Postural instability and fall risk in Parkinson's disease: impaired dual tasking, pacing, and bilateral coordination of gait during the "ON" medication state

The interplay between gait and specific cognitive faculties, in particular executive function (EF) and dual tasking abilities, has been described in healthy adults and in patients with Parkinson??s disease (PD). There is, however, little direct evidence on the relationship between cognitive function, gait, and fall risk in PD, especially in the ??ON?? state (i.e., under the influence of the anti-parkinsonian medications). To address this issue, we evaluated cognitive function and gait under usual walking and dual-task conditions in 30 patients with PD in the ON state of the medication cycle. Subjects were classified as fallers or non-fallers based on their history. A computerized battery quantified cognitive function. Gait was assessed under three conditions: (1) Usual walking, (2) While subtracting serial 3?s, and (3) While subtracting serial 7?s. The EF and attention scores were lower in the fallers, compared to non-fallers (P????0.037), but general measures of cognition, e.g., memory, (P?=?0.341) were not. Gait speed, variability, and the bilateral coordination of gait were worse in the fallers in all conditions. The DT effects on gait variability and bilateral coordination were larger in the fallers (P?=?0.044, P?=?0.061, respectively). These results suggest that patients with PD who have a high risk of falling are more sensitive to DT effects, perhaps as a result of relatively poor EF. These cognitive and motor deficits may increase the likelihood of loss of balance during everyday attention-demanding tasks among patients with PD.     

Effects of instructed focus and task difficulty on concurrent walking and cognitive task performance in healthy young adults

Dual task paradigms can be used to examine the interactions between cognition and the control of posture and gait. Measuring and interpreting changes in dual task performance is challenging, however, because many factors can influence performance. This study examined the effects of instructed focus and walking task difficulty, and the interaction between these factors, on dual task performance in healthy young adults. Fifteen participants performed a cognitive task while walking with either a usual base or a narrow base of support. Participants were instructed to focus on either the cognitive task or walking. Trade-offs both within and between tasks were assessed using the modified attention allocation index and the performance operating characteristic. Instructed focus influenced both the cognitive task and walking. Performance on the cognitive task was faster with instructions to focus on the cognitive task, and walking was faster (and more accurate in the narrow-base condition) with instructions to focus on walking. Walking task difficulty did not affect cognitive performance but did affect walking, with faster walking in the usual-base versus narrow-base condition. There was evidence of an interaction, with greater effects of instructed focus on the cognitive task during usual versus narrow-base walking. These results support the idea that the ability to flexibly shift attention allocation and task performance in response to instructions depends on the difficulty of the postural control task. The modified attention allocation index and the performance operating characteristic were instrumental in fully characterizing trade-offs between and within tasks in order to understand dual task performance changes. A clearer understanding of the factors that affect dual task walking and the interactions between these factors has important implications for the assessment of dual task performance in both clinical and research settings.     

Regularity of center-of-pressure trajectories depends on the amount of attention invested in postural control

The influence of attention on the dynamical structure of postural sway was examined in 30 healthy young adults by manipulating the focus of attention. In line with the proposed direct relation between the amount of attention invested in postural control and regularity of center-of-pressure (COP) time series, we hypothesized that: (1) increasing cognitive involvement in postural control (i.e., creating an internal focus by increasing task difficulty through visual deprivation) increases COP regularity, and (2) withdrawing attention from postural control (i.e., creating an external focus by performing a cognitive dual task) decreases COP regularity. We quantified COP dynamics in terms of sample entropy (regularity), standard deviation (variability), sway-path length of the normalized posturogram (curviness), largest Lyapunov exponent (local stability), correlation dimension (dimensionality) and scaling exponent (scaling behavior). Consistent with hypothesis 1, standing with eyes closed significantly increased COP regularity. Furthermore, variability increased and local stability decreased, implying ineffective postural control. Conversely, and in line with hypothesis 2, performing a cognitive dual task while standing with eyes closed led to greater irregularity and smaller variability, suggesting an increase in the "efficiency, or "automaticity" of postural control". In conclusion, these findings not only indicate that regularity of COP trajectories is positively related to the amount of attention invested in postural control, but also substantiate that in certain situations an increased internal focus may in fact be detrimental to postural control.     

Postural after-effects of stepping on an inclined surface

In previous studies, blindfolded, healthy subjects exhibited an after-effect of leaning while standing on a horizontal surface after a period of standing on an inclined surface. We investigated whether this kinesthetic after-effect would transfer from one task to another by asking blindfolded subjects to stand on a horizontal surface after stepping-in-place on an incline. Results showed that all subjects demonstrated a forward trunk leaning after-effect lasting from half a minute to over 6 min after stepping on a 10 degrees -toes-up incline for 2.5 min. For 5/7 subjects, the amplitude of the leaning after-effect was very similar following stepping or standing on the inclined surface. The similarity of the post-incline lean between the standing and stepping conditions suggests a common underlying mechanism for the after-effect following standing and walking on a gradient and suggests that prolonged maintenance of a constant ankle or leg posture is not a prerequisite condition for the after-effect. The transfer of a postural effect built-up during a locomotor task to a postural after-effect during a standing task is consistent with a central adaptive mechanism that adjusts the surface-referenced set point for whole body postural orientation for both gait and posture.     

Age-related changes in prefrontal activity during walking in dual-task situations: A fNIRS study

Background

Previous studies suggest that the human gait is under control of higher-order cognitive processes, located in the frontal lobes, such that an age-related degradation of cognitive capabilities has a negative impact on gait.

Methods

Using functional Near-Infrared-Spectroscopy (fNIRS) we investigate the frontocortical hemodynamic correlates of dual-task walking in two conditions. 15 young and 10 older individuals walked on a treadmill while completing concurrent tasks that had either visual (checking) or verbal-memory (alphabet recall) demands. We compared subjects' motor performance, as well as their prefrontal activity in single- and dual-task walking.

Results

Our behavioral data partly confirm previous accounts on higher dual-task costs in stepping parameters (i.e., decreased step duration) in old age, particularly with a visual task and negative dual-task cost (i.e., improved performance) during the verbal task in young adults. Functional imaging data revealed little change of prefrontal activation from single- to dual-task walking in young individuals. In the elderly, however, prefrontal activation substantially decreased during dual-task walking with a complex visual task.

Conclusion

We interpret these findings as evidence for a shift of processing resources from the prefrontal cortex to other brain regions when seniors face the challenge of walking and concurrently executing a visually demanding task.     

不同类型和负荷双任务对健康人动态姿势控制的影响

目的 通过对比不同负荷认知双任务行走和运动双任务行走时下肢表面肌电(surface electromyography, sEMG)信号及动态稳定性的差异,探究不同类型和负荷双任务对健康人动态姿势控制的影响。方法 利用无线sEMG测试仪和三维运动捕捉系统同时采集28名受试者不同负荷认知双任务行走和运动双任务行走时平均肌电(average electromyography, AEMG)和动态稳定性指标。采用双因素重复测量方差分析任务类型(认知任务和运动任务)和任务负荷(简单任务和困难任务)对人体下肢sEMG和动态稳定性的影响以及两者之间的交互作用。结果 简单负荷行走时,左右股二头肌和右胫前肌AEMG均小于困难负荷行走(P<0.05),左胫前肌简单运动双任务行走时AEMG小于困难运动双任务行走(P<0.05)。右腓肠肌困难认知双任务行走时AEMG小于困难运动双任务行走(P<0.05),简单认知双任务行走时AEMG大于困难认知双任务行走(P<0.05),简单运动双任务行走时AEMG小于困难运动双任务行走(P<0.05);简单认知双任务行走动态稳定裕度(margin...     

The ability of people with Parkinson’s disease to modify dual-task performance in response to instructions during simple and complex walking tasks

Gait impairments are a common and consequential motor symptom in Parkinson’s disease (PD). A cognitive strategy that incorporates instructions to concentrate on specific parameters of walking is an effective approach to gait rehabilitation for persons with PD during single-task and simple dual-task walking conditions. This study examined the ability to modify dual-task walking in response to instructions during a complex walking task in people with PD compared to healthy older adults (HOA). Eleven people with PD and twelve HOA performed a cognitive task while walking with either a usual base or a narrow base of support. Dual-task walking and cognitive task performance were characterized under two conditions—when participants were instructed focus on walking and when they were instructed to focus on the cognitive task. During both usual base and narrow base walking, instructions affected cognitive task response latency, with slower performance when instructed to focus on walking compared to the cognitive task. Regardless of task or instructions, cognitive task performance was slower in participants with PD compared to HOA. During usual base walking, instructions influenced gait speed for both people with PD and HOA, with faster gait speed when instructed to focus on walking compared to the cognitive task. In contrast, during the narrow base walking, instructions affected gait speed only for HOA, but not for people with PD. This suggests that among people with PD the ability to modify walking in response to instructions depends on the complexity of the walking task.     

双任务介入对社区脑卒中患者步态参数及其对称性的影响

目的 对比社区脑卒中患者单任务步行与不同类型和不同负荷双任务步行时步态参数及其对称性的差异。方法 利用 Simi Motion 三维动作分析系统采集 20 名处于慢性恢复期的社区脑卒中患者在单任务步行及不同负荷认知双任务步行和运动双任务步行时步态参数,并间接计算出其对称指数。 采用单因素重复测量方差分析对比单任务步行与不同双任务步行时步态参数及其对称性差异。 结果 与单任务步行相比,社区脑卒中患者在高低负荷认知任务介入时步速、患侧步长、健侧摆动相占比均降低,困难认知任务介入时健侧步宽和健侧、患侧支撑相占增加、健侧步长和患侧摆动相占比降低,摆动相占比对称指数减小(P<0. 05)。 结论 社区脑卒中患者主要通过降低步速、缩减步长、降低摆动相占比、增加步宽和支撑相占比,改变步态模式来应对认知任务干扰,对于步态稳定性,高负荷认知任务的介入,会增加社区脑卒中患者摆动相占比的不对称性程度,降低其步态稳定性。     

Single and dual task tests of gait speed are equivalent in the prediction of falls in older people: A systematic review and meta-analysis

Although simple assessments of gait speed have been shown to predict falls as well as hospitalisation, functional decline and mortality in older people, dual task gait speed paradigms have been increasingly evaluated with respect to fall prediction. Some studies have found that dual task walking paradigms can predict falls in older people. A systematic review and meta-analysis was conducted to determine whether dual task walking paradigms involving a secondary cognitive task have greater ability to predict falls than single walking tasks. The meta-analytic findings indicate single and dual task tests of gait speed are equivalent in the prediction of falls in older people and sub-group analyses revealed similar findings for studies that included only cognitively impaired participants, slow walkers or used secondary mental-tracking or verbal fluency tasks.     

Effects of a secondary task on obstacle avoidance in healthy young adults

Research on attention and gait stability has suggested that the process of recovering gait stability requires attentional resources, but the effect of performing a secondary task on stability during obstacle avoidance is poorly understood. Using a dual-task paradigm, the present experiment investigated the extent to which young adults are able to respond to a secondary auditory Stroop task (requiring executive attentional network resources) concurrently with obstacle crossing during gait when compared with performing unobstructed walking or sitting (control task). Our results demonstrated that as the level of difficulty in the postural task increased, there was a significant reduction in verbal response time from congruent to incongruent conditions in the auditory Stroop task, but no differences in gait parameters, indicating that these postural tasks require attention, and that young adults use a strategy of modulating the auditory Stroop task performance while keeping stable gait performance under the dual-task situations. Our findings suggest the existence of a hierarchy of control within both postural task (obstacle avoidance requires the most information processing resources) and dual-task (with gait stability being a priority) conditions.     

Incomplete inactivation and rapid recovery of voltage-dependent sodium channels during high-frequency firing in cerebellar Purkinje neurons

The ability of individuals to adapt locomotion to constraints associated with the complex environments normally encountered in everyday life is paramount for survival. Here, we tested the ability of 24 healthy young adults to adapt to a rightward prism shift (～11.3°) while either walking and stepping to targets (i.e., precision stepping task) or stepping over an obstacle (i.e., obstacle avoidance task). We subsequently tested for generalization to the other locomotor task. In the precision stepping task, we determined the lateral end-point error of foot placement from the targets. In the obstacle avoidance task, we determined toe clearance and lateral foot placement distance from the obstacle before and after stepping over the obstacle. We found large, rightward deviations in foot placement on initial exposure to prisms in both tasks. The majority of measures demonstrated adaptation over repeated trials, and adaptation rates were dependent mainly on the task. On removal of the prisms, we observed negative aftereffects for measures of both tasks. Additionally, we found a unilateral symmetric generalization pattern in that the left, but not the right, lower limb indicated generalization across the 2 locomotor tasks. These results indicate that the nervous system is capable of rapidly adapting to a visuomotor mismatch during visually demanding locomotor tasks and that the prism-induced adaptation can, at least partially, generalize across these tasks. The results also support the notion that the nervous system utilizes an internal model for the control of visually guided locomotion.     

Gait asymmetry in patients with Parkinson’s disease and elderly fallers: when does the bilateral coordination of gait require attention?

While it is known that certain pathologies may impact on left-right symmetry of gait, little is known about the mechanisms that contribute to gait symmetry or how high in the hierarchy of the control of gait symmetry is regulated in humans. To assess the contribution of cognitive function to gait symmetry, we measured gait asymmetry (GA) in three subject groups, patients with Parkinson's disease (PD, n = 21), idiopathic elderly fallers (n = 15), and healthy elderly controls (n = 11). All subjects walked, under two walking conditions: usual walking and dual tasking (cognitive loading) condition. For each subject, the swing time (SW) was calculated and averaged across strides for the left and right feet (SWL and SWR). GA was defined as: 100 x /ln(SWR/SWL)/. For both the PD patients and the elderly fallers GA values were significantly higher during the usual walking condition, as compared with the control group (P < 0.01). In addition, for both the PD patients and the elderly fallers, GA significantly increased when they walked and performed a dual task, compared with the usual walking condition (P < 0.003). In contrast, dual tasking did not affect the GA of the healthy controls (P = 0.518). GA was associated with gait speed and gait variability, but no correlations were found between GA and the asymmetry of the classic PD motor symptoms. Thus, the results suggest that the ability to generate a steady, rhythmic walk with a bilaterally coordinated gait does not rely heavily on mental attention and cognitive resources in healthy older adults. In contrast, however, when gait becomes impaired and less automatic, GA apparently relies on cognitive input and attention.     

不同任务介入对青年行走动态稳定性及 双任务成本的影响

目的 对比不同双任务行走时动态稳定性及双任务稳定性成本的差异。方法利用三维运动捕捉系统采集40名受试者不同双任务行走时的运动学数据,并间接计算相关动态稳定性指标。采用单因素重复测量方差分析对比单任务行走与不同双任务行走步态参数及动态稳定性差异,采用双因素重复测量方差分析双任务类型（认知任务和运动任务）和任务负荷（简单任务和困难任务）对人体双任务稳定性成本的影响以及两者之间的交互作用。结果 与单任务相比,不同双任务介入时步速均降低（P<0.05）,步频和动态稳定性均增加（P<0.05）,在2倍运动负荷介入时步长小于单任务步行（P<0.05）,1倍认知任务和2倍认知任务介入时步宽大于单任务步行（P<005）。简单认知双任务稳定性成本大于简单运动双任务稳定性成本（P<0.05）,困难认知双任务稳定性成本小于困难运动双任务（P<005）,简单运动双任务稳定成本小于困难运动双任务（P<0.05）。结论 与单任务行走相比,不同双任务的介入均会增加人体动态稳定性;对于双任务稳定性成本,不同任务类型以及不同任务负荷之间存在交互效应。当任务负荷较高时,认知任务的双任务成本较低,即认知任务的负向干扰幅度增大,会损害机体的动态姿势控制能力。当第2任务为运动任务时,较低负荷下对人体动态稳定性的负向干扰幅度增大,降低动态姿势控制能力。     

Dynamical structure of center-of-pressure trajectories in patients recovering from stroke

In a recent study, De Haart et al. (Arch Phys Med Rehabil 85:886-895, 2004) investigated the recovery of balance in stroke patients using traditional analyses of center-of-pressure (COP) trajectories to assess the effects of health status, rehabilitation, and task conditions like standing with eyes open or closed and standing while performing a cognitive dual task. To unravel the underlying control processes, we reanalyzed these data in terms of stochastic dynamics using more advanced analyses. Dimensionality, local stability, regularity, and scaling behavior of COP trajectories were determined and compared with shuffled and phase-randomized surrogate data. The presence of long-range correlations discarded the possibility that the COP trajectories were purely random. Compared to the healthy controls, the COP trajectories of the stroke patients were characterized by increased dimensionality and instability, but greater regularity in the frontal plane. These findings were taken to imply that the stroke patients actively (i.e., cognitively) coped with the stroke-induced impairment of posture, as reflected in the increased regularity and decreased local stability, by recruiting additional control processes (i.e., more degrees of freedom) and/or by tightening the present control structure while releasing non-essential degrees of freedom from postural control. In the course of rehabilitation, dimensionality stayed fairly constant, whereas local stability increased and regularity decreased. The progressively less regular COP trajectories were interpreted to indicate a reduction of cognitive involvement in postural control as recovery from stroke progressed. Consistent with this interpretation, the dual task condition resulted in less regular COP trajectories of greater dimensionality, reflecting a task-related decrease of active, cognitive contributions to postural control. In comparison with conventional posturography, our results show a clear surplus value of dynamical measures in studying postural control.     

Coordination of grasping and walking in Parkinson’s disease

Studies on grasp control underlying manual dexterity in people with Parkinson disease (PD) suggest that anticipatory grasp control is mainly unaffected during discrete tasks using simple two-digit grasp. Nevertheless, impaired hand function during daily activities is one of the most disabling symptoms of PD. As many daily grasping activities occur during functional movements involving the whole body, impairments in anticipatory grasp control might emerge during a continuous dynamic task such as object transport during walking. In this case, grasp control must be coordinated along with multiple body segments. The present study investigated the effect of PD on anticipatory grasp control and intersegmental coordination during walking with a hand-held object. Nine individuals with idiopathic PD (tested OFF and ON medication) and nine healthy age-matched controls carried a grip instrument between their right thumb and index finger during self-paced and fast walking. Although the amplitude of grip forces was higher in standing and walking for subjects with PD, both subjects with PD and control subjects coupled grip and inertial force changes in an anticipatory fashion while walking. However, gait-induced motions of the object relative to that of the trunk (i.e., dampening) was reduced in subjects with PD. Medication increased the dampening in all subjects with PD. We suggest that these differences are associated with impairments in intersegmental coordination.     

Relative contributions of balance and voluntary leg-coordination deficits to cerebellar gait ataxia

Different cerebellar regions participate in balance control and voluntary limb coordination, both of which might be important for normal bipedal walking. We wanted to determine the relative contributions of balance versus leg-coordination deficits to cerebellar gait ataxia in humans. We studied 20 subjects with cerebellar damage and 20 control subjects performing three tasks: a lateral weight-shifting task to measure balance, a visually guided stepping task to measure leg- coordination, and walking. We recorded three-dimensional joint position data during all tasks and center of pressure coordinates during weight-shifting. Each cerebellar subject was categorized as having no detectable deficits, a balance deficit only, a leg-placement deficit only, or both deficits. We then determined the walking abnormalities associated with each of these categories. Five of 10 measures of gait ataxia were abnormal in cerebellar subjects with a balance deficit, but only 1 was abnormal in cerebellar subjects with a leg-placement deficit. Furthermore, subjects with a balance deficit performed worse than subjects with a leg-placement deficit on 9 of the 10 gait measures. Finally, performance on the balance task, but not the leg-placement task, explained a significant proportion of the variance in walking speed for the entire cerebellar group. We conclude that balance deficits are more closely related to cerebellar gait ataxia than leg-placement deficits. Our findings are consistent with animal literature, which has suggested that cerebellar control of balance and gait are interrelated, and dissociable from cerebellar control of voluntary, visually guided limb movements.     

Attention modulates adaptive motor learning in the ‘broken escalator’ paradigm

The physical stumble caused by stepping onto a stationary (broken) escalator represents a locomotor aftereffect (LAE) that attests to a process of adaptive motor learning. Whether such learning is primarily explicit (requiring attention resources) or implicit (independent of attention) is unknown. To address this question, we diverted attention in the adaptation (MOVING) and aftereffect (AFTER) phases of the LAE by loading these phases with a secondary cognitive task (sequential naming of a vegetable, fruit and a colour). Thirty-six healthy adults were randomly assigned to 3 equally sized groups. They performed 5 trials stepping onto a stationary sled (BEFORE), 5 with the sled moving (MOVING) and 5 with the sled stationary again (AFTER). A ‘Dual-Task-MOVING (DTM)’ group performed the dual-task in the MOVING phase and the ‘Dual-Task-AFTEREFFECT (DTAE)’ group in the AFTER phase. The ‘control’ group performed no dual task. We recorded trunk displacement, gait velocity and gastrocnemius muscle EMG of the left (leading) leg. The DTM, but not the DTAE group, had larger trunk displacement during the MOVING phase, and a smaller trunk displacement aftereffect compared with controls. Gait velocity was unaffected by the secondary cognitive task in either group. Thus, adaptive locomotor learning involves explicit learning, whereas the expression of the aftereffect is automatic (implicit). During rehabilitation, patients should be actively encouraged to maintain maximal attention when learning new or challenging locomotor tasks.     

A cognitive dual task affects gait variability in patients suffering from chronic low back pain

Chronic pain and gait variability in a dual-task situation are both associated with higher risk of falling. Executive functions regulate (dual-task) gait variability. A possible cause explaining why chronic pain increases risk of falling in an everyday dual-task situation might be that pain interferes with executive functions and results in a diminished dual-task capability with performance decrements on the secondary task. The main goal of this experiment was to evaluate the specific effects of a cognitive dual task on gait variability in chronic low back pain (CLBP) patients. Twelve healthy participants and twelve patients suffering from CLBP were included. The subjects were asked to perform a cognitive single task, a walking single task and a motor-cognitive dual task. Stride variability of trunk movements was calculated. A two-way ANOVA was performed to compare single-task walking with dual-task walking and the single cognitive task performance with the motor-cognitive dual-task performance. We did not find any differences in both of the single-task performances between groups. However, regarding single-task walking and dual-task walking, we observed an interaction effect indicating that low back pain patients show significantly higher gait variability in the dual-task condition as compared to controls. Our data suggest that chronic pain reduces motor-cognitive dual-task performance capability. We postulate that the detrimental effects are caused by central mechanisms where pain interferes with executive functions which, in turn, might contribute to increased risk of falling.     

Frontal plane dynamic stability and coordination in subjects with cerebellar degeneration

Objective attempts to characterize postural control in subjects with cerebellar (Cb) pathology have focused primarily on sagittal plane responses to static standing, semi-dynamic standing, and platform perturbation. Repeated, dynamic, functional movement may provide a better opportunity to study the effects of ataxia on frontal plane postural stability. The purpose of this investigation was to quantify lateral stability using center of gravity (CG) and center of pressure (CP) movement analysis, and to examine motor responses necessary to complete a repetitive stepping task. Whole body kinematic and kinetic data were collected as patients with Cb degeneration and non-disabled volunteers repeatedly ascended forward and descended backward from a 7.6-cm step to the beat of a metronome. Cb subjects demonstrated significantly greater lateral CG instability, consistent with increased CG velocity and displacement variability in the frontal plane compared to non-disabled subjects. Significantly greater lateral CP displacement was found in subjects with Cb degeneration. Phase plot patterns from patients with Cb degeneration showed poor movement quality, indicated by abruptly changing CG phase plot patterns and abnormal CG acceleration and deceleration phases. Ataxic postural reactions were observed consistently during lateral weight shifting phases toward the stance limb. We hypothesized that lateral postural instability in Cb subjects stems from altered lower extremity intersegmental coordination and inadequate lateral CG velocity control. Frontal plane CG instability may necessitate a wide-based gait. Despite the varied neuroanatomic sites of degenerative Cb pathology, subjects with Cb pathology demonstrated similar CG movement patterns and altered motor strategies to avoid destabilization. Dynamic assessment provides important information regarding frontal plane instability not revealed by static assessment methods. These findings suggest that a dynamic, constrained stepping task effectively differentiates Cb and non-disabled volunteers, contributing to our knowledge of the effect of ataxic movement disturbances on frontal plane postural stability and lower limb coordination.     

Gait adaptations to simultaneous cognitive and mechanical constraints

Previous studies have shown that walking is not a purely automatic motor task but places demands on sensory and cognitive systems. We set out to investigate whether complex walking tasks, as when walking down a steeper gradient while performing a concurrent cognitive task, would demand gait adaptation beyond those required for walking under low-challenge conditions. Thirteen healthy young individuals walked at their self-selected speed on a treadmill at different inclinations (0, −5 and −10%). Gait spatio-temporal measures, pelvis angular excursion, and sacral centre of mass (CoM) motion were acquired while walking or while walking and performing a mental tracking task. Repeated-measures ANOVAs revealed that decreasing treadmill inclination from 0 to −10% resulted in significant decreased walking speed (P < 0.001), decreased stride length (P < 0.001), increased pelvis tilt (P = 0.006) and obliquity variability (P = 0.05), decreased pelvis rotation (P = 0.02), and increased anterio-posterior (A-P) CoM displacement (P = 0.015). Compared to walking alone, walking under dual-task condition resulted in increased step width (P < 0.001), and increased medio-lateral (M-L) CoM displacement (P = 0.039) regardless of inclination grade, while sagittal plane dynamics did not change. Findings suggest that gait adapts differently to cognitive and mechanical constraints; the cognitive system is more actively involved in controlling frontal than sagittal plane gait dynamics, while the reverse is true for the mechanical system. Finally, these findings suggest that gait adaptations maintain the ability to perform concurrent tasks while treadmill walking in healthy young adults.