Zone 2 outside: how to plan a ride without stops, and why a few red lights do not ruin it

Does stopping ruin a Zone 2 ride?

No. The adaptations easy riding targets build from total time at low intensity across weeks, not from one unbroken block on one day. In the training-distribution research, the low-intensity share is counted in hours per week [Seiler 2010]. A minute at a light subtracts a minute from that total. It does not erase the 50 minutes before it.

The case for easy volume is well supported. Seiler's review of elite endurance athletes found that roughly 80% of training sessions sit at low intensity, with the hard work layered on top [Seiler 2010]. In a crossover study of 12 trained cyclists, six weeks of a polarized distribution (about 80% low intensity, 20% high, 6.4 hours a week) raised peak power 8% against 3% for a threshold-heavy block of 7.5 hours [Neal et al. 2013]. Stöggl and Sperlich found the same pattern in 48 well-trained athletes over nine weeks: the polarized group gained 11.7% in VO2peak [Stöggl & Sperlich 2014].

Read that last study carefully, because it cuts both ways. The high-volume group, which did mostly easy work with no hard sessions, did not improve further. Easy riding is the base the hard days sit on, not a complete program. Its job is volume at low strain, and a ride with stops still does that job.

There is no study on traffic lights and endurance training, so what follows is reasoning from mechanism, not a measured effect. Take a two-hour ride with 15 stops of 45 seconds each. That is about 11 minutes stopped, or 9% of the ride. If you want the full two hours of riding, add 11 minutes at the end. Heart rate falls during each stop and climbs back within a minute or two of riding, and nothing in the physiology suggests a short pause undoes the aerobic work already done.

What stops actually change: time in zone, heart rate and the surge

Stops cost three things. You lose moving minutes, unless you extend the ride. Heart rate gets harder to read, because it falls at each stop and lags on each restart. And each green light tempts a hard restart. The surge is the one that changes the ride, so ride away from lights in an easy gear.

Time in zone is the easy fix. Turn on auto-pause and count moving minutes at Zone 2, not elapsed time. A route that takes 2 hours 20 minutes on the clock may hold only 1 hour 55 minutes of riding. Plan the ride by the riding time you want, and expect the clock to run longer on a town route.

The surge is the real cost. Getting a bike from standstill back to 30 km/h takes a short, hard effort, and many riders sprint it out of habit. On your own file, the first seconds after a green often sit far above threshold. Twenty of those turn a Zone 2 ride into twenty small sprints with easy riding in between. None of them is dangerous, but together they add strain the easy day was meant to avoid. Pull away in a low gear, sit down, and let speed come back over 20 to 30 seconds.

Heart rate is the third cost. It lags power by tens of seconds, so a rider who restarts by heart rate pushes too hard while the number is still low from the stop. Use power or breathing for the first minute after each stop. Stops also blur the long-ride trace you would use to read cardiovascular drift, the slow rise in heart rate at steady power as stroke volume falls [Coyle & González-Alonso 2001]. If you want that read, take it from an unbroken stretch of the ride, not from the whole file.

Even with no stops at all, outdoor power is noisy. In 20 competitive cyclists doing 20-minute time trials, mean power indoors and outdoors was the same (280 vs 284 W), but within-ride variation outdoors was about double (SD 69 vs 33 W) [Jeffries et al. 2019]. A Zone 2 ride outside will never draw the flat line a trainer does. Judge it by average power and time in zone, not by every spike.

Hills on a Zone 2 ride: ride by a ceiling, not a target

On rolling roads, set a ceiling for the climbs, not a number to hold everywhere. Zone 2 spans roughly 56-75% of FTP [Allen et al. 2019]. Keep climbs under the top of that range, shift early and spin, and accept low power on the descents. A flat route is not required. A steady 2-4% climb is some of the best Zone 2 terrain there is.

Hills push power up because gravity sets the cost of each meter. A 6% ramp at a speed that feels normal can take a 70 kg rider well above Zone 2. Hold the ceiling by shifting before the grade bites and letting speed drop. If a short ramp still forces you over, a minute at tempo does not change what the ride was. A ride with ten such minutes is a different ride, so pick a flatter road or lower gearing.

On descents power falls to near zero. Pedal lightly where it is safe, and do not make up the lost watts with a harder push on the next flat. Average power on a hilly Zone 2 ride runs lower than on a flat one, and that is fine.

The best terrain is often a long, gentle climb. At 2-4% the road gives steady resistance with no traffic-light stops on most rural climbs, and power stays inside the band with little effort. Rolling roads with short, gentle rises work too. The terrain to avoid is steep and repeated: a road of 10% kickers makes the ceiling impossible to hold. For the harder end of the week, the same terrain logic runs the other way in our spoke on threshold intervals without hills.

How to plan a Zone 2 loop with fewer stops

Count junctions, not only meters of climbing. The best Zone 2 routes leave town early and stay on roads where you have priority: rural roads, river or canal paths, and laps of a quiet loop. Put the unavoidable stop-heavy part at the start and end, so the warm-up and cool-down absorb the lights.

This is the easy end of the rule that runs through doing intervals outside: pick the road for the workout, not the workout for the road. A threshold set needs a long uninterrupted stretch. A Zone 2 ride needs fewer stops across its whole length. The questions to ask a route are the same: how many junctions, how much traffic, and how steep are the climbs.

Four layouts work in most places. A long out-and-back on one rural road has two junction-heavy ends and an easy middle. A quiet loop of 5-15 km, such as a lake road, a business park at the weekend or a circuit of country lanes, can be lapped for as long as the plan asks. A river or canal path has few crossings, but share it at an easy pace and slow down for walkers. And a ride that leaves before the morning rush meets fewer cars at the same lights.

To check a route before you ride it, draw it in Komoot, Ride with GPS or Strava routes and count the junctions and lights along it on the map. A loop you already ride with few stops beats a new one that only looks good on paper. AdaptCycling's Suggested Routes offers loops sized to the day's planned riding time from your own speed and drops loops with too much busy road. It does not count traffic lights, so check the junctions yourself.

If the only roads near you are a grid of lights, the trainer is a fair answer for the easy day. An hour of uninterrupted Zone 2 indoors does the same aerobic job, and the outdoor ride can move to the weekend, when you have time to ride out of town first.

Quick answers

Sources cited in this guide

1. 01
   Seiler 2010. What is best practice for training intensity and duration distribution in endurance athletes?. International Journal of Sports Physiology and Performance.
2. 02
   Neal et al. 2013. Six weeks of a polarized training-intensity distribution leads to greater physiological and performance adaptations than a threshold model in trained cyclists. Journal of Applied Physiology.
3. 03
   Stöggl & Sperlich 2014. Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Frontiers in Physiology.
4. 04
   Coyle & González-Alonso 2001. Cardiovascular drift during prolonged exercise: new perspectives. Exercise and Sport Sciences Reviews.
5. 05
   Jeffries et al. 2019. An Analysis of Variability in Power Output During Indoor and Outdoor Cycling Time Trials. International Journal of Sports Physiology and Performance.
6. 06
   Allen et al. 2019. Training and Racing with a Power Meter (3rd ed.). VeloPress.

More inside How to do intervals outside

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