Author ORCID Identifier

Date Available


Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation




Kinesiology and Health Promotion

First Advisor

Dr. Robert Shapiro


Background: Obesity is a chronic disease characterized by a body mass index (BM1) of ≥ 30 kg/m2 which negatively impacts the musculoskeletal system and has been found to be a major contributing factor to obesity-induced biomechanical alterations during activities of daily living (ADLs). A certain level of mobility is required for all populations to maintain independence and a good quality of life becomes more difficult with excess weight. Using a reduced weight-bearing activity, such as the Alter Gravity treadmill, would be beneficial in an obese population to reduce the load on the joints and potentially decrease the risk of weight bearing injury while maintaining normal gait mechanics. The purpose of this dissertation was to determine the biomechanical effects of excess weight and weight distribution on ADLs. To address this, two different weight gain models were created to simulate central (CL) and peripheral (PL) weight gain compared to an obese group (OW), and normal weight group (UL) during different activities of daily living (ADLs). The purpose of the third study was to compare lower extremity joint kinematics and muscle activation patterns between obese and normal individuals at different levels of body support (100, 75, and 50%) while walking in the AlterG treadmill.

Methods: 14 normal weight (BMI: 22.4 ± 1.8 kg/m2, age: 23.4 ± 3.6 yrs) and 17 obese (BMI: 33.2 ± 2.3 kg/m2, age: 31.6 ± 8.0 years) adults participated in different ADLs (gait and descending a set of stairs). Normal weight participants were loaded with two different external loads sufficient to increase their BMI by 5 kg/m2 (~22.6% body mass).

Kinematic and kinetic data were collected with 3D motion analysis. Frontal plane hip and knee angles and moments were calculated.

Results: During gait, the obese group walked at a significantly slower velocity compared to UL. Step length was 8.7% longer in UL and 7.4% longer in the CL compared to the OW. PL more closely mirrored the OW group in step length, flexion moment and extension moment and the CL more closely mirrored the obese group in sagittal plane knee and hip excursion, and peak hip flexion moment and extension moment during gait

During the transition from descending stair walking to level gait, it was found that the PL, but not CL, decreased step length, increased step width, and increased proportion of the gait cycle spent in stance. During the transition from walking down the stairs to level gait it was found that CL and PL affect temporal spatial variables differently. PL also reduced peak hip adduction angle, increased peak hip flexion moment, decreased peak hip extension, decreased sagittal plane hip excursion, and decreased frontal plane hip excursion. Conversely, CL reduced peak hip flexion moment and trended to reduce peak hip extension moment.

To determine the effects of reduced body mass per se on improved biomechanics, we needed a model that would prevent associated changes in segmental volume. Therefore, using an AlterG treadmill facilitated this method. At 100 % BW support, mean ST and VM EMG activity were significantly higher in the obese compared to the normal weight groups. There were also differences found at 75 % BW support in ST in the obese being greater than the normal.

Conclusions: Combined, the overall results of this dissertation suggest that weight gain is able to be modeled but is variable and task specific. The CL has proven to be the weight gain model that which elicits a better biomechanical obese response when normal weight individuals are loaded. Further work is needed to understand how to truly mimic obesity with an external load.

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