Adaptability of gait and balance across the adult lifespan

Human walking has evolved from walking on four legs to walking on two legs. During walking on two legs balance is challenged more, since there is a longer period of standing on one leg. Gait adaptability, the ability to adjust walking to a potential loss of balance, is needed to maintain the ability to walk. An impaired ability to adapt gait makes walking more vulnerable to internal and external perturbations and increases the risk of falling. When people get older, gait adaptability might be affected because of changes in walking and balance performance, which would make older adults more vulnerable to a loss of balance. This thesis shed light on the effects of age on adaptability in walking and balance. We examined adaptability in walking and balance using the split-belt paradigm. People walked on a treadmill with two belts, one for each foot, that could be controlled separately. Walking was disturbed by speeding up one of the treadmill belts, so one treadmill belt ran faster than the other belt. We found that when people get older, a different adaptation strategy is used to adapt to walking on split-belt treadmill and dynamic balance is affected. On the other hand, muscle activation and walking symmetry were not affected in older adults while walking on the split-belt treadmill. In conclusion, we showed that increasing age affected certain features of adaptability of gait and walking and left other features unaffected. Thus, this thesis increased our understanding of age-related changes in walking and balance performance

Multivariate Analyses and Classification of Inertial Sensor Data to Identify Aging Effects on the Timed-Up-and-Go Test

Many tests can crudely quantify age-related mobility decrease but instrumented versions of mobility tests could increase their specificity and sensitivity. The Timed-up-and-Go (TUG) test includes several elements that people use in daily life. The test has different transition phases: rise from a chair, walk, 180° turn, walk back, turn, and sit-down on a chair. For this reason the TUG is an often used test to evaluate in a standardized way possible decline in balance and walking ability due to age and or pathology. Using inertial sensors, qualitative information about the performance of the sub-phases can provide more specific information about a decline in balance and walking ability. The first aim of our study was to identify variables extracted from the instrumented timed-up-and-go (iTUG) that most effectively distinguished performance differences across age (age 18-75). Second, we determined the discriminative ability of those identified variables to classify a younger (age 18-45) and older age group (age 46-75). From healthy adults (n = 59), trunk accelerations and angular velocities were recorded during iTUG performance. iTUG phases were detected with wavelet-analysis. Using a Partial Least Square (PLS) model, from the 72-iTUG variables calculated across phases, those that explained most of the covariance between variables and age were extracted. Subsequently, a PLS-discriminant analysis (DA) assessed classification power of the identified iTUG variables to discriminate the age groups. 27 variables, related to turning, walking and the stand-to-sit movement explained 71% of the variation in age. The PLS-DA with these 27 variables showed a sensitivity and specificity of 90% and 85%. Based on this model, the iTUG can accurately distinguish young and older adults. Such data can serve as a reference for pathological aging with respect to a widely used mobility test. Mobility tests like the TUG supplemented with smart technology could be used in clinical practice

Effects of Aging and Task Prioritization on Split-Belt Gait Adaptation

Background: Age-related changes in the sensorimotor system and cognition affect gait adaptation, especially when locomotion is combined with a cognitive task. Performing a dual-task can shift the focus of attention and thus require task prioritization, especially in older adults. To gain a better understanding of the age-related changes in the sensorimotor system, we examined how age and dual-tasking affect adaptive gait and task prioritization while walking on a split-belt treadmill.Methods: Young (21.5 ± 1.0 years, n = 10) and older adults (67.8 ± 5.8 years, n = 12) walked on a split-belt treadmill with a 2:1 belt speed ratio, with and without a cognitive Auditory Stroop task. Symmetry in step length, limb excursion, and double support time, and strategy variables swing time and swing speed were compared between the tied-belt baseline (BL), early (EA) and late split-belt adaptation (LA), and early tied-belt post-adaptation (EP).Results: Both age groups adapted to split-belt walking by re-establishing symmetry in step length and double support time. However, young and older adults differed on adaptation strategy. Older vs. young adults increased swing speed of the fast leg more during EA and LA (0.10–0.13 m/s), while young vs. older adults increased swing time of the fast leg more (2%). Dual-tasking affected limb excursion symmetry during EP. Cognitive task performance was 5–6% lower during EA compared to BL and LA in both age groups. Older vs. young adults had a lower cognitive task performance (max. 11% during EA).Conclusion: Healthy older adults retain the ability to adapt to split-belt perturbations, but interestingly age affects adaptation strategy during split-belt walking. This age-related change in adaptation strategy possibly reflects a need to increase gait stability to prevent falling. The decline in cognitive task performance during early adaptation suggests task prioritization, especially in older adults. Thus, a challenging motor task, like split-belt adaptation, requires prioritization between the motor and cognitive task to prevent adverse outcomes. This suggests that task prioritization and adaptation strategy should be a focus in fall prevention interventions

Adaptive Control of Dynamic Balance across the Adult Lifespan

Introduction The ability to adapt dynamic balance to perturbations during gait deteriorates with age. To prevent age-related decline in adaptive control of dynamic balance, we must first understand how adaptive control of dynamic balance changes across the adult lifespan. We examined how adaptive control of the margin of stability (MoS) changes across the lifespan during perturbed and unperturbed walking on the split-belt treadmill. Methods Seventy-five healthy adults (age range, 18-80 yr) walked on an instrumented split-belt treadmill with and without split-belts. Linear regression analyses were performed for the mediolateral (ML) and anteroposterior (AP) MoS, step length, single support time, step width, double support time, and cadence during unperturbed and perturbed walking (split-belt perturbation), with age as predictor. Results Age did not significantly affect dynamic balance during unperturbed walking. However, during perturbed walking, the ML MoS of the leg on the slow belt increased across the lifespan due to a decrease in bilateral single support time. The AP MoS did not change with aging despite a decrease in step length. Double support time decreased and cadence increased across the lifespan when adapting to split-belt walking. Age did not affect step width. Conclusions Aging affects the adaptive control of dynamic balance during perturbed but not unperturbed treadmill walking with controlled walking speed. The ML MoS increased across the lifespan, whereas bilateral single support times decreased. The lack of aging effects on unperturbed walking suggests that participants' balance should be challenged to assess aging effects during gait. The decrease in double support time and increase in cadence suggests that older adults use the increased cadence as a balance control strategy during challenging locomotor tasks

Do gait and muscle activation patterns change at middle-age during split-belt adaptation?

Advancing age affects gait adaptability, but it is unclear if such adaptations to split-belt perturbations are already affected at middle-age. Changes in neuromuscular control, that already start at middle-age, may underlie the age-related changes in gait adaptation. Thus, we examined the effects of age on adaptations in gait and muscle activation patterns during split-belt walking in healthy young and middle-aged adults. Young (23.3±3.13 years) and middle-aged adults (55.3±2.91 years) walked on an instrumented split-belt treadmill. Both age groups adapted similarly by reducing asymmetry in step length and double support time. Surface EMG was recorded from eight leg muscles bilaterally. Principal Component Analysis (PCA) was applied to the EMG data of all subjects, for the fast and slow leg separately, to identify muscle activation patterns. The principal components consisted of i.e. temporal projections that were analyzed with Statistical Parametric Mapping (SPM). The functional muscle groups, identified by PCA, increased activation during early adaptation and post-adaptation, and decreased activation over time similarly in both age groups. Extra activation peaks of the plantar- and dorsiflexors suggest a role in gait modulation during split-belt walking. Both young and middle-aged adults re-established gait symmetry and showed adaptation effects in the muscle activation patterns. Since the adaptation of muscle activation patterns parallels adaptation of gait symmetry, changes in muscle activation likely underlie the changes in step parameters during split-belt adaptation. In conclusion, split-belt adaptation, in terms of gait and muscle activation patterns, is still preserved at middle-age, suggesting that age-related differences occur later in the lifespan

Effects of Aging and Task Prioritization on Split-Belt Gait Adaptation

Background: Age-related changes in the sensorimotor system and cognition affect gait adaptation, especially when locomotion is combined with a cognitive task. Performing a dual-task can shift the focus of attention and thus require task prioritization, especially in older adults. To gain a better understanding of the age-related changes in the sensorimotor system, we examined how age and dual-tasking affect adaptive gait and task prioritization while walking on a split-belt treadmill. Methods: Young (21.5 ± 1.0 years, n = 10) and older adults (67.8 ± 5.8 years, n = 12) walked on a split-belt treadmill with a 2:1 belt speed ratio, with and without a cognitive Auditory Stroop task. Symmetry in step length, limb excursion, and double support time, and strategy variables swing time and swing speed were compared between the tied-belt baseline (BL), early (EA) and late split-belt adaptation (LA), and early tied-belt post-adaptation (EP). Results: Both age groups adapted to split-belt walking by re-establishing symmetry in step length and double support time. However, young and older adults differed on adaptation strategy. Older vs. young adults increased swing speed of the fast leg more during EA and LA (0.10–0.13 m/s), while young vs. older adults increased swing time of the fast leg more (2%). Dual-tasking affected limb excursion symmetry during EP. Cognitive task performance was 5–6% lower during EA compared to BL and LA in both age groups. Older vs. young adults had a lower cognitive task performance (max. 11% during EA). Conclusion: Healthy older adults retain the ability to adapt to split-belt perturbations, but interestingly age affects adaptation strategy during split-belt walking. This age-related change in adaptation strategy possibly reflects a need to increase gait stability to prevent falling. The decline in cognitive task performance during early adaptation suggests task prioritization, especially in older adults. Thus, a challenging motor task, like split-belt adaptation, requires prioritization between the motor and cognitive task to prevent adverse outcomes. This suggests that task prioritization and adaptation strategy should be a focus in fall prevention interventions