Running popularity has led to a rise in chronic lower limb injuries resulting from cumulative loading. Many of these injuries are tibial stress fractures. Tibial accelerometers are commonly used to measure tibial stress and may even be predictive of injury at the distal limb. Lower body positive pressure (LBPP) treadmills have become increasingly popular amongst athletes and practitioners to prevent and treat lower limb injuries by reducing effective body weight (BW) through mechanical support. The purpose of this thesis is to investigate if BW unloading affects tibial acceleration (TA) and shock attenuation. Twelve trained distance runners (Sex: 6 males and 6 females; Age: 18-30 years) were recruited for this study. TA was measured through two Blue Trident, IMeasureU step units located at the distal tibiae. A STATSports Apex unit was also used to measure acceleration at the superior trunk and calculate shock attenuation for each limb. It was found that BW unloading had no discernable effect on mean peak TA and shock attenuation, bone stimulus, or contact time, regardless of running speed. However, a significant relationship was observed between running speed and both mean peak TA and bone stimulus where an increase in speed led to an increase in TA and bone stimulus. Furthermore, running speed did not affect shock attenuation or contact time. In conclusion, BW unloading did not alter gait kinematics in trained distance runners. / Master of Science / Running popularity has led to a rise in chronic lower limb injuries, particularly stress fractures at the shin or tibia bone, due to greater impact forces and "stiffer" landings. Tibial accelerometers are commonly used to measure these impact forces and may even be predictive of injury at the tibia bone near the ankle. The process of reducing these impact forces is called shock attenuation. Lower body positive pressure (LBPP) treadmills have become increasingly popular amongst athletes and practitioners to prevent and treat lower limb injuries by unloading body weight (BW) through mechanical support. The purpose of this thesis is to investigate if BW unloading affects tibial acceleration (TA) and shock attenuation. Twelve trained distance runners (Sex: 6 males and 6 females; Age: 18-30 years) were recruited for this study. TA was measured through two Blue Trident, IMeasureU step units located at the shin. A STATSports Apex unit was also used to measure impact at the upper trunk and calculate shock attenuation for each limb. It was found that BW unloading did not affect mean peak TA and shock attenuation, bone stimulus, or contact time, regardless of running speed. However, running speed significantly affected both mean peak TA and bone stimulus where an increase in speed led to an increase in TA and bone stimulus. Furthermore, running speed did not affect shock attenuation or contact time. In conclusion, BW unloading did not alter impact forces in trained distance runners. Caution is advised for individuals with injuries at the shin when using LBPP treadmills.

Necessary for effective ambulation, head stability affords optimal conditions for the perception of visual information during dynamic tasks. This maintenance of head-in-space equilibrium is achieved, in part, by the attenuation of the high frequency impact shock resulting from ground contact. While a great deal of experimentation has been done on the matter during steady state locomotion, little is known about how head stability or dynamic visual acuity is maintained during asymmetric walking. In this study, fifteen participants were instructed to walk on a split-belt treadmill for ten minutes while verbally reporting the orientation of a randomized Landolt-C optotype that was projected at heel strike. Participants were exposed to the baseline, adaptation, and washout conditions, as characterized by belt speed ratios of 1:1, 1:3, and 1:1, respectively. Step length asymmetry, shock attenuation, high (impact) and low (active) frequency head signal power, and dynamic visual acuity scores were averaged across the first and last fifty strides of each condition. Over the course of the first fifty strides, step length asymmetry was significantly greater during adaptation than during baseline (p d =2.442). Additionally, high frequency head signal power was significantly greater during adaptation than during baseline (p d =1.227), indicating a reduction in head stability. Shock attenuation was significantly lower during adaptation than during baseline (p d =-0.679), and a medium effect size suggests that dynamic visual acuity was lower during adaptation than during baseline as well (p =0.052; d =0.653). When comparing the baseline and adaptation conditions across the last fifty strides, however, many of these decrements were greatly reduced. The results of this study indicate that the locomotor asymmetry imposed by the split-belt treadmill during the early adaptation condition is responsible for moderate decrements to shock attenuation, head stability, and dynamic visual acuity. Moreover, the relative reduction in magnitude of these decrements across the last fifty strides underscores the adaptive nature of the locomotor and visuomotor systems.