Understanding the body’s kinematic/kinetic responses and motor adaptation to unpredictable gait perturbation induced by a split-belt treadmill in young and older adults

Falls are one of the major leading causes of death for the elderly, and the number of fall-related deaths has been increasing with a steadily increased older population in the USA. Falls result in physical injuries and psychological injuries, which affect the quality of life in older adults. Unexpected gait perturbations (e.g., slips and trips) are the major leading cause of falls, and it makes up approximately 59% of falls in the community-dwelling elders. Age-related changes (e.g., decline in muscle strength and the function of the neuromuscular system) affect balance control in older adults, which contributes to higher fall rates. Although physical exercises (e.g., balance, ambulatory, and resistance training) have been utilized to enhance muscle strength and balance control, which may help to decrease fall rates, the effects of physical exercises on improving fall rates are still controversial. Instead, fall-inducing systems using external mechanisms such as slippery contaminants, external obstacles, and split-belt treadmills have been developed to investigate the response mechanisms of gait perturbations (e.g., kinematics, kinetics, and muscles responses) in young and older adults. Furthermore, fall-inducing systems have been used to improve the body’s responses to gait perturbations depending on motor adaptation principles (e.g., decreased forward center of mass (COM) velocity and trunk forward rotation after repeated exposure to the perturbations), which is more task-specific than physical exercises. However, some limitations were not fully addressed in previous studies. First, although the compensatory limb’s stepping response (i.e., the opposite side of the perturbed limb) is typical for unexpected gait perturbations, most previous studies have evaluated the perturbed limb’s joint moments. Second, although trip perturbations cause greater fall-related injuries than slip perturbations in the older population, most previous studies investigated the differences of muscle responses and joint moments between young and older adults for slip perturbations, not for trip perturbations. Third, no studies have quantitatively investigated young and older groups’ trial-to-trial adaptations based on the kinematic responses after the repetitive trip perturbations induced by a split-belt treadmill. The first study of this dissertation examined joint moments of the compensatory limb during the first stepping response after an unexpected trip or slip gait perturbations and compared the results to normal walking in the young adults. The results of the first study showed that the ankle, knee, and hip joint moments of the compensatory limb were higher after gait perturbations than during normal walking, and the joint moments were greater with the slip than the trip perturbations. The second study investigated joint moments and muscle responses of the compensatory limb to trip perturbations in young and older adults to determine whether joint moments and muscle responses differ significantly with ages. The results indicated that joint moments and muscle activations were higher for young adults than older adults after trip perturbations, and muscle co-contractions were higher for older adults. The third study assessed trial-to-trial adaptations of the reactive kinematic responses to repetitive trip perturbations in young and older adults. The result showed that adaptation took place with both young and older adults, however, the rate of adaptation was faster in young adults. The results of this dissertation will contribute to understanding the mechanisms of joint moments and muscle responses of the compensatory limb to unexpected gait perturbations and motor adaptation abilities in young and older adults. This will help develop a better strategy of therapeutic regimens utilizing fall-inducing technologies for young and older adults to improve the compensatory responses to gait perturbations, which may help reduce fall rates.