Effect of the subjective intensity of fatigue and interoception on perceptual regulation and performance during sustained physical activity

Background The subjective experience of fatigue impairs an individual’s ability to sustain physical endurance performance. However, precise understanding of the specific role perceived fatigue plays in the central regulation of performance remains unclear. Here, we examined whether the subjective intensity of a perceived state of fatigue, pre-induced through prior upper body activity, differentially impacted performance and altered perceived effort and affect experienced during a sustained, isometric contraction in lower body. We also explored whether (cardiac) interoception predicted the intensity of experienced perceptual and affective responses and moderated the relationships between constructs during physical activity. Methods Using a repeated-measures study design, thirty male participants completed three experimental conditions, with the intensity of a pre-induced state of fatigue manipulated to evoke moderate (MOD), severe (SEV) and minimal (control; CON) intensity of perceptions prior to performance of the sustained contraction. Results Performance of the sustained contraction was significantly impaired under a perceived state of fatigue, with reductions of 10% and 14% observed in the MOD and SEV conditions, respectively. Performance impairment was accompanied by greater perceived effort and more negative affective valence reported during the contraction. However, effects were limited to comparisons to CON, with no difference evident between the two experimental trials (i.e. MOD vs. SEV). Individuals’ awareness of their accuracy in judging resting heartbeats was shown to predict the subjective intensity of fatigue experienced during the endurance task. However, interoception did not moderate the relationships evident between fatigue and both perceived effort and affective valence. Conclusions A perceived state of fatigue limits endurance performance, influencing both how effortful activity is perceived to be and the affective experience of activity. Though awareness of interoceptive representations of bodily states may be important to the subjective experience of fatigue, interoception does not modulate the relationships between perceived fatigue and other perceptual (i.e. effort) and affective constructs.

Sarcolemmal Excitability, M-Wave Changes, and Conduction Velocity During a Sustained Low-Force Contraction

This study was undertaken to investigate whether sarcolemmal excitability is impaired during a sustained low-force contraction [10% maximal voluntary contraction (MVC)] by assessing muscle conduction velocity and also by analyzing separately the first and second phases of the muscle compound action potential (M wave). Twenty-one participants sustained an isometric knee extension of 10% MVC for 3min. M waves were evoked by supramaximal single shocks to the femoral nerve given at 10-s intervals. The amplitude, duration, and area of the first and second M-wave phases were computed. Muscle fiber conduction velocity, voluntary surface electromyographic (EMG), perceived effort, MVC force, peak twitch force, and temperature were also recorded. The main findings were: (1) During the sustained contraction, conduction velocity remained unchanged. (2) The amplitude of the M-wave first phase decreased for the first ~30s (−7%, p<0.05) and stabilized thereafter, whereas the second phase amplitude increased for the initial ~30s (+7%, p<0.05), before stabilizing. (3) Both duration and area decreased steeply during the first ~30s, and then more gradually for the rest of the contraction. (4) During the sustained contraction, perceived effort increased fivefold, whereas knee extension EMG increased by ~10%. (5) Maximal voluntary force and peak twitch force decreased (respectively, −9% and −10%, p<0.05) after the low-force contraction. Collectively, the present results indicate that sarcolemmal excitability is well preserved during a sustained 10% MVC task. A depression of the M-wave first phase during a low-force contraction can occur even in the absence of changes in membrane excitability. The development of fatigue during a low-force contraction can occur without alteration of membrane excitability.

Flexibility of microstructural adaptions in airway smooth muscle

The airway smooth muscle undergoes an elastic transition during a sustained contraction, characterized by a gradual decrease in hysteresivity caused by a relatively greater rate of increase in elastance than resistance. We recently demonstrated that these mechanical changes are more likely to persist after a large strain when they are acquired in dynamic versus static conditions; as if the microstructural adaptations liable for the elastic transition are more flexible when they evolve in dynamic conditions. The extent of this flexibility is undefined. Herein, contracted ovine tracheal smooth muscle strips were kept in dynamic conditions simulating tidal breathing (sinusoidal length oscillations at 5% amplitude) and then subjected to simulated deep inspirations (DI). Each DI was straining the muscle by either 10, 20 or 30% and was imposed at either 2, 5, 10 or 30 min after the preceding DI. The goal was to assess whether, and the extent by which, the time-dependent decrease in hysteresivity is preserved following the DI. The results show that the time-dependent decrease in hysteresivity seen pre-DI was preserved after a strain of 10%, but not after a strain of 20% or 30%. This suggests that the microstructural adaptations liable for the elastic transition withstood a strain at least twofold greater than the oscillating strain that pertained during their evolution (10 versus 5%). We propose that a muscle adapting in dynamic conditions forges microstructures exhibiting a substantial degree of flexibility.

Vasorelaxation endothelium-independent of the ethyl acetate phase from aerial parts of Solanum paludosum Moric. envolves channels-calcium L-type blockade

Previous results showed the ethyl acetate phase (SP-AcOEt), obtained from aerial parts of Solanum paludosum, relaxed the aorta isolated in the endothelium-dependent and -independent manner. The vasorelaxant effects of SP-AcOEt was not characterized on aorta rings endothelium-denuded, thus this work aimed to elucidate the mechanisms endothelium-independent vasorelaxation on rat isolated aorta. The aorta was isolated from Wistar rats and mounted in glass baths containing 6 mL of normal Krebs physiological solution with pH at 7.4. The preparation was maintained at 37ºC and bubbled continuously with a mixture of 95% O2 and 5% CO2. Aortic rings were maintained for 1 hour by a resting tension of 1g and next were contracted with phenylephrine after the sustained contraction ACh was added to access the integrity of the endothelium. SP-AcOEt relaxed pre-contracted aorta by KCl-30mM or -80mM in a similar manner, suggesting blockade CaV, but not channel-K+ participating. SP-AcOEt also inhibited the contraction induced by CaCl2 and relaxed pre-contracted aorta by (±)-BayK8644 (EC50 = 16.9±1.3 μg/mL), which confirms the involvement of L-type CaV blockade. SP-AcOEt presented vasorelaxation endothelium-independent that involves L-type CaV blockade.

An instrument for tongue performance assessment in activities associated with digital games: content and construct validity

ABSTRACT Purpose: to analyze the content and construct validity of an instrument for tongue performance assessment in activities associated with digital games. Methods: to analyze content validity, ten speech-language pathologists answered a questionnaire in which each item of the instrument and the set of items were judged as to its representativeness. The content validity index and the modified Kappa statistics were calculated. To analyze construct validity, 20 participants, with age between 8 and 13 years, (10 children with weak tongues and 10 children with normal tongue strength) performed a game activity with the T-Station, involving 12 targets with 2 N of strength and 5 s of time for sustained contraction for each target. The performance was compared, for each item of the instrument, between groups. Results: most of the items obtained satisfactory score according to the speech-language pathologist’s evaluation. Children with reduced tongue force had a poorer performance than those with normal tongue force, with a statistically significant difference in three items of the instrument. Conclusion: the instrument proved to be valid as a method for evaluating performance in activities associated with the T-Station.

Spatial Distribution and Asymmetry of Surface Electromyography on Lumbar Muscles of Soldiers with Chronic Low Back Pain

This study investigated spatial distribution and asymmetry of surface electromyography on lumbar muscles during a sustained contraction in soldiers with and without chronic low back pain. Twenty healthy soldiers and twenty chronic low back pain (CLBP) soldiers had performed the Sorensen test with a duration of 60 seconds. The corresponding muscle fatigue, spatial distribution, and the asymmetry of muscle activity over bilateral paraspinal lumbar regions were measured by the high-density surface electromyography (HDsEMG). The paired and independent samples t-tests were performed to compare the degree of muscle fatigue and asymmetry. The repeated-measures analyses of variance (ANOVA) were used to compare spatial distribution between groups and muscle fatigue. The baseline characteristics of soldiers between groups were comparable. CLBP soldiers had significantly less muscle fatigue on both sides of erector spinae compared to healthy ones. The spatial distribution was significantly associated with the group factor but independent of muscle fatigue. In addition, the asymmetry of erector spinae activity in the CLBP soldiers was significantly higher than the healthy one. In conclusion, uneven spatial distribution and asymmetry of lumbar muscle activity play significant roles in CLBP patients. The HDsEMG could be used as an objective method in distinguishing the function of the erector spinae between healthy individuals and CLBP patients during 1 min sustained contraction.

Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance

This review used a narrative summary of findings from studies that focused on isometric strength training (IST), covering the training considerations that affect strength adaptations and its effects on sports related dynamic performances. IST has been shown to induce less fatigue and resulted in superior joint angle specific strength than dynamic strength training, and benefited sports related dynamic performances such as running, jumping and cycling. IST may be included into athletes’ training regime to avoid getting overly fatigue while still acquiring positive neuromuscular adaptations; to improve the strength at a biomechanically disadvantaged joint position of a specific movement; to improve sports specific movements that require mainly isometric contraction; and when athletes have limited mobility due to injuries. To increase muscle hypertrophy, IST should be performed at 70–75% of maximum voluntary contraction (MVC) with sustained contraction of 3–30 s per repetition, and total contraction duration of>80–150 s per session for>36 sessions. To increase maximum strength, IST should be performed at 80–100% MVC with sustained contraction of 1–5 s, and total contraction time of 30–90 s per session, while adopting multiple joint angles or targeted joint angle. Performing IST in a ballistic manner can maximize the improvement of rate of force development.

Spatial Reorganization of Myoelectric Activities in Extensor Digitorum for Sustained Finger Force Production

The study aims to explore the spatial distribution of multi-tendinous muscle modulated by central nervous system (CNS) during sustained contraction. Nine subjects were recruited to trace constant target forces with right index finger extension. Surface electromyography (sEMG) of extensor digitorum (ED) were recorded with a 32-channel electrode array. Nine successive topographic maps (TM) were obtained. Pixel wise analysis was utilized to extract subtracted topographic maps (STM), which exhibited inhomogeneous distribution. STMs were characterized into hot, warm, and cool regions corresponding to higher, moderate, and lower change ranges, respectively. The relative normalized area (normalized to the first phase) of these regions demonstrated different changing trends as rising, plateauing, and falling over time, respectively. Moreover, the duration of these trends were found to be affected by force level. The rising/falling periods were longer at lower force levels, while the plateau can be achieved from the initial phase for higher force output (45% maximal voluntary contraction). The results suggested muscle activity reorganization in ED plays a role to maintain sustained contraction. Furthermore, the decreased dynamical regulation ability to spatial reorganization may be prone to induce fatigue. This finding implied that spatial reorganization of muscle activity as a regulation mechanism contribute to maintain constant force production.