1,721,058 research outputs found
The limit to exercise tolerance in humans: mind over muscle?
No full textIn exercise physiology, it has been traditionally assumed that high-intensity aerobic exercise stops at the point commonly called exhaustion because fatigued subjects are no longer able to generate the power output required by the task despite their maximal voluntary effort. We tested the validity of this assumption by measuring maximal voluntary cycling power before (mean +/- SD, 1,075 +/- 214 W) and immediately after (731 +/- 206 W) (P < 0.001) exhaustive cycling exercise at 242 +/- 24 W (80% of peak aerobic power measured during a preliminary incremental exercise test) in ten fit male human subjects. Perceived exertion during exhaustive cycling exercise was strongly correlated (r = -0.82, P = 0.003) with time to exhaustion (10.5 +/- 2.1 min). These results challenge the long-standing assumption that muscle fatigue causes exhaustion during high-intensity aerobic exercise, and suggest that exercise tolerance in highly motivated subjects is ultimately limited by perception of effort
Effects of isolated locomotor muscle fatigue on pacing and time trial performance
No full textPurpose 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. Keywords: Perception of effort, Cycling exercise, Eccentric fatigue, Pacing strategy, Exercise tolerance, Electromyograph
Exertional Fatigue in Patients With CKD
No full textBackground: Fatigue is one of the most prevalent symptoms in chronic kidney disease (CKD). However, fatigue mechanisms are poorly understood due in part to nonspecific definitions. This study investigates exertional fatigue during simulated activities of daily living, focusing on oxygen delivery and utilization. Study Design: "Explanatory" matched-cohort study. Participants & Setting: 13 patients with CKD (stages 3b-4; mean age, 62 ± 13 [SD] years) and 13 healthy controls, mean matched for age, height, body mass and composition, and physical activity level. Participants completed an incremental cycle ergometer test to simulate energy expenditure of typical activities of daily living. Factor: 4 exercise intensities: 1, 1.8, 2.4, and 3.1 metabolic equivalent tasks (METs). Outcomes: The primary outcome was exertional fatigue by rating of perceived exertion (RPE) on a 6-20 scale. Measurements: Other multidimensional measures of fatigue: UK Short Form Health Survey 36 (UK SF-36) Vitality and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) subscales. Physiologic measures of the oxygen transport and utilization chain (expired gas analysis, cardiac output, and arterial oxygen content) and blood lactate. Results: RPE was increased in patients compared with controls at 2.4 (10.5 [ie, light] ± 2.7 vs 8.7 [very light] ± 1.7 units) and 3.1 (12.5 [somewhat hard] ± 2.6 vs 10.2 [light] ± 1.7 units) METs (interaction P = 0.03), which was consistent with higher chronic fatigue in patients by both the UK SF-36 Vitality (P = 0.01) and FACIT-Fatigue (P = 0.004) subscales. Arterial oxygen content was decreased in patients (P = 0.001), but cardiac output and oxygen extraction ratio were unchanged, decreasing oxygen delivery (P = 0.04). Respiratory exchange ratio (P = 0.004) and blood lactate production (P = 0.002) were increased. Limitations: Those inherent to a matched-cohort study. Conclusions: Using a novel application of the outcome measure RPE, patients with non-dialysis-dependent CKD reported considerable exertional fatigue during simulated activities of daily living. Poor compensation for mild anemia contributed to this symptom. In addition to anemia, the entire oxygen transport chain needs to be targeted to treat fatigue in patients with CKD. © 2012 National Kidney Foundation, Inc
Facial electromyography as a measure of effort during physical and mental tasks
No full textFacial 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. © 2012 by Nova Science Publishers, Inc. All rights reserved
Frowning muscle activity and perception of effort during constant-workload cycling
No full textWe 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 ± 3% peak power output (Ppeak)], or the severe-intensity (80 ± 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. © 2011 Springer-Verlag
Cortical substrates of the effects of caffeine and time-on-task on perception of effort
No full textCaffeine intake results in a decrease in perception of effort, but the cortical substrates of this perceptual effect of caffeine are unknown. The aim of this randomized counterbalanced double-blind crossover study was to investigate the effect of caffeine on the motor-related cortical potential (MRCP) and its relationship with rating of perceived effort (RPE). We also investigated whether MRCP is associated with the increase in RPE occurring over time during submaximal exercise. Twelve healthy female volunteers performed 100 intermittent isometric knee extensions at 61 ± 5% of their maximal torque 1.5 h after either caffeine (6 mg/kg) or placebo ingestion, while RPE, vastus lateralis electromyogram (EMG), and MRCP were recorded. RPE and MRCP amplitude at the vertex during the first contraction epoch (0–1 s) were significantly lower after caffeine ingestion compared with placebo (P < 0.05) and were significantly higher during the second half of the submaximal intermittent isometric knee-extension protocol compared with the first half (P < 0.05). No significant effects of caffeine and time-on-task were found for EMG amplitude and submaximal force output variables. The covariation between MRCP and RPE across both caffeine and time-on-task (r10 = ?0.335, P < 0.05) provides evidence in favor of the theory that perception of effort arises from neurocognitive processing of corollary discharges from premotor and motor areas of the cortex. Caffeine seems to reduce perception of effort through a reduction in the activity of cortical premotor and motor areas necessary to produce a submaximal force, and time-on-task has the opposite effect
Effect of a Mediterranean type diet on inflammatory and cartilage degradation biomarkers in patients with osteoarthritis
Full text linkObjectives: To investigate the effects of a Mediterranean type diet on patients with osteoarthritis (OA). Participants: Ninety-nine volunteers with OA (aged 31 - 90 years) completed the study (83% female). Setting: Southeast of England, UK. Design: Participants were randomly allocated to the dietary intervention (DIET, n = 50) or control (CON, n = 49). The DIET group were asked to follow a Mediterranean type diet for 16 weeks whereas the CON group were asked to follow their normal diet. Measurements: All participants completed an Arthritis Impact Measurement Scale (AIMS2) pre-, mid- and post- study period. A subset of participants attended a clinic at the start and end of the study for assessment of joint range of motion, ROM (DIET = 33, CON = 28), and to provide blood samples (DIET = 29, CON = 25) for biomarker analysis (including serum cartilage oligomeric matrix protein (sCOMP) (a marker of cartilage degradation) and a panel of other relevant biomarkers including pro- and anti-inflammatory cytokines). Results: There were no differences between groups in the response of any AIMS2 components and most biomarkers (p > 0.05), except the pro-inflammatory cytokine IL-1?, which decreased in the DIET group (~47%, p = 0.010). sCOMP decreased in the DIET group by 1 U/L (~8%, p = 0.014). There was a significant improvement in knee flexion and hip rotation ROM in the DIET group (p < 0.05). Conclusions: The average reduction in sCOMP in the DIET group (1 U/L) represents a meaningful change, but the longer term effects require further study
Do we really need a central governor to explain brain regulation of exercise performance?
No full textIn this paper two different models of brain regulation of exercise performance are critically compared: the central governor model proposed by Noakes and colleagues, and an alternative psycholobiological model based on motivational intensity theory. © Springer-Verlag 2008
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