Sweet Spot 2x20 — Free Zwift Workout
(.zwo Download)
Two 20-minute blocks at 88-94% FTP with 5 minutes easy between. The highest-return aerobic session per minute of fatigue cost.
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
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How long do you have?
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Free .zwo file. Drop it in your Zwift workouts folder — it shows up under Custom Workouts the next time you launch the app.
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Sweet Spot 2x20: prescription + science
Two 20-minute blocks at 88–94% FTP is the highest aerobic return per minute of fatigue. Here's the physiology behind training just below threshold — and how to slot it into your week.
“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 just below threshold
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 — hard enough to stress the aerobic system, easy enough that you can accumulate 40+ minutes without the lactate climb that cuts threshold sessions short.
Among cyclists with an identical VO2 max, the fraction of it they can hold at lactate threshold is what separates the strong from the dropped [2]. Raising that sustainable fraction is exactly what repeated sub-threshold work trains.
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 [3]. Two 20-minute blocks deliver that stimulus at far less neuromuscular cost than threshold or VO2 work, which is why it anchors most base and build weeks.
How to use it
One to two sweet-spot sessions a week is plenty alongside your easy volume. Hold the prescribed band — drifting up into threshold turns a repeatable session into a costly one. Build by adding minutes to each block before you add intensity.
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.
- 02Coyle et al. 1988. Determinants of endurance in well-trained cyclists. Journal of Applied Physiology, 1988.
- 03Holloszy & Coyle 1984. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. Journal of Applied Physiology, 1984.
Sweet Spot 2x20: common questions
Is a 2×20 sweet spot workout enough in one session?
Yes. Two 20-minute blocks give you 40 minutes of quality sub-threshold time — the dose most base and build weeks are built around. Extend to 2×25 or add a third block before you add intensity.
What power should sweet spot be?
Roughly 88–94% of your FTP. The generator sets the band from the FTP you enter, so the .zwo targets the right watts automatically.
How often should I do sweet spot?
One to two sessions a week works for most riders training 6–10 hours. More than that and you start eating into the easy volume that makes the hard work pay off.
Sweet spot vs threshold — what's the difference?
Threshold sits at 95–105% of FTP and accumulates fatigue fast; sweet spot sits just below at 88–94%, so you can do far more total time at a slightly lower stimulus. Sweet spot builds the base; threshold sharpens it.
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