Aging Affects the Demands and Patterns in Active Control Under Different Sensory-Conflicted Conditions

The margin of stability is affected differently when walking under quasi-random treadmill perturbations with or without full visual support

Background

Sensory-motor perturbations have been widely used to assess astronauts' balance in standing during pre-/post- spaceflight. However, balance control during walking, where most falls occur, was less studied in these astronauts. A study found that applying either visual or platform oscillations reduced the margin of stability (MOS) in the anterior-posterior direction (MOSap) but increased MOS in the medial-lateral direction (MOSml) as a tradeoff. This tradeoff induced an asymmetric gait. This study extended the current knowledge to investigate overall stability under unpredictable environments. This study aimed to determine (1) whether quasi-random treadmill perturbations with or without full vision support would result in a significant reduction in MOSap but an increase in MOSml and (2) regardless of whether vision support was provided, quasi-random treadmill perturbations might result in asymmetric gait patterns.

Methods

Twenty healthy young adults participated in this study. Three experimental conditions were semi-randomly assigned to these participants as follows: (1) the control condition (Norm), walking normally with their preferred walking speed on the treadmill; (2) the treadmill perturbations with full vision condition (Slip), walking on the quasi-random varying-treadmill-belt-speeds with full vision support; and (3) the treadmill perturbations without full vision condition (Slip_VisionBlocked, blackout vision through customized vision-blocked goggles), walking on the quasi-random varying-treadmill-belt-speeds without full vision support. The dependent variables were MOSap, MOSml, and respective symmetric indices. A one-way repeated ANOVA measure or Friedman Test was applied to investigate the differences among the conditions mentioned above.

Results

There was an increase in MOSap in Slip (p = 0.001) but a decrease in MOSap in Slip_VisionBlocked (p = 0.001) compared to Norm condition. The MOSml was significantly greater in both Slip and Slip_VisionBlocked conditions compared to the Norm condition (p = 0.011; p < 0.001). An analysis of Wilcoxon signed-rank tests revealed that the symmetric index of MOSml in Slip_VisionBlocked (p = 0.002) was greater than in the Norm condition.

Conclusion

The novelty of this study was to investigate the effect of vision on the overall stability of walking under quasi-random treadmill perturbations. The results revealed that overall stability and symmetry were controlled differently with/without full visual support. In light of these findings, it is imperative to take visual support into consideration while developing a sensory-motor training protocol. Asymmetric gait also required extra attention while walking on the quasi-random treadmill perturbations without full vision support to maintain overall stability.

Different types of plantar vibration affect gait characteristics differently while walking on different inclines

Background

Plantar vibration has been widely used to strengthen the sensation of the somatosensory system, further enhancing balance during walking on a level surface in patients with stroke. However, previous studies with plantar vibration only involved the level surface, which neglected the importance of inclined/declined walking in daily life. Thus, combining the plantar vibration and inclined/declined walking might answer a critical research question: whether different types of plantar vibration had different effects on gait characteristics during walking on different inclines.

Methods

Eighteen healthy young adults were recruited. Fifteen walking conditions were assigned randomly to these healthy adults (no, sub-, and supra-threshold plantar vibration × five different inclines: +15%, +8%, 0%, -8%, -15% grade). A motion capture system with eight cameras captured 12 retro-reflective markers and measured the stride time, stride length, step width, and respective variabilities.

Results

A significant interaction between vibration and inclination was observed in the stride time (p < 0.0001) and step width (p = 0.015). Post hoc comparisons found that supra-threshold vibration significantly decreased the stride time (-8%: p < 0.001; -15%: p < 0.001) while the sub-threshold vibration significantly increased the step width (-8%: p = 0.036) in comparison with no plantar vibration.

Conclusions

When walking downhill, any perceivable (supra-threshold) vibration on the plantar area decreased the stride time. Also, the increase in step width was observed by non-perceivable (sub-threshold) plantar vibration while walking uphill. These observations were crucial as follows: (1) applying sub-threshold plantar vibrations during uphill walking could increase the base of support, and (2) for those who may need challenges in locomotor training, applying supra-threshold vibration during downhill walking could reach this specific training goal.

The impact of unexpected platform perturbation on ankle proprioception ability in static and dynamic starting positions

AIMS

To examine the relationship between ankle proprioception and the ability to maintain balance with increased magnitudes of unexpected perturbations; and to compare the participants' ability to maintain balance following perturbations when starting from static and dynamic positions.

METHODS

Sixty physical education students (average 24.6 years) were tested for proprioception ability (AUC scores) and balance challenges presented on a perturbation treadmill. The degree at which participants lost postural balance was recorded in seven starting positions: standing-eyes-open (SO), standing-eyes-closed (SC), tandem-dominant (TD), tandem non-dominant, (TND) single-leg lateral side perturbation (SLP), single-leg medial side perturbation (SMP), and walking. Perturbation scores were analysed divided by tertiles. Multidimensional Unfolding SPSS Statistics 25 (PREFSCAL) was used to examine the relationships between data sets.

RESULTS

AUC scores of both dominant and non-dominant legs were significantly correlated with SO (r = 0.316; r = 0.445), SC (r = 0.364; r = 0.413), TD (r = 0.346; r = 0.308), and walking (r = 0.265; r = 0.439), respectively. In the dominant-leg, AUC scores of individuals with below-median SO scores were significantly worse compared to those with median SO scores (p = .046). In the non-dominant leg, individuals with above-median SC had significantly better AUC scores compared to those with lower-than-median SC (p = .008). Those with median and above-median SO and walking achieved better AUC scores than those with below-median (SO: p = .049, p = .004; walking: p = .016, p < .001, respectively). In dimension I, the SLP and SMP were located opposite one another; in dimension II, the TD and TND were located at the upper side, whereas SC, SO and walking were at the lowest side.

CONCLUSIONS

AUC scores were significantly correlated with the level at which postural balance was lost, whereby the better the proprioception ability, the better the ability to maintain balance. As such, the ability to maintain balance is harder in tandem positions than in standing and walking positions. This ability differed when perturbations were to the lateral or medial sides.

Different Types of Visual Perturbation Induced Different Demands and Patterns in Active Control: Implication for Future Sensorimotor Training

Background: Sensorimotor training using visual perturbations has been widely applied to astronauts for rapidly handling and adapting to unpredictable environments. However, these visual perturbations might not be strong enough to trigger long-term effects. Therefore, this study aimed to develop a novel sensorimotor training paradigm using pseudo-random visual perturbations and to determine the demands and patterns of active control under different types of visual perturbations.

Method: Thirty healthy young adults participated in this study. Four walking conditions were randomly assigned to these participants: 1) walking without optic flow (NoOptic), 2) walking with the optic flow (Optic), 3) walking under reduced visual capability (Vre), and 4) walking under perturbed optic flow (Vpe). The dependent variables were the step length variability, the step width variability, the 95% confidence interval ellipse area, the long axis of the ellipse, and the short axis of the ellipse.

Results: The results indicated that 1) the step length variability and the ellipse area were greater in Vre compared to Optic (p < 0.001, p < 0.001). Moreover, the step width variability and ellipse area were greater in Vpe than Optic (p < 0.001, p = 0.002).

Conclusion: The abovementioned results demonstrated that 1) walking in both Vre and Vpe conditions required greater demands and different patterns in active controls compared to the Optic condition, suggesting both Vre and Vpe conditions could be applied for sensorimotor training; 2) the Vre condition would be the first choice if there were no concerns in potential trips on the treadmill.

Different Types of Mastoid Process Vibrations Affect Dynamic Margin of Stability Differently

The vestibular system is critical for human locomotion. Any deteriorated vestibular system leads to gait instability. In the past decades, these alternations in gait patterns have been majorly measured by the spatial-temporal gait parameters and respective variabilities. However, measuring gait characteristics cannot capture the full aspect of motor controls. Thus, to further understand the effects of deteriorated vestibular system on gait performance, additional measurement needs to be taken into consideration. This study proposed using the margin of stability (MOS) to identify the patterns of dynamic control under different types of mastoid vibrations in walking. This study hypothesized that (1) using the MOS method could facilitate the understanding of another aspect of motor control induced by different types of mastoid vibrations, and (2) applying the mastoid vibrations could induce the asymmetric MOS. Twenty healthy young adults were recruited. Two electromechanical vibrotactile transducers were placed on the bilateral mastoid process to apply different types of vestibular vibrations (bilateral, unilateral, and no vibration). A motion capture system with eight cameras was used to measure the MOSap (margin of stability in the anterior-posterior direction), MOSml (margin of stability in the medial-lateral direction), and respective variabilities. The results were in line with the hypotheses that both bilateral and unilateral mastoid vibrations significantly increased MOSap (p = 0.036, p < 0.001), MOSml (p = 0.012, p < 0.001), and respective variabilities p = 0.001, p < 0.001; p = 0.001, p < 0.01 when compared to the no vibration condition. Also, significantly larger MOSml (p = 0.001), MOSml variability (p < 0.023), MOSap (p < 0.001), and MOSap variability (p = 0.002) were observed under the unilateral vibration condition than that observed under the bilateral vibration condition. The above-mentioned result found that different types of mastoid vibrations affected the MOS differently, suggesting different patterns of control mechanisms under different sensory-conflicted situations. Besides, a significant difference between the dominant and non-dominant legs was observed in MOSml. Moreover, applying the unilateral mastoid vibrations induced a greater symmetric index of MOSml, suggesting that more active control in balance was needed in the medial-lateral than in the anterior-posterior direction.

The Effect of Inclines on Joint Angles in Stroke Survivors During Treadmill Walking

Stroke severely affects the quality of life, specifically in walking independently. Thus, it is crucial to understand the impaired gait pattern. This gait pattern has been widely investigated when walking on a level treadmill. However, knowledge about the gait pattern when walking on inclines is scarce. Therefore, this study attempted to fulfill this knowledge gap. In this study, 15 stroke survivors and 15 age/height/weight healthy controls were recruited. The participants were instructed to walk on three different inclines: 0°, 3°, and 6°. The participants were required to walk on each incline for 2 min and needed to complete each incline two times. The dependent variables were the peak values for ankle/knee/hip joint angles and the respective variability of these peak values. The results showed that an increment of the incline significantly increased the peak of the hip flexion and the peak of the knee flexion but did not affect the peak values of the ankle joints in the paretic leg in these stroke survivors. In comparison with the healthy controls, lower hip extension, lower hip flexion, lower knee flexion, and lower ankle plantar flexion were observed in stroke survivors. A clinical application of this work might assist the physical therapists in building an effective treadmill training protocol.