The effectiveness of the interval length exhibits variability, further indicating that there is no one best way to implement working sets. For example, one study suggested that a 30s interval improved the performance of a 20 minute power test more than the 5 minute intervals, while this was true because the mean power was higher in the short intervals with the 30s duration. But Contrarily, some studies indicated that the longest duration, 4x8 minute intervals provided the greatest performance gains. There is more to this than just the length of the interval; intensity and time of the intervals also matters. Both short and long intervals have some purpose in an athelete’s training program.