LAUSR

Studies on single muscle fibre passive material properties often report relatively large variation in elastic modulus, and it is not clear where this variation arises. This study was designed to determine if the elastic modulus is inherently different between type 1 and type 2 muscle fibres. Vastus lateralis fibres (n=93), from ten young men, were mechanically tested using a cumulative stretch-relaxation protocol. SDS-PAGE classified fibres as type 1 or 2. While there was a difference in elastic modulus between fibre types (p=0.0019), an unexpected inverse relationship was found between fibre diameter and elastic modulus (r=-0.64; p<0.001). As fibre type and diameter are not independent, a one-way ANCOVA including fibre diameter as a covariate was run; this eliminated the effect of fibre type on elastic modulus (p=0.1935). To further explore the relationship between fibre size and elastic properties, we tested whether stiffness was linearly related to fibre cross-sectional area, as would be expected for a homogenous material. Passive stiffness was not linearly related to fibre area (p<0.001), which can occur if single muscle fibres are better represented as composite materials. The rule of mixtures for composite materials was used to explore whether the presence of a stiff perimeter-based fibre component could explain the observed results. The model (R2=0.38) predicted a perimeter-based modulus of 8,800 ± 2,600 kPa/µm, which is within the range of basement membrane moduli reported in the literature.