Threshold intervals outdoors: finding the road for a 2×20
Threshold intervals need the right road more than most sessions. Twenty minutes at FTP leaves no room for a junction, a descent or a village halfway through. This guide covers what kind of road a threshold session needs, how to find one near you and what to do when there isn’t one.
How much road you need
A threshold interval is usually 8 to 20 minutes at 95–105% of FTP. Count minutes, not kilometres: a 20-minute interval needs 20 minutes of riding with nothing that makes you brake.
If nothing near you is that long, split the session. 3×15 or 4×10 at the same intensity gives similar training with shorter road.
Climb or flat
A steady climb is the easiest place to hold threshold: the gradient holds the power for you and there’s no coasting. A 4–7% climb that lasts the length of the interval is ideal. Steeper ramps push you over the target, and a climb with flat sections or dips breaks the effort.
On the flat, threshold is harder to hold because you go fast and every bend, junction and gust shows up in the power. Long straight roads, quiet valley roads and bike paths without crossings work best. A headwind helps: you get the same power at a lower speed.
Put the junctions in the recoveries
Go through the route and mark everything that makes you stop or slow down: lights, give-way junctions, roundabouts, villages, sharp bends. Then place the intervals between them, and let the recoveries and the ride between intervals take the junctions. A loop that repeats one good road, or an out-and-back on it, is often simpler than a long route that has to find several. The guide to planning a route for interval training covers this step by step.
Pacing outside
Outside, power varies more than on a trainer. Look at the lap average rather than the 3-second power, and start each interval a little under the target: the first minutes always feel easier than they are. Hard efforts take attention away from traffic, so ride a new road once at an easy pace before you use it for intervals.
A route that fits the intervals
The Gritmaps library has Threshold 2×20 and Threshold 3×15, and the Hard instant workout puts efforts around threshold into any duration from 30 minutes to 4 hours. You can also use a threshold workout from intervals.icu or TrainingPeaks.
Routes are scored on how closely the predicted power, with the wind forecast for your start time, follows the targets, and on whether each interval can be ridden without a break. Intersections, traffic lights and dense urban sections are penalised inside hard efforts, and busy roads lower the score. The route result shows where each interval falls on the map and on the elevation profile. With Premium, free during the beta, you can send the route and the workout to your Garmin or Wahoo. Generating routes is free. Create your free account and find the road for your next threshold session.
