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Methodological considerations in measuring specific force in human single skinned muscle fibres

Research output: Contribution to journalReview articlepeer-review

Original languageEnglish
Article numbere13719
Pages (from-to)e13719
JournalActa Physiologica
Issue number3
Early online date19 Jul 2021
E-pub ahead of print19 Jul 2021
PublishedNov 2021

Bibliographical note

Funding Information: We thank Ms Karen Poole for her help with designing the literature search strategy. We also thank Dr Edward T. Peltzer, who wrote the Matlab script files for the model II regression analysis and Professor Glen Lichtwark who assisted with updating the script file for the RCW figure. Publisher Copyright: © 2021 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd

King's Authors


Chemically skinned fibres allow the study of human muscle contractile function in vitro. A particularly important parameter is specific force (SF), that is, maximal isometric force divided by cross-sectional area, representing contractile quality. Although SF varies substantially between studies, the magnitude and cause of this variability remains puzzling. Here, we aimed to summarize and explore the cause of variability in SF between studies. A systematic search was conducted in Medline, Embase and Web of Science databases in June 2020, yielding 137 data sets from 61 publications which studied healthy, young adults. Five-fold differences in mean SF data were observed. Adjustments to the reported data for key methodological differences allowed between-study comparisons to be made. However, adjustment for fibre shape, swelling and sarcomere length failed to significantly reduce SF variance (I2 = 96%). Interestingly, grouping papers based on shared authorship did reveal consistency within research groups. In addition, lower SF was found to be associated with higher phosphocreatine concentrations in the fibre activating solution and with Triton X-100 being used as a skinning agent. Although the analysis showed variance across the literature, the ratio of SF in single fibres containing myosin heavy chain isoforms IIA or I was found to be consistent across research groups. In conclusion, whilst the skinned fibre technique is reliable for studying in vitro force generation of single fibres, the composition of the solution used to activate fibres, which differs between research groups, is likely to heavily influence SF values.

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