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

Area of Science:

• Muscle physiology
• Skeletal muscle research
• In vitro muscle contractility

Background:

• Chemically skinned fibres are used to study human muscle contractile function in vitro.
• Specific force (SF) is a key measure of muscle contractile quality, calculated as maximal isometric force divided by cross-sectional area.
• Significant variability in reported SF values exists across studies, with the causes remaining unclear.

Purpose of the Study:

• To systematically review and identify the causes of variability in specific force (SF) measurements between studies.
• To explore methodological factors that may contribute to the wide range of SF data in the literature.

Main Methods:

• A systematic literature search was performed across Medline, Embase, and Web of Science databases.
• 137 datasets from 61 publications on healthy young adults were analyzed.
• Data were adjusted for methodological differences, including fibre shape, swelling, sarcomere length, and activating solution composition.

Main Results:

• A five-fold difference in mean SF was observed across studies.
• Adjustments for fibre shape, swelling, and sarcomere length did not significantly reduce SF variance (I² = 96%).
• Lower SF was associated with higher phosphocreatine concentrations and the use of Triton X-100 in the skinning solution.
• Ratios of SF for myosin heavy chain isoforms IIA and I were consistent across research groups.

Conclusions:

• The skinned fibre technique is reliable for assessing in vitro force generation.
• Variability in SF is significantly influenced by the composition of the fibre activating solution, which differs between research groups.
• Standardization of activating solutions may improve consistency in SF measurements across studies.