A concurrent attention-demanding task did not interfere with balance recovery function in standing and walking among young adults – An explorative laboratory study

Factors leading to falls in transfemoral prosthesis users: a case series of prosthesis-side stumble recovery responses

BACKGROUND

Falls due to stumbling are prevalent for transfemoral prosthesis users and may lead to increased injury risk. This preliminary case series analyzes the transfemoral prosthesis user stumble recovery response to highlight key deficits in current commercially-available prostheses and proposes potential interventions to improve recovery outcomes.

METHODS

Six transfemoral prosthesis users were perturbed on their prosthetic limb at least three times while walking on a treadmill using obstacle perturbations in early, mid and late swing. Kinematic data were collected to characterize the response, while fall rate and key kinematic recovery metrics were used to assess the quality of recovery and highlight functional deficits in current commercially-available prostheses.

RESULTS

Across all participants, 13 (54%) of the 24 trials resulted in a fall (defined as > 50% body-weight support) with all but one participant (83%) falling at least once and two participants (33%) falling every time. In contrast, in a previous study of seven young, unimpaired, non-prosthesis users using the same experimental apparatus, no falls occurred across 190 trials. For the transfemoral prosthesis users, early swing had the highest rate of falling at 64%, followed by mid-swing at 57%, and then late swing at 33%. The trend in falls was mirrored by the kinematic recovery metrics (peak trunk angle, peak trunk angular velocity, forward reach of the perturbed limb, and knee angle at ground contact). In early swing all four metrics were deficient compared to non-prosthesis user controls. In mid swing, all but trunk angular velocity were deficient. In late swing only forward reach was deficient.

CONCLUSION

Based on the stumble recovery responses, four potential deficiencies were identified in the response of the knee prostheses: (1) insufficient resistance to stance knee flexion upon ground contact; (2) insufficient swing extension after a perturbation; (3) difficulty initiating swing flexion following a perturbation; and (4) excessive impedance against swing flexion in early swing preventing the potential utilization of the elevating strategy. Each of these issues can potentially be addressed by mechanical or mechatronic changes to prosthetic design to improve quality of recovery and reduce the likelihood a fall.

Factors leading to falls in transfemoral prosthesis users: a case series of sound-side stumble recovery responses

Background

Transfemoral prosthesis users’ high fall rate is related to increased injury risk, medical costs, and fear of falling. Better understanding how stumble conditions (e.g., participant age, prosthesis type, side tripped, and swing phase of perturbation) affect transfemoral prosthesis users could provide insight into response deficiencies and inform fall prevention interventions.

Methods

Six unilateral transfemoral prosthesis users experienced obstacle perturbations to their sound limb in early, mid, and late swing phase. Fall outcome, recovery strategy, and kinematics of each response were recorded to characterize (1) recoveries versus falls for transfemoral prosthesis users and (2) prosthesis user recoveries versus healthy adult recoveries.

Results

Out of 26 stumbles, 15 resulted in falls with five of six transfemoral prosthesis users falling at least once. By contrast, in a previously published study of seven healthy adults comprising 214 stumbles using the same experimental apparatus, no participants fell. The two oldest prosthesis users fell after every stumble, stumbles in mid swing resulted in the most falls, and prosthesis type was not related to strategy/fall outcomes. Prosthesis users who recovered used the elevating strategy in early swing, lowering strategy in late swing, and elevating or lowering/delayed lowering with hopping in mid swing, but exhibited increased contralateral (prosthetic-side) thigh abduction and trunk flexion relative to healthy controls. Falls occurred if the tripped (sound) limb did not reach ample thigh/knee flexion to sufficiently clear the obstacle in the elevating step, or if the prosthetic limb did not facilitate a successful step response after the initial sound-side elevating or lowering step. Such responses generally led to smaller step lengths, less anterior foot positioning, and more forward trunk flexion/flexion velocity in the resulting foot-strikes.

Conclusions

Introducing training (e.g., muscle strength or task-specific motor skill) and/or modifying assistive devices (e.g., lower-limb prostheses or exoskeletons) may improve responses for transfemoral prosthesis users. Specifically, training or exoskeleton assistance could help facilitate sufficient thigh/knee flexion for elevating; training or prosthesis assistance could provide support-limb counteracting torques to aid in elevating; and training or prosthesis assistance could help initiate and safely complete prosthetic swing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-022-01070-y.

Task-prioritization and balance recovery strategies used by young healthy adults during dual-task walking

BACKGROUND

Maintaining dynamic balance is an essential task during walking, with foot-placement playing a critical role. Dual-task studies analyzing steady-state walking with cognitive loads have found healthy adults prioritize cognitive task performance at the expense of maintaining control of their balance. However, few studies have focused on the influence of cognitive loads on more difficult motor tasks, such as walking with unexpected foot-placement perturbations. Individuals often recover from a loss of balance using an ankle or hip strategy; however, how cognitive loads affect these balance recovery strategies remains unknown.

RESEARCH QUESTION

How do individuals prioritize cognitive resources and does the balance recovery strategy used change following mediolateral foot-placement perturbations during steady-state walking when performing cognitive tasks of increasing difficulty?

METHODS

Fifteen young healthy adults walked during unperturbed and perturbed conditions with increasing cognitive loads (no cognitive load, attentive listening, spelling short words backwards and spelling long words backwards). No specific task-prioritization instructions were given. Medial and lateral foot-placement perturbations were applied prior to heel-strike during random steps.

RESULTS

Cognitive performance decreased between the unperturbed and perturbed conditions. While balance control decreased during perturbed relative to unperturbed walking, the additional cognitive load had little effect on balance control during the perturbations. Lastly, the balance recovery strategy used, as measured by peak joint moments at the ankle and hip, was unaffected by the additional cognitive loads.

SIGNIFICANCE

Individuals appear to prioritize their balance control over cognitive performance when experiencing foot-placement perturbations and do not change their balance recovery strategy with the addition of a cognitive load. These results highlight the flexibility of task-prioritization in young adults and provide a foundation for future studies analyzing neurologically impaired populations.

Balance recovery stepping responses during walking were not affected by a concurrent cognitive task among older adults

Background

Most of older adults’ falls are related to inefficient balance recovery after an unexpected loss of balance, i.e., postural perturbation. Effective balance recovery responses are crucial to prevent falls. Due to the considerable consequences of lateral falls and the high incidence of falls when walking, this study aimed to examine the effect of a concurrent cognitive task on older adults’ balance recovery stepping abilities from unannounced lateral perturbations while walking. We also aimed to explore whether cognitive performance accuracy is affected by perturbed walking and between task trade-offs.

Methods

In a laboratory-based study, 20 older adults (> 70 years old) performed the following test conditions: (1) cognitive task while sitting; (2) perturbed walking; and (3) perturbed walking with a concurrent cognitive task. The cognitive task was serial numbers subtraction by seven. Single-step and multiple-step thresholds, highest perturbation achieved, 3D kinematic analysis of the first recovery step, and cognitive task performance accuracy were compared between single-task and dual-task conditions. Between task trade-offs were examined using dual-task cost (DTC).

Results

Single-step and multiple-step thresholds, number of recovery step trials, number of foot collision, multiple-step events and kinematic recovery step parameters were all similar in single-task and dual-task conditions. Cognitive performance was not significantly affected by dual-task conditions, however, different possible trade-offs between cognitive and postural performances were identified using DTC.

Conclusions

In situations where postural threat is substantial, such as unexpected balance loss during walking, balance recovery reactions were unaffected by concurrent cognitive load in older adults (i.e., posture first strategy).

The study was approved by the Helsinki Ethics Committee of Soroka University Medical Center in Beer-Sheva, Israel (ClinicalTrials.gov Registration number NCT04455607, ID Numbers: Sor 396–16 CTIL; 02/07/2020).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-02969-w.

Dual Tasking during Trip Recovery and Obstacle Clearance among Young, Healthy Adults in Human Factors Research

Trip-induced falls are extremely common in ergonomic settings. Such situations can lead to fatal or non-fatal injuries, affecting the workers’ quality of life and earning capacity. Dual tasking (DT) is a leading cause of trips and ineffective obstacle clearance among workers. DT increases their attentional demand, challenging both postural control and concurrent secondary tasks. As the human brain has limited attentional processing capacity, even young, healthy adults need to prioritize duties during DT. This article aimed to analyze these secondary task types and their applications in recent trip-related studies conducted on young, healthy adults. An extensive review of the recent trip-related literature was performed to provide a condensed summary of the dual tasks used. In previous trip-related literature, distinct types of secondary tasks were used. The choice of the concurrent task must be made vigilantly depending on the occupation, environmental context, available resources, and feasibility. DT can be used as a tool to train workers on selective attention, which is a lifesaving skill in ergonomic settings, especially in the occupations of roofers, construction workers, or truck drivers. Such training can result in successful obstacle clearance and trip recovery skills, which eventually minimizes the number of falls at the workplace.

The influence of cognitive load on balance control during steady-state walking

For an individual to successfully walk, they must maintain control of their dynamic balance. However, situations that require increased cognitive attention may impair an individual's ability to actively control their balance. While dual-task studies have analyzed walking-while-talking conditions, few studies have focused specifically on the influence of cognitive load on balance control. The purpose of this study was to assess how individuals prioritize their cognitive resources and control dynamic balance during dual-task conditions of varying difficulty. Young healthy adults (n = 15) performed two single-task conditions (spelling-while-standing and treadmill walking with no cognitive load) and three dual-task conditions (treadmill walking with increasing cognitive load: attentive listening and spelling short and long words backwards). Cognitive performance did not change between the single- and dual-task as measured by spelling percent error and response rate (p = 0.300). Balance control, assessed using the range of whole-body angular momentum, did not change between the no load and listening conditions, but decreased during the short and long spelling conditions (p < 0.001). These results highlight that in young adults balance control decreases during dual-task treadmill walking with increased cognitive loads, but their cognitive performance does not change. The decrease in balance control suggests that participants prioritized cognitive performance over balance control during these dual-task walking conditions. This work offers additional insight into the automaticity of walking and task-prioritization in healthy young individuals and provides the basis for future studies to determine differences in neurologically impaired populations.