weight condition on a gradient of 10°. Under the same condition, the corresponding peak forces acting at the acromioclavicular joint were 910 N, 1078 N, and 727 N. In the existing literature, the focus has always been on the glenohumeral joint and loading of the sternoclavicular and acromioclavicular joints was not evaluated. The results of this research show that the peak forces acted at the acromioclavicular joint are comparable to those at the glenohumeral joint, further suggesting that the loading on the acromioclavicular joint should be considered, in addition to the glenohumeral joint, while evaluating risk of musculoskeletal disorders due to pushing and pulling activities.

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