Helma M. de Morree

Locomotor muscle fatigue increases cardiorespiratory responses and reduces performance during intense cycling exercise independently from metabolic stress

Locomotor muscle fatigue, defined as an exercise-induced reduction in maximal voluntary force, occurs during prolonged exercise, but its effects on cardiorespiratory responses and exercise performance are unknown. In this investigation, a significant reduction in locomotor muscle force (-18%, P < 0.05) was isolated from the metabolic stress usually associated with fatiguing exercise using a 100-drop-jumps protocol consisting of one jump every 20 s from a 40-cm-high platform. The effect of this treatment on time to exhaustion during high-intensity constant-power cycling was measured in study 1 (n = 10). In study 2 (n = 14), test duration (871 +/- 280 s) was matched between fatigue and control condition (rest). In study 1, locomotor muscle fatigue caused a significant curtailment in time to exhaustion (636 +/- 278 s) compared with control (750 +/- 281 s) (P = 0.003) and increased cardiac output. Breathing frequency was significantly higher in the fatigue condition in both studies despite similar oxygen consumption and blood lactate accumulation. In study 2, high-intensity cycling did not induce further fatigue to eccentrically-fatigued locomotor muscles. In both studies, there was a significant increase in heart rate in the fatigue condition, and perceived exertion was significantly increased in study 2 compared with control. These results suggest that locomotor muscle fatigue has a significant influence on cardiorespiratory responses and exercise performance during high-intensity cycling independently from metabolic stress. These effects seem to be mediated by the increased central motor command and perception of effort required to exercise with weaker locomotor muscles.

Perception of effort reflects central motor command during movement execution

It is thought that perception of effort during physical tasks is the conscious awareness of the central motor command sent to the active muscles. The aim of this study was to directly test this hypothesis by experimentally varying perception of effort and measuring movement-related cortical potential (MRCP). Sixteen healthy, recreationally active men made unilateral dynamic elbow flexions to lift a light (20% one repetition maximum, 1RM) and a heavier (35% 1RM) weight with a fatigued arm and a nonfatigued arm while rating of perceived effort (RPE), biceps brachii electromyogram (EMG), and MRCP were recorded. RPE, EMG amplitude, and MRCP amplitude at Cz during weight raising increased with weight and with muscle fatigue. There was a significant correlation between RPE and MRCP amplitude at the vertex during the weight raising epoch. This study provides direct neurophysiological evidence that perception of effort correlates with central motor command during movement execution.

Talking yourself out of exhaustion: the effects of self-talk on endurance performance

PURPOSE The psychobiological model of endurance performance proposes that the perception of effort is the ultimate determinant of endurance performance. Therefore, any physiological or psychological factor affecting the perception of effort will affect endurance performance. Accordingly, this novel study investigated the effects of a frequently used psychological strategy, motivational self-talk (ST), on RPE and endurance performance. METHODS In a randomized between-group pretest-posttest design, 24 participants (mean ± SD age = 24.6 ± 7.5 yr, VO2max = 52.3 ± 8.7 mL·kg·min) performed two constant-load (80% peak power output) cycling time-to-exhaustion (TTE) tests, punctuated by a 2-wk ST intervention or a control phase. RESULTS A group (ST vs Control) × test (pretest vs posttest) mixed-model ANOVA revealed that ST significantly enhanced TTE test from pretest to posttest (637 ± 210 vs 750 ± 295 s, P < 0.05) with no change in the control group (486 ± 157 vs 474 ± 169 s). Moreover, a group × test × isotime (0%, 50%, and 100%) mixed-model ANOVA revealed a significant interaction for RPE, with follow-up tests showing that motivational self-talk significantly reduced RPE at 50% isotime (7.3 ± 0.6 vs 6.4 ± 0.8, P < 0.05), with no significant difference in the control group (6.9 ± 1.9 vs 7.0 ± 1.7). CONCLUSIONS This study is the first to demonstrate that ST significantly reduces RPE and enhances endurance performance. The findings support the psychobiological model of endurance performance and illustrate that psychobiological interventions designed to specifically target favorable changes in the perception of effort are beneficial to endurance performance. Consequently, this psychobiological model offers an important and novel perspective for future research investigations.

The face of effort: frowning muscle activity reflects effort during a physical task.

It is a common observation that exertion of effort is associated with a specific facial expression. However, this facial expression has never been quantified during physical tasks and its relationship with effort is unknown. The aims of the present study were to measure frowning muscle activity during a physical task with electromyography (EMG) and to investigate the relationship between facial EMG and effort. Effort was experimentally manipulated by increasing task difficulty and inducing muscle weakness. Twenty men performed leg extensions with four relative workloads. The fatigue group (n=10) repeated the leg extensions after fatiguing eccentric exercise, and the control group repeated just the leg extensions. Facial EMG amplitude, ratings of perceived effort (RPE), and leg EMG amplitude increased significantly with increasing task difficulty and with muscle fatigue. Facial EMG, RPE, and leg EMG all correlated significantly. The results suggest that frowning muscle activity reflects effort during physical tasks.

Cortical substrates of the effects of caffeine and time-on-task on perception of effort

Caffeine 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.

Estimation of Maximal Oxygen Uptake via Submaximal Exercise Testing in Sports, Clinical, and Home Settings

Assessment of the functional capacity of the cardiovascular system is essential in sports medicine. For athletes, the maximal oxygen uptake

Comparison between electrocardiogram- and photoplethysmogram-derived features for atrial fibrillation detection in free-living conditions

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High-intensity exercise and carbohydrate-reduced energy-restricted diet in obese individuals

(V·O2max) provides valuable information about their aerobic power. In the clinical setting, the