Near-InfraRed Spectroscopy Provides a Reproducible Estimate of Muscle Aerobic Capacity, but Not Whole-Body Aerobic Power.

Near-infrared spectroscopy (NIRS) during repeated limb occlusions is a noninvasive tool for assessing muscle oxidative capacity. However, the method's reliability and validity remain under investigation. This study aimed to determine the reliability of the NIRS-derived mitochondrial power of the musculus vastus lateralis and its correlation with whole-body (cycling) aerobic power (V̇O2 peak). Eleven healthy active men (28 ± 10 y) twice (2 days apart) underwent repeated arterial occlusions to induce changes in muscle oxygen delivery after 15 s of electrical muscle stimulation. The muscle oxygen consumption (mV̇O2) recovery time and rate (k) constants were calculated from the NIRS O2Hb signal. We assessed the reliability (coefficient of variation and intraclass coefficient of correlation [ICC]) and equivalency (t-test) between visits. The results showed high reproducibility for the mV̇O2 recovery time constant (ICC = 0.859) and moderate reproducibility for the k value (ICC = 0.674), with no significant differences between visits (p > 0.05). NIRS-derived k did not correlate with the V̇O2 peak relative to body mass (r = 0.441, p = 0.17) or the absolute V̇O2 peak (r = 0.366, p = 0.26). In conclusion, NIRS provides a reproducible estimate of muscle mitochondrial power, which, however, was not correlated with whole-body aerobic capacity in the current study, suggesting that even if somewhat overlapping, not the same set of factors underpin these distinct indices of aerobic capacity at the different (peripheral and whole-body systemic) levels.

Regular short-duration breaks do not prevent mental fatigue and decline in cognitive efficiency in healthy young men during an office-like simulated mental working day: An EEG study.

Employees in Europe work on average 7.2 h per day. Prolonged periods of uninterrupted cognitive activity during the working day can cause changes in motivation, mental fatigue, and deterioration in cognitive function. In this exploratory study, we aimed to determine the effectiveness of taking 10-min breaks for light exercise every 50 min in preventing these negative effects during a simulated 7-h office-like computer work. Eighteen healthy young adult men (aged 26 ± 3 years) who did not work in an office participated. The effects of 7 h of office-like work with 10-min breaks every 50 min on central nervous system activity, cognitive function, mood, and motivation were investigated and compared with those measured on a control day without work. Our study found that engaging in 7 h of mental work similar to that found in an office environment, with 10-min breaks every 50 min, can negatively impact cognitive efficiency, suppress brain neural network activity, and cause mental fatigue. These effects do not fully recover after a 4.5-h rest. Additionally, taking short breaks during the workday does not prevent mental exhaustion or impairments in cognitive function. These findings should be considered when discussing strategies to prevent mental exhaustion caused by mental work.

High-volume intermittent maximal intensity isometric exercise caused great stress, although central motor fatigue did not occur.

To establish whether very high-volume, high-intensity isometric exercise causes stress to the body and how it affects peripheral and central fatigue. Nineteen physically active healthy male subjects (21.2 ± 1.7 years; height - 1.82 ± 0.41 m, body weight - 79.9 ± 4.5 kg; body mass index - 24.3 ± 2.1 kg/m2) volunteered to participate in this study. They participated in two experiments 3-5 days apart. Each experiment comprised six series of 60-s maximum voluntary contraction (MVC) force (knee extension) achieved as rapidly as possible. This very high-volume, high-intensity exercise (HVHIE) was performed at different quadriceps muscle lengths: short (SL) and long (LL). The MVC and the electrically stimulated contractile properties of the muscle were measured prior to HVHIE, immediately after and 3 min after each series, and at 3, 10, and 30 min after the end of HVHIE. We found that HVHIE caused high levels of stress (cortisol levels approximately doubled, heart rate and the root mean square successive difference of interval (RMSSD) decreased by about 75%); lactate increased to 8-11 mmol/L, voluntary and 100 Hz stimulation-induced force (recorded immediately after HVHIE) decreased by 55% at LL and 40% at SL. However, the central activation ratio during MVC did not change after either exercise. Isometric HVHIE performed using one leg caused high levels of stress (RMSSD decreased, cortisol increased after HVHIE equally at SL and LL; La increased more while exercising at LL) and the voluntary and electrostimulation-induced muscle force significantly decreased, but muscle central activation during MVC did not decrease.

Exposure to total 36-hr sleep deprivation reduces physiological and psychological thermal strain to whole-body uncompensable passive heat stress in young adult men.

Total sleep deprivation (TSD) is associated with endothelial dysfunction and a consequent decrease in vascular reactivity and increase in peripheral vascular resistance. These effectors compromise the body's ability to thermoregulate in hot and cold stress conditions. We investigated heat-unacclimated young adult men (26 ± 2 years) to determine whether 36 hr of TSD compared to an 8 or 4-hr sleep condition, would suppress the responses of the autonomic system (body rectal temperature [Tre ], heart rate [HR], root mean square of successive interbeat intervals, physiological strain, blood pressure [BP], circulating blood catecholamines, sweating rate and subjective sensations) to whole-body uncompensable passive heat stress in traditional Finnish sauna heat (Tair  = 80-90°C, rh = 30%). Sauna bathing that induced whole-body hyperthermia had a residual effect on reducing BP in the 8-hr and 4-hr sleep per night conditions according to BP measurements. By contrast, 36 hr of total wakefulness led to an increase in BP. These observed sleep deprivation-dependent differences in BP modifications were not accompanied by changes in the blood plasma epinephrine and norepinephrine concentrations. However, during sauna bathing, an increase in BP following 36 hr of TSD was accompanied by significant decreases in body Tre , HR and physiological strain, together with a diminished sweating rate, enhanced vagus-mediated autonomic control of HR variability, and improved thermal perception by the subjects. Our results suggest the impaired ability of the body to accumulate external heat in the body's core under uncompensable passive heat conditions following 36 hr of TSD, because of the TSD-attenuated autonomic system response to acute heat stress.

Effects of two nights of sleep deprivation on executive function and central and peripheral fatigue during maximal voluntary contraction lasting 60s.

PURPOSEː: The current study aimed at assessing the effect of a trial of two nights of sleep deprivation (SDT) on mood, sleepiness, motivation and cognitive and motor performance. METHODSː: Thirty-six healthy young and physically active adult men (17 in the control group and 19 in the SDT group) completed a 48-h control or 48-h SDT. For the SDT, participants did not sleep for 48 h. Executive function (attention and inhibitory control) in the Go/No-Go and Stroop tests, mood, sleepiness, motivation, heart rate variability (HRV), motor performance in a hand grip strength test, and 60-s maximal isometric contraction (MVC-60 s) of knee extension were evaluated at 9-11 am on consecutive days 1, 2, and 3. RESULTS: One night of sleep deprivation increased sleepiness, decreased mood, motivation and motor endurance but did not affect executive function (as measured in the Stroop and Go/No-Go tests), the MVC for hand and leg knee extensor muscles, and peripheral motor fatigue in the leg MVC-60 s task. However, the central activation ratio (CAR) decreased significantly during the MVC-60 s. The SDT significantly contributed to the decrease in these functions. That is, the SDT reduced executive function (increased reaction time during Go/No-Go test), MVC of knee extension, and the CAR before and after the MVC-60 s. By contrast, the SDT did not increase CAR immediately after the MVC-60 s and did not decrease the rate of torque development (RTD). CONCLUSIONSː: The SDT significantly impaired mood, motivation and increased sleepiness and HRV, reduced MVC of knee extensor muscles (but not RTD) and motor performance during the MVC-60 s and worsened executive function (attention and inhibitory control) only during the Go/No-Go task. However, the SDT did not reduce hand grip strength and CAR immediately after the MVC-60 s of knee extensor muscles.

Effect of knee extensors muscles fatigue on bilateral force accuracy, variability, and coordination.

The aim of this study was to test the effect of fatigue of the knee extensors muscles on bilateral force control accuracy, variability, and coordination in the presence and absence of visual feedback. Twenty-two young physically active subjects (18 males, 4 females) were divided into two groups and performed 210 submaximal sustained bilateral isometric contractions of knee extensors muscles with and without visual feedback. One group performed a symmetrical task-both legs were set at identical positions (60° knee flexion)-while the other group performed an asymmetrical task (60° and 30° knee flexion). We used the framework of the uncontrolled manifold hypothesis to quantify two variance components: one of them did not change total force (VUCM), while the other did (VORT). Performance of bilateral isometric contractions reduced voluntary and electrically induced force without changes in bilateral force control variability and accuracy. Bilateral force production stability and accuracy were higher in both tasks with visual feedback. Synergistic (anti-phase) structure of force control between the lower limbs occurred and the values of synergy index were higher only during the performance of the asymmetrical task with visual feedback. In addition, greater bilateral force control accuracy was observed during the performance of the asymmetrical task (with and without visual feedback), despite no differences in within-trial variability of both tasks.

"Two sides of the same coin": constant motor learning speeds up, whereas variable motor learning stabilizes, speed-accuracy movements.

PURPOSE: The aim of this study was to determine the time course of the trade-off between speed and accuracy, intraindividual variability, and movement transfer and retention (4 weeks after learning) of speed-accuracy tasks. METHODS: The participants in this study were healthy adults randomly divided into three groups (control versus constant versus variable). They were aged 19-24 years, and 30 (15 men and 15 women) were in each group. Participants had to perform various tasks with the right dominant hand: (a) simple reaction test; (b) maximal velocity measurement; and (c) a speed-accuracy task. RESULTS: During constant and variable learning, the trade-off in a speed-accuracy task in specific situations shifted toward improved motor planning and motor execution speed, and to reduced intraindividual variability. However, during variable learning, the maximal velocity and variability of motor planning time did not change. Constant learning effectively transferred into variable tasks in terms of reaction time, average velocity and maximal velocity, and these effects were greater than those associated with variable learning. However, the effects of constant learning did not transfer fully into the performance variability of variable movements. Variable learning effectively transferred into constant tasks for the coefficient of variation of the path of movement, average velocity, maximal velocity and reaction time. The retention effect depended neither on learning nor task specificity (constant versus variable tasks). CONCLUSION: Constant learning speeds up but does not stabilize speed-accuracy movements in variable tasks; whereas, variable learning stabilizes but does not speed up speed-accuracy movements in constant tasks.

Accelerated muscle contractility and decreased muscle steadiness following sauna recovery do not induce greater neuromuscular fatigability during sustained submaximal contractions.

Acute whole-body hyperthermia (WBH) increases blood markers concentration of stress, impairs motor drive to exercising muscles, and decreases resistance to neuromuscular fatigability. The functional natural residual consequences of WBH on neuromuscular functions remain unclear. We aimed to investigate the effects of residual WBH on voluntary and electrically induced ankle plantar flexor contractility properties, motor drive transmission (reflexes), muscle torque steadiness, resistance to neuromuscular fatigability, and markers of stress as the body temperature recovers naturally to normothermia. WBH was induced by Finnish sauna bathing in 16 apparently healthy young (24 ±â€¯4 years) adult men. Motor performance was monitored before and 2 h after the sauna, and immediately after submaximal exercise (120 s at 50% of maximal voluntary contraction). Markers of stress were monitored before and 2 h after the sauna. Finnish sauna exposure induced moderate to severe WBH (rectal temperature, 38.5-39.6 °C). At 2 h after the sauna, rectal temperature had recovered to the preheating level (preheating 37.11 ±â€¯0.33 °C versus postheating 37.00 ±â€¯0.29 °C, p > .05). Post-sauna recovery was accompanied by slowed salivary free cortisol diurnal kinetics, whereas noradrenaline, dopamine, and serotonin did not persist into the 2 h recovery after the sauna. Although recovery to normothermia after a sauna led to a greater acceleration of muscle contractility properties and decreased muscle steadiness, sustained isometric submaximal contraction did not provoke greater neuromuscular fatigability.

Post-sauna recovery enhances brain neural network relaxation and improves cognitive economy in oddball tasks.

OBJECTIVE: The aim of this study was to investigate the post-sauna residual consequences on brain neural network arousal, information processing and cognitive performance. METHODS: Sixteen male subjects (24 ± 1 yr.) participated in the study. Whole-body hyperthermia was induced with Finnish sauna bathing. Before and 90 min after the sauna, resting electroencephalography (EEG) for spectral analysis and EEG event-related potentials (ERPs) during oddball tasks by two modalities (auditory and visual) were recorded. RESULTS: Sauna bathing increased rectal temperature (Tre, 37.11 ± 0.33 °C to 38.84 ± 0.32 °C) and heart rate (HR, 65.63 ± 9.39 bpm to 151.0 ± 21.8 bpm). At 90 min after the sauna, Tre (37.00 ± 0.29 °C) and HR (72.1 ± 2.80 bpm) recovered to baseline levels. An increase was found in alpha power following sauna recovery. In the visual task modality, post-sauna recovery led to enhancement in the N2 amplitude with centroparietal distribution and decreases in P3 amplitude with distribution along the frontoparietal axis for executive motor-cognitive processing. In the auditory task modality, post-sauna recovery led to a decrease in P3 amplitude with a frontoparietal distribution and this change was accompanied by auditory N2 amplitude enhancement along the centroparietal distribution for non-target cognitive processing. No significant differences in task performance were found. CONCLUSION: Post-sauna recovery to normothermia led to enhanced resting neural network relaxation followed by increases in cognitive processing economy for the given oddball tasks. The auditory processing was not affected more by post-sauna recovery than was visual processing. Post-sauna recovery modifications in ERP components (stimulus processing) were insufficient to affect cognitive performance in both visual and auditory task modalities.

Task-relevant cognitive and motor functions are prioritized during prolonged speed-accuracy motor task performance.

This study aimed to explore the effect of prolonged speed-accuracy motor task on the indicators of psychological, cognitive, psychomotor and motor function. Ten young men aged 21.1 ± 1.0 years performed a fast- and accurate-reaching movement task and a control task. Both tasks were performed for 2 h. Despite decreased motivation, and increased perception of effort as well as subjective feeling of fatigue, speed-accuracy motor task performance improved during the whole period of task execution. After the motor task, the increased working memory function and prefrontal cortex oxygenation at rest and during conflict detection, and the decreased efficiency of incorrect response inhibition and visuomotor tracking were observed. The speed-accuracy motor task increased the amplitude of motor-evoked potentials, while grip strength was not affected. These findings demonstrate that to sustain the performance of 2-h speed-accuracy task under conditions of self-reported fatigue, task-relevant functions are maintained or even improved, whereas less critical functions are impaired.