Local knee heating increases spinal and supraspinal excitability and enhances plantar flexion and dorsiflexion torque pr
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ORIGINAL ARTICLE
Local knee heating increases spinal and supraspinal excitability and enhances plantar flexion and dorsiflexion torque production of the ankle in older adults Henrikas Paulauskas1 · Neringa Baranauskiene1 · Junli Wang1 · Daiva Mikucioniene2 · Nerijus Eimantas1 · Marius Brazaitis1 Received: 6 February 2020 / Accepted: 25 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose Aging is associated with progressive loss of active muscle mass and consequent decreases in resting metabolic rate and body temperature, and slowing of nerve conduction velocities and muscle contractility. These effectors compromise the ability of the elderly to maintain an upright posture during sudden balance perturbation, increase the risk of falls, and lead to self-imposed reduction in physical activity. Short-term superficial acute heating can modulate the neural drive transmission to exercising muscles without any marked change in deep-muscle temperature. Methods To determine whether the short-term (5 min) application of local passive knee-surface heating (next-to-skin temperature, ~ 44 °C) in healthy older subjects of both sexes (64–74 years; eight men/eight women) enhances reflex excitability, we compared the voluntarily and electrically induced ankle muscle torque production and contractile properties with those of healthy younger subjects of both sexes (21–35 years, 10 men/10 women). Results The application of local heating (vs. control) increased the maximal Hoffman reflex (Hmax), the maximal volitional wave (Vsup) amplitude, and the Hmax/Mmax amplitude ratio, and decreased Vsup latency only in older adults. In the older adults (vs. younger adults), the application of local heating (vs. control trial) was accompanied by a significant increase in maximal voluntary peak torque, rate of torque development, and isokinetic peak torque of plantar flexion/dorsiflexion muscle contraction. Conclusion The spinal and supraspinal reflex excitability of older adults increased during local knee-heating application. The improved motor drive transmission observed in older adults was accompanied by increased voluntarily induced torque production of the ankle muscles during isometric/isokinetic contractions. Keywords Knee cap · Passive heating · Current · Electrical stimulation Abbreviations ANOVA Analysis of variance CON Control experiment CT Contraction time Communicated by Toshio Moritani. * Nerijus Eimantas [email protected] * Marius Brazaitis [email protected] 1
Institute of Sports Science and Innovation, Lithuanian Sports University, Sporto 6, 44221 Kaunas, Lithuania
Faculty of Mechanical Engineering and Design, Kaunas University of Technology, Studentu 56, 51424 Kaunas, Lithuania
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EMG Electromyography Hmax Maximal Hoffmann reflex Hreflex Hoffman reflex Hmax/Mmax The ratio of maximal H- and M-wave amplitudes HRT Half-relaxation time HT Experimental trial with local heating Mmax Maximal muscle compound action potential MnF Mean frequency MVC Maximal volun
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