Complex sentence: The original protocol set a 2:1 ratio of work to recovery periods, for example, 30--40 seconds of hard sprinting alternated with 15--20 seconds of jogging or walking.
Split into simpler sentences: The original protocol set a 2:1 ratio for work to recovery periods. For example, a runner would alternate 30--40 seconds of hard sprinting with 15--20 seconds of jogging or walking.