Push Pull Legs is a free iPhone app designed by Mark Bragg, focusing on the concept of Progressive Overload in weightlifting. The app helps users track their workout progress by measuring the load on their muscles through weight, repetitions, and time. By following the principles of lifting heavy, training to failure, and maintaining progressive overload, users can optimize their gains effectively.

The app allows users to log their workouts set by set, customize their regimen, add new exercises on the go, and view past workouts in the database log. Each set is timed, enhancing the workout experience and ensuring efficient progression tracking.