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Frontal cortex activation during electrical muscle stimulation as revealed by functional near-infrared spectroscopy| old_uid | 9444 |
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| title | Frontal cortex activation during electrical muscle stimulation as revealed by functional near-infrared spectroscopy |
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| start_date | 2010/12/15 |
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| schedule | 10h30 |
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| online | no |
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| details | Membre invité externe par le groupe Propulsys |
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| summary | Electrical muscle stimulation (EMS) is a widely applied technique in clinical medicine and sports training to generate muscle contractions by activating peripheral motor axons. Although less well studied, EMS can also activate peripheral sensory axons that send proprioceptive and pain signals from the muscle to the sensory, motor and association cortices, thereby increasing cortical excitability and activation. The effects of increasing EMS intensity on frontal cortex (FC) activation have not been fully clarified. The aim of this study was to investigate by functional near-infrared spectroscopy (fNIRS) the FC oxygenation response to EMS-evoked contractions at increasing current intensity, and to compare these changes to voluntary contractions (VOL). METHODS. Nine healthy males underwent an EMS session with one arm and 24 h later performed VOL exercise with the contralateral arm. The EMS (30 Hz) and VOL exercise consisted of 30 rhythmic (1-s) isometric contractions at 30% of maximal voluntary contraction (MVC) for the first 60 s, followed by 30 maximal intensity rhythmic (1-s) isometric contractions (VOL at 100% MVC and EMS at the maximal tolerable current amplitude at 30 Hz) for the next 60 s. The maximal intensity contractions were continued until MVC decreased by ~30%. A NIRO-200 oximeter was used to measure oxygenated (O2Hb) and deoxygenated hemoglobin (HHb) concentration changes on the FC contralateral to the exercising arm during the two sessions. The average of every 15 s values for O2Hb and HHb and their area under the curve (AUC) during the first 60 s (30% MVC) and second 60 s (maximal intensity) were determined. RESULTS. In VOL, O2Hb did not change (P > 0.05) during 30% MVC; however, O2Hb progressively increased (P < 0.05) at 100% MVC, and O2Hb was greater (P < 0.05) during 100% MVC than 30% MVC. In EMS, O2Hb increased (P < 0.05) during 30% MVC, and thereafter progressively increased (P < 0.05) with increased current amplitude (i.e., maximum pain threshold), and both variables were correlated (r = 0.7, P < 0.001). O2Hb AUC was greater (P < 0.05) for EMS than VOL at 30% MVC, but no difference (P > 0.05) in O2Hb AUC was evident between EMS and VOL at the respective maximal intensity. O2Hb progressively returned to the baseline at the end of VOL or EMS. HHb decreased (P < 0.05) during 30% MVC and increased (P < 0.05) at the end of 100% MVC in VOL, but HHb did not change (P > 0.05) in the EMS condition. DISCUSSION. These results confirm that in VOL the FC plays a role in modulating the strength of the elbow flexor muscles and ensuring a correct execution of motor tasks. It was suggested that in EMS the FC may play a role in integrating sensorimotor information and evaluating an emotional response to pain. Conclusion. This study demonstrated intensity related increases in FC activation during EMS and VOL elbow flexor exercise using fNIRS. |
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| responsibles | Hoffmann, Marin |
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