“…e.g., McCulloch et al, 1992 ; Martins et al, 1998 ; Nash and Hunter, 2000 ; Blemker et al, 2005 ; Röhrle et al, 2008 ; Heidlauf et al, 2016 ; Schmid et al, 2019 ), the active-strain approach employs a multiplicative decomposition of the deformation gradient tensor (cf. e.g., Kondaurov and Nikitin, 1987 ; Taber and Perucchio, 2000 ; Nardinocchi and Teresi, 2007 ; Ambrosi et al, 2011a ; Ehret et al, 2011 ; Stålhand et al, 2011 ; Hernández-Gascón et al, 2013 ; Giantesio and Musesti, 2017 ; Seydewitz et al, 2019 ) to incorporate the muscles' active behavior. Any continuum-mechanical formulation, however, is (almost) worthless without appropriate experimental data that characterize the mechanical behavior of the material itself and which is essential for accurately calibrating a specific constitutive model.…”