scholarly journals Heat acclimation has a protective effect on the central but not peripheral nervous system

2017 ◽  
Vol 123 (4) ◽  
pp. 816-824 ◽  
Author(s):  
Sebastien Racinais ◽  
Mathew G. Wilson ◽  
Nadia Gaoua ◽  
Julien D. Périard
Keyword(s):  
Working Memory ◽  
Executive Function ◽  
Conduction Velocity ◽  
Heat Acclimation ◽  
H Reflex ◽  
Voluntary Activation ◽  
Neural Drive ◽  
M Wave ◽  
Neural Adaptations ◽  
C 50

This study aimed to clarify the pathway mediating hyperthermia-induced alterations in neural drive transmission and determine if heat acclimation protects voluntary muscle activation and cognitive function in hyperthermic humans. Electrically evoked potentials (H reflex and M wave), executive function (special planning and working memory), and maximal voluntary isometric contractions (120 s) were assessed in 14 participants in control conditions [CON, 24°C, 40% relative humidity (RH)] and in a hyperthermic state (HYP, 44–50°C, 50% RH) on consecutive days in a counterbalanced order. Thereafter, participants were passively heat acclimated for 11 days (1 h per day, 48–50°C, 50% RH) before repeating the initial assessments. Heat acclimation decreased rectal temperature in CON (−0.2°C, P < 0.05), but participants were maintained at ~39°C in HYP. Heat acclimation increased the time required to reach 39°C (+9 min), along with sweat rate (+0.7 l/h), and serum extracellular expression of heat shock protein 72 (eHSP72; +20%) in HYP ( P < 0.05). M-wave and H-reflex amplitudes were lower in HYP than CON ( P < 0.05) and were not protected by heat acclimation. Nerve conduction velocity was faster in HYP than CON ( P < 0.05) without being influenced by heat acclimation. These results suggest that peripheral neural drive transmission in the hyperthermic state is primarily affected by axonal conduction velocity rather than synaptic failure. Executive function, voluntary activation, and the ability to sustain torque were impaired in HYP ( P < 0.05). However, despite no perceptual changes ( P > 0.05), heat acclimation restored executive function, while protecting the ability to sustain voluntary activation and torque production during a prolonged contraction in hyperthermia ( P < 0.05). Ultimately, heat acclimation induces beneficial central but not peripheral neural adaptations. NEW & NOTEWORTHY Heat acclimation restores planning accuracy and working memory in hyperthermic humans, together with the supraspinal capacity to sustain motor drive during a sustained maximal voluntary contraction. Electrically evoked potential data (M wave, H reflex) indicate that heat acclimation does not protect against hyperthermia-induced impairments in peripheral neural drive transmission. Heat acclimation induces beneficial central but not peripheral neural adaptations.

scholarly journals Maximal strength training-induced increase in efferent neural drive is not reflected in relative protein expression of SERCA

2021 ◽  
Author(s):  
Tiril Tøien ◽  
Håvard Haglo ◽  
Stian Kwak Nyberg ◽  
Shalini Vasudev Rao ◽  
Astrid Kamilla Stunes ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Expression ◽  
Strength Training ◽  
High Intensity ◽  
Force Production ◽  
H Reflex ◽  
Maximal Strength ◽  
Neural Drive ◽  
M Wave ◽  
Neural Adaptations

Abstract Introduction Maximal strength training (MST), performed with heavy loads (~ 90% of one repetition maximum; 1RM) and few repetitions, yields large improvements in efferent neural drive, skeletal muscle force production, and skeletal muscle efficiency. However, it is elusive whether neural adaptations following such high intensity strength training may be accompanied by alterations in energy-demanding muscular factors. Methods Sixteen healthy young males (24 ± 4 years) were randomized to MST 3 times per week for 8 weeks (n = 8), or a control group (CG; n = 8). Measurements included 1RM and rate of force development (RFD), and evoked potentials recordings (V-wave and H-reflex normalized to M-wave (M) in the soleus muscle) applied to assess efferent neural drive to maximally contracting skeletal muscle. Biopsies were obtained from vastus lateralis and analyzed by western blots and real-time PCR to investigate the relative protein expression and mRNA expression of Sarcoplasmic Reticulum Ca2+ ATPase (SERCA) 1 and SERCA2. Results Significant improvements in 1RM (17 ± 9%; p < 0.001) and early (0–100 ms), late (0–200 ms) and maximal RFD (31–53%; p < 0.01) were observed after MST, accompanied by increased maximal Vmax/Msup-ratio (9 ± 14%; p = 0.046), with no change in H-reflex to M-wave ratio. No changes were observed in the CG. No pre- to post-training differences were found in mRNA or protein expressions of SERCA1 and SERCA2 in either group. Conclusion MST increased efferent neural drive to maximally contracting skeletal muscle, causing improved force production. No change was observed in SERCA expression, indicating that responses to high intensity strength training may predominantly be governed by neural adaptations.

scholarly journals Passive heat acclimation improves skeletal muscle contractility in humans

2017 ◽  
Vol 312 (1) ◽  
pp. R101-R107 ◽  
Author(s):  
S. Racinais ◽  
M. G. Wilson ◽  
J. D. Périard
Keyword(s):  
Skeletal Muscle ◽  
Contractile Function ◽  
Sweat Rate ◽  
Heat Exposure ◽  
Heat Acclimation ◽  
Voluntary Activation ◽  
Ambient Conditions ◽  
Muscle Contractility ◽  
C 50 ◽  
Time Required

The aim of this study was to investigate the effect of repeated passive heat exposure (i.e., acclimation) on muscle contractility in humans. Fourteen nonheat-acclimated males completed two trials including electrically evoked twitches and voluntary contractions in thermoneutral conditions [Cool: 24°C, 40% relative humidity (RH)] and hot ambient conditions in the hyperthermic state (Hot: 44–50°C, 50% RH) on consecutive days in a counterbalanced order. Rectal temperature was ~36.5°C in Cool and was maintained at ~39°C throughout Hot. Both trials were repeated after 11 days of passive heat acclimation (1 h per day, 48–50°C, 50% RH). Heat acclimation decreased core temperature in Cool (−0.2°C, P < 0.05), increased the time required to reach 39°C in Hot (+9 min, P < 0.05) and increased sweat rate in Hot (+0.7 liter/h, P < 0.05). Moreover, passive heat acclimation improved skeletal muscle contractility as evidenced by an increase in evoked peak twitch amplitude both in Cool (20.5 ± 3.6 vs. 22.0 ± 4.0 N·m) and Hot (20.5 ± 4.7 vs. 22.0 ± 4.0 N·m) (+9%, P < 0.05). Maximal voluntary torque production was also increased both in Cool (145 ± 42 vs. 161 ± 36 N·m) and Hot (125 ± 36 vs. 145 ± 30 N·m) (+17%, P < 0.05), despite voluntary activation remaining unchanged. Furthermore, the slope of the relative torque/electromyographic linear relationship was improved postacclimation ( P < 0.05). These adjustments demonstrate that passive heat acclimation improves skeletal muscle contractile function during electrically evoked and voluntary muscle contractions of different intensities both in Cool and Hot. These results suggest that repeated heat exposure may have important implications to passively maintain or even improve muscle function in a variety of performance and clinical settings.

Central and peripheral contributions to fatigue in relation to level of activation during repeated maximal voluntary isometric plantar flexions

2004 ◽  
Vol 96 (1) ◽  
pp. 218-225 ◽  
Author(s):  
Maria M. Nordlund ◽  
Alf Thorstensson ◽  
Andrew G. Cresswell
Keyword(s):  
Presynaptic Inhibition ◽  
Central Fatigue ◽  
H Reflex ◽  
Joint Torque ◽  
Medial Gastrocnemius ◽  
Voluntary Activation ◽  
Peripheral Fatigue ◽  
M Wave ◽  
Postactivation Depression ◽  
Electromyographic Signals

This study aimed to investigate central and peripheral contributions to fatigue during repeated maximal voluntary isometric plantar flexions (MVCs). Changes in joint torque, level of activation (LOA), resting twitch amplitude (RT), electromyographic signals (EMG), and presynaptic inhibition of Ia afferents were investigated during 9 bouts of 10 MVCs. MVCs lasted for 2 s and were separated by 1 s. The interval between bouts was 10 s. Electrical stimulation was applied to the tibial nerve; at rest to evoke RTs, M waves, and two (1.5-s interval) H reflexes; with the soleus EMG at 30% of that during MVC to evoke M waves and two H reflexes; and during MVCs to measure LOA. Over the nine bouts, LOA decreased by 12.6% and RT by 16.2%. EMG root mean square during MVCs remained unchanged for the soleus and tibialis anterior muscles, but it decreased for medial gastrocnemius. Peripheral fatigue (decrease in RT) was positively correlated to LOA, whereas central fatigue (decrease in LOA) was not. Depression of both H reflexes suggests that presynaptic inhibition after the first bout was partly induced by homosynaptic postactivation depression of the Ia terminal. The H-reflex-to-M-wave ratio increased with fatigue in both passive and active states, with no change in the ratio of the second H reflex to the first, thereby indicating a decrease of presynaptic inhibition during fatigue. The results indicate that both central and peripheral mechanisms contributed to the fatigue observed during repeated MVCs and that the development of peripheral fatigue was influenced by the level of voluntary activation and initial plantar flexor torque.

scholarly journals Lifelong strength training mitigates the age-related decline in efferent drive

2016 ◽  
Vol 121 (2) ◽  
pp. 415-423 ◽  
Author(s):  
Runar Unhjem ◽  
Mona Nygård ◽  
Lene T. van den Hoven ◽  
Simranjit K. Sidhu ◽  
Jan Hoff ◽  
...  
Keyword(s):  
Strength Training ◽  
Plantar Flexion ◽  
H Reflex ◽  
Voluntary Activation ◽  
M Wave ◽  
Reflex Amplitude ◽  
Age Related ◽  
Musculus Soleus ◽  
V Wave ◽  
Voluntary Contractions

Recently, we documented age-related attenuation of efferent drive to contracting skeletal muscle. It remains elusive if this indication of reduced muscle strength is present with lifelong strength training. For this purpose, we examined evoked potentials in the calf muscles of 11 [71 ± 4 (SD) yr] strength-trained master athletes (MA) contrasted with 10 (71 ± 4 yr) sedentary (SO) and 11 (73 ± 6 yr) recreationally active (AO) old subjects, as well as 9 (22 ± 2 yr) young controls. As expected, MA had higher leg press maximal strength (MA, 185 ± 32 kg; AO, 128 ± 15 kg; SO, 106 ± 11 kg; young, 147 ± 22 kg, P < 0.01) and rate of force development (MA, 5,588 ± 2,488 N/s; AO, 2,156 ± 1,100 N/s; SO, 2,011 ± 825 N/s; young, 3,663 ± 1,140 N/s, P < 0.05) than the other groups. MA also exhibited higher musculus soleus normalized V waves during maximal voluntary contractions (MVC) [maximal V wave amplitude/maximal M wave during MVC (Vsup/Msup); 0.28 ± 0.15] than AO (0.13 ± 0.06, P < 0.01) and SO (0.11 ± 0.05, P < 0.01), yet lower than young (0.45 ± 0.12, P < 0.01). No differences were apparent between the old groups in H reflex recorded at rest or during MVC [maximal H reflex amplitude/maximal M wave during rest (Hmax/Mmax); maximal H reflex amplitude during MVC/maximal M wave during MVC (Hsup/Msup)], and all were lower ( P < 0.01) than young. MA (34.4 ± 2.1 ms) had shorter ( P < 0.05) H reflex latency compared with AO (36.4 ± 3.7 ms) and SO (37.3 ± 3.2 ms), but longer ( P < 0.01) than young (30.7 ± 2.0 ms). Using interpolated twitch analysis, MA (89 ± 7%) had plantar flexion voluntary activation similar to young (90 ± 6%), and this was higher ( P < 0.05), or tended to be higher ( P = 0.06–0.09), than SO (83 ± 10%) and AO (84 ± 5%). These observations suggest that lifelong strength training has a protective effect against age-related attenuation of efferent drive. In contrast, no beneficial effect seems to derive from habitual recreational activity, indicating that strength training may be particularly beneficial for counteracting age-related loss of neuromuscular function.

scholarly journals Prolonged muscle inactivity and evaluation of peripheral neuromuscular features in patients hospitalized in Intensive Care Units

2019 ◽  
Vol 12 (2) ◽  
pp. 50-64
Author(s):  
George Elesnitsalis ◽  
Ioannis Amiridis ◽  
Dimitrios Patikas ◽  
Ioanna Vekili ◽  
Maria Vourvou
Keyword(s):  
Intensive Care ◽  
Critically Ill ◽  
Conduction Velocity ◽  
Soleus Muscle ◽  
Critically Ill Patients ◽  
Tibial Nerve ◽  
H Reflex ◽  
Apache Ii Score ◽  
M Wave ◽  
Stimulation Of

Introduction: Polyneuromyopathy constitutes a common complication in critically ill patients of the Intensive Care Unit (ICU) and in the last few years it appears to be identified as a syndrome detectable in the limbs and respiratory muscles. It is associated with the difficulties during weaning from mechanical ventilation. Aim: The present study investigates the reflective reaction of the soleus muscle following an electrical stimulation of the tibial nerve in intubated critically ill patients hospitalized in ICU with no medical history prior to their admission. Methods: Thirteen (13) patients who had been hospitalized for more than five (5) days and had a high APACHE II score (>15) and 13 age-matched control subjects were asked to participate in the present study on a volunteer basis. During the study, as reflective response parameters the range of the H-reflex and M-wave of the soleus muscle, as well as the conduction velocity of the tibial nerve, after electro-stimulation of the tibial nerve at the popliteal-fossa level, were assessed Results: Statistical analysis revealed significantly lower values in the ICU patients compared to healthy controls in both H-reflex range (p<0,049) and the M-wave range (p<0,041), as well as conduction velocity (p<0,001) of the tibial nerve. Conclusions: It is concluded that the reflective response of the soleus muscle as well as the tibial nerve’s conduction velocity are affected in critically ill patients hospitalized in ICU. The study of the above neurological parameters can provide further insights into the establishment and progress of polyneuromyopathy of critically ill patients in ICUs.

Working Memory in ADHD and Depression: An Examination of Common Executive Function Deficits

2012 ◽  
Author(s):  
Kaley Mirabal ◽  
Lisa J. Kasper ◽  
R. Matt Alderson ◽  
Kristen L. Hudec
Keyword(s):  
Working Memory ◽  
Executive Function ◽  
Executive Function Deficits

Predictions of Actions and Their Justifications in False-Belief Tasks: The Role of Executive Function

2014 ◽  
Vol 45 (4) ◽  
pp. 500-510 ◽  
Author(s):  
Adam Putko ◽  
Agata Złotogórska
Keyword(s):  
Working Memory ◽  
Executive Function ◽  
Language Development ◽  
Executive Control ◽  
Working Memory Capacity ◽  
Mental States ◽  
False Belief ◽  
Current Location ◽  
False Belief Tasks ◽  
Development Of Language

Abstract The main objective of this study was to examine whether children’s ability to justify their action predictions in terms of mental states is related, in a similar way as the ability to predict actions, to such aspects of executive function (EF) as executive control and working memory. An additional objective was to check whether the frequency of different types of justifications made by children in false-belief tasks is associated with aforementioned aspects of EF, as well as language. The study included 59 children aged 3-4 years. The ability to predict actions and to justify these predictions was measured with false-belief tasks. Luria’s hand-game was used to assess executive control, and the Counting and Labelling dual-task was used to assess working memory capacity. Language development was controlled using an embedded syntax test. It was found that executive control was a significant predictor of the children’s ability to justify their action predictions in terms of mental states, even when age and language were taken into account. Results also indicated a relationship between the type of justification in the false-belief task and language development. With the development of language children gradually cease to justify their action predictions in terms of current location, and they tend to construct irrelevant justifications before they begin to refer to beliefs. Data suggest that executive control, in contrast to language, is a factor which affects the development of the children’s ability to justify their action predictions only in its later phase, during a shift from irrelevant to correct justifications.

Dissociating the Impact of Auditory Access and Language Access in Deaf Children’s Cognitive Development

2020 ◽  
pp. 98-122
Author(s):  
Matthew L. Hall
Keyword(s):  
Working Memory ◽  
Executive Function ◽  
Cognitive Development ◽  
Implicit Learning ◽  
Educational Practice ◽  
Verbal Working Memory ◽  
Psychological Theory ◽  
Future Research ◽  
Language Access ◽  
The Impact

Deaf and hard of hearing (DHH) children have been claimed to lag behind their hearing peers in various domains of cognitive development, especially in implicit learning, executive function, and working memory. Two major accounts of these deficits have been proposed: one based on a lack of auditory access, and one based on a lack of language access. This chapter reviews these theories in relation to the available evidence and concludes that there is little evidence of direct effects of diminished auditory access on cognitive development that could not also be explained by diminished language access. Specifically, reports of deficits in implicit learning are not broadly replicable. Some differences in executive function do stem from deafness itself but are not necessarily deficits. Where clinically relevant deficits in executive function are observed, they are inconsistent with the predictions of accounts based on auditory access, but consistent with accounts based on language access. Deaf–hearing differences on verbal working memory tasks may indicate problems with perception and/or language, rather than with working memory. Deaf–hearing differences on nonverbal tasks are more consistent with accounts based on language access, but much more study is needed in this area. The chapter concludes by considering the implications of these findings for psychological theory and for clinical/educational practice and by identifying high-priority targets for future research.

scholarly journals Acute Effects of Kinesiology Taping Stretch Tensions on Soleus and Gastrocnemius H-Reflex Modulations

2021 ◽  
Vol 18 (9) ◽  
pp. 4411
Author(s):  
Yung-Sheng Chen ◽  
Shi Zhou ◽  
Zachary J. Crowley-McHattan ◽  
Pedro Bezerra ◽  
Wei-Chin Tseng ◽  
...  
Keyword(s):  
H Reflex ◽  
Triceps Surae ◽  
Reflex Modulation ◽  
Hoffmann Reflex ◽  
Acute Effects ◽  
Physically Active ◽  
M Wave ◽  
Subject Design ◽  
Minor Influence ◽  
Order Paper

This study examined the acute effects of stretch tensions of kinesiology taping (KT) on the soleus (SOL), medial (MG), and lateral (LG) gastrocnemius Hoffmann-reflex (H-reflex) modulation in physically active healthy adults. A cross-over within-subject design was used in this study. Twelve physically active collegiate students voluntarily participated in the study (age = 21.3 ± 1.2 years; height = 175.6 ± 7.1 cm; body weight = 69.9 ± 7.1 kg). A standard Y-shape of KT technique was applied to the calf muscles. The KT was controlled in three tension intensities in a randomised order: paper-off, 50%, and 100% of maximal stretch tension of the tape. The peak-to-peak amplitude of maximal M-wave (Mmax) and H-reflex (Hmax) responses in the SOL, MG, and LG muscles were assessed before taping (pre-taping), taping, and after taping (post-taping) phases in the lying prone position. The results demonstrated significantly larger LG Hmax responses in the pre-taping condition than those in the post-taping condition during paper-off KT (p = 0.002). Moreover, the ΔHmax/Mmax of pre- and post-taping in the SOL muscle was significantly larger during 50%KT tension than that of paper-off (p = 0.046). In conclusion, the stretch tension of KT contributes minor influence on the spinal motoneuron excitability in the triceps surae during rest.

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