July 6, 2026 · 6 min read

Over-Unders — How to Train Your Legs to Handle Burning Lactate

Over-Unders are intervals where you alternate between just over threshold (105–110% FTP, the "over") and just under it (88–95% FTP, the "under"), with no full recovery between phases. The goal isn't "mental toughness" — you're training your muscles' ability to clear lactate while still working, because in the "under" phase the body has to metabolize what it built up during the "over." It's one of the most effective tools for variable-pace riding: climbs, attacks, riding in a bunch.

The burning in your legs isn't "lactic acid as waste" — it's rising hydrogen ions and lactate above threshold that the body can't clear fast enough. Over-Unders deliberately push you into that state, then — instead of letting you rest — force you to work under threshold, where you must "process" the accumulated lactate without stopping. Repeated many times, this teaches muscles and mitochondria to take up lactate more efficiently as fuel.

What the protocol looks like in numbers

For a rider with a 260 W FTP, a classic Over-Under looks like this:

• 3×12 min, alternating inside each block: 2 min "under" @ 90% FTP (234 W) and 1 min "over" @ 108% FTP (281 W).
• Recovery between blocks: 5–6 min easy in Zone 1 (120–140 W).
• Heart rate during the block drifts up, hitting 170–178 BPM in the "over" phases and never fully dropping in the "under" phases — that's intentional.

Watch the "under": it is not rest. 90% FTP is still hard after a phase above threshold — and that incomplete relief is what builds the adaptation. If heart rate fully resets in the "under," you set it too low.

How is an Over-Under different from a plain threshold interval?

Plain threshold intervals hold a steady ~100% FTP; an Over-Under deliberately oscillates around threshold, training you to cross it in both directions. That better mirrors real riding, where power jumps around — and it develops lactate clearance harder than holding one steady value.

Why it works on lactate threshold

The adaptation targets two things: lactate transporters (MCTs) and mitochondrial density. The "over" phase produces lactate faster than you can clear it; the "under" phase forces its uptake as fuel rather than further accumulation. Trained cyclically, this pushes your second threshold (LT2) upward — and that's what determines how long you can hold a high pace. You'll see the effect as a higher FTP and, more importantly, as a smaller power drop across repeated hard efforts. You'll read your threshold more precisely once you tie power to TSS and your load chart on variable sessions.

What power zone is the "over," and what zone is the "under"?

The "under" sits in the upper Zone 3 / lower Zone 4 (88–95% FTP), and the "over" enters Zone 4/5 (105–110% FTP) in the 7-zone Coggan model. If you're lost in the zones, revisit the guide to power zones in cycling and set your trainer's gates exactly on those values.

The most common mistakes

• "Over" too high — riding 120% FTP instead of 108% turns the Over-Under into a VO2max interval and you won't finish the session after the second block.
• "Under" too low — dropping to 75% FTP gives full recovery and cancels the entire point.
• FTP from thin air — the whole protocol depends on an accurate threshold. Set it from a fresh Ramp Test, not a result from six months ago.
• Too much per week — Over-Unders are a hard threshold session (~70–85 TSS). One, at most two per week, interleaved with other interval schemes and aerobic volume.

Summary

Over-Unders aren't about "getting used to pain" — they're about training the physiological ability to clear lactate while riding above threshold. Keep the "over" at 105–110% FTP, the "under" at 88–95%, and don't let heart rate fully fall between phases. Judge success not by how much your legs burned, but by whether FTP rises after 4–6 weeks and whether the chart shows a smaller power drop across repeated efforts above threshold. If you can't finish the third block at target power — lower the "over," not your ambitions.

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