Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Mechanical Engineering

Major Professor

Jack F. Wasserman

Committee Members

John D. Landes, J. A. M. Boulet


Lower back disorders are observed to be the most significant problem for most of the industrial workers who operate commercial vehicles. A person sitting can have 40% higher load on the lumbar spine than when standing. Human core muscles related to spinal movement respond to rapid potential motions related to external acceleration inputs of vibration in order to control body posture, the increased muscle tension can result in muscle fatigue. The over use of muscles, vibration exposure combined with dehydration of spine and long term seating can lead to lower back pain and axial discomfort to the drivers. Electromyography (EMG) is a technique used to monitor and analyze the electrical activation of the muscle.

It has been found that the human spine has a natural frequency of 4-8Hz for natural upper body motion caused by curvature motion for the human spine. Trucks have historically produced the critical frequency which resulted in spinal problems for drivers. The purpose of air-ride seats is to reduce the critical frequency amplitudes. Muscular tension can move the natural frequencies to higher level to evaluate the response of the muscle to the expanded acceleration levels in the range of the spinal natural frequency.

A Flex Comp Infinity device, Sonosens® monitor and accelerometers are mounted on the driver of the tractor trailer to collect EMG, ultrasound and acceleration data, respectively. Three testing trials are performed to examine the EMG data, which is correlated with the ultrasonic data and acceleration data collected during the tests. Standard data was collected on the driver using the standard commercial long hall tractor trailer on normal roads.

The main purpose of the current research is to collect and analyze the physiological activity of the Erector spinae, Gluteus medius and Rectus abdominis muscles that relate to the lower back disorders. Present thesis work also examines spinal motions of the human body when exposed to whole-body vibrations.

The study results show that the Erector spinae muscle activity is higher than that of Rectus abdominis and Gluteus medius muscles. Also the muscle fatigue on all the core muscles is observed to occur after 1hr 40 mins to 2 hr, and lasts for nearly 10 mins.The EMG results are compared to the acceleration and ultrasonic data, which were also collected during the test. It is observed that approximately 75% of the ultrasonic results and 60% of acceleration data correlate with EMG results. More accurate results can be expected if more tests are carried out. This research is highly useful to carry out further investigation in the areas of whole body vibration and the muscular response to reduce the level of excitation.

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