Sex Differences in Arm Muscle Fatigability With Cognitive Demand in Older Adults

Wrist rotation metrics as digital biomarkers for detecting physio-cognitive decline syndrome in older adults

INTRODUCTION

Physio-cognitive decline syndrome (PCDS) is a reversible condition affecting physical and cognitive health in older adults. Early detection is essential to facilitate timely interventions. This study aimed to evaluate wrist rotation metrics as potential biomarkers for PCDS and explore their applicability in digital health tools.

METHODS

This pilot study recruited 50 community-dwelling individuals aged 50 years or older from Yi-Lan County, Taiwan, including 19 with PCDS and 31 robust participants. Wrist rotation movements were assessed using a custom device, and statistical analyses, including logistic regression and receiver operating characteristic (ROC) curve analysis, were performed to evaluate the diagnostic accuracy of the metrics.

RESULTS

Two rotation metrics, Rotate (60°-30°) and the ratio Rotate (30°-90°)/Rotate (60°-90°), were significantly associated with PCDS. The ratio metric demonstrated high sensitivity, making it suitable for initial screening, while Rotate (60°-30°) exhibited high specificity, supporting its use as a confirmatory test. These complementary roles highlight the potential of these metrics in tiered diagnostic frameworks.

CONCLUSIONS

Wrist rotation metrics show promise as scalable and non-invasive tools for detecting PCDS. These findings support their integration into digital platforms, such as smartphone applications, for early screening and intervention. Further studies are needed to validate these findings in larger, diverse populations and to assess their utility in monitoring disease progression and guiding interventions to improve physical and cognitive health.

The Influence of Mental Fatigue on Physical Performance and Its Relationship with Rating Perceived Effort and Enjoyment in Older Adults

The study investigated the influence of mental fatigue on older people's enjoyment during a series of physical exercises. Using a randomized cross-over design, participants (n = 35) completed a 6-minute walking test - 6MWT, a Timed Up and Go-TUG test and three sets of knee extension exercise (first set: KE1, second set: KE2, third set: KE3) under two experimental conditions (control or mental fatigue). The Nonparametric Analysis of Longitudinal Data in Factorial Experiments was used to compare the number of repetitions performed during three sets of resistance exercise between conditions. The same analysis method was applied to compare the perception of effort and enjoyment across five moments (Post-6MWT, Post-TUG, Post-KE1, Post-KE2, Post-KE3) and two conditions and the Visual Analogue Scales (VAS) across four moments (baseline, Pre-6MWT, Pre-TUG, Pre-KE) and two conditions. Mental fatigue did not affect the physical function, perception of effort and enjoyment of exercise in older people. Participants, however, reported higher enjoyment for walking and dynamic balance compared to strength exercise. Mental fatigue had no effect on the physical function, perception of effort and enjoyment of exercise of older people. Participants presented a higher enjoyment for walking and dynamic balance compared to strength exercise. Given the importance of resistance exercises for health, clinicians should prioritize resources to education programs emphasizing the benefits of resistance exercise in both short- and long-term health. Including social interaction opportunities in physical exercise programs and prescribing activities appropriate to participants' ability levels could enhance engagement and adherence.

Muscle endurance, neuromuscular fatigability, and cognitive control during prolonged dual-task in people with chronic obstructive pulmonary disease: a case-control study

PURPOSE

Recent studies suggest that, compared to healthy individuals, people with chronic obstructive pulmonary disease (pwCOPD) present a reduced capacity to perform cognitive-motor dual-task (CMDT). However, these studies were focused on short-duration CMDT offering limited insight to prolonged CMDT inducing fatigue, which can be encountered in daily life. The present study aimed to explore the effect of adding a cognitive task during repeated muscle contractions on muscle endurance, neuromuscular fatigability, and cognitive control in pwCOPD compared to healthy participants.

METHODS

Thirteen pwCOPD and thirteen age- and sex-matched healthy participants performed submaximal isometric contractions of the knee extensors until exhaustion in two experimental sessions: (1) without cognitive task and (2) with a concurrent working memory task (i.e., 1-back task). Neuromuscular fatigability (as well as central and peripheral components measured by peripheral magnetic stimulation), cognitive performance, and perceived muscle fatigue were assessed throughout the fatiguing tasks.

RESULTS

Independently to the experimental condition, pwCOPD exhibited lower muscle endurance compared to healthy participants (p = 0.039), mainly explained by earlier peripheral fatigue and faster attainment of higher perceived muscle fatigue (p < 0.05). However, neither effect of cognitive task (p = 0.223) nor interaction effect (group × condition; p = 0.136) was revealed for muscle endurance. Interestingly, cognitive control was significantly reduced only in pwCOPD at the end of CMDT (p < 0.015), suggesting greater difficulty for patients with dual tasking under fatigue.

CONCLUSION

These findings provide novel insights into how and why fatigue develops in COPD in dual-task context, offering a rationale for including such tasks in rehabilitation programs.

Adding a sustained attention task to a physically demanding cycling exercise exacerbates neuromuscular fatigue and impairs cognitive performance in both normoxia and hypoxia

PURPOSE

Both cognitive motor dual-tasks (CMDT) protocols and hypoxic environments have been associated with significant impairments in cognitive and physical performance. We aimed to determine the effects of hypoxia on cognitive performance and neuromuscular fatigue during a highly physically demanding CMDT.

METHODS

Fifteen young adults completed a first session involving a cognitive task (CTLCOG) followed by cycling exercise (CTLEX) in normoxia. After that, they randomly participated in CMDT sessions in normoxia (DTNOR) and hypoxia (DTHYP). The physical exercise consisted of 20 min cycling at a "hard" perceived effort, and the cognitive task consisted of 15 min sustained attention to response time task (SART). Concurrent psycho-physiological measurements included: quadriceps neuromuscular fatigue (peripheral/central components from femoral nerve electrostimulation), prefrontal cortex (PFC) oxygenation by near-infrared spectroscopy, and perception of effort.

RESULTS

SART performance significantly decreased in DTNOR (-15.7 ± 15.6%, P < 0.01) and DTHYP (-26.2 ± 16.0%, P < 0.01) compared to CTLCOG (-1.0 ± 17.7%, P = 0.61). Peripheral fatigue similarly increased across conditions, whereas the ability of the central nervous system to activate the working muscles was impaired similarly in DTNOR (-6.1 ± 5.9%, P < 0.001) and DTHYP (-5.4 ± 7.3%, P < 0.001) compared to CTLEX (-1.1 ± 0.2%, P = 0.52). Exercise-induced perception of effort was higher in DTHYP vs. DTNOR and in DTNOR vs. CTLEX. This was correlated with cognitive impairments in both normoxia and hypoxia. PFC deoxygenation was more pronounced in DTHYP compared to DTNOR and CTLEX.

CONCLUSION

In conclusion, performing a sustained attention task together with physically challenging cycling exercise promotes central neuromuscular fatigue and impairs cognitive accuracy; the latter is particularly noticeable when the CMDT is performed in hypoxia.

The Restorative Effects of Nature Exposure on The Self-Regulation Resources in Mentally Fatigued Soccer Players: A Randomized Controlled Trial

Interventions involving exposure to nature can increase self-regulatory resources. However, this improvement has never been examined in mentally fatigued soccer players who have insufficient resources to self-regulate and maintain specific performances. The present study aims to investigate how exposure to nature influences the self-regulation capability of university soccer players who are mentally fatigued. The participants aged 18-24 years (M = 20.73 ± 2.00), with an average training duration of 5.14 ± 1.31 years, were randomly divided into six different groups (three experimental groups and three control groups). Each experimental group was compared with its corresponding control group using three different intervention durations: 4.17 min, 8.33 min, and 12.50 min. A forty-five-minute Stroop task was used to induce mental fatigue, followed by the intervention. The indicators of self-regulation, both physiological (heart rate variability, or HRV) and psychological (competitive state anxiety), were recorded. Experimental Group 3 (12.50 min intervention) only showed significant improvement in HRV (p = 0.008, d = 0.93), competitive state anxiety (cognitive and somatic anxiety p = 0.019, d = 0.86; state confidence p = 0.041, d = 0.797) compared to control group 3. Nature exposure significantly improves self-regulation in mentally fatigued soccer players. Specifically, the 12.50 min intervention showed the greatest improvements in both HRV and competitive state anxiety, suggesting that a longer duration of nature exposure enhances mental restoration more effectively.

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.

Influence of visual feedback and cognitive challenge on the age-related changes in force steadiness

Force steadiness can be influenced by visual feedback as well as presence of a cognitive tasks and potentially differs with age and sex. This study determined the impact of altered visual feedback on force steadiness in the presence of a difficult cognitive challenge in young and older men and women. Forty-nine young (19-30 yr; 25 women, 24 men) and 25 older (60-85 yr; 15 women; 10 men) performed low force (5% of maximum) static contractions with the elbow flexor muscles in the presence and absence of a cognitive challenge (counting backwards by 13) either with low or high visual feedback gain. The cognitive challenge reduced force steadiness (increased force fluctuation amplitude) particularly in women (cognitive challenge × sex: P < 0.05) and older individuals (cognitive challenge × age: P < 0.05). Force steadiness improved with high-gain visual feedback compared with low-gain visual feedback (P < 0.01) for all groups (all interactions: P > 0.05). Manipulation of visual feedback had no influence on the reduced force steadiness in presence of the cognitive challenge for all groups (all P > 0.05). These findings indicate that older individuals and women have greater risk of impaired motor performance of the upper extremity if steadiness is required during a low-force static contraction. Manipulation of visual feedback had minimal effects on the reduced force steadiness in presence of a difficult cognitive challenge.

Cognitive challenge as a probe to expose sex- and age-related differences during static contractions

Despite activities of daily living being frequently performed simultaneously with a cognitive task, motor function is often investigated in isolation, which can hinder the applicability of findings. This brief review presents evidence that 1) performing a cognitive challenge simultaneously with a motor task can negatively impact force steadiness and fatigability of limb muscles during a static contraction, 2) the negative impact on old adults (>65 years old), particularly older women is greater than young when a cognitive challenge is simultaneously performed with a static motor task, 3) age-related mechanisms potentially explain impairments in motor performance in the presence of a cognitive challenge, and 4) the mechanisms for the age-related decrements in motor performance can be distinct between men and women. These observations are highly relevant to the older adults, given the increased risk of accidents and injury when a motor task is performed with a high cognitive-demand task, especially in light of the expanding reliance on an aging workforce.

Effect of Mental Task on Sex Differences in Muscle Fatigability: A Review

Previous research demonstrated that there are observable sex differences in developing muscle fatigue when mental task during fatiguing activity is present; however, there is no available review on this matter. Therefore, this review aimed to summarize the findings of previous studies investigating the effect of mental task on muscle fatigue in men and women. To conduct the review, we utilized searches using the electronic databases Web of Science, PubMed, Scopus, and EBSCO Cinahl Ultimate. The studies included had no limited publication date and examined the effects of mental task on muscle fatigue in a healthy adult population of any age. The evaluation was performed using the following criteria: time to failure, or subjective scale in various modifications (visual analog scale-VAS, rate of perceived effort-RPE, rate of perceived fatigue-RPF, rate of perceived discomfort-RPD). A total of seven studies met the set criteria, which were subsequently analyzed. Heavy mental task (more demanding math tasks) can reduce the time to failure for both men and women, with the reduction being more pronounced for women than for men. For light mental task (simple math tasks), no reduction in time to failure was observed to a great extent. The mental task in any of the included studies did not affect the subjective perception of fatigue, effort, discomfort, or pain. Although the studies investigating the effect of mental task on sex differences in muscle fatigability are limited, based on our findings we can assume that in jobs requiring heavier mental task, women may be more prone to the faster development of muscle fatigue; thus, employers might consider paying attention to the possibility of adequate rest.

Tremor, finger and hand dexterity and force steadiness, do not change after mental fatigue in healthy humans

The effects of mental fatigue have been studied in relation to specific percentages of maximal aerobic or anaerobic efforts, maximal voluntary contractions or the performance of sport specific skills. However, its effects on tremor, dexterity and force steadiness have been only marginally explored. The present work aimed at filling this gap. In twenty-nine young individuals, measurement of postural, kinetic and isometric tremor, pinch force steadiness and finger and hand dexterity were performed before and after either 100 min of mental fatigue or control tasks. During the interventions blood pressure, oxygen saturation and heart rate and perceived effort in continuing the task were recorded every 10 minutes. Tremor was analysed in both time (standard deviation) and frequency domain (position, amplitude and area of the dominant peak) of the acceleration signal. Finger dexterity was assessed by Purdue pegboard test and hand dexterity in terms of contact time in a buzz wire exercise. Force steadiness was quantified as coefficient of variation of the force signal. Postural, kinetic and isometric tremors, force steadiness and dexterity were not affected. Higher oxygen saturation values and higher variability of heart rate and blood pressure were found in the intervention group during the mental fatigue protocol (p < .001). The results provide no evidence that mental fatigue affects the neuromuscular parameters that influence postural, kinetic or isometric tremor, force steadiness and dexterity when measured in single-task conditions. Increased variability in heart rate may suggest that the volunteers in the intervention group altered their alert/stress state. Therefore, it is possible that the alterations that are commonly observed during mental fatigue, and that could have affected tremor, steadiness and dexterity only last for the duration of the cognitive task and are not detectable anymore soon after the mental task is terminated.

Less Is More-Cyclists-Triathlete's 30 min Cycling Time-Trial Performance Is Impaired With Multiple Feedback Compared to a Single Feedback

Purpose: The purpose of this article was to (i) compare different modes of feedback (multiple vs. single) on 30 min cycling time-trial performance in non-cyclist’s and cyclists-triathletes, and (ii) investigate cyclists-triathlete’s information acquisition.

Methods: 20 participants (10 non-cyclists, 10 cyclists-triathletes) performed two 30 min self-paced cycling time-trials (TT, ∼5–7 days apart) with either a single feedback (elapsed time) or multiple feedback (power output, elapsed distance, elapsed time, cadence, speed, and heart rate). Cyclists-triathlete’s information acquisition was also monitored during the multiple feedback trial via an eye tracker. Perceptual measurements of task motivation, ratings of perceived exertion (RPE) and affect were collected every 5 min. Performance variables (power output, cadence, distance, speed) and heart rate were recorded continuously.

Results: Cyclists-triathletes average power output was greater compared to non-cyclists with both multiple feedback (227.99 ± 42.02 W; 137.27 ± 27.63 W; P < 0.05) and single feedback (287.9 ± 60.07 W; 131.13 ± 25.53 W). Non-cyclist’s performance did not differ between multiple and single feedback (p > 0.05). Whereas, cyclists-triathletes 30 min cycling time-trial performance was impaired with multiple feedback (227.99 ± 42.02 W) compared to single feedback (287.9 ± 60.07 W; p < 0.05), despite adopting and reporting a similar pacing strategy and perceptual responses (p > 0.05). Cyclists-triathlete’s primary and secondary objects of regard were power (64.95 s) and elapsed time (64.46 s). However, total glance time during multiple feedback decreased from the first 5 min (75.67 s) to the last 5 min (22.34 s).

Conclusion: Cyclists-triathletes indoor 30 min cycling TT performance was impaired with multiple feedback compared to single feedback. Whereas non-cyclist’s performance did not differ between multiple and single feedback. Cyclists-triathletes glanced at power and time which corresponds with the wireless sensor networks they use during training. However, total glance time during multiple feedback decreased over time, and therefore, overloading athletes with feedback may decrease performance in cyclists-triathletes.

Oscillations in neural drive and age-related reductions in force steadiness with a cognitive challenge

A cognitive challenge when imposed during a low-force isometric contraction will exacerbate sex- and age-related decreases in force steadiness, but the mechanism is not known. We determined the role of oscillations in the common synaptic input to motor units on force steadiness during a muscle contraction with a concurrent cognitive challenge. Forty-nine young adults (19-30 yr; 25 women, 24 men) and 36 old adults (60-85 yr; 19 women, 17 men) performed a cognitive challenge (counting backward by 13) during an isometric elbow flexion task at 5% of maximal voluntary contraction. Single-motor units were decomposed from high-density surface EMG recordings. For a subgroup of participants, motor units were matched during control and cognitive challenge trials, so the same motor unit was analyzed across conditions. Reduced force steadiness was associated with greater oscillations in the synaptic input to motor units during both control and cognitive challenge trials ( r = 0.45-0.47, P < 0.01). Old adults and young women showed greater oscillations in the common synaptic input to motor units and decreased force steadiness when the cognitive challenge was imposed, but young men showed no change across conditions (session × age × sex, P < 0.05). Oscillations in the common synaptic input to motor units is a potential mechanism for altered force steadiness when a cognitive challenge is imposed during low-force contractions in young women and old adults. NEW & NOTEWORTHY We found that oscillations in the common synaptic input to motor units were associated with a reduction in force steadiness when a cognitive challenge was imposed during low-force contractions of the elbow flexor muscles in young women and old men and women but not young men. Age- and sex-related muscle weakness was associated with these changes.

Influence of cognitive load on the dynamics of neurophysiological adjustments during fatiguing exercise

We aimed to determine the neurophysiological mechanisms associated with reduced endurance performance during cognitive-motor dual task at different levels of cognitive load, compared to a motor task alone. Eighteen healthy men performed isometric quadriceps contractions at 15% of maximal voluntary contraction (blocks of 170 s interspaced by neuromuscular evaluations) until exhaustion. This task was performed on three separate days: (a) in the absence of concomitant cognitive task, (b) with concomitant 1-back task, and (c) with concomitant 2-back task. Autonomic nervous system activity, perceived exertion, and cognitive performance were continuously monitored. Peripheral and central determinants of neuromuscular function were assessed at rest, between each block, and at task failure using femoral nerve stimulation. Endurance time was shorter during 2-back (982 ± 545 s) and 1-back (1,128 ± 592 s) conditions, compared with control (1,306 ± 836 s). Voluntary activation level was lower in 2-back (87.1%; p < 0.001) and 1-back (88.6%; p = 0.04) conditions compared to control (91.2%) at isotime (100% of the shortest test duration). Sympathetic activity showed a greater increase in 2-back condition compared to control. Perceived muscular exertion was higher during 2-back than during control. Cognitive performance decreased similarly with time during both cognitive-motor dual task but was always lower during 2-back condition. Motor performance is reduced when adding a concomitant demanding memory task to a prolonged isometric exercise. This can be explained by the interaction of various psychological and neurophysiological factors including higher perceived exertion, greater perturbations of autonomic nervous system activity, and cerebral impairments leading to earlier onset of central fatigue.

Performance Fatigability: Mechanisms and Task Specificity

Performance fatigability is characterized as an acute decline in motor performance caused by an exercise-induced reduction in force or power of the involved muscles. Multiple mechanisms contribute to performance fatigability and originate from neural and muscular processes, with the task demands dictating the mechanisms. This review highlights that (1) inadequate activation of the motoneuron pool can contribute to performance fatigability, and (2) the demands of the task and the physiological characteristics of the population assessed, dictate fatigability and the involved mechanisms. Examples of task and population differences in fatigability highlighted in this review include contraction intensity and velocity, stability and support provided to the fatiguing limb, sex differences, and aging. A future challenge is to define specific mechanisms of fatigability and to translate these findings to real-world performance and exercise training in healthy and clinical populations across the life span.

Short-Term Effects of Kinesio Taping on Muscle Recruitment Order During a Vertical Jump: A Pilot Study

CONTEXT

Kinesio taping is commonly used in sports and rehabilitation settings with the aim of prevention and treatment of musculoskeletal injuries. However, limited evidence exists regarding the effects of 24 and 72 hours of kinesio taping on trunk and lower limb neuromuscular and kinetic performance during a vertical jump.

OBJECTIVE

The purpose of this study was to analyze the short-term effects of kinesio taping on height and ground reaction force during a vertical jump, in addition to trunk and lower limb muscle latency and recruitment order.

DESIGN

Single-group pretest-posttest.

SETTING

University laboratory.

PARTICIPANTS

Twelve male athletes from different sports (track and field, basketball, and soccer).

INTERVENTIONS

They completed a single squat and countermovement jump at basal time (no kinesio taping), 24, and 72 hours of kinesio taping application on the gluteus maximus, biceps femoris, rectus femoris, gastrocnemius medialis, and longissimus.

MAIN OUTCOME MEASURES

Muscle onset latencies were assessed by electromyography during a squat and countermovement jump, in addition to measurements of the jump height and normalized ground reaction force.

RESULTS

The kinesio taping had no effect after 24 hours on either the countermovement or squat jump. However, at 72 hours, the kinesio taping increased the jump height (P = .02; d = 0.36) and normalized ground reaction force (P = .001; d = 0.45) during the countermovement jump. In addition, 72-hour kinesio taping reduced longissimus onset latency (P = .03; d = 1.34) and improved muscle recruitment order during a countermovement jump.

CONCLUSIONS

These findings suggest that kinesio taping may improve neuromuscular and kinetic performance during a countermovement jump only after 72 hours of application on healthy and uninjured male athletes. However, no changes were observed on a squat jump. Future studies should incorporate a control group to verify kinesio taping's effects and its influence on injured athletes.

The Relevance of Sex Differences in Performance Fatigability

Performance fatigability differs between men and women for a range of fatiguing tasks. Women are usually less fatigable than men, and this is most widely described for isometric fatiguing contractions and some dynamic tasks. The sex difference in fatigability is specific to the task demands so that one mechanism is not universal, including any sex differences in skeletal muscle physiology, muscle perfusion, and voluntary activation. However, there are substantial knowledge gaps about the task dependency of the sex differences in fatigability, the involved mechanisms, and the relevance to clinical populations and with advanced age. The knowledge gaps are in part due to the significant deficits in the number of women included in performance fatigability studies despite a gradual increase in the inclusion of women for the last 20 yr. Therefore, this review 1) provides a rationale for the limited knowledge about sex differences in performance fatigability, 2) summarizes the current knowledge on sex differences in fatigability and the potential mechanisms across a range of tasks, 3) highlights emerging areas of opportunity in clinical populations, and 4) suggests strategies to close the knowledge gap and understanding the relevance of sex differences in performance fatigability. The limited understanding about sex differences in fatigability in healthy and clinical populations presents as a field ripe with opportunity for high-impact studies. Such studies will inform on the limitations of men and women during athletic endeavors, ergonomic tasks, and daily activities. Because fatigability is required for effective neuromuscular adaptation, sex differences in fatigability studies will also inform on optimal strategies for training and rehabilitation in both men and women.

The aging neuromuscular system and motor performance

Age-related changes in the basic functional unit of the neuromuscular system, the motor unit, and its neural inputs have a profound effect on motor function, especially among the expanding number of old (older than ∼60 yr) and very old (older than ∼80 yr) adults. This review presents evidence that age-related changes in motor unit morphology and properties lead to impaired motor performance that includes 1) reduced maximal strength and power, slower contractile velocity, and increased fatigability; and 2) increased variability during and between motor tasks, including decreased force steadiness and increased variability of contraction velocity and torque over repeat contractions. The age-related increase in variability of motor performance with aging appears to involve reduced and more variable synaptic inputs that drive motor neuron activation, fewer and larger motor units, less stable neuromuscular junctions, lower and more variable motor unit action potential discharge rates, and smaller and slower skeletal muscle fibers that coexpress different myosin heavy chain isoforms in the muscle of older adults. Physical activity may modify motor unit properties and function in old men and women, although the effects on variability of motor performance are largely unknown. Many studies are of cross-sectional design, so there is a tremendous opportunity to perform high-impact and longitudinal studies along the continuum of aging that determine 1) the influence and cause of the increased variability with aging on functional performance tasks, and 2) whether lifestyle factors such as physical exercise can minimize this age-related variability in motor performance in the rapidly expanding numbers of very old adults.

The effect of cognitive fatigue on prefrontal cortex correlates of neuromuscular fatigue in older women

BACKGROUND

As the population of adults aged 65 and above is rapidly growing, it is crucial to identify physical and cognitive limitations pertaining to daily living. Cognitive fatigue has shown to adversely impact neuromuscular function in younger adults, however its impact on neuromuscular fatigue, and associated brain function changes, in older adults is not well understood. The aim of the study was to examine the impact of cognitive fatigue on neuromuscular fatigue and associated prefrontal cortex (PFC) activation patterns in older women.

METHODS

Eleven older (75.82 (7.4) years) females attended two sessions and performed intermittent handgrip exercises at 30 % maximum voluntary contraction (MVC) until voluntary exhaustion after a 60-min control (watching documentary) and 60-min cognitive fatigue (performing Stroop Color Word and 1-Back tests) condition. Dependent measures included endurance time, strength loss, PFC activity (measured using fNIRS), force fluctuations, muscle activity, cardiovascular responses, and perceived discomfort.

RESULTS

Participants perceived greater cognitive fatigue after the 60-min cognitive fatigue condition when compared to the control condition. While neuromuscular fatigue outcomes (i.e., endurance time, strength loss, perceived discomfort), force fluctuations, and muscle activity were similar across both the control and cognitive fatigue conditions, greater decrements in PFC activity during neuromuscular fatigue development after the cognitive fatigue condition were observed when compared to the control condition.

CONCLUSION

Despite similar neuromuscular outcomes, cognitive fatigue was associated with blunted PFC activation during the handgrip fatiguing exercise that may be indicative of neural adaptation with aging in an effort to maintain motor performance. Examining the relationship between cognitive fatigue and neuromuscular output by imaging other motor-related brain regions are needed to provide a better understanding of age-related compensatory adaptations to perform daily tasks that involve some levels of cognitive demand and physical exercise, especially when older adults experience them sequentially.