Gait characteristics during inadvertent obstacle contacts in young, middle-aged and older adults.

BACKGROUND: When stepping over obstacles, analyses have focused on the successful trials to understand adaptive gait. However, examination of the inadvertent trips that occasionally occur in the laboratory can provide a rich source of information regarding the gait characteristics underlying trip-related falls. RESEARCH QUESTION: What gait variables during obstacle crossing are associated with inadvertent obstacle contacts, and are these variables different across the lifespan? METHODS: Three age groups included: young adults (20-35 years, N = 20), middle-aged adults (50-64 years, N = 15), and older adults (65-79 years, N = 19). A stationary, visible obstacle (26 cm tall) was placed in the middle of a walkway. Foot trajectories and head angles were compared between contact and non-contact trials. RESULTS: Twelve participants contacted the obstacle: seven young adults (3.5% of young adult trials), two middle-aged adults (1.3%), and three older adults (1.6%). Young and middle-aged adults contacted primarily with the trail limb, while older adults contacted primarily with the lead limb. Contacts occurred for different reasons: Most young adult contact trials had appropriate foot placement, but inadequate elevation; middle-aged and older adults demonstrated inappropriate foot placement before the obstacle, leading to foot contact during the swing phase. SIGNIFICANCE: Lower contact rates in the middle-aged and older adults indicates that the cautious strategies adopted during obstacle crossing are effective. Higher contact rates in young adults may indicate trial-and-error exploratory behavior. Inappropriate foot placement in the middle-aged and older adults may indicate impaired ability to gather obstacle position information during the approach phase.

Changes in the control of obstacle crossing in middle age become evident as gait task difficulty increases.

BACKGROUND: Age-associated physiological changes result in modified gait, such as slower speed, for older adults. Identifying the onset of age-related gait changes will provide insight into the role of aging on locomotor control. It is expected that a more challenging gait task (obstacle crossing) puts more demands on physiological systems, and may reveal gait modifications in a middle-aged group that are not evident in an easier gait task (level walking). RESEARCH QUESTION: To identify the effect of advancing age on gait as a function of increasing locomotor challenge during an obstacle crossing task. METHODS: Three age groups (young, middle-aged, and older adults) stepped over an obstacle placed in a 15 m walkway. Task challenge ranged from low to high in four conditions: unobstructed gait, 3, 10, and 26 cm obstacles. Gait measures were calculated during the approach and crossing steps. RESULTS: Significant interactions were observed for gait speed (age by height by step, p < 0.01), foot placement variability (age by step, p < 0.01) and foot clearance (age by height, p = 0.05). Relative to young adults, older adults walked slower in all conditions and had higher foot clearances for the 10 and 26 cm obstacles. Middle-aged adults walked with speeds and foot clearances that were not different from young adults in the lower gait challenge conditions, and changed to values that were not different from older adults in the highest gait challenge conditions. Foot placement variability was greater for the middle-aged and older groups, but only in the last two steps before the obstacle. SIGNIFICANCE: Multiple gait changes were observed as early as middle-age, and changes in speed and foot clearance became more evident as task difficulty increased. The increased gait challenge placed more demands on the neuromuscular system, revealing age-related gait modifications that were not evident in the level walking gait task.

Coupling of postural and manual tasks in expert performers.

The purpose of this study was to investigate the integration of bimanual rhythmic movements and posture in expert marching percussionists. Participants (N=11) performed three rhythmic manual tasks [1:1, 2:3, and 2:3-F (2:3 rhythm played faster at a self-selected tempo)] in one of three postures: sitting, standing on one foot, and standing on two feet. Discrete relative phase, postural time-to-contact, and coherence analysis were used to analyze the performance of the manual task, postural control, and the integration between postural and manual performance. Across all three rhythms, discrete relative phase mean and variability results showed no effects of posture on rhythmic performance. The complexity of the manual task (1:1 vs. 2:3) had no effect on postural time-to-contact. However, increasing the tempo of the manual task (2:3 vs. 2:3-F) did result in a decreased postural time-to-contact in the two-footed posture. Coherence analysis revealed that the coupling between the postural and manual task significantly decreased as a function of postural difficulty (going from a two-footed to a one-footed posture) and rhythmic complexity (1:1 vs. 2:3). Taken together, these results demonstrate that expert marching percussionists systematically decouple postural and manual fluctuations in order to preserve the performance of the rhythmic movement task.

Prospective dynamic balance control during the swing phase of walking: stability boundaries and time-to-contact analysis.

This study examined the prospective control of the swing phase in young healthy adults while walking at preferred speed over unobstructed ground and during obstacle clearance. Three aspects of swing were examined: (1) the relation of the body Center of Mass (CoM) to the stability boundaries at the base of support; (2) a dynamic time-to-contact analysis of the CoM and swing foot to these boundaries; and (3) the role of head movements in the prospective control of gait and field of view assessment. The time-to-contact analysis of CoM and swing foot showed less stable swing dynamics in the trail foot compared to the lead foot in the approach to the unstable equilibrium, with the CoM leading the swing foot and crossing the anterior stability boundary before the swing foot. Compensations in temporal coupling occurred in the trail limb during the late swing phase. Time-to-contact analysis of head movement showed stronger prospective control of the lead foot, while fixation of the field of view occurred earlier in swing and was closer to the body in the obstacle condition compared to unobstructed walking. The dynamic time-to-contact analysis offers a new approach to assessing the unstable swing phase of walking in different populations.

Effect of head orientation on postural control during upright stance and forward lean.

Sensory feedback from the vestibular system and neck muscle stretch receptors is critical for the regulation of postural control. The postural relationship of the head to the trunk is a major factor determining the integration of sensory feedback and can be interfered with by varying head orientation. This study assessed how 60-s of standing with the head neutral, flexed, or extended impacted postural stability during upright stance and during forward lean in 13 healthy participants (26 ±5 years old). During both quiet upright stance and maximal forward lean, head extension increased postural center of pressure (COP) velocity and decreased the COP time-to-contact the anterior stability boundary compared with the head neutral condition. Head flexion did not differ from head neutral for either of the stance conditions. This study demonstrates that interfering with the head-trunk relationship by adopting extended, but not flexed, head orientations interferes with postural control that may impact postural stability during both quiet upright stance and maximal forward lean conditions.

Postural control in women with multiple sclerosis: effects of task, vision and symptomatic fatigue.

People with multiple sclerosis (MS) often report problems with balance, which may be most apparent during challenging postural tasks such as leaning or reaching, and when relying on non-visual sensory systems. An additional obstacle facing people with MS is a high incidence of symptomatic fatigue (>70%). The purpose of this study was to investigate the changes in balance during upright stance in individuals with mild-to-moderate disability due to MS under normal and restricted vision and different levels of self-reported fatigue. Limb loading asymmetry, sway and magnitude of postural shift in center of pressure, and time-to-contact the stability boundary of the center of mass and center of pressure were assessed during quiet standing and maximal lean and reach tasks. Compared to controls, people with MS displayed greater postural sway, greater loading asymmetry, and shorter time-to-contact during quiet standing. In the postural perturbation tasks the MS group had smaller postural shifts and reduced stability compared to controls in the direction perpendicular to the lean and reach. Limiting vision increased loading asymmetry during quiet standing and postural instability during backward lean in the MS group. Inducing additional fatigue in the MS group did affect postural control in the more challenging balance conditions but had no impact during quiet upright standing. The results of this study indicate subtle changes in postural control during standing in people with mild-to-moderate impairments due to MS.

Age-related changes in upper body adaptation to walking speed in human locomotion.

Assessments of changes in gait stability due to aging and disease are predominantly based on lower extremity kinematic and kinetic data. These gait changes are also often based on comparisons at preferred speed only. The purpose of this experiment was to: (1) examine age-related changes in range of motion and coordination of segments of the upper body during locomotion; and (2) investigate the effects of a systematic walking velocity manipulation on rotational motion and coordination. Participants (n=30) walked on a motor driven treadmill at speeds ranging from 0.2 to 1.8m/s and were divided into three groups with mean ages of 23.3, 49.3 and 72.6 years, respectively. Seven high-speed infrared cameras were used to record three-dimensional kinematics of the pelvis, trunk and head. Dependent variables were amplitude of segmental and joint rotations, as well as relative phase to assess coordination between segments. Although no differences in stride parameters were found between the groups, age-related changes in movement amplitude in response to speed manipulations were observed for all segments and joints. Pelvic rotations in sagittal, frontal and transverse planes of motion were systematically reduced with age. Older individuals showed reduced trunk flexion-extension in the sagittal plane and increased trunk axial rotation in the transverse plane. Coordination analysis showed reduced compensatory movement between pelvis and trunk in older individuals. These findings support the importance of systematic manipulation of walking velocity and three-dimensional upper body kinematics in assessing age-related changes in locomotor stability and adaptability.

Postural orientation: age-related changes in variability and time-to-boundary.

The relation between age-specific postural instability and the detection of stability boundaries was examined. Balance control was investigated under different visual conditions (eyes open/closed) and postural orientations (forward/backward lean) while standing on a force platform. Dependent variables included center of pressure variability and the time-to-contact of the center of pressure with the stability boundaries around the feet (i.e., time-to-boundary). While leaning maximally, older individuals (ages 55-69) showed increased center of pressure variability compared to no lean, while younger subjects (ages 24-38) showed a decrease. These significant differences were found only in anterior-posterior direction. No significant age-specific differences were found between eyes open and eyes closed conditions. Time-to-boundary analysis revealed reduced spatio-temporal stability margins in older individuals in both anterior-posterior and medio-lateral directions. Time-to-boundary variability, however, was not significantly different between the groups in both medio-lateral and anterior-posterior direction. These results show the importance of boundary relevant center of pressure measures in the study of postural control, especially concerning the lateral instability often observed in older adults.