The phrase "stayed on treadmill" can be expressed in many different ways using synonyms. For example, one could say "remained on the exercise machine," "continued walking on the treadmill," or "persisted with the cardio workout." Other options might include "kept up the running pace," "maintained the exertion level," or "stuck to the physical activity regimen." No matter how one chooses to say it, the essential meaning remains the same: that the individual in question committed to and followed through with their exercise routine, by staying on the treadmill to complete their workout session.