High-impact physical activity has a positive influence on bone health in humans. High-impact activity generates significant ground reaction forces (GRFs) between the plantar surface of the foot and the ground surface. However, the methods of assessment of plantar GRF are limited outside of a laboratory setting. We present a wearable device featuring force sensor resistors placed on the plantar surface of the foot which may present a feasible alternative to current laboratory technology. This paper presents the design, development, and validation of such a wearable system for the assessment of plantar GRF during various forms of physical activity. GRF estimates from the wearable device were moderately correlated with the gold-standard technology during physical activity, yet estimates during walking were highly variable. Future work should be directed toward individual anatomical site analysis to increase the accuracy of force estimates in a wider range of dynamic activities while also optimizing wearability of the system.