Obese and older adults are reported to have a higher rate of mobility limitation and are at a higher risk of fall compared to healthy-weight and young counterparts. To help identify potential mechanisms of these mobility limitations and higher risk of falls, the purpose of the research within this dissertation was to investigate the effects of obesity and age on muscle strength, gait, and balance recovery. Three experimental studies were conducted. The purpose of the first study was to investigate the effects of obesity and age on extension and flexion strength at the hip, knee, and ankle. Absolute strength among obese participants was higher in dorsiflexion, knee extension, and hip flexion compared to healthy-weight participants. Strength relative to body mass was lower among obese participants in all joints/exertions. This lack of uniformity across the 6 exertions is likely due to the still unclear underlying biomechanical mechanism responsible for these strength differences, which may also be influenced by aging. The purpose of the second study was to investigate the effects of obesity, age and, their interactions on relative effort at the hip, knee, and ankle during gait. The peak relative effort for each joint/exertion was expressed by peak NMM during gait as a percentage of the maximum available NMM. The relative effort in hip, knee, and ankle was higher among obese compared to healthy-weight participants. This higher relative effort in hip, knee, and especially in the ankle can be a contributing factor to compromised walking ability among obese individuals. The purpose of the third study was to investigate the effects of age-related strength loss on non-stepping balance recovery capability after a perturbation while standing, without constraining the movements to ankle strategy. The balance recovery capability was quantified by the maximum recoverable platform displacement (MRPD) that was withstood without stepping. Two experiments were conducted. The first experiment involved human subjects and the results suggested that MRPD was lower among older participants compared to young participants. The second experiment involved a simulation study to manipulate muscle strength at hip, knee, and ankle. The results suggested that MRPD was reduced in cases of loss of strength in ankle plantar flexion and hip flexion compared to the young model and did not differ in rest of the cases. The finding suggested that plantar flexor strength plays a major role in capability to recover balance even though the movement was not constrained to the ankle. / Ph. D.

The purpose of this study was to determine the reliability of two new alternative portable methods for measuring maximal isometric force measures while performing the standard mid-thigh pull. One method, the bar grip method, required the use of the trunk and upper extremity muscles, while the second method, the pelvic belt method, did not. Both methods demonstrated good test-retest reliability via randomized repeated measures over 24-36 hours. Interestingly, the pelvic belt method generally demonstrated average maximal forces up to 65% higher than the bar method. There was a good relationship between both methods. These new alternative methods could provide strength coaches an option for a more efficient, cost-effective, portable means for the mid-thigh pull test.

Patients in the intensive care unit (ICU) setting are prone to develop muscle weakness and the causes are multi-factorial. Muscle strength in adult, critically ill patients on mechanical ventilation decreases with immobility. The influence of muscle strength on different muscle groups and its influence on progressive mobility in the adult, critically ill patient on mechanical ventilation has not been examined. Identifying muscle strength in this patient population can benefit overall muscle health and minimize muscle deconditioning through a progressive mobility plan. The objective of this dissertation was to describe muscle strength in different muscle groups and to describe the influence of muscle strength on mobility in critically ill adult patients on mechanical ventilation (MV). Fifty ICU patients were enrolled in this descriptive, cross sectional study. Abdominal core, bilateral hand grip and extremity strength was measured using three measurement tools. Mobility was measured using the following scale: 0=lying in bed; 1=sitting on edge of bed; 2=sitting on edge of bed to standing; 3=walking to bedside chair and 4=walking >7 feet from the standing position. Predictors of mobility were examined using stepwise regression. Abdominal core, bilateral hand grip and extremity strength demonstrated statistically significant relationships with all variables. Extremity strength accounted for 82% of the variance in mobility and was the sole predictor (β=0.903; F=212.9; p=0.000). Future research addressing the outcomes of implementing a mobility protocol in this patient population and prioritizing when such a protocol should be implemented would be beneficial to ongoing plans to decrease MV, ICU and hospital days. Muscle strength tests implemented at the bedside are crucial to implementing a progressive mobility plan for critically ill adults while they are on MV therapy.