Influence of a self-regulated cognitive dual task on time to failure and complexity of submaximal isometric force control

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.

Immersive Virtual Reality Decreases Work Rate and Manipulates Attentional Focus During Self-Regulated Vigorous Exercise

To determine the effect of immersive virtual reality use on finishing time of a vigorous-intensity self-regulated exercise task, and on relevant psychological variables. Healthy untrained adults (N = 21; 10 men/11 women; age = 22.9 ± 7.2 years; BMI = 24.0 ± 4.5 kg/m2) completed 1500-m exercise bouts on a rowing ergometer in a counterbalanced and randomized order, with and without use of a headset-delivered virtual reality fitness program. Heart rate, rating of perceived exertion, affective valence, and attentional focus were collected every 300 m, in addition to finishing time. Data were analyzed with repeated measures as appropriate. Intensity of both exercise bouts was considered vigorous according to heart rate results (>77% maximal heart rate). Finishing time was faster in the control condition (449.57 ± 82.39 s) than in the virtual reality condition (463.00 ± 91.78 s), p = .007. Compared to the control condition, the virtual reality condition was characterized by a more external attentional focus (52.38 ± 18.22 vs. 38.76 ± 17.81, p < .001). No differences were observed for remaining variables as a result of condition (p > .05 for all). When a headset-delivered VR program was used during a self-regulated vigorous-intensity exercise task, participants were 13.6 seconds (~3%) slower than in a control condition. Attentional focus was manipulated to be more external with VR use, which may have ultimately distracted from the exercise objective. Recommendations for selecting an appropriate virtual reality experience for a given exercise task are discussed.

Effects of Combining Occupationally Relevant Physical and Cognitive Tasks. A Systematic Review

OBJECTIVES

Physical and cognitive tasks occur together in many occupations. Previous reviews of combined tasks have mainly focused on their effects in a sports context. This review investigated to which extent combinations (concurrent or alternating) of occupationally relevant physical and cognitive tasks influence responses reflecting biomechanical exposure, stress, fatigue, performance, and well-being.

METHODS

We searched Scopus, Pubmed, Cinahl, and Psychinfo for controlled experiments investigating the effects of combinations of occupationally relevant physical and cognitive tasks in participants aged 18 to 70. In total, we identified 12 447 records. We added recent papers that had cited these studies (n = 573) to arrive at a total of 13 020 publications. After screening for relevance, 61 studies remained, of which 57 were classified to be of medium or high quality. Of the 57 studies, 51 addressed concurrent tasks, 5 alternating tasks, and 1 both concurrent and alternating tasks.

RESULTS

Most studies of concurrent physical and cognitive tasks reported negative effects, if numerically small, on indicators of biomechanical exposure, fatigue, and performance, compared to a physical task alone. Results were mixed for stress indicators, and well-being was too little studied to justify any conclusions. Effects depended on the tasks, including their intensity and complexity. Alternating physical and cognitive tasks did not appear to influence outcomes much, compared to having passive breaks in-between physical tasks.

CONCLUSIONS

The reviewed evidence indicated that concurrent physical and cognitive work tasks have negative, yet small effects on biomechanical indicators, fatigue and performance, compared to performing the physical task alone, but only if the physical task is intense, and the cognitive task is complex. Alternating between physical and cognitive tasks may have similar effects as breaking up physical tasks by passive breaks, but studies were few. Future studies should address ecologically valid combinations of physical and cognitive tasks, in particular in controlled field studies devoted to the long-term effects of combined work.

The use of non-linear tools to analyze the variability of force production as an index of fatigue: A systematic review

Background: Fatigue is a process that results in a decreased ability to produce force, and which could eventually affect performance and increase the risk of injury. Force variability analysis has been proposed to describe the level of fatigue with the purpose of detecting the development of fatigue. Variability is credited to play a functional and adaptive role through which the components of a system self-organize to solve a motor problem. Non-linear tools have been applied to analyze the variability of physiological signals, revealing that the structure of motor fluctuations provides relevant information about the functional role of variability. It has been suggested that the presence of lower complexity in the variability structure could reveal a less functional and adaptative state (e.g., ageing or illness). In the last years, an increased number of studies have applied these techniques to force variability analysis in relation to fatigue. Objective: To provide an overview of the current knowledge on the use of non-linear tools on force variability as a fatigue index. Methods: Following PRISMA guidelines, a systematic search of SPORTDiscus, Scopus, Web of Science and PubMed was carried out. Studies included were: a) original studies that analyzed the effect of fatigue on humans during an action focused on force production; b) published studies with their title and abstract in English; c) studies that applied non-linear tools on a signal directly related to force production. Results: Twenty-five studies were included in this review. The relationship between fatigue and the complexity of force variability, the type of action and relative intensity, the nature of the signal and the non-linear tools used, and the methods of data acquisition and processing were identified. Conclusion: The articles reviewed suggest that fatigue leads to a decrease in complexity mostly in isometric contractions, but this is not as clear in dynamic contractions. This fatigue-induced loss of complexity seems to be a result of changes in the nervous system at the central level, albeit triggered by peripheral mechanisms. It should be noted that non-linear tools are affected by the relative intensity of contraction, non-stationarity, and the acquisition and treatment of the signal.

The Neuromuscular Fatigue-Induced Loss of Muscle Force Control

Neuromuscular fatigue is characterised not only by a reduction in the capacity to generate maximal muscle force, but also in the ability to control submaximal muscle forces, i.e., to generate task-relevant and precise levels of force. This decreased ability to control force is quantified according to a greater magnitude and lower complexity (temporal structure) of force fluctuations, which are indicative of decreased force steadiness and adaptability, respectively. The “loss of force control” is affected by the type of muscle contraction used in the fatiguing exercise, potentially differing between typical laboratory tests of fatigue (e.g., isometric contractions) and the contractions typical of everyday and sporting movements (e.g., dynamic concentric and eccentric contractions), and can be attenuated through the use of ergogenic aids. The loss of force control appears to relate to a fatigue-induced increase in common synaptic input to muscle, though the extent to which various mechanisms (afferent feedback, neuromodulatory pathways, cortical/reticulospinal pathways) contribute to this remains to be determined. Importantly, this fatigue-induced loss of force control could have important implications for task performance, as force control is correlated with performance in a range of tasks that are associated with activities of daily living, occupational duties, and sporting performance.

Ageing and skeletal muscle force control: current perspectives and future directions

During voluntary muscle contractions, force output is characterized by constant inherent fluctuations, which can be quantified either according to their magnitude or temporal structure, that is, complexity. The presence of such fluctuations when targeting a set force indicates that control of force is not perfectly accurate, which can have significant implications for task performance. Compared to young adults, older adults demonstrate a greater magnitude and lower complexity in force fluctuations, indicative of decreased steadiness, and adaptability of force output, respectively. The nature of this loss‐of‐force control depends not only on the age of the individual but also on the muscle group performing the task, the intensity and type of contraction and whether the task is performed with additional cognitive load. Importantly, this age‐associated loss‐of‐force control is correlated with decreased performance in a range of activities of daily living and is speculated to be of greater importance for functional capacity than age‐associated decreases in maximal strength. Fortunately, there is evidence that acute physical activity interventions can reverse the loss‐of‐force control in older individuals, though whether this translates to improved functional performance and whether lifelong physical activity can protect against the changes have yet to be established. A number of mechanisms, related to both motor unit properties and the behavior of motor unit populations, have been proposed for the age‐associated changes in force fluctuations. It is likely, though, that age‐associated changes in force control are related to increased common fluctuations in the discharge times of motor units.

Physiological complexity: influence of ageing, disease and neuromuscular fatigue on muscle force and torque fluctuations

NEW FINDINGS

What is the topic of this review? Physiological complexity in muscle force and torque fluctuations, specifically the quantification of complexity, how neuromuscular complexityis altered by perturbations and the potential mechanism underlying changes in neuromuscular complexity. What advances does it highlight? The necessity to calculate both magnitude- and complexity-based measures for the thorough evaluation of force/torque fluctuations. Also the need for further research on neuromuscular complexity, particularly how it relates to the performance of functional activities (e.g. manual dexterity, balance, locomotion).

ABSTRACT

Physiological time series produce inherently complex fluctuations. In the last 30 years, methods have been developed to characterise these fluctuations, and have revealed that they contain information about the function of the system producing them. Two broad classes of metrics are used: (1) those which quantify the regularity of the signal (e.g. entropy metrics); and (2) those which quantify the fractal properties of the signal (e.g. detrended fluctuation analysis). Using these techniques, it has been demonstrated that ageing results in a loss of complexity in the time series of a multitude of signals, including heart rate, respiration, gait and, crucially, muscle force or torque output. This suggests that as the body ages, physiological systems become less adaptable (i.e. the systems' ability to respond rapidly to a changing external environment is diminished). More recently, it has been shown that neuromuscular fatigue causes a substantial loss of muscle torque complexity, a process that can be observed in a few minutes, rather than the decades it requires for the same system to degrade with ageing. The loss of torque complexity with neuromuscular fatigue appears to occur exclusively above the critical torque (at least for tasks lasting up to 30 min). The loss of torque complexity can be exacerbated with previous exercise of the same limb, and reduced by the administration of caffeine, suggesting both peripheral and central mechanisms contribute to this loss. The mechanisms underpinning the loss of complexity are not known but may be related to altered motor unit behaviour as the muscle fatigues.

The Relevance of Dual Tasking for Improving Trunk Muscle Endurance After Back Surgery

OBJECTIVE

To determine the effect of dual tasking on trunk muscle endurance in patients after lumbar diskectomy.

DESIGN

Cross-sectional study.

SETTING

Rehabilitation hospital setting.

PARTICIPANTS

Individuals (N=14) undergoing primary lumbar diskectomy.

INTERVENTION

Using a randomized design on 2 separate days, muscle endurance was evaluated during prone bridging and Biering-Sorensen tests. Each test was randomly performed under 2 cognitive conditions: single task without cognitive condition and self-regulated dual task (ie, mathematical task).

MAIN OUTCOME MEASURES

The primary outcomes were time to failure and pain assessed by the visual analog scale from 0 to 100 mm. The secondary outcomes were kinesiophobia assessed by the Tampa Scale and disability assessed by the Oswestry Disability Index. Associations were tested using a repeated measures analysis of variance with relevant interaction test.

RESULTS

A significant interaction between condition, endurance tests, and kinesiophobia (P=.005) was found. The post hoc comparison showed positive effects between cognitive conditions in both endurance tests (prone bridging test: mean difference, 15.7s; 95% confidence interval [CI], 7.5-24s; P=.001; Biering-Sorensen test: mean difference, 7.9s; 95% CI, 1.9-14s; P=.014). The linear regression analysis between the Tampa Scale for Kinesiophobia and the difference of time to failure between cognitive conditions showed a positive correlation only during the Biering-Sorensen test (r=0.80; P=.001).

CONCLUSIONS

A self-regulated dual task increases trunk muscle endurance in patients after lumbar diskectomy. The results suggest that the difference observed in time to failure between the single task and dual task is associated with fear avoidance, especially during back extension. This strategy seems especially relevant for patients with high levels of fear avoidance and may be used to improve trunk muscle endurance.

Effects of dual-task demands on the complexity and task performance of submaximal isometric handgrip force control

PURPOSE

To determine the effect of cognitive-motor dual-task load on temporal structure irregularity (complexity) of motor output and task performance of submaximal isometric contractions.

METHODS

Twelve young, sedentary subjects performed handgrip isometric contractions until failure at 50% of maximal voluntary contraction under mathematical self-regulated dual-task (own pace; SDT), regulated dual-task (imposed pace; RDT), and control. Force signal complexity was calculated by sample entropy at the initial, middle, and final thirds. Task performance was assessed by muscle fatigue (time to failure and rate of median frequency of the radial flexor of the carpus), force and math task error, and self-perceived difficulty.

RESULTS

Only RDT decreased complexity with respect to control (17.4% ± 12.6%, p = 0.005), all conditions decreased complexity by the final third (Control: 52.8% ± 18.7%, p < 0.001; SDT: 41.1% ± 32.1%, p = 0.003; RDT: 19.1% ± 21.9%, p = 0.035). Conditions did not affect time to failure, and only RDT decreased the rate of median frequency (0.1%/s ± 0.1%/s, p = 0.020). Inferior force error rate was increased by conditions (SDT: 1.5% ± 0.8%, p < 0.001; RDT: 2% ± 1.5%, p = 0.002). Math error was only augmented by RDT (from 9.9 ± 6.7 to 51.7 ± 18.8, p < 0.001), categorized as "very hard" in 85.7% of participants (p = 0.015).

CONCLUSION

Only the RDT condition reduced complexity and neuromuscular fatigue while increasing force error rate of the handgrip's motor output, without affecting time to failure. A highly demanding dual-task may become a strategy to modify the organization of the hand force motor output, which may contribute to its motor adaptations.

Muscle Fatigue in the Three Heads of Triceps Brachii During Intensity and Speed Variations of Triceps Push-Down Exercise

The objective of this study was to investigate the effects of changes in exercise intensity and speed on the three heads of the triceps brachii (TB) during triceps push-down exercise until task failure. Twenty-five subjects performed triceps push-down exercise at three different intensities (30, 45, and 60% 1RM) and speeds (slow, medium, and fast) until failure, and surface electromyography (sEMG) signals were recorded from the lateral, long and medial heads of the TB. The endurance time (ET), number of repetitions (NR) and rate of fatigue (ROF) were analyzed. Subsequently, the root-mean-square (RMS), mean power frequency (MPF) and median frequency (MDF) under no-fatigue (NF) and fatigue (Fa) conditions were statistically compared. The findings reveal that ROF increases with increase in the intensity and speed, and the opposite were obtained for the ET. The ROF in the three heads were comparable for all intensities and speeds. The ROF showed a significant difference (P < 0.05) among the three intensities and speeds for all heads. The three heads showed significantly different (P < 0.05) MPF and MDF values for all the performed exercises under both conditions, whereas the RMS values were significantly different only under Fa conditions. The current observations suggest that exercise intensity and speed affect the ROF while changes in intensity do not affect the MPF and MDF under Fa conditions. The behavior of the spectral parameters indicate that the three heads do not work in unison under any of the conditions. Changes in the speed of triceps push-down exercise affects the lateral and long heads, but changes in the exercise intensity affected the attributes of all heads to a greater extent.

Cognitive stress changes the attributes of the three heads of the triceps brachii during muscle fatigue

INTRODUCTION

Cognitive stress (CS) changes the peripheral attributes of a muscle, but its effect on multi-head muscles has not been investigated. The objective of the current research was to investigate the impact of CS on the three heads of the triceps brachii (TB) muscle.

METHODS

Twenty-five young and healthy university students performed a triceps push-down exercise at 45% one repetition maximum (1RM) with and without CS until task failure, and the rate of fatigue (ROF), endurance time (ET) and number of repetitions (NR) for both exercises were analyzed. In addition, the first and last six repetitions of each exercise were considered non-fatiguing (NF) and fatiguing (Fa), respectively, and the root mean square (RMS), mean power frequency (MPF) and median frequency (MDF) for each exercise repetition were evaluated.

RESULTS

The lateral and long head showed significant differences (P<0.05) in the ROF between the two exercises, and all the heads showed significant (P<0.05) differences in the RMS between the two exercises under NF conditions. Only the long head showed a significant difference (P<0.05) in the MPF and MDF between the two exercises. CS increases the ET (24.74%) and NR (27%) of the exercise. The three heads showed significant differences (P<0.05) in the RMS, MPF and MDF under all exercise conditions.

CONCLUSION

A lower ROF was obtained with CS. In addition, the RMS was found to be better approximator of CS, whereas MPF and MDF were more resistant to the effect of CS. The results showed that the three heads worked independently under all conditions, and the non-synergist and synergist head pairs showed similar behavior under Fa conditions. The findings from this study provide additional insights regarding the functioning of each TB head.

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.

The effect of 8 weeks of treatment with transcranial pulsed electromagnetic fields on hand tremor and inter-hand coherence in persons with Parkinson's disease

BACKGROUND

Parkinson's disease (PD) tremor comprises asymmetric rest and postural tremor with unilateral onset. Tremor intensity can be amplified by stress and reduced by attention, and the medical treatment is complex. Mirror movements and unintentional synchronization of bimanual movements, possibly caused by insufficient inhibition of inter-hemispheric crosstalk, have been reported in PD, indicating a lag of lateralization. Potential neuroprotective effects of pulsed electromagnetic fields (PEMF) have been reported in-vitro and in rodents, as have influences of PEMF on human tremor. The aim was to investigate the effect of 8 weeks daily transcranial PEMF treatment (T-PEMF) of persons with PD on rest and postural hand tremor characteristics and on inter-hand coherence.

METHODS

Hand accelerations of 50 PD participants with uni- or bilateral tremor participating in a clinical trial were analysed. A rest and postural tremor task performed during serial subtraction was assessed before and after 8 weeks of T-PEMF (30 min/day, 50 Hz, ±50 V, 3 ms squared pulses) or placebo treatment (sham stimulation 30 min/day). Forty matched healthy persons (no treatment) were included as reference. Intensity and inter-hand coherence related measures were extracted.

RESULTS

The T-PEMF treatment decreased the inter-hand coherence in the PD group with unilateral postural tremor. The PD group with unilateral postural tremor was less clinically affected by the disease than the PD group with bilateral postural tremor. However, no differences between T-PEMF and placebo treatment on either intensity related or coherence related measures were found when all persons with PD were included in the analyses. The peak power decreased and the tremor intensity tended to decrease in both treatment groups.

CONCLUSIONS

Eight weeks of T-PEMF treatment decreased inter-hand coherence in the PD group with unilateral postural tremor, while no effects of T-PEMF treatment were found for the entire PD group. The unilateral postural tremor group was less clinically affected than the bilateral postural tremor group, suggesting that early treatment initiation may be beneficial. In theory, a reduced inter-hand coherence could result from a neuronal treatment response increasing inter-hemispheric inhibition. However, this requires further studies to determine. Studies of even longer treatment periods would be of interest.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT02125032. Registered 29 April 2014, https://clinicaltrials.gov/ct2/show/NCT02125032?term=NCT02125032&rank=1.