How to plan a route for interval training
On a trainer, an interval workout is easy to follow: the screen shows the target and the clock does the rest. Outside, the road decides how long you can hold an effort before a junction, a descent or a red light cuts it short. This guide covers how to choose a route by hand, so that the hard parts of the workout land on road that can carry them and the easy parts fall where you have to slow down anyway.
Start from the workout, not the map
Write the workout down as a list of blocks with their durations, for example a 15-minute warm-up, 4 × 8 minutes at threshold with 4 minutes easy between them, and a 10-minute cool-down. The work intervals are what the route has to serve. The warm-up, the recoveries and the cool-down are flexible and can take up whatever road is left.
Then look at the longest interval. That one number rules out more roads than anything else: a 3-minute VO2max effort fits almost anywhere, while a 20-minute threshold block needs a long climb or a long, quiet road.
Match each interval to a climb or an unbroken flat
Climbs are the easiest place to hold a steady effort, because the gradient keeps the load on and there is no reason to coast. Look for a climb that takes a little longer than the interval at your target effort, so the interval ends before the top instead of the hill running out first. How long a climb takes depends on its gradient and on your power, so estimate it from a previous ride up it, or from a similar climb, rather than from its length.
If there is no climb long enough, look for a flat or gently rising road with no junctions, roundabouts or traffic lights for the length of the interval. Short, hard efforts work on small rises. Long efforts below threshold work on flat roads, as long as nothing makes you stop.
Count minutes between stops, not kilometres
A route that looks clean on a map can still break every interval. Go through it and mark everything that makes you brake or stop: give-way junctions, traffic lights, roundabouts, sharp bends, villages, level crossings, gates on gravel tracks. Then estimate how many minutes of riding lie between those points at your interval pace. An interval needs a gap at least as long as itself.
Thinking in minutes also keeps speed in the picture. At threshold, 8 minutes on a flat road can be 5 km, and on a 7% climb closer to 1.5 km. The same interval needs very different stretches of road depending on where you ride it.
Put stops, turnarounds and descents in the recoveries
Recoveries are where the route can be untidy. Plan them where you would slow down anyway: the descent after a climb, the junction at the end of a straight, the edge of a village. The turning point of an out-and-back is a natural place for one.
Keep descents out of the work intervals. On a descent your power drops to almost nothing whatever you do, so an interval that runs over the top of a hill loses its last minutes.
Use out-and-backs and repeated segments
When you have one good stretch of road, ride it more than once. Repeating the same climb gives you identical intervals with the descent as the recovery, which suits hill repeats and VO2max sets. On a quiet, flat road, an out-and-back lets you ride one interval out, recover through the turn, and ride the next one on the way back.
Repeats also make the session easier to compare from one week to the next, because the road stays the same and only your numbers change.
Ride the hard efforts into the wind on flat ground
On a flat road, wind changes the effort more than anything else. Check the forecast and plan the work intervals into the wind. A headwind lets you hold high power at a moderate speed, and the tailwind on the way back becomes the recovery. With a tailwind, high power on the flat means high speed, which is harder to hold steady and leaves less time to react at junctions.
Judge an interval by its average, and switch to heart rate or feel when power won’t hold
Outside, power never stays as flat as it does on a trainer. Small rises, bends and gusts move it around, and that is normal. Press the lap button at the start and end of each effort, or let your bike computer run the structured workout, and judge each interval by its lap-average power rather than by the number of the moment.
Some terrain doesn’t let you hold power at all: rolling roads, loose gravel, technical singletrack. There, heart rate or perceived effort (RPE) is a better target. Heart rate lags a minute or so behind the effort, so give it time at the start of each interval before you judge it.
Choose quiet roads and quiet times
Hard efforts take attention away from traffic. Choose roads with little traffic and a clear view ahead, keep junctions and villages in the recoveries, and ride the session when the roads are quiet, for example early in the morning. Ride a new route once at an easy pace before you use it for intervals, so you know where the hazards are.
Letting Gritmaps do the search
Planning a route this way works, but it takes time with a map, and it gets harder the further you are from roads you know. Gritmaps does this search for you. You pick how long and how hard, or a structured workout, and it finds a real route where the terrain fits the intervals.
It works with power, heart-rate and RPE targets, for road, gravel and mountain biking. Generating routes is free. Sending the route and the workout to your Garmin or Wahoo is part of Premium, free during the beta, along with the advanced features listed in the plans.