Coach's Call Threshold 3x6 18 minutes at FTP across three 6-minute reps with short recoveries — the most threshold work that fits a 30-minute session, and the top of the short-window range before threshold-2x10 takes over at 33 min. Ronnestad et al. (2025, Eur J Sport Sci 25:e70067, doi:10.1002/ejsc.70067) found a block of ~90% FTP / ~3mM intervals improved 15-min power (+4.9%) and power at 4mM (+4.5%) more than a matched HIT block in 22 well-trained cyclists. Rep intensity follows the library's rep-length curve. No trial of this exact structure is cited. bike