Supraspinal Fatigue and Neural-evoked Responses in Lowlanders and Sherpa at 5050 m

Purpose At high-altitude, Lowlanders exhibit exacerbated fatigue and impaired performance. Conversely, Sherpa (native Highlanders) are known for their outstanding performance at altitude. Presently, there are no reports comparing neuromuscular fatigue and its etiology between Lowlanders and native Sherpa at altitude. Methods At 5050 m, nine age-matched Lowlanders and Sherpa (31±10 vs. 30±12 years, respectively) completed a 4-minute sustained isometric elbow flexion at 25% maximal voluntary (MVC) torque. Mid-minute, stimuli were applied to the motor cortex and brachial plexus to elicit a motor evoked potential (MEP) and maximal compound muscle action potential (Mmax), respectively. Supraspinal fatigue was assessed as the reduction in cortical voluntary activation (cVA) from pre- to post-fatigue. Cerebral haemoglobin concentrations and tissue oxygenation index (TOI) were measured over the prefrontal cortex by near-infrared spectroscopy. Results Pre-fatigue, MVC torque and cVA were significantly greater for Lowlanders than Sherpa (79.5±3.6 vs. 50.1±11.3N·m, and 95.4±2.7 vs. 88.2±6.6%, respectively). With fatigue, MVC torque and cVA declined similarly for both groups (~24-26% and ~5-7%, respectively). During the task, MEP area increased more and sooner for Lowlanders (1.5min) than Sherpa (3.5min). Mmax area was lower than baseline throughout fatigue for Lowlanders but unchanged for Sherpa. TOI increased earlier for Lowlanders (2min) than Sherpa (4min). Total haemoglobin increased only for Lowlanders (2min). Mmax was lower while TOI and total haemoglobin were higher for Lowlanders than Sherpa during the second half of the protocol. Conclusion Although neither MVC torque loss nor development of supraspinal fatigue was different between groups, neural evoked responses and cerebral oxygenation indices were less perturbed in Sherpa. This represents an advantage for maintenance of homeostasis, presumably due to bequeathed genotype and long-term altitude adaptations. Correspondence: Dr. Chris McNeil, School of Health and Exercise Sciences, Faculty of Health and Social Development, The University of British Columbia – Okanagan Campus, 133-1147 Research Road, Kelowna, British Columbia, Canada, V1V 1V7. E-mail: chris.mcneil@ubc.ca. Tel.: +1-250-807-9664, Fax: +1-250-807-9865 This work was supported by the Natural Sciences and Engineering Research Council of Canada (DG 435912-2013) and the Canada Foundation for Innovation / British Columbia Knowledge Development Fund (32260). The authors declare they have no conflict of interest. The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation and do not constitute endorsement by the American College of Sports Medicine. Accepted for Publication: 27 July 2018. © 2018 American College of Sports Medicine

from Sports Medicine via xlomafota13 on Inoreader https://ift.tt/2OPgdH3
via IFTTT