CSS Threshold 100s

About 1,700 m, 40 to 45 minutes. The bread-and-butter fitness set once you know your CSS pace. Warm-up: 300 easy, then 4 x 50 build, 15 s rest. Main: 10 x 100 at CSS pace with 10 to 15 s rest. Cool-down: 200 easy. The pace should feel steady and uncomfortable rather than desperate, and the last 100 should match the first. If you fade by more than three seconds, lengthen the rest rather than slowing down. Scale it by repeats: 6 x 100 makes a 1,300 m morning, 15 x 100 a 2,200 m one. Holding the same pace on 10 s rest instead of 15 s is the clearest sign you are getting fitter.