Sweet Spot 3x15 — Free Zwift Workout
(.zwo Download)
Three 15-minute blocks at 88-94% FTP with 5 minutes easy between. Forty-five minutes of sub-threshold work, broken so each block stays honest — the base-season progression from the 2x20.
Built by Jim Camut. JB Cycling Academy 2004–09 · PCS-verified · Cyclingnews diarist alumnus.
Where are you in your riding?
Trains consistently — doesn't race
What do you want from this workout?
88–94% FTP — sustained aerobic stress
Optimize for…
Same session for every mass-start discipline. Only gravel differs, riding the blocks at a lower cadence.
How long do you have?
Live preview
Pick your settings
Free .zwo file. Drop it in your Zwift workouts folder — it shows up under Custom Workouts the next time you launch the app.
Or build your own custom workout →
Sweet Spot 3x15: prescription + science
Three 15-minute blocks at 88–94% FTP is 45 minutes of sub-threshold work with two resets built in. Here's why splitting the dose into shorter blocks protects the quality — and when to pick it over a 2×20.
“Sweet spot” is a coaching term for the band just below lactate threshold (~88–94% FTP). No study tested it by name — the citations below establish the threshold physiology it targets.
Why block length matters
Functional threshold power is the highest output you can hold in a quasi-steady state for about an hour [1]. Sweet spot sits just under that ceiling, so the limit on a session is rarely the power itself — it's how long you hold the band before the effort drifts up into threshold and starts charging threshold-sized fatigue.
Three 15-minute blocks put 45 minutes in the band with two recoveries to reset posture, cadence and breathing. That is the same quality time as a 2×22, with the drift reset twice as often.
What the work actually changes
Sustained aerobic efforts drive mitochondrial density and oxidative-enzyme content in the trained muscle — the machinery that lets you make more power before lactate accumulates [2]. The stimulus tracks total time in the band, so 3×15 and 2×20 are close cousins. Pick whichever you can finish at the prescribed watts.
When to choose 3×15 over 2×20
Take the 3×15 early in a base block, coming back from time off, or when you know your power sags in the last five minutes of a 20-minute block. Move to the 2×20 once the 15s stop feeling hard. Among riders with the same VO2 max, the fraction of it they can hold at lactate threshold is what separates them [3] — and that fraction is trained by finishing blocks at the right watts, not by starting longer ones you fade through.
Peer-reviewed sources
- 01Borszcz et al. 2018. Functional Threshold Power in Cyclists: Validity of the Concept and Physiological Responses. International Journal of Sports Medicine, 2018.
- 02Holloszy & Coyle 1984. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. Journal of Applied Physiology, 1984.
- 03Coyle et al. 1988. Determinants of endurance in well-trained cyclists. Journal of Applied Physiology, 1988.
Sweet Spot 3x15: common questions
Is 3×15 better than 2×20 for sweet spot?
Neither is better in the abstract. 3×15 gives you 45 minutes in the band against 40, with an extra recovery to reset form. Choose it when a 20-minute block is where your power starts sagging, and move up when it isn't.
What power should a 3×15 sweet spot be?
Roughly 88–94% of your FTP, the same band as any sweet-spot session. The generator sets the watts from the FTP you enter.
How long is the 3×15 workout in total?
75 minutes: a 15-minute warm-up, three 15-minute blocks with 5 minutes easy between them, and a 5-minute cool-down.
How often can I ride sweet spot?
One to two sessions a week suits most riders training 6–10 hours. More than that eats into the easy volume that makes the hard work pay off.
Go deeper
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