Outdoor riding is one of the best parts of triathlon training. Fresh air, real terrain, and the satisfaction of covering actual ground. But for many athletes, the way they execute their outdoor rides is actively undermining the fitness they are trying to build.
The culprit is the same issue that plagues heart rate training: a reliance on averages.
The Average Power Trap
Here is a scenario that plays out on almost every outdoor ride. You have been prescribed a zone 2 endurance ride at 180 watts. You head out, the road is flat, and you settle into a comfortable rhythm at 175 watts. Then you hit a hill.
On the hill, you naturally push harder. Your power climbs to 240, maybe 260 watts. It feels like a reasonable effort for a climb. Then you crest the hill, the road tips downward, and you coast. Power drops to 80 watts. Maybe less. Over the next flat section you settle back to 175.
At the end of the ride, you check your average power: 182 watts. Right on target. But the training stimulus you received was nothing like a steady 180-watt ride. You spent significant time well above your target zone on the climbs and significant time well below it on the descents. The average looks correct, but the actual physiological stress is completely different from what was intended.
Why This Matters
When you push to 240 watts on a climb during what should be a zone 2 ride, you are recruiting muscle fibres and energy systems that belong to zone 3 or even zone 4. This is exactly the kind of mistake that makes sub-threshold work harder than it should be. This accumulates fatigue that a genuine zone 2 ride would not create. You finish the session more tired than you should be, your recovery takes longer, and the aerobic adaptation you were targeting is compromised.
The coasting on descents does not cancel this out. Your body does not work on averages. The minutes spent at 240 watts happened, and your body has to recover from them regardless of how many minutes you spent at 80 watts on the way down.
Your body does not experience averages. It experiences every moment. And the moments above target are the ones doing the damage.
How to Fix Your Outdoor Rides
The solution is not to avoid riding outside. It is to change how you manage intensity on varied terrain.
Cap Your Power on Climbs
If your target is 180 watts, then 180 watts is your ceiling - including on the hills. When the road goes up, shift to an easier gear, slow down, and keep your power under the cap. Yes, you will go slower up hills than you are used to. That is the point. The session is about spending time at the correct intensity, not about getting up the hill quickly.
Stay Active on Descents
Rather than coasting on descents, keep pedalling at a light resistance. Even 100 to 120 watts on a downhill keeps your legs turning over and contributes to time spent in the correct training zone. Free-wheeling for minutes at a time creates dead spots in your session that add to the duration without contributing to the training effect.
Focus on Time at Intensity
Shift your mindset from average power to time spent at the correct intensity. After a ride, look at your power distribution rather than just the average number. How many minutes were spent in zone 2? How many were above it? The goal is to maximise the time spent in the intended zone, and that requires active management throughout the ride.
When to Choose the Trainer Instead
There are sessions where an indoor trainer will simply deliver a better training stimulus than riding outside. Steady-state endurance work, threshold intervals with specific power targets, and recovery rides are all easier to execute precisely on a trainer where the terrain does not interfere with your intensity.
This does not mean you should never ride outside. Outdoor riding develops bike handling skills, builds mental toughness, and keeps training enjoyable. But if the purpose of a session is to spend 90 minutes at a specific power output, and your local roads make that difficult, the trainer is the better choice for that particular workout.
The best approach is to use both strategically. Ride outside when the terrain suits the session. Use the trainer when precision matters most. Either way, stop relying on averages and start paying attention to where you are actually spending your time.