Isometric Handgrip Task Research Articles

Investigating psychobiological causes and mechanisms in functional seizures and functional motor symptoms: Study protocol.

Advances have been made in understanding the aetiology of functional neurological disorder (FND); however, its pathophysiological mechanisms have not been definitively demonstrated. Evidence suggests interacting roles for altered emotional processing and interoception, elevated autonomic arousal, and dissociation, but there is limited evidence demonstrating their causal influence on specific FND symptoms. Our superordinate aim is to elucidate potentially shared and distinct aetiological factors and mechanisms in two common FND subtypes, functional seizures (FS) and functional motor symptoms (FMS). This study has a multimodal, mixed between- and within-groups design. The target sample is 50 individuals with FS, 50 with FMS, 50 clinical controls (anxiety/depression), and 50 healthy controls. Potential aetiological factors (e.g., adverse life events, physical/mental health symptoms, dissociative tendencies, interoceptive insight/sensibility) will be assessed with a detailed medical history interview and self-report questionnaires. A laboratory session will include a neurocognitive battery, psychophysiological testing, cardiac interoception and time estimation tasks and an isometric handgrip task. A subsample will undergo magnetic resonance imaging, including structural, resting-state and task-based scans combined with psychophysiological recording. Remote monitoring with ecological momentary assessment and wearables will measure variability in FND symptoms and their potential predictors/correlates for ≥2 weeks in patients' daily lives. Longitudinal follow-ups at 3, 6, and 12-months will monitor longer-term outcomes in the clinical groups. This study employs multimodal research methods to rigorously examine several putative mechanisms in FND, at subjective/experiential, behavioural, and physiological levels. The study will test causal hypotheses about the role of altered emotional processing, autonomic arousal, dissociation and interoception in the initiation or exacerbation of FND symptoms, directly comparing these processes in FS and FMS to healthy and clinical controls. This is the first study of its kind, with potential to reveal important targets for prevention and treatment of FND in future.

Differential control of sympathetic outflow to muscle and skin during physical and cognitive stressors

PurposeSympathetic nerve activity towards muscle (MSNA) and skin (SSNA) regulates various physiological parameters. MSNA primarily functions in blood pressure and flow, while SSNA operates in thermoregulation. Physical and cognitive stressors have been shown to have effects on both types of sympathetic activity, but there are inconsistencies as to what these effects are. This article aims to address the discrepancies in the literature and compare MSNA and SSNA responses.MethodsMicroelectrode recordings were taken from the common peroneal nerve in 29 participants: MSNA (n = 21), SSNA (n = 16) and both MSNA and SSNA (n = 8). Participants were subjected to four different 2-min stressors: two physical (isometric handgrip task, cold pressor test) and two cognitive (mental arithmetic task, Stroop colour–word conflict test), the latter of which saw participants separated into responders and non-responders to the stressors. It was hypothesised that the physical stressors would have a greater effect on MSNA than SSNA, while the cognitive stressors would operate conversely.ResultsPeristimulus time histogram (PSTH) analysis showed the mental arithmetic task to significantly increase both MSNA and SSNA; the isometric handgrip task and cold pressor test to increase MSNA, but not SSNA; and Stroop test to have no significant effects on changing MSNA or SSNA from baseline. Additionally, stress responses did not differ between MSNA and SSNA in participants who had both sets of data recorded.ConclusionsThis study has provided evidence to support the literature which claims cognitive stressors increase sympathetic activity, and provides much needed SSNA data in response to stressors.

Analysis of the force–time curve and median frequency of surface electromyographic signals during isometric hand grip test for estimation of a temporal pattern for muscle strengthening

This work presents methods developed for the analysis of dynamometric and electromyographic signals acquired during sustained maximal isometric hand grip tasks. In these analyses, we try to find a temporal pattern that could indicate the beginning of the decrease in hand grip strength. This information is essential for choosing the best isometric activity time for hand rehabilitation. The technique applied to the dynamometric signal was to find the time interval that precedes the drop of the isometric force RMS (root mean square) curve to values lower than the effective value. The technique applied to the surface electromyography (sEMG) signals was the identification of the instant when the lowest value of the median frequency of the signal occurs. The dynamometry data collection was carried out bilaterally in 19 men and 21 women. The electromyography data collection was carried out bilaterally in only 19 women. The statistical results (5% significance level) for the dynamometry data indicated that the time from the beginning of the test to the beginning of the decay of strength was approximately 7.6 $$\pm$$ 3.2 s, while the results for the sEMG data indicated that the time from the beginning of the test to the appearance of the lowest value of the median frequency was approximately 10.1 $$\pm$$ 2.9 s. The method of using the RMS values of the Force, presented by this work, found results of approximately 7 s, while the method most currently used (Median Frequency) found values of approximately 10 s. These results may help the rehabilitation professional to decide with more security the isometric time of exercises.

Stressed in afterthought: Neuroendocrine effects of social self-threat during physical effort are counteracted by performance feedback after stress exposure

Social self-threat during physical stress, such as exposure to the cold pressor test and isometric handgrip test, has been shown to induce activation of the HPA axis, in addition to autonomic responses. However, previous research has suggested that dysfunctional post-event processing may play a major role in neuroendocrine reactivity at initial as well as subsequent social stress exposure. In the present study, we investigated how the interplay of context (i.e. performance feedback) with state (i.e., self-esteem) as well as trait-like factors (i.e., ruminative tendencies) affects stress responses to repeated, short bouts of physical activity. On two sessions, 1 week apart, 53 participants (27 women) performed an isometric handgrip task for 3 min, during which they were exposed to social-evaluative threat. In addition, participants received fake feedback on their performance immediately after the task, labeling it as either ‘above’ (positive) or ‘below average’ (negative). In addition to neuroendocrine (cortisol), cardiovascular (heart rate, blood pressure) and subjective stress reactivity, performance-related and social dimensions of state self-esteem were assessed before and after stress induction. Substantial increases in cardiovascular parameters were found on both days, regardless of feedback condition. However, positive feedback led to significantly diminished neuroendocrine responses on day 1, whereas baseline cortisol on session 2 was significantly higher in the negative feedback group. Conversely, social self-esteem decreased after stress induction on both days only for participants who had received negative feedback. Changes in self-esteem reported on day 1 were associated with increased baseline cortisol at the second session, while interindividual differences in self-reported (trait) rumination were associated with cortisol reactivity at session 1. Taken together, the results suggest that effects of social evaluation during short periods of physical stress rely on post-event processing and might be counteracted by positive appraisal directly after stress exposure. Post-hoc framing (in terms of success vs. failure) may predict subsequent stress-related hormonal effects better than task demands per se, which should be considered as a potential moderator in future acute stress research, but might also be relevant to many practical applications in fields ranging from sports/performance to health psychology.

Cognitive-Perceptual-Affective-Motivational Dynamics During Incremental Workload Accounting for Exertion Tolerance.

Inquiry of the psychological states during the exercise experience failed to fully account for the role of motivation to adhere and the disposition of exertion tolerance (ET). The current study expands the scope of the integrated cognitive-perceptual-affective framework by measuring the motivation to sustain effort in two physical tasks and accounting for ET. Thirty male participants performed cycling and isometric handgrip tasks to assess the progression of the rating of perceived exertion, attentional focus, affective responses, and motivation to adhere, along with an incremental workload. The ET was determined by a handgrip task time to voluntary exhaustion. The findings indicated significant time effects and linear trends for perceived exertion, attentional focus, affect, and perceived arousal but not motivation to adhere during the handgrip and cycling tasks. The ET played a key role in the integrity of the model, particularly in perceptual, attentional, and affective responses. The intended model serves to stimulate new research into adaptation mechanisms.

Energy investment and motivation: The additive impact of task demand and reward value on exerted force in hand grip tasks

According to motivational intensity theory, individuals are motivated to conserve energy when pursuing goals. They should invest only the energy required for success and disengage if success is not important enough to justify the required energy. We tested this hypothesis in five experiments assessing exerted muscle force in isometric hand grip tasks as indicator of energy investment. Our results provided mixed evidence for motivational intensity theory. Corroborating its predictions, energy investment was a function of task demand. However, we did not find evidence for the predicted disengagement, and we observed that participants exerted in most conditions more force than required. Furthermore, the data could be better explained by a model that predicted an additive effect of task demand and success importance than by models drawing on motivational intensity theory’s predictions. These results illustrate the strong link between energy investment and task demand but challenge motivational intensity theory’s primacy of energy conservation.

The effect of mild whole-body cold stress on isometric force control during hand grip and key pinch tasks.

Prolonged exposure to cold can impair manual performance, which in turn can affect work task performance. We investigated whether mild whole-body cold stress would affect isometric force control during submaximal hand grip and key pinch tasks. Twelve male participants performed isometric hand grip and key pinch tasks at 10% and 30% of maximal voluntary contraction (MVC) for 30 and 10 s respectively, in cold (8 °C) and control (25 °C) conditions. Finger temperature decreased significantly by 18.7 ± 2.1 °C and continuous low-intensity shivering in the upper trunk increased significantly in intensity and duration during cold exposure. Rectal temperature decreased similarly for the 8 °C and 25 °C exposures. Force variability (FCv) was <2% for the hand grip tasks, and <3% for the key pinch tasks. No significant changes in FCv or force accuracy were found between the ambient temperatures. In conclusion, isometric force control during hand grip and key pinch tasks was maintained when participants experienced mild whole-body cold stress compared with when they were thermally comfortable.

HEART AUTONOMIC CONTROL DURING STATIC SUBMAXIMAL CONTRACTIONS: INFLUENCE OF TASK FEATURES

Background: Isometric exercise is important to cardiac rehabilitation, but understanding how different tasks can interfere with the Heart Rate Variability (HRV) still needs some clarification. Objective: To compare the Autonomic Nervous System (ANS) behavior during submaximal isometric tasks involving different muscle groups. Methods: Six healthy males ([Formula: see text] years old) performed two submaximal isometric tasks (30%) of knee extension and handgrip, sustained for 3[Formula: see text]min each, using visual feedback to maintain force levels. Successive RR intervals were recorded along the task, as well as for 5[Formula: see text]min before the task. Linear and nonlinear methods were used to obtain HRV parameters from successive RR intervals. Student [Formula: see text] test was used to compare the data with significant level set as [Formula: see text]. Results: Time domain parameters as well as the nonlinear parameters were significantly higher during the handgrip task. Conclusions: Submaximal isometric handgrip task is associated with a lower vagal withdrawal, when compared to submaximal isometric knee extension, suggesting that handgrip task promotes greater cardioprotection during exercise, while the isometric knee extension task could induce better adaptations to training.

Rate of force development to evaluate the neuromuscular fatigue and recovery after an intermittent isometric handgrip task with different blood flow restriction conditions

Abstract Aim: To investigate the neuromuscular fatigue and recovery after an intermittent isometric handgrip exercise (IIHE) executed until failure with different blood flow restriction (BFR) conditions (free flow, partial and total vascular restriction). Methods: Thirteen healthy men carried out an IIHE at 45% of maximum voluntary isometric force (MVIF) until failure with total restriction (TR), partial restriction (PR) or free flow (FF). The rate of force development (RFD) was extracted from the MIVF over the time intervals of 0-30, 0-50, 0-100, and 0-200ms and normalized by MVIF [relative RFD (RFDr)]. Results: The RFDr decreased significantly (p<0.01) after the IIHE in all BFR conditions and time intervals studied, remaining lower for five minutes. The medians of the RFDr in FF condition were significantly lower (p=0.01) at 30ms (1.56 %MVIF·s-1) and 50ms (1.70 %MVIF·s-1) when compared to TR at 30ms (2.34 %MVIF·s-1) and 50ms (2.63 %MVIF·s-1) in minute 1 post failure. Conclusions: These results show that, regardless of the blood flow restriction level, there is no RFD recovery five minutes after an exhaustive IIHE. When the task was executed with FF, the reduction of the RFD was greater when compared with the TR condition.

Intra-session and Inter-day Reliability of the Myon 320 Electromyography System During Sub-maximal Contractions.

Electromyography systems are widely used within the field of scientific and clinical practices. The reliability of these systems are paramount when conducting research. The reliability of Myon 320 Surface Electromyography System is yet to be determined. This study aims to determine the intra-session and inter-day reliability of the Myon 320 Surface Electromyography System. Muscle activity from fifteen participants was measured at the anterior deltoid muscle during a bilateral front raise exercise, the vastus lateralis muscle during a squat exercise and the extensor carpi radialis brevis (ECRB) muscle during an isometric handgrip task. Intra-session and inter-day reliability was calculated by intraclass correlation coefficient, standard error of measurement and coefficient of variation (CV). The normalized root mean squared (RMS) surface electromyographic signals produced good intra-session and inter-day testing intraclass correlation coefficient values (range: 0.63–0.97) together with low standard error of measurement (range: 1.49–2.32) and CV (range: 95% Confidence Interval = 0.36–12.71) measures for the dynamic-and-isometric contractions. The findings indicate that the Myon 320 Surface Electromyography System produces good to fair reliability when examining intra-session and inter-day reliability. Findings of the study provide evidence of the reliability of electromyography between trials which is essential during clinical testing.

Getting a Grip on the Handgrip Task: Handgrip Duration Correlates with Neuroticism But Not Conscientiousness.

Questions regarding the replicability of key findings in the self-regulation literature (e.g., ego-depletion effect) have led some to call for a more thorough evaluation of commonly used measures of self-control. The isometric handgrip task is one such measure. The current study examined correlates of handgrip persistence using data drawn from a larger randomized controlled trial. Handgrip persistence was measured both at baseline and following a physical stressor (cold pressor test). Correlations were examined between handgrip performance and personality traits theoretically closely linked with self-regulation: conscientiousness and neuroticism. Baseline handgrip performance was correlated with several measures drawn from the nomological network of self-regulation including measures of trait neuroticism, mindfulness, anxiety sensitivity, perceived stress, and positive affect, although not with trait conscientiousness. Baseline handgrip predicted aversiveness experienced during the physical stressor, while changes in handgrip performance tracked changes in implicit and explicit negative affect (i.e., affective reactivity). These associations were largely maintained when controlling for variables highly correlated with overall grip strength (i.e., gender, height, and weight), although correlations separated by gender suggest associations were primarily driven by female participants. Results support future research using the handgrip task.

High cardiorespiratory fitness in early to late middle age preserves the cortical circuitry associated with brain-heart integration during volitional exercise.

This study tested the hypothesis that high cardiorespiratory fitness (peak oxygen uptake) preserves the cortical circuitry associated with cardiac arousal during exercise in middle- to older-aged individuals. Observations of changes in heart rate (HR) and in cortical blood oxygenation level-dependent (BOLD) images were made in 52 healthy, active individuals (45-73 yr; 16 women, 36 men) across a range of fitness (26-66 ml·kg-1·min-1). Seven repeated bouts of isometric handgrip (IHG) at 40% maximal voluntary contraction force were performed with functional magnetic resonance imaging at 3 T, with each contraction lasting 20 s and separated by 40 s of rest. HR responses to IHG showed high variability across individuals. Linear regression revealed that cardiorespiratory fitness was not a strong predictor of the HR response (r2 = 0.09). In a region-of-interest analysis both the IHG task and the HR time course correlated with increased cortical activation in the bilateral insula and decreased activation relative to baseline in the anterior and posterior cingulate and medial prefrontal cortex (MPFC). t-Test results revealed greater deactivation at the MPFC with higher fitness levels beyond that of guideline-based activity. Therefore, whereas high cardiorespiratory fitness failed to affect absolute HR responses to IHG in this age range, a select effect was observed in cortical regions known to be associated with cardiovascular arousal.NEW & NOTEWORTHY Our first observation suggests that fitness does not strongly predict the heart rate (HR) response to a volitional handgrip task in middle- to older-aged adults. Second, the BOLD response associated with the handgrip task, and with the HR time course, was associated with response patterns in the cortical autonomic network. Finally, whereas high cardiorespiratory fitness failed to affect absolute HR responses to isometric handgrip in this age range, a select effect was observed in cortical regions known to be associated with cardiovascular arousal, beyond that achieved through healthy active living.

P106. Brain connectivity in a simple motor task characterized by dynamic causal modeling of EEG FMRI signal

Introduction Dynamic causal modeling (DCM) based on functional magnetic resonance imaging (FMRI) and magneto-/electroencephalographic (MEEG) data has increasingly extended the understanding of intrinsic brain network dynamics in a variety of functional systems (Friston et al., Curr Opin Neurobiol, 2013). In the motor system, several studies have used DCM to detect causal information flow from secondary to primary motor areas during simple movements and bimanual coordination (Grefkes et al., Neuroimage, 2008). There is also evidence for non-linear cross-frequency interactions among motor areas (Chen et al., J of Neuroscience, 2010; Herz et al., Neuroimage, 2012). As such, data based on MEEG and FMRI provide complementary and synergistic insights into the dynamics of motor networks due to the higher spatial resolution of brain activity by FMRI versus the frequency-resolved coupling revealed by MEEG. A study combining FMRI- and EEG-based DCM for induced responses (DCM-IR) using the same task in the same participants to directly compare network architectures deriving from BOLD response and spectral neuroelectric dynamics has not been conducted so far. Specifically, such an approach is of interest as both modalities share principal similarities in the formulation of the DCM. We hypothesized that DCM based on induced responses and the BOLD-signal would reveal a similar network architecture. Methods To test this, we measured 14 young healthy individuals during a simple isometric hand grip task using FMRI and EEG separately, set up a common model space of six equally plausible models and modeled the coupling parameters within a core motor network during the right hand grip. Results Bayesian Model Selection revealed strongest evidence for a fully connected model in DCM for FMRI and a sparsely connected model in DCM-IR, comparing the individual interregional coupling parameters revealed interesting similarities: First, both modalities showed a significant grip-related increase in facilitatory coupling from the left SMA onto the left M1. Second, the left PMv also exerted a positive coupling onto the left M1 with a significant result for DCM-IR and a trend of significance for DCM for fMRI. Frequency-resolved coupling showed that the information flow from SMA to M1 was a linear alpha to alpha interaction but also a nonlinear cross-frequency interaction between faster oscillations in SMA (18–25 Hz) and full range alpha to beta (9–22 Hz) in left M1. Coupling between PMv and M1 was found from upper alpha (10–13 Hz) to lower beta (14–22 Hz). Conclusion The strategy of informing EEG source space configurations with FMRI location priors, cross-validating basic connectivity maps and then looking at the details of frequency coding allows for a deeper insight into the motor network architecture in the human brain. These results thus undermine the importance of these functional connections and validate the methodological approach of DCM to explore network architecture. Furthermore, extending findings from previous studies showing a covariation of the BOLD-signal and alpha/beta band power (Ritter et al., Human Brain Mapping, 2009; Yuan et al., Neuroimage, 2010), we here present evidence that these two signals not only share similarities in local activation patterns but also in the connectivity domain.

Examination of contraction-induced muscle pain as a behavioral correlate of physical activity in women with and without fibromyalgia

Purpose: This study aimed to compare muscle pain intensity during a sustained isometric contraction in women with and without fibromyalgia (FM), and examine the association between muscle pain and self-reported levels of physical activity. Methods: Fourteen women with FM and 14 healthy women completed the study, where muscle pain ratings (MPRs) were obtained every 30 s during a 3 min isometric handgrip task at 25% maximal strength, and self-reported physical activity was quantified using the Baecke Physical Activity Questionnaire. Results: Women with FM were less physically active than healthy controls. During the isometric contraction, MPR progressively increased in both groups at a comparable rate, but women with FM generally reported a greater intensity of muscle pain than healthy controls. Among all women, average MPR scores were inversely associated with self-reported physical activity levels. Conclusions: Women with FM exhibit augmented muscle pain during isometric contractions and reduced physical activity than healthy controls. Furthermore, contraction-induced muscle pain is inversely associated with physical activity levels. These observations suggest that augmented muscle pain may serve as a behavioral correlate of reduced physical activity in women with FM.Implications for RehabilitationWomen with fibromyalgia experience a greater intensity of localized muscle pain in a contracting muscle compared to healthy women.The intensity of pain during muscle contraction is inversely associated with the amount of physical activity in women with and without fibromyalgia.Future studies should determine whether exercise adherence can be improved by considering the relationship between contraction-induced muscle pain and participation in routine physical activity.

Goal pursuit and energy conservation: energy investment increases with task demand but does not equal it

According to motivational intensity theory, energy investment in goal pursuit is determined by the motivation to avoid wasting energy. Two experiments tested this hypothesis by manipulating the difficulty of an isometric hand grip task across four levels in a between-persons (Study 1) and a within-persons (Study 2) design. Supporting motivational intensity theory’s prediction, the results showed that invested energy—indicated by exerted grip force—was a function of task difficulty: The higher the difficulty, the higher the energy investment. However, the data also indicated that participants invested considerably more energy than required, questioning the primacy of energy conservation.

Isometric handgrip (IHG) training‐induced reductions in resting blood pressure: reactivity to a 2‐minute handgrip task identifies responders and non‐responders in young normotensive individuals (LB661)

In people with hypertension, systolic blood pressure (SBP) reactivity to an isometric handgrip task (IHGT), but not a cold pressure task (CPT), is predictive of IHG training‐induced reductions in resting SBP. To investigate whether these findings could be extended to include young normotensives, resting BP and BP reactivity to an IHGT (2‐minute sustained contraction at 30% maximal voluntary contraction, MVC) and a CPT (2‐minute hand immersion in a cold water bath) were measured prior to and following 10 weeks of IHG training (4, 2‐minute IHG contractions at 30% MVC, using alternating hands, interspersed with 1‐minute rest periods, 3X/week) in 7 normotensive individuals (3 females, 4 males; age=25 ± 5.7 years). BP reactivity was derived by calculating the difference between peak stress BP and mean baseline resting BP. Significant training‐induced reductions in resting SBP (p&lt;0.001) were strongly correlated with pre‐training SBP reactivity to the IHGT (r=‐0.8, p=0.03), but not the CPT (r= 0.2, p=0.6). These preliminary findings suggest that SBP reactivity to a short and simple handgrip task can be used as a predictive tool to identify who will respond best to IHG training. It might be possible to further explore how the IHG training stimulus could be optimized in non‐responders, to ensure that they too, experience reductions in resting BP.Grant Funding Source: Supported by University of Windsor Kinesiology seed grant

Evidence for a medial prefrontal cortex–hippocampal axis associated with heart rate control in conscious humans

Cardiovascular arousal correlates to activity within the medial prefrontal cortex (MPFC). Additional evidence provides anatomical and functional links between the MPFC and hippocampus (HC). This study tested the hypothesis that the MPFC and HC form a sub-network associated with rapid heart rate (HR) responses to volitional effort. Primary analyses were performed on 29 individuals (18 males) ranging from 21 to 80 years of age, who produced a HR response >3bpm to an isometric handgrip (IHG) task. HR and cortical activity were recorded using functional magnetic resonance imaging with blood oxygen level-dependent contrast. The average change in HR from baseline was 6bpm ±2. Activity in the MPFC and left HC was reduced relative to baseline in all subjects when correlated with the HR time course. Measures of connectivity demonstrated that the MPFC engaged in significantly stronger functional connectivity to the left HC during a 40% IHG task. Effective connectivity revealed a directionality of influence from the MPFC to the left HC. A second group (n=15) of individuals without a HR response (~1bpm) to IHG were studied post-hoc and these individuals showed no deactivation in either the MPFC or left HC. These results suggest the presence of a MPFC–HC axis that participates in the neurally-mediated HR response to exercise.

How can reward contribute to efficient self-control? Reinforcement of task-defined responses diminishes ego-depletion

We examined whether reinforcement learning of habitual actions diminishes ego depletion after a cognitive control task. Participants performed the Stroop task after a card selection task, in which one group was reinforced to respond to colors in the Stroop task (Stroop-color group) while another group was reinforced to respond to colors not in the Stroop task (non-Stroop-color group). We measured ego depletion in terms of decrement in endurance on an isometric handgrip task after the Stroop task. The Stroop-color group exhibited less decrease in their isometric handgrip endurance compared to the non-Stroop-color group. These results suggest that the former needed less effort for cognitive control during conflict processing, as reinforcement learning make task-defined response habitual. This finding provides a new perspective on the role of reward in cognitive control.

Neural Correlates of Physical and Mental Fatigue

The purpose of this study was to determine the neural and muscular correlates of physical and mental fatigue. Twelve young and healthy participants (balanced by gender) performed three fatiguing conditions: 1) isometric handgrip task (HG) at 30% maximum voluntary contraction (MVC); 2) mental arithmetic (MA); and 3) combined handgrip and mental arithmetic (HG+MA). Prefrontal cortex activation, muscle activity, and task performance measures (force fluctuations and mental performance) were obtained continuously during the fatiguing conditions. Results indicated no significant difference in muscle activity and force fluctuations between the HG and HG+MA condition. Compared to the HG condition, an initial increase in the prefrontal cortex activation was observed during the HG+MA condition, with a subsequent decrease at exhaustion. Cortical activation during the MA condition was significantly lower than the other conditions across the entire duration of the fatiguing trial. Participants performed poorly with mental arithmetic during the HG+MA condition compared to the MA condition. The results suggest that the dynamic changes in the prefrontal cortex during the combined HG+MA condition, compared to the HG or MA condition, occur due to the interaction of physical and mental fatigue, which may have important implications for physical and cognitive performance.

Task difficulty effects on exerted force in an isometric hand-grip task: Mixed evidence for energy conservation

Task difficulty effects on exerted force in an isometric hand-grip task: Mixed evidence for energy conservation