Estimation of contractile parameters of successive twitches in unfused tetanic contractions of single motor units – A proof-of-concept study using ultrafast ultrasound imaging in vivo

Rohlén, RobinUmeå University,Lund University,Lunds universitet,Umeå universitet,Radiofysik,Department of Biomedical Engineering, Lund University, Lund, Sweden,Umeå Univ, Dept Radiat Sci Radiat Phys Biomed Engn, Umeå, Sweden.;Lund Univ, Dept Biomed Engn, Lund, Sweden.,Avdelningen för Biomedicinsk teknik,Institutionen för biomedicinsk teknik,Institutioner vid LTH,Lunds Tekniska Högskola,LTH profilområde: Teknik för hälsa,LTH profilområden,Departments at LTH,Faculty of Engineering, LTH,LTH Profile Area: Engineering Health,LTH Profile areas,Faculty of Engineering, LTH (författare)

During a voluntary contraction, motor units (MUs) fire a train of action potentials, causing summation of the twitch forces, resulting in fused or unfused tetanus. Twitches have been important in studying whole-muscle contractile properties and differentiation between MU types. However, there are still knowledge gaps concerning the voluntary force generation mechanisms. Current methods rely on the spike-triggered averaging technique, which cannot track changes in successive twitches’ properties in response to individual neural firings. This study proposes a method that estimates successive twitches contractile parameters of single MUs during low force voluntary isometric contractions in human biceps brachii. We used a previously developed ultrafast ultrasound imaging method to estimate unfused tetanic activity signals of single MUs. A twitch decomposition model was used to decompose unfused tetanic activity signals into individual twitches. This study found that the contractile parameters varied within and across MUs. There was an association between the inter-spike interval and the contraction time (r = 0.49, p < 0.001) and the half-relaxation time (r = 0.58, p < 0.001), respectively. The method shows the proof-of-concept to study MU contractile properties of individual twitches in vivo, which can provide further insights into the force generation mechanisms of voluntary contractions and response to individual neural discharges.

Raikova, RositsaInstitute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Sofia, Bulgaria,Bulgarian Acad Sci, Inst Biophys & Biomed Engn, Sofia, Bulgaria. (författare)
Stålberg, ErikUppsala universitet,Klinisk neurofysiologi,Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden(Swepub:uu)eriksb (författare)
Grönlund, ChristerUmeå University,Umeå universitet,Radiofysik,Umeå Univ, Dept Radiat Sci Radiat Phys Biomed Engn, Umeå, Sweden.(Swepub:umu)chgr0009 (författare)
Umeå universitetRadiofysik (creator_code:org_t)

Av författaren/redakt...: Rohlén, Robin; Raikova, Rositsa; Stålberg, Erik; Grönlund, Christ ...

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