Threshold Over-Unders — Free Zwift Workout
(.zwo Download)
Two minutes at 95% FTP, one minute at 105% FTP, repeated through a 15-20 minute block. Trains lactate clearance — the engine behind holding a pack on a surging climb.
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?
95–105% FTP — over-unders teaching lactate clearance
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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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Threshold Over-Unders: prescription + science
Two minutes at 95% FTP, one minute at 105%, repeated — over-unders train your body to clear lactate while you keep riding hard. Here's the physiology behind the burn.
Over-unders are a coaching construct. The citations below establish the lactate-clearance physiology the workout applies — not a test of this specific protocol.
Lactate is fuel, not waste
Lactate isn't a dead-end waste product — it's continuously produced and shuttled between cells to be burned as fuel [1]. The “under” segments are where your working muscles clear and oxidize the lactate the “over” segments produced.
What training changes
Endurance training raises your lactate clearance rate — trained muscle takes up and burns more lactate at a given intensity [2]. That capacity is built on more lactate-transport protein (MCT1) in the muscle, which endurance work upregulates [3]. Over-unders rehearse exactly this loop: produce, clear, produce, clear.
Why it matters for racing
Holding a surging pack on a climb means repeatedly going over threshold and recovering without sitting up. Over-unders train the clearance machinery that lets you absorb those surges instead of cracking.
Peer-reviewed sources
- 01
- 02Bergman et al. 1999. Active muscle and whole body lactate kinetics after endurance training in men. Journal of Applied Physiology, 1999.
- 03Dubouchaud et al. 2000. Endurance training, expression, and physiology of LDH, MCT1, and MCT4 in human skeletal muscle. American Journal of Physiology-Endocrinology and Metabolism, 2000.
Threshold Over-Unders: common questions
What are over-under intervals?
Blocks that alternate just above threshold (the “over”, ~105% FTP) and just below (the “under”, ~95% FTP) without full recovery, training your body to clear lactate while still riding hard.
What percent FTP are over-unders?
A common shape is 95% FTP for the unders and 105% for the overs. The generator sets the watts from the FTP you enter.
What do over-unders train?
Lactate clearance and the metabolic ability to recover from surges without easing off — the engine behind holding a pack on a surging climb.
How often should I do over-unders?
Once a week inside a build block is typical. They're demanding — pair them with easy days, not another hard session back-to-back.
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