This paper describes a biohybrid actuator consisting of a microgrooved thin film, powered by contractile, aligned skeletal muscle cells. The system was made of a thermoplastic elastomer [SBS, poly(styrene-block-butadiene-block-styrene)]. We prepared SBS thin films with different thicknesses (0.5-11.7 μm) and Young's moduli (46.7-68.6 MPa) to vary their flexural rigidity. The microgrooves on the SBS thin film resembled the microstructure of the extracellular matrix of muscle and facilitated the alignment and differentiation of skeletal muscle cells. Electrical stimulation was applied to self-standing biohybrid thin films to trigger their contraction, enabled by the low flexural rigidity of the SBS thin film. Finite element model simulations were also examined to predict their contractile behavior. We achieved the prediction of displacements, which were rather close to the actual values of the SBS thin film: the discrepancy was <5% on the X axis. These results pave the way for in silico prediction of the contractile capabilities of elastomeric thin films. This study highlights the potential of microgrooved SBS thin films as ultraflexible platforms for biohybrid machines.