Effects of isolated locomotor muscle fatigue on pacing and time trial performance

Purpose: Locomotor muscle fatigue impairs exercise performance during time to exhaustion tests. However, its effect on self-regulation of power output (pacing) is unknown. The primary aim of this study was to investigate the effects of locomotor muscle fatigue on pacing and time trial performance. Methods: Ten healthy recreationally active men completed a 15-min time trial on a cycle ergometer 30 min after undergoing an eccentric fatiguing protocol designed to induce a substantial strength loss in the knee extensor muscles without inducing significant metabolic stress. This fatigue condition was compared with a control condition, using a randomly counterbalanced AB/BA crossover design. Results: Total work completed during the 15-min cycling time trial was significantly reduced by 4.8 % in the fatigue condition compared with the control condition. This was caused by a significant reduction in power output. Rating of perceived exertion was significantly higher in the fatigue condition compared with the control condition only during the first 3 min of the time trial. Heart rate and vastus lateralis integrated electromyogram were not significantly different between the two conditions. Conclusion: The results show that participants with fatigued locomotor muscles reduce their pace but do not change their pacing strategy. As a result, there was a significant reduction in time trial performance. As predicted by the psychobiological model of exercise performance, a slower pace may be a behavioral response to compensate for the significant increase in perception of effort induced by locomotor muscle fatigue. \ua9 2013 Springer-Verlag Berlin Heidelberg

Frowning muscle activity and perception of effort during constant-workload cycling

We have recently demonstrated that electromyogram (EMG) amplitude of the frowning muscles correlates with perception of effort during leg-extension exercise. However, during aerobic exercise the relationship between facial EMG and perception of effort has never been investigated. The aim of the present study was to investigate whether facial EMG reflects perception of effort also during constant-workload cycling. We investigated the effects of exercise duration and exercise intensity on facial EMG of the corrugator supercilii muscles, rating of perceived effort, heart rate, and blood lactate concentration. Twenty recreationally active male and female volunteers performed a constant-workload time to exhaustion test on a cycle ergometer. Participants were randomly allocated to the heavy-intensity [63 \ub1 3% peak power output (Ppeak)], or the severe-intensity (80 \ub1 5% Ppeak) group. The results show that facial EMG can differentiatebetween two exercise intensities during constant-workload cycling. The effects of exercise duration are inconclusive. Facial EMG increased over time in the severe-intensity group, but not in the heavy-intensity group. Future studies testing a wider range of exercise intensities are required to establish a correlation between facial EMG and exercise intensity during aerobic exercise, and further investigations are needed to establish why there is a discrepancy between facial EMG and perception of effort during lower-intensity aerobic exercise. \ua9 2011 Springer-Verlag

Facial electromyography as a measure of effort during physical and mental tasks

Facial electromyography (EMG) is a psychophysiological technique that has been used in the study of emotions. However, there is also some research employing this technique to study the facial expression of effort. Using facial EMG, it has been shown that facial muscle activity is related to effort during mental tasks. It was found that facialEMG amplitude increases with task difficulty and with time on task during a two-choice serial reaction task. However, a relationship between facial EMG and effort has not always been found during mental tasks. Recently, we have started to employ facial EMG to study effort during physical tasks. We have found, by manipulating exercise intensity and muscle fatigue during a leg-extension task, that facial EMG correlates positively with effort during weightlifting exercise. We have also demonstrated that facial EMG reflects exercise intensity during constant-workload cycling to exhaustion. Interestingly, we found that facial EMG increases significantly with exercise duration during high-intensity cycling, but not during moderate-intensity cycling. A plausible neurobiological mechanism that might explain the relationship between facial EMG and effort is motor overflow. Motor overflow refers to involuntary muscle contractions that may accompany voluntary muscle contractions. This is thought to be caused by spreading of excitation in the motor cortex, because of increased excitability. In healthy adults, motor overflow is usually seen only during tasks that require considerable (physical) effort. This might explain the difference between high-intensity exercise, where the relationship between facial EMG and effort is strong and consistent, and moderate-intensity exercise or mental tasks, where a relationship between facial EMG and effort has not consistently been found. Facial EMG may be used in the future alongside rating of perceived effort as an extra, more objective measure of effort. This might have additional value in groups of people who have difficulties with rating effort, or when it is hard to obtain ratings, for example during maximal efforts of a few seconds and very high-intensity exercise of short duration. An additional benefit of facial EMG as a measure of effort is that it is a continuous measure. \ua9 2012 by Nova Science Publishers, Inc. All rights reserved

Central nervous system involvement in the autonomic responses to psychological distress

Psychological distress can trigger acute coronary syndromes and sudden cardiac death in vulnerable patients. The primary pathophysiological mechanism that plays a role in stress-induced cardiac events involves the autonomic nervous system, particularly disproportional sympathetic activation and parasympathetic withdrawal. This article describes the relation between psychological distress and autonomic nervous system function, with a focus on subsequent adverse cardiovascular outcomes. The role of the central nervous system in these associations is addressed, and a systematic review is presented of studies examining the association between stress-induced central nervous system responses measured by neuroimaging techniques and autonomic nervous system activation. Results of the systematic review indicate that the primary brain areas involved in the autonomic component of the brain-heart association are the insula, medial prefrontal cortex, and cerebellum (based on 121 participants across three studies that fitted the inclusion criteria). Other areas involved in stress-induced autonomic modulation are the (anterior) cingulate cortex, parietal cortex, somatomotor cortex/precentral gyrus, and temporal cortex. The interaction between central and autonomic nervous system responses may have implications for further investigations of the brain-heart associations and mechanisms by which acute and chronic psychological distress increase the risk of myocardial infarction, cardiac arrhythmias, and sudden cardiac death. Keywords: Autonomic nervous system, Mental stress, Central autonomic network, Heart rate variability, Functional brain imagin

Fatigue in Brain Tumor Patients: The Role of Tumor Location and Autonomic Modulation

Research protocol Fatigue in Brain Tumor Patients (Short Title in Dutch: Vermoeidheid bij Patiënten met een Hersentumor). Final version, 31 July 2012

Fatigue in Brain Tumor Patients: The Role of Tumor Location and Autonomic Modulation

Research protocol Fatigue in Brain Tumor Patients (Short Title in Dutch: Vermoeidheid bij Patiënten met een Hersentumor). Final version, 31 July 2012

Fatigue after neurosurgery in patients with a brain tumor: the role of autonomic dysregulation and disturbed sleep.

Background  Fatigue is prevalent in patients with a brain tumor and high levels of fatigue persist after neurosurgical tumor resection. The underlying mechanisms are insufficiently understood and this study examines the role of autonomic nervous system dysregulation and objective sleep characteristics in fatigue among post-surgical patients.  Methods Patients undergoing craniotomy (N = 52; age 52.1 +/- 15.0 years; 44% women) were evaluated at 3 months after surgery (median = 86 days). Fatigue was measured using the Multidimensional Fatigue Inventory. Autonomic nervous system indices were based on 24-h heart rate variability (HRV) analysis. Sleep parameters were measured using actigraphy: total sleep duration, efficiency, onset latency and wake after sleep onset (WASO). Data analyses of this cross-sectional study included correlation and multiple regression analysis.  Results  Fatigue scores were significantly elevated in tumor resection patients compared to healthy reference norms (p's < 0.05) with no differences between patients with glioma (N = 32) versus meningioma (N = 20). Associations between HRV indices and fatigue were non-significant (r values 0.25). Sleep duration was associated with physical fatigue (r = 0.35, p = 0.02), whereas WASO was associated with mental fatigue levels (r = 0.40, p = 0.006). Disturbed sleep measures were associated with HRV indices of reduced parasympathetic nervous system activity in glioma patients but not in meningioma patients.  Conclusions  Multiple nocturnal awakenings may result in mental fatigue and longer sleep time was associated with physical fatigue, which may reflect compensatory sleep patterns. Future intervention studies addressing sleep quality may be beneficial in treating fatigue in patients following neurosurgery for tumor resection