© Springer Japan 2016. Many assistive devices designed to reduce fatigue on muscles during work are in development. Building models of human sensory and motor functions is helpful when creating devices to effectively and safely assist us in daily life. There is a sense of force associated with voluntary muscular exertion, which contributes to the perception of weight. Researchers in the field of perceptual psychology have investigated human perception characteristics of force over the years. These models of perception characteristics of force are helpful to evaluate subjective efforts associated with intuitive, safe, and easy-to-use products. In this chapter, two research studies are addressed in detail. The first study aims to model the perception characteristics of force, and explore its application in developing a perception prediction method during steering. This study estimates the muscle activity when using a steering wheel based on a three-dimensional musculoskeletal model, develops a perception conversion model that follows the Weber-Fechner law, and describes the experimental results that confirm the feasibility of the proposed force perception prediction. The second study aims to explore the challenges in developing wearable assistive technology that can enhance humans’ force perception capability by unloading voluntary muscle activation. This study measures the force perception capability of participants with different postures to investigate how differences in voluntary muscle activation affect force perception capability. Based on the experiments, a muscle-assistive wearable device that unloads the upper limb is developed, and the improvement in sensorimotor capability when voluntary muscle activation is reduced while wearing the device is evaluated.