Publication Date



Open access

Embargo Period


Degree Type


Degree Name

Doctor of Philosophy (PHD)


Industrial Engineering (Engineering)

Date of Defense


First Committee Member

Shihab Asfour

Second Committee Member

Francesco Travascio

Third Committee Member

Moataz Eltoukhy

Fourth Committee Member

Mohamed Fahmy

Fifth Committee Member

Arzu Onar-Thomas


Manual material handling (MMH) contributes to a large percentage of musculoskeletal disorders. Examples of its fundamental activities are lifting and carrying tasks that can be accomplished in several strategies, with each one imposing different types of stresses on the musculoskeletal system. These types of stresses may perturb the stability of the human body and may cause falls. Therefore, the goal of this study was to investigate the effect of MMH tasks on postural and locomotion stability using motion capturing system. Postural and dynamic stability were measured using new stability measures that were introduced in this study. A point inside the BoS, which represents the optimal location of stability (i.e. CBoS), was the reference point for quantifying stability. Postural stability was measured by finding the deviation of the body’s CoM from the CBoS. Using the proposed measures, the effect of lifting task on postural stability was investigated. Eight subjects lifted 25, 35 and 45 lbs. box to 30” and 60” shelf heights. Manual material lifting of heavy weights significantly destabilized the human body in both directions. Moreover, the heights of the working surfaces that force the body to be changed from the upright gesture exacerbated the effect on postural stability. Therefore, it is recommended that, whenever possible, the working surface during lifting tasks to be at elbow height in order to keep the upright posture of the human body. In addition, this study adds to the knowledge used for designing manual material carrying tasks from the perspective of locomotion stability, gait measures and loads at the lumbar spine. Gait stability was measured by finding the deviation between the CBoS and the CoM extrapolated with its velocity. Thirty participants carried 10 and 30 lbs loads via frontal, lateral, bilateral, and posterior carriages. Frontal and lateral methods generated the most unstable conditions compared to the others. The unstable locomotion forced the gait parameters to be significantly altered in order to maintain stability. Additionally, the postures maintained in these conditions resulted in significantly high compression, shear forces, and moment acting at the L5/S1 disc when compared to the other carrying methods. Moreover, heavier weights exacerbated the effect on the dependent variables. Notably, bilateral and posterior carrying methods provided results comparable to the unloaded walking baseline. In conclusion, to reduce the potential risks associated with load carrying, the recommendation to split the load between both hands or carrying it posteriorly should be taken into account while designing MMH activities.


Ergonomics; Manual Material Handling Activities; Stability; Spinal loads; Gait