Biomechanics of Cart Pushing

Author:

Greenert, Katie Patricia

Graduate Program:

Mechanical Engineering

Degree:

Master of Science

Document Type:

Master Thesis

Date of Defense:

June 08, 2016

Committee Members:

Stephen Jacob Piazza, Thesis Advisor/Co-Advisor

Keywords:

cart pushing
lower extremity biomechanics

Abstract:

Gait abnormalities are common in elderly adults and can lead to a loss of mobility. Tests of function, such as gait speed testing, can help identify these abnormalities. However, having more sensitive tests of functions could identify abnormalities sooner, allowing issues to be addressed before they become more problematic. Tasks involving walking while pushing carts or similar devices are a common activity in everyday life. Examples include shopping carts at supermarkets and department stores, baby strollers, lawn mowers, and wheel barrows. Some occupations such as postal workers, movers, and warehouse workers are required to push heavy loads frequently throughout the course of their shift. However, little information is known about how lower extremity biomechanics adapt to pushing carts with different loading conditions. This knowledge could lead to a better understanding of the functional demands of cart pushing and help increase safety in the workplace. It could also provide a better understanding of how gait adapts to other challenging tasks and lead to the development of more effective tests of function. In this study we compared lower extremity biomechanics in level walking at a speed of 1.2 m/s to pushing a cart under six different loading conditions. The first three tasks focused solely on the cart. In the first task, subjects were asked to push an empty shopping cart. In the second task, a 20 kg weight was added to the cart. Then in the third task, an additional 20 kg weight was added to the cart for a total mass of 40 kg. In the next three tasks, a wooden box was mounted to the front of the cart, acting as a sled and increasing the frictional force acting on the cart. In the fourth task, all of the weight was removed from the cart and a 10 kg weight was placed in the sled. In the fifth task an additional 10 kg weight was added to the sled for a total of 20 kg in the sled. In the sixth task, with 20 kg still in the sled, a 40 kg weight was added to the cart. Nineteen healthy, young adults served as subjects. Joint angles, moments, powers, and the work done by the ankle, knee, and hip muscles were calculated and compared to the corresponding values computed for the level walking task. These comparisons allowed us to examine how the ankle, knee, and hip joints adapted to the various tasks and which lower extremity muscle groups contributed the most work as the tasks became more challenging. In the three cart tasks, the total amount of work done by the hip, knee, and ankle decreased or remained the same as that found in level walking. The average peak joint moments and powers were less than in level walking. This suggests that for the lower extremity, once the cart is moving, pushing a cart with or without weight is actually less difficult than level walking at the same pace. In the three subsequent sled tasks, the total amount of work done by the hip, knee, and ankle increased compared to level walking. The peak joint moments and powers were greater than or equal to that of level walking. The percentage of work done by the knee increased while the percentage of work done by the ankle decreased. This suggests that for the lower extremities, sled pushing tasks are more difficult than level walking and could be useful as functional tests to detect gait modifications in elderly adults. Further studies should be done to investigate this possibility.