30/30 Intervals — Why They Work So Well Thirty seconds isn't really long enough to accumulate a high level of blood lactate, so you're unlikely to hit a critical limit in that short window. But it is enough time to accelerate, settle into a hard effort for 15–20 seconds, then decelerate as you hit the recovery. Despite the short rest, heart rate stays fairly elevated — typically only dropping by about 5–10 bpm — so cardiovascular demand remains close to VO₂max across the set. That 30-second recovery isn’t just about catching your breath — it gives myoglobin in the muscle just enough time to reload its oxygen store. That makes it easier to hit high power again on the next rep, and it allows fast-twitch fibres to engage more fully. These fibres don’t cope well with long efforts, but short repeats with matched recovery give them a better endurance training effect. From an athlete’s point of view, these sessions usually feel surprisingly manageable. Riders often report finishing feeling energised rather than cooked — very different from the kind of fatigue you'd get after a traditional VO₂max session with longer reps. That’s why I use 30/30s frequently in training blocks — they work well, especially when managing load, and the results on the power curve speak for themselves.