Association of vastus lateralis diffusion properties with in vivo quadriceps contractile function in premenopausal women

Background: Diffusion tensor imaging (DTI) parameters correlate with muscle fiber composition, but it is unclear how these relate to in vivo contractile function. Purpose: To determine the relationship between DTI parameters of the vastus lateralis (VL) and in vivo knee extensor contractile. Methods: Thirteen healthy, premenopausal women underwent magnetic resonance imaging of the mid-thigh to determine patellar tendon moment arm length and quadriceps cross-sectional area. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) of the VL were determined using diffusion tensor imaging (DTI). Participants underwent an interpolated twitch (ITT) experiment before and after a fatiguing concentric-eccentric isokinetic knee extension (60°·s⁻¹). During the ITT, supramaximal electrical stimuli were delivered to elicit twitch responses from the knee extensors before, during, and after a maximal voluntary isometric contraction (MVIC). Knee extensor-specific tension during twitch and MVIC were calculated from isometric torque data. Pearson's correlations were used to determine the relationship between muscle contractile properties and DTI parameters. Results: MD and RD were moderately correlated with peak twitch force and rate of force development. FA and AD were moderately inversely related to percent change in MVIC following exercise. Conclusion: MD and RD are associated with in vivo quadriceps twitch properties but not voluntary strength, which may reflect the mechanical properties of constituent fiber types. FA and AD appear to relate to MVIC strength following fatiguing exercise.