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Henderson TT, Taylor JL, Thorstensen JR, Tucker MG, Kavanagh JJ. Enhanced availability of serotonin limits muscle activation during high-intensity, but not low-intensity, fatiguing contractions. J Neurophysiol 2022; 128:751-762. [PMID: 36001790 DOI: 10.1152/jn.00182.2022] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Serotonin (5-HT) modulates motoneuron excitability during muscle contractions, where the release of 5-HT in the central nervous system (CNS) is linked to the intensity of physical activity. Although there is evidence that enhanced availability of 5-HT can exacerbate fatigue, these effects on the development of fatigue during different contraction intensities are largely unknown. The purpose of this study was to investigate how enhanced 5-HT availability affects voluntary muscle activation and corticospinal excitability during fatigue-inducing contractions. Two experiments were performed. In the first experiment (n = 11), twelve isometric elbow flexions at 20% maximal voluntary contractions (MVC) were performed for 2-min each with 40-s rest periods. In the second experiment (n = 14), twelve maximal isometric elbow flexions were held for 10-s each with 40-s rest periods. In both experiments, the selective serotonin reuptake inhibitor (20 mg paroxetine), or a placebo, was administered in a two-way crossover-design. Muscle responses to transcranial magnetic stimulation (TMS) of the motor cortex (both experiments 1 and 2), as well as motor point stimulation of the elbow flexors (experiment 2) were assessed. Paroxetine reduced both motor cortical (p = 0.018) and motor point voluntary activation (p = 0.036) during the maximal contraction protocol. Paroxetine also reduced exercise-induced lengthening of the TMS silent period during the submaximal (p = 0.037) and maximal (p = 0.002) contraction protocols. Activation of inhibitory 5-HT1A receptors on motoneurons likely exacerbated exercise-induced reductions in voluntarily drive to the elbow flexors. However, 5-HT modulation of motor activity also appeared at the supraspinal level.
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Affiliation(s)
- Tyler T Henderson
- Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
| | - Janet L Taylor
- School of Medical and Health Sciences, Edith Cowan University, Perth, Australia.,Neuroscience Research Australia, Sydney, Australia
| | - Jacob R Thorstensen
- Child Health Research Centre, The University of Queensland, Brisbane, Australia
| | - Murray G Tucker
- Barwon Health, University Hospital Geelong, Geelong, Australia
| | - Justin J Kavanagh
- Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
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de Almeida Azevedo R, Jazayeri D, Yeung ST, Khoshreza R, Millet GY, Murias JM, Aboodarda SJ. The effects of pain induced by blood flow occlusion in one leg on exercise tolerance and corticospinal excitability and inhibition of the contralateral leg in males. Appl Physiol Nutr Metab 2022; 47:632-648. [PMID: 35201916 DOI: 10.1139/apnm-2021-0597] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Experiencing pain in one leg can alter exercise tolerance and neuromuscular fatigue (NMF) responses in the contralateral leg; however, the corticospinal modulations to non-local experimental pain induced by blood flow occlusion remain unknown. In three randomized visits, thirteen male participants performed 25% of isometric maximal voluntary contraction (25%IMVC) to task failure with one leg preceded by (i) 6-min rest (CON), (ii) cycling at 80% of peak power output until task failure with the contralateral leg (CYCL) or (iii) CYCL followed by blood flow occlusion (OCCL) during 25%IMVC. NMF assessments (IMVC, voluntary activation [VA] and potentiated twitch [Qtw]) were performed at baseline and task failure. During the 25%IMVC, transcranial magnetic stimulations were performed to obtain motor evoked potential (MEP), silent period (SP), and short intracortical inhibition (SICI). 25%IMVC was shortest in OCCL (105±50s) and shorter in CYCL (154±68s) than CON (219±105s) (P<0.05). IMVC declined less after OCCL (-24±19%) and CYCL (-27±18%) then CON (-35±11%) (P<0.05). Qtw declined less in OCCL (-40±25%) compared to CYCL (-50±22%) and CON (-50±21%) (P<0.05). VA was similar amongst conditions. MEP and SP increased and SICI decreased throughout the task while SP was longer for OCCL compared to CYC condition (P<0.05). The results suggest that pain in one leg diminishes contralateral limb exercise tolerance and NMF development and modulate corticospinal inhibition in males. Novelty: Pain in one leg diminished MVC and twitch force decline in the contralateral limb Experimental pain induced by blood flow occlusion may modulation corticospinal inhibition of the neural circuitries innervating the contralateral exercise limb.
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Affiliation(s)
| | | | | | | | | | - Juan M Murias
- University of Calgary, Faculty of Kinesiology, KNB 434, 2500 University Drive NW, Calgary, Alberta, Canada, T2N1N4;
| | - Saied Jalal Aboodarda
- University of Calgary , Faculty of Kinesiology, 2500 University Drive NW, Calgary, Canada, T2N 1N4;
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Fernandes GL, Orssatto LBR, Shield AJ, Trajano GS. Runners with mid-portion Achilles tendinopathy have greater triceps surae intracortical inhibition than healthy controls. Scand J Med Sci Sports 2021; 32:728-736. [PMID: 34897835 DOI: 10.1111/sms.14111] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2021] [Revised: 11/25/2021] [Accepted: 12/05/2021] [Indexed: 11/29/2022]
Abstract
OBJECTIVES This study aimed to investigate short-interval intracortical inhibition (SICI) and muscle function in the triceps surae of runners with mid-portion Achilles tendinopathy (AT). METHODS Runners with (n = 11) and without (n = 13) AT were recruited. Plantar flexor isometric peak torque and rate of torque development (RTD) were measured using an isokinetic dynamometer. Triceps surae endurance was measured as single-leg heel raise (SLHR) to failure test. SICI was assessed using paired-pulse transcranial magnetic stimulation during a sustained contraction at 10% of plantar flexor isometric peak torque. RESULTS Triceps surae SICI was 14.3% (95% CI: -2.1 to 26.4) higher in AT than in the control group (57.9%, 95% CI: 36.2 to 79.6; and 43.6% 95% CI: 16.2 to 71.1, p = 0.032) irrespective of the tested muscle. AT performed 16 (95% CI: 7.9 to 23.3, p < 0.001) fewer SLHR repetitions on the symptomatic side compared with controls, and 14 (95% CI: 5.8 to 22.0, p = 0.004), fewer SLHR repetitions on the non-symptomatic compared with controls. We found no between-groups differences in isometric peak torque (p = 0.971) or RTD (p = 0.815). PERSPECTIVE Our data suggest greater intracortical inhibition for the triceps surae muscles for the AT group accompanied by reduced SLHR endurance, without deficits in isometric peak torque or RTD. The increased SICI observed in the AT group could be negatively influencing triceps surae endurance; thus, rehabilitation aiming to reduce intracortical inhibition should be considered to improve patient outcomes. Furthermore, SLHR is a useful clinical tool to assess plantar flexor function in AT patients.
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Affiliation(s)
- Gabriel L Fernandes
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Australia
| | - Lucas B R Orssatto
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Australia
| | - Anthony J Shield
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Australia
| | - Gabriel S Trajano
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Australia
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4
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Otieno LA, Semmler JG, Smith AE, Sidhu SK. Submaximal isometric fatiguing exercise of the elbow flexors has no age-related effect on GABA B mediated inhibition. J Appl Physiol (1985) 2021; 132:167-177. [PMID: 34855523 DOI: 10.1152/japplphysiol.00288.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Age-related changes in the neuromuscular system can result in differences in fatigability between young and older adults. Previous research has shown that single joint isometric fatiguing exercise of small muscle results in an age-related compensatory decrease in GABAB mediated inhibition. However, this has yet to be established in a larger muscle group. In 15 young (22 ± 4 years) and 15 older (65 ± 5 years) adults, long interval cortical inhibition (LICI; 100 ms ISI) and corticospinal silent period (SP) were measured in the biceps brachii during a 5% EMG contraction using transcranial magnetic stimulation (TMS) before, during and after a submaximal contraction (30% MVC force) held intermittently to task failure. Both age groups developed similar magnitude of fatigue (~24% decline in MVC; P = 0.001) and ~28% decline in LICI (P = 0.001) post fatiguing exercise. No change in SP duration was observed during and immediately following fatigue (P = 0.909) but ~ 6% decrease was seen at recovery in both age groups (P<0.001)." Contrary to previous work in a small muscle, these findings suggest no age-related differences in GABAB mediated inhibition following single joint isometric fatiguing exercise of the elbow flexors, indicating that GABAB modulation with ageing may be muscle group dependent. Furthermore, variations in SP duration and LICI modulation during and post fatigue in both groups suggest that these measures are likely mediated by divergent mechanisms.
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Affiliation(s)
- Lavender A Otieno
- Discipline of Physiology, Adelaide Medical School, The University of Adelaide, Adelaide, Australia
| | - John G Semmler
- Discipline of Physiology, Adelaide Medical School, The University of Adelaide, Adelaide, Australia
| | - Ashleigh Elizabeth Smith
- Alliance for Research in Exercise, Nutrition and Activity (ARENA), Allied Health and Human Performance, University of South Australia, City East Campus, Australia
| | - Simranjit K Sidhu
- Discipline of Physiology, Adelaide Medical School, The University of Adelaide, Adelaide, Australia
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Nuzum ND, Teo WP, Macpherson H, Loughman A, Szymlek-Gay EA, Hendy A. Inhibition, excitation and bilateral transfer following a unilateral complex finger-tapping task in young and older adults. Eur J Neurosci 2021; 54:6608-6617. [PMID: 34535926 DOI: 10.1111/ejn.15467] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 09/09/2021] [Accepted: 09/11/2021] [Indexed: 11/29/2022]
Abstract
Neuroplasticity underpins motor learning, with abnormal neuroplasticity related to age-associated motor declines. Bilateral transfer of motor learning, through rehabilitation, may mitigate these declines; however, the magnitude of transfer may be reduced in older populations. This study investigated excitatory and inhibitory pathways in the trained and untrained hemispheres following unilateral training of a complex finger-tapping task across ageing. Fifteen young (26.2 ± 3.8 years) and 11 older adults (63.7 ± 15.4 years) received transcranial magnetic stimulation, although surface electromyography was recorded from the extensor digitorum communis (EDC) and abductor pollicis brevis (APB), before and after practicing a complex finger-tapping task with the dominant hand. Excitability, inhibition (expressed as percent change scores from pre- to post-training), motor task performance and bilateral transfer were assessed between groups. Investigation of hemispheric differences within each group was completed for measures that significantly differed between groups. There were no between-group differences in task performance or bilateral transfer, with task performance improving post-training irrespective of group for both hands (p < 0.05). Pre- to post-inhibition change scores of the untrained EDC muscle increased (p = 0.034) in older compared with younger adults, indicating reduced inhibition in older adults. Inhibition change scores significantly differed between hemispheres for the young group only (p = 0.037). Only the younger group presented with hemispheric lateralisation, providing some support for the Hemispheric Asymmetry Reduction in OLDer adults (HAROLD) hypothesis. Whether this reduction is evidence of de-differentiation or compensation will need to be confirmed with additional measures.
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Affiliation(s)
- Nathan D Nuzum
- Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, Victoria, Australia
| | - Wei-Peng Teo
- Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, Victoria, Australia.,Physical Education and Sports Science Academic Group, National Institute of Education, Nanyang Technological University, Singapore, Singapore
| | - Helen Macpherson
- Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, Victoria, Australia
| | - Amy Loughman
- Food & Mood Centre, IMPACT Institute, School of Medicine, Deakin University, Geelong, Victoria, Australia
| | - Ewa A Szymlek-Gay
- Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, Victoria, Australia
| | - Ashlee Hendy
- Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, Victoria, Australia
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