Coach's Call Threshold 3x8 8-min intervals at maximal sustainable effort are directly supported by Seiler et al. (2013, Scand J Med Sci Sports 23:74-83, doi:10.1111/j.1600-0838.2011.01351.x): in 35 trained recreational cyclists, 4x8min (~90% HRpeak) produced a larger VO2peak gain (+11.4%) than 4x4 or 4x16. This 3x8 @ 98-102% FTP is a reduced-volume variant of that studied 4x8 protocol, trading one interval for slightly higher per-rep intensity; it accumulates substantial time near threshold while training repeatability. bike