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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, Robin LU orcid ; Raikova, Rositsa ; Stålberg, Erik and Grönlund, Christer (2022) In Journal of Electromyography and Kinesiology 67.
Abstract

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... (More)

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.

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Contribution to journal
publication status
published
subject
in
Journal of Electromyography and Kinesiology
volume
67
article number
102705
publisher
Elsevier
external identifiers
  • scopus:85138451119
  • pmid:36155330
ISSN
1050-6411
DOI
10.1016/j.jelekin.2022.102705
language
English
LU publication?
yes
id
9ea57dfa-e83c-4d23-8b9e-7bc0a1d3cdbd
date added to LUP
2022-12-27 15:24:16
date last changed
2024-06-28 01:41:11
@article{9ea57dfa-e83c-4d23-8b9e-7bc0a1d3cdbd,
  abstract     = {{<p>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 &lt; 0.001) and the half-relaxation time (r = 0.58, p &lt; 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.</p>}},
  author       = {{Rohlén, Robin and Raikova, Rositsa and Stålberg, Erik and Grönlund, Christer}},
  issn         = {{1050-6411}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Journal of Electromyography and Kinesiology}},
  title        = {{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}},
  url          = {{http://dx.doi.org/10.1016/j.jelekin.2022.102705}},
  doi          = {{10.1016/j.jelekin.2022.102705}},
  volume       = {{67}},
  year         = {{2022}},
}