Effects of motor fatigue on walking stability and variability during concurrent cognitive challenges

Performance during attention-demanding walking conditions in older adults

BACKGROUND

Conventional balance and gait assessments for fall risk screening are often conducted under unperturbed conditions. However, older adults can allocate their attention to motor tasks (balance or walking) without revealing performance deficiencies, posing a challenge in identifying those with compromised gait and balance.

RESEARCH QUESTIONS

Do community-dwelling older adults exhibit greater changes in cognitive and/or walking performance under balance-challenging conditions compared to typical dual-task walking conditions?

METHODS

Twenty-nine healthy, community-dwelling older adults performed four cognitive tasks (visual and auditory Stroop tasks, Clock task, and Paced Auditory Serial Addition Test) while walking with and without lateral treadmill sways (Perturbed vs. Unperturbed) and during standing. We calculated dual-task costs (DTC) and walking perturbation effects (WPE) as the percentage of change in cognitive and walking performance between dual and single-task conditions and between Perturbed and Unperturbed conditions, respectively.

RESULTS

Older adults exhibited similar DTC and WPE on cognitive task performance. However, in walking performance, they demonstrated significantly greater WPE than DTC across all gait and stability measures (p < 0.01), including the mean and variability of stride and margins of stability (MOS) measures, the variability of trunk movement and lower-limb joint angles, and the local stability measures. Older adults took shorter but wider steps, exhibited shorter MOSAP but greater MOSML, and experienced increased movement variability and walking instability to a greater extent than during dual-task walking. Overall, changes in variability and stability measures were more pronounced than those in mean gait measures.

SIGNIFICANCE

Introducing destabilizing perturbations to increase the task demands of balance and gait assessments is a more effective method to challenge older adults compared to simply adding a concurrent cognitive task. Fall screening assessments for community-dwelling older adults should incorporate balance-challenging conditions, such as introducing gait perturbations.

Notes on the margin of stability

The concept of the 'extrapolated center of mass (XcoM)', introduced by Hof et al., (2005, J. Biomechanics 38 (1), p. 1-8), extends the classical inverted pendulum model to dynamic situations. The vector quantity XcoM combines the center of mass position plus its velocity divided by the pendulum eigenfrequency. In this concept, the margin of stability (MoS), i.e., the minimum signed distance from the XcoM to the boundaries of the base of support was proposed as a measure of dynamic stability. Here we describe the conceptual evolution of the XcoM, discuss key considerations in the estimation of the XcoM and MoS, and provide a critical perspective on the interpretation of the MoS as a measure of instantaneous mechanical stability.

Wrist Extensor Muscle Fatigue During a Dual Task With Two Muscular and Cognitive Load Levels in Younger and Older Adults

OBJECTIVE

To examine the effect of concurrent physical and cognitive demands as well as age on indicators of muscle fatigue at the wrist.

BACKGROUND

There are few studies examining risk indicators for musculoskeletal disorders associated with work-related physical and cognitive demands that often occur simultaneously in the workplace.

METHODS

Twenty-four gender-balanced older and 24 gender-balanced younger (mean age 60 and 23 years) participants performed four 30 min dual tasks. Tasks differed by the muscular load level during force tracking: 5% and 10% of maximum voluntary contraction force (MVC) and concurrent cognitive demands on the working memory: easy and difficult. Muscle fatigue was assessed by MVC decline and changes in surface electromyography (increased root mean square: RMS, decreased median frequency: MF) at the extensor digitorum (ED) and extensor carpi ulnaris (EU).

RESULTS

A decline in MVC was found in all participants when tracking was performed at 10% MVC (mean ± SD: 137.9 ± 49.2 - 123.0 ± 45.3 N). Irrespective of age, muscular, or cognitive load, RMS increased (ED 12.3 ± 6.5 - 14.1 ± 7.0% MVE, EU 15.4 ± 7.6 - 16.9 ± 8.6% MVE) and MF decreased (ED 85.4 ± 13.6 - 83.2 ± 12.8 Hz, EU 107.2 ± 17.1 - 104.3 ± 16.7 Hz) in both muscles. However, changes in MF of EU tended to be more pronounced in the older group at higher cognitive and lower muscular load, without reaching statistical significance.

CONCLUSION

Maximum voluntary contraction indicated no interaction between muscle fatigue, cognitive load, or age. However, the tendencies toward altered muscle activity due to an increase in cognitive load and older age suggest muscular adaptations while maintaining tracking performance during the onset of fatigue signs in the sEMG signal.

APPLICATION

If the tendencies in muscle activity are confirmed by further studies, ergonomic assessments in industrial workplaces should consider cognitive load and age when describing the risk of musculoskeletal disorders.

Effects of muscular and mental fatigue on spatiotemporal gait parameters in dual task walking in young, non-frail and frail older adults

BACKGROUND

Dual-task (DT) walking is of great interest in clinical evaluation to evaluate frailty or cognitive declines in older adults. Frail older adults are known to adopt different walking strategy to overcome fatigue. However, no studies evaluated the effect of muscular or mental fatigue on dual-task walking strategy and the difference between frail and non-frail older adults.

AIMS

Evaluate the effect of mental and muscular fatigue on spatio-temporal parameters in dual-task walking in young, non-frail and frail older adults.

METHODS

59 participants divided into 20 young (Y) (24.9 ± 3 years old), 20 non-frail (NF) (75.8 ± 4.9 years old) and 19 frail older adults (F) (81 ± 4.7 years old) performed single-task (ST) walking, single-task cognitive (serial subtraction of 3), and dual-task (subtraction + walking) for 1 min at their fast pace. Gait speed, step length, step length variability, stance and swing phase time, single and double support time, cadence, gait speed variability were recorded in single- and dual-task walking. The dual-task effect (DTE) was calculated as ((DT - ST)/ST) × 100). Generalized linear mixed models (GLMM) were used to compare the effects of mental and muscular fatigue on gait and cognitive variables between the groups.

RESULTS

The DTE walking parameters were worse in F compared to NF or Y but no significant effect of fatigue were highlighted except for swing time and single support time DTEs.

CONCLUSIONS

The results were mitigated but a clear difference in dual-task spatio-temporal parameters was found between F and NF which brings hope into the capacity of DT to better reveal frailty.

Effects of induced motor fatigue on walking mechanics and energetics

Lower-body robotic exoskeletons can be used to reduce the energy demand of locomotion and increase the endurance of wearers. Understanding how motor fatigue affects walking performance may lead to better exoskeleton designs to support the changing physical capacity of an individual due to motor fatigue. The purpose of this study was to investigate the effects of motor fatigue on walking mechanics and energetics. Treadmill walking with progressively increased incline gradient was used to induce motor fatigue. Twenty healthy young participants walked on an instrumented treadmill at 1.25 m/s and 0° of incline for 5 min before (PRE) and after (POST) motor fatigue. We examined lower-limb joint mechanics, metabolic cost, and the efficiency of positive mechanical work (η+work). Compared to PRE, participants had increased net metabolic power by ∼14% (p < 0.001) during POST. Participants also had increased total-limb positive mechanical power (Total P+mech) by ∼4% during POST (p < 0.001), resulting in a reduced η+work by ∼8% (p < 0.001). In addition, the positive mechanical work contribution of the lower-limb joints during POST was shifted from the ankle to the knee while the negative mechanical work contribution was shifted from the knee to the ankle (all p < 0.017). Although greater knee positive mechanical power was generated to compensate for the reduction in ankle positive power after motor fatigue, the disproportionate increase in metabolic cost resulted in a reduced walking efficiency. The findings of this study suggest that powering the ankle joint may help delay the onset of the lower-limb joint work redistribution observed during motor fatigue.

Fatigue Effect on Minimal Toe Clearance and Toe Activity during Walking

This study investigates the effects of fatigue on the process of walking in young adults using the developed clog-integrated sensor system. The developed sensor can simultaneously measure the forefoot activity (FA) and minimum toe clearance (MTC). The FA was evaluated through the change in the contact area captured by a camera using a method based on a light conductive plate. The MTC was derived from the distance between the bottom surface of the clog and ground obtained using a time of flight (TOF) sensor, and the clog posture was obtained using an acceleration sensor. The induced fatigue was achieved by walking on a treadmill at the fastest walking speed. We evaluated the FA and MTC before and after fatigue in both feet for 14 participants. The effects of fatigue manifested in either the FA or MTC of either foot when the results were evaluated by considering the participants individually, although individual variances in the effects of fatigue were observed. In the dominant foot, a significant increase in either the FA or MTC was observed in 13 of the 14 participants. The mean MTC in the dominant foot increased significantly (p = 0.038) when the results were evaluated by considering the participants as a group.

Gait balance control after fatigue: Effects of age and cognitive demand

BACKGROUND

Fatigue is a commonly mentioned symptom in older adults, and walking under the influence of fatigue frequently occurs in daily activities. Studies have reported individual effects from fatigue or cognitive demand on gait performance. However, the information on how fatigue and cognitive demand interact to affect gait balance control is still lacking.

RESEARCH QUESTION

How does fatigue affect walking balance control in young and older adults with and without performing a concurrent cognitive task?

METHODS

We collected and analyzed motion data from 17 young and 17 older adults, who performed over-ground walking with and without a concurrent working memory test, before and after been fatigued by performing repetitive sit-to-stand movements. Three-way ANOVAs were used for statistical analysis with Age (young and older adults), Fatigue (pre- and post-fatigue), and Task (single-task and dual-task) as factors.

RESULTS

From pre- to post-fatigue, an increased gait velocity was observed during dual-task walking regardless of age (p = .02). Only young adults demonstrated a significant increase in mediolateral center of mass displacement (M-L CoM) at post-fatigue (p = .019). Accuracies of the working memory test were not affected by Age, Task, or Fatigue.

SIGNIFICANCE

Our findings revealed that gait balance control, as measured by the M-L CoM, deteriorated post-fatigue in young adults. Older adults maintained their mediolateral body sway from pre-fatigue to post-fatigue. Fatigue effects were not further exacerbated during dual-task walking, and similar cognitive performance was maintained as performance fatigability increased.

Exploring the role of the left DLPFC in fatigue during unresisted rhythmic movements

Understanding central fatigue during motor activities is important in neuroscience and different medical fields. The central mechanisms of motor fatigue are known in depth for isometric muscle contractions; however, current knowledge about rhythmic movements and central fatigue is rather scarce. In this study, we explored the role of an executive area (left dorsolateral prefrontal cortex [DLPFC]) in fatigue development during rhythmic movement execution, finger tapping (FT) at the maximal rate, and fatigue after effects on the stability of rhythmic patterns. Participants (n = 19) performed six sets of unresisted FT (with a 3 min rest in‐between). Each set included four interleaved 30 s repetitions of self‐selected (two repetitions) and maximal rate FT (two repetitions) without rest in‐between. Left DLPFC involvement in the task was perturbed by transcranial static magnetic stimulation (tSMS) in two sessions (one real and one sham). Moreover, half of the self‐selected FT repetitions were performed concurrently with a demanding cognitive task, the Stroop test. Compared with sham stimulation, real tSMS stimulation prevented waning in tapping frequency at the maximal rate without affecting perceived levels of fatigue. Participants' engagement in the Stroop test just prior to maximal FT reduced the movement amplitude during this mode of execution. Movement variability at self‐selected rates increased during Stroop execution, especially under fatigue previously induced by maximal FT. Our results indicate cognitive‐motor interactions and a prominent role of the prefrontal cortex in fatigue and the motor control of simple repetitive movement patterns. We suggest the need to approach motor fatigue including cognitive perspectives.

We show the fundamental role of executive areas in fatigue caused by very simple repetitive movements. Fatigue developed less during the maximal frequency of movement production, while the left DLPFC received magnetic stimulation (in right‐handers). The role of cognitive‐motor interaction in fine motor control was also clear when participants engaged in cognitive tasks. At the clinical level, our work reinforces the need to treat fatigue from a comprehensive perspective.

Motor adaptation to cognitive challenges and walking perturbations in healthy young adults

BACKGROUND

Cognitive-walking interference is manifested when simultaneously performing a cognitive task while walking. However, majority of the dual-task walking paradigms incorporated relatively short testing trials and were focused on posing a cognitive challenge by adding a secondary cognitive task but not introducing walking perturbations.

RESEARCH QUESTION

How do healthy young adults adapt to concurrent cognitive challenges and walking perturbations in terms of task prioritization and adaptation strategies to control walking stability?

METHODS

Eighteen healthy young participants walked with and without (1) continuous treadmill platform sways (Perturbed and Unperturbed walking), and (2) performing one of the cognitive tasks: visual and auditory Stroop tasks, Clock task, Paced Auditory Serial Addition Test (PASAT), and walk only. Primary outcome measures included cognitive task performance, mediolateral dynamic margins of stability (MOS_ML), M-L local dynamic stability, stride time variability and the dual-task interference (DTI) on these measures.

RESULTS

Gait adjustments made during Perturbed walking did not improve walking stability but instead, showing more local instability and greater gait variability (all p < 0.001) than Unperturbed walking. Participants increased average MOS_ML during Clock and PASAT compared to Walk Only for both Perturbed and Unperturbed walking (THSD, p < 0.05). Participants had significantly less DTI on stride time variability during Unperturbed walking than during Perturbed walking (p < 0.001). Participants also had significantly greater DTI on PASAT performance during Perturbed than during Unperturbed walking (THSD, p < 0.05) SIGNIFICANCE: Participants prioritized the walking task under a more challenging walking condition although the adjustments made during Perturbed walking were not sufficient to maintain a similar level of walking stability as Unperturbed walking. Adjustments to the cognitive-walking challenges were differed by the type of cognitive tasks. The current findings suggest that cognitive tasks involving both working memory and information processing or visuospatial recognition or attention have greater impact on gait especially during the perturbed walking condition.

Dual-task treadmill walking at self-paced versus fixed speeds

BACKGROUND

Investigating cognitive-motor interference on the treadmill allows for better examination of motor adaptation to the dual-task challenges through the information of continuous strides. However, one of the major critiques for conducting dual-task investigation on a treadmill is the use of a constant, fixed walking speed, constraining the natural fluctuations of the speed of human walking, which could be addressed by using the self-paced feature of a feedback-controlled treadmill.

RESEARCH QUESTION

Do people use different adaptation and task prioritization strategies during the dual-task treadmill walking at self-paced versus fixed speeds?

METHODS

Eighteen healthy younger participants walked on an instrumented treadmill (1) under two speed conditions: self-paced and fixed-speed, and (2) with and without each of the four different cognitive tasks. Dynamic margins of stability (MOS), step spatiotemporal measures, kinematic variability, and local dynamic stability were computed for each trial.

RESULTS

Participants had significantly more local instability during self-paced than fixed-speed treadmill walking. The often-reported response of reducing stride time variability during dual-task, fixed-speed walking was not observed during dual-task, self-paced walking. In addition, there were significantly greater dual-task interference effects on stride time variability and local dynamic stability as well as the Paced Auditory Serial Addition Test performance during self-paced walking. Reduced variability in the lower-extremity joint angles, trunk motion and position, and MOS measures were observed both in dual-task, self-paced and fixed-speed walking.

SIGNIFICANCE

Healthy younger adults had different task prioritization and greater dual-task effects on gait stability and cognitive performance during self-paced versus fixed-speed walking. However, similar adaptation strategies, in terms of gait adjustments, were used for the two walking conditions. The results suggest that self-paced treadmill walking is more challenging than the fixed-speed walking and can serve as a better alternative to the overground walking than the fixed-speed walking for the dual-task investigation.

Local dynamic stability during long-fatiguing walks in people with multiple sclerosis

BACKGROUND

Altered balance/stability during walking is common in people with multiple sclerosis (PwMS). While dynamic gait stability has been related to falling and localized muscle fatigue, it has rarely been studied in MS. Specifically, the effects of walking-related fatigue on dynamic stability are unclear in PwMS.

RESEARCH QUESTIONS

1) Are temporal changes in dynamic stability during long-walks different among PwMS and healthy controls (HC)? 2) Is there a relationship between stability and walking performance changes in PwMS?

METHODS

Twenty-five PwMS and ten HC participated in the six-minute walk test (6MWT) wearing six-wireless inertial sensors. Local dynamic stability (LDS) during gait was quantified by maximum-finite-time Lyapunov exponents (λS), where larger λS indicates less stable dynamics. Linear mixed models were fit to compare changes in LDS and walking performance over time among two groups. Additionally, the percent changes in λS and distance from minute 1 to 6 were recorded as Dynamic Stability Index (DSI6-1) and Distance-Walked Index (DWI6-1) respectively. Finally, Pearson correlation compared the association between DSI6-1 and DWI6-1.

RESULTS

A significant group*time interaction was found for LDS. PwMS did not have different LDS than HC until minute-4 of walking, and differences persisted at minute-6. Further, PwMS walked significantly shorter distances and demonstrated a greater decline in walking performance (DWI6-1) during the 6MWT. Finally, DSI6-1 and DWI6-1 were significantly correlated in PwMS. Significance The dynamic stability differences among PwMS and HC were only apparent after 3-minutes of walking and ∼60% of PwMS became less stable over time, supporting the use of long walks in MS to capture stability changes during the motor task performance. A significant relationship between the decline in stability and poor walking performance over time during the 6MWT suggested a possible role of walking-related fatigue in the worsening of balance during long walks in PwMS.

Minimal effects of age and prolonged physical and mental exercise on healthy adults' gait

BACKGROUND

Gait adaptability in old age can be examined by responses to various perturbations. Fatigability due to mental or muscle exercises can perturb internal cognitive and muscle resources, necessitating adaptations in gait.

RESEARCH QUESTION

What are the effects of age and mental and muscle fatigability on stride outcomes and gait variability?

METHODS

Twelve older (66-75yrs) and twelve young (20-25 yrs) adults walked at 1.2 m/s before and after two fatigue conditions in two separate sessions. Fatigue conditions were induced by repetitive sit-to-stand task (RSTS) and by 30-min of mental tasks and randomized between days (about a week apart). We calculated the average and coefficient of variation of stride length, width, single support, swing time and cadence, and the detrended fluctuations analysis (DFA) based on 120 strides time intervals. We also calculated multi-scale sample entropy (MSE) and the maximal Lyapunov exponent (λmax) of mediolateral (ML) and anteroposterior (AP) of the Center of Pressure (CoP) trajectories.

RESULTS

In both age groups, RSTS modestly affected stride length, single support time, cadence, and CV of stride length (p ≤ 0.05), while the mental task did not affect gait. After fatigability, λmax - ML increased (p ≤ 0.05), independent of fatigue condition. All observed effects were small (η²: 0.001 to 0.02).

SIGNIFICANCE

Muscle and mental fatigability had minimal effects on gait in young and healthy older adults possibly because treadmill walking makes gait uniform. It is still possible that age-dependent muscle activation underlies the uniform gait on the treadmill. Age- and fatigability effects might be more overt during real life compared with treadmill walking, creating a more effective model for examining gait and age adaptability to fatigability perturbations.