A shoe can include a sock liner assembly configured to receive a reflectant panel and a midsole assembly configured to receive an optical sensor. The optical sensor can include an optical source configured to emit a beam directed to the reflectant panel and an optical detector configured to detect a portion of the beam reflected by the reflectant panel. The optical sensor can be configured to measure a relative displacement between the sock liner assembly and the midsole assembly based on a change of the detected portion of the beam caused by the relative displacement.