Some workouts don’t seem intimidating until you’re a few minutes in. The 90/30 fartlek is one of them: 90 seconds of strong running followed by 30 seconds easy, repeated over several kilometres. It’s straightforward, but it demands control, pacing and patience, building on exactly what most runners need. It will help build solid fitness gradually and won’t leave you feeling flattened for days.
The workout
Warm up with 15–20 minutes of easy jogging, then add a few drills and short accelerations to get your legs firing.
Run continuously for 6 to 10 kilometres, alternating between: 90 seconds at around threshold effort (roughly the pace you could hold for an hour), and 30 seconds at the faster end of your easy pace (just enough to stay in rhythm while catching your breath).
Finish it off with 5–10 minutes of easy running.
Keep the terrain flat, if you can. If you’re on trails, adjust your effort, rather than pace.
Why it works
The 90/30 might look easy at first glance, but it quickly turns into what elite coach and top American masters runner Mario Fraioli calls a “sneaky hard” effort. The alternating rhythm forces you to sit just below your limit, with intervals that are long enough to feel the strain, and then short enough that you can’t fully recover before the next surge.
As Fraioli explains, the beauty of the session is in how it teaches pacing and awareness. It’s designed to help runners learn where that invisible red line sits, and how to stay controlled without slipping too far above or below it. By the final mile or two, most runners find themselves digging in, not because the pace changes, but because the fatigue catches up. That, Fraioli writes, is the point. The workout offers a real-time sense of how your body responds under pressure, and how to manage that effort more intelligently the next time.
How to make it your own
If you’re newer to fartlek workouts, start with 3 to 5 kilometres (or even less) instead of 6, and stretch the recovery to 45 seconds, if needed. The key is keeping it smooth.
If you’re more experienced, extend the workout to 10 to 13 kilometres, or bring the harder intervals closer to 10K pace.
If you run trails, use the same timing, but focus on effort rather than pace. Try 90 seconds of strong climbing, then 30 seconds of controlled jogging.
