Determining footwear replacement based on piezoelectric output

An article of apparel, a system, and methods include a structural material configured to enable the article of footwear to the worn on a body. A wireless transmission circuit is included and a piezoelectric generator is positioned with respect to the structural material in a configuration to be flexed to induce a voltage signal output. A voltage sensor is configured to sense the voltage profile and output a sensor signal indicative of the voltage profile. An electronic data storage, coupled to the voltage sensor, is configured to store voltage profile information based on the sensor data. A comparator, coupled to the electronic data storage, is configured to identify a change in the voltage profile information over time. The wireless transmission circuit is configured to transmit data indicative of a physical status of the article of footwear based on the change in the voltage profile information over time.