Flexible wearable sensors that combine excellent flexibility, high elasticity, sensing capabilities, and outstanding biocompatibility are gaining increasing attention. In this study, we successfully develop a robust and elastic hydrogel-based flexible wearable sensor by modulating molecular structures combined with metal ion coordination. We leverage three N-acryloyl amino acid monomers, including N-acryloyl glycine (AG), N-acryloyl alanine (AA), and N-acryloyl valine (AV) with different hydrophobic groups adjacent to the carboxyl group, to copolymerize with acrylamide (AM) in the presence of Zr4+ for hydrogel preparation in one step (P(AM3-AG/AA/AV0.06)-Zr0.034+ hydrogels). Our investigation reveals that the P(AM3-AV0.06)-Zr0.034+ hydrogel with the most hydrophobic side group demonstrates superior mechanical properties (1.1 MPa tensile stress, 3566 kJ m-3 toughness and 1.3 kJ m-2 fracture energy) and resilience to multiple tensile (30% strain, 500 cycles) and compression cycling (50% strain, 500 cycles). Moreover, the P(AM3-AV0.06)-Zr0.034+ hydrogel exhibits good biocompatibility and high conductivity (1.1 S m-1) and responsivity (GF = 16.21), and is proved to be suitable as a flexible wearable sensor for comprehensive human activity monitoring.