Monitoring human physiological conditions using flexible, stretchable strain sensors is an effective approach to prevent and treat critical illnesses, emergencies, and infectious diseases. However, achieving ultralow detection limits, high sensitivity, and a wide detection range in a cost-effective manner is challenging. In this study, a strain sensor was developed by embedding an adhesive hydrogel composed of polyvinyl alcohol, starch, and glutaraldehyde into conductive fibers made from thermoplastic polyurethane. By leveraging the high sensitivity of the conductive fibers and the wide detection range of the hydrogel, a robust dual-layer continuous conductive network was formed through their synergistic interaction. Tensile strength tests and other assessments indicated that the sensitivity of the sensor increased from a gauge factor of 49.32 (for fiber-based sensors) to 74.18, while the detection range expanded from 250 to 400%. Furthermore, the sensor demonstrated a low detection limit (0.6%), fast response and recovery times (80 ms/120 ms), and durability exceeding 800 cycles. Tests on pulse monitoring, joint movement, and voice recognition confirmed the significant applicability of the sensor for real-time monitoring of various physiological activities throughout a human's life. This study aims to provide technical support for the development of flexible wearable systems.