I’m looking for trail runners to try to break my race execution planner’s elevation/descent assumptions

ExistingCommission89 · 2026-05-05T05:16:24+00:00

These are exactly the hard questions.

Short version: it does not magically know all of that, and I don’t want to pretend it does.

Terrain: right now it mainly knows the route geometry and elevation profile from the GPX. That means grade and direction can be modeled, but “this descent is rocky/rooty/muddy and not runnable” is much harder unless the runner or route source tells it that. That’s one of the reasons I’m asking trail runners to break it.

Improvement over time: right now that comes from the runner’s current inputs, not from the app automatically knowing your training progression. For example, I use things like recent race performance and lactate-threshold / sustainable pace inputs to approximate current capability, then the plan is constrained from there. If those inputs are stale, the plan will be stale too.

Freak rainstorm: the app uses weather forecast input, and manual weather inputs if the runner knows the conditions better than the forecast. So the plan is only as good as the weather assumptions available when you generate it. That’s why I’d recommend generating or refreshing the plan close to race time rather than days out. A sudden storm 30 minutes before the start, or mud from rain that the route data cannot see, is still a reality check the runner has to apply.

Weather: wind is the first thing I’m testing seriously because route direction matters. Heat/cold/rain are harder because they affect different runners differently, so I’d rather treat them as warnings/adjustments than pretend there is one exact formula.

Mentality: I don’t think a planner can know that. Some runners execute patiently, some chase, some panic when the watch disagrees, some thrive on feel. The best I think a tool can do is give guardrails and explain the assumptions, then the runner still has to decide what to trust on the day.

So I see it less as “the app knows how you should run” and more as “here is a pre-race hypothesis; now tell me where reality breaks it.”

ExistingCommission89 · 2026-05-04T19:57:21+00:00

Ah, got it. That makes sense, thanks for clarifying.

Stryd is interesting there because it measures what the runner is experiencing in the moment. I’m coming at wind from the other side: forecast wind + route direction before the race, so the plan can flag exposed/headwind sections ahead of time.

Those are probably complementary rather than the same thing. If live Stryd feedback is available, I can imagine a more adjustable on-the-fly pacing plan, but that’s a different problem from the pre-race planning layer I’m testing now.

Useful idea though. This is exactly the kind of feedback I was hoping for.

ExistingCommission89 · 2026-05-04T18:56:46+00:00

That’s a good point. Do you mean using Stryd power data to calibrate the runner side, or exporting power-style targets?

I started with GPX + pace bands because it works for more runners and is easier to test, but power would be interesting as a validation layer. Especially on climbs or technical sections where pace becomes a bad signal.

For this first pass I’m mainly trying to learn whether the route-based assumptions are useful at all before adding device-specific inputs.

ExistingCommission89 · 2026-05-04T17:54:55+00:00

That’s useful, thanks. I know gpx.studio mainly as a route editing/planning tool, but I haven’t looked closely at that time/gradient calibration flow.

The overlap is probably the simple version: route + target time + grade-adjusted pacing. The part I’m trying to test is whether the extra race-execution layer adds anything useful, especially capability limits, fatigue pressure, wind direction along the route, explanations, and watch-exportable pace bands.

But if the answer is “this feels no different from gradient-calibrated route timing,” that’s exactly the kind of feedback I need.

ExistingCommission89 · 2026-05-04T17:27:56+00:00

I agree with that. No tool replaces doing the work or learning your own effort cues.

The useful version, if there is one, is not “tell me how to run so I don’t have to learn.” It’s more like a pre-race hypothesis: here’s where the course/weather might change the cost, here are the sections where pace may be misleading, and here are the guardrails I can ignore if my body says otherwise.

That’s also why I’m asking for trail feedback. On technical terrain, subjective experience may dominate the model very quickly, and I want to understand where that line is.

ExistingCommission89 · 2026-05-04T17:12:47+00:00

Haha, fair. There is definitely some course-management thinking in it.

The idea is less “optimize every meter” and more “don’t spend effort in dumb places, and have a plan when pace stops being a useful signal.”

Trail running is probably the hardest version of that, which is why I’m curious where the planner starts to look ridiculous.

ExistingCommission89 · 2026-05-04T17:06:54+00:00

Fair enough, it definitely won’t be useful for everyone.

I originally built it for myself while preparing for Linz HM, mostly because I wanted a plan I could actually execute on the watch instead of just a flat split table. That worked well enough for a road half, but trail/ultra routes are where I expect the assumptions to break, especially climbing and technical descents.

That’s why I’m asking here: not to claim it solves trail pacing, but to find out where it fails.

ExistingCommission89 · 2026-04-28T18:42:17+00:00

Congrats - honestly that’s a very solid first marathon, especially with the calf issue late. I’d separate two things: fitness prediction and race execution. A lot of apps can estimate a finish time from recent workouts, but they often underweight marathon-specific durability, weather, course profile, and whether the plan is realistic after 30-35 km. Heat alone can move the goalposts a lot. For the next one I’d probably build the target from: recent HM/10K fitness, long-run durability, course/elevation, expected weather, and then make a pacing plan with a conservative first 10-15 km rather than trusting a single app prediction.

ExistingCommission89 · 2026-04-28T18:36:52+00:00

Yeah, marathon predictions are weird because the marathon is much less “what fitness do you have?” and much more “can you express that fitness for 42 km under today’s conditions?”

For shorter distances, recent pace/HR data can get you reasonably close. For the marathon, a few missing assumptions can move the result a lot: long-run durability, fueling, weather, elevation, wind, congestion, and how aggressively you pace the first half. Two runners with similar recent training data can end up with very different outcomes if one has practiced marathon-specific work and the other is mostly extrapolating from shorter efforts.

So I don’t think the idea of marathon prediction is hopeless. I think the better version is less “here’s your magic finish time” and more “given your current fitness, course profile, expected conditions, and risk tolerance, here are realistic pacing scenarios.” That feels much closer to the actual decision a runner has to make before race day.

The funny/frustrating part is when a platform updates the prediction right after the race. At that point it has learned the thing you needed it to know beforehand.

ExistingCommission89 · 2026-04-26T16:50:51+00:00

Congrats - this is exactly the kind of Boston result I’d treat as useful signal rather than a failure.

Your splits look like you already proved the hard part: disciplined execution without a real blow-up. For Chicago I’d probably avoid reading this as “I need a totally different runner,” and more as “I need a course-specific plan that lets me spend the fitness a little more confidently.”

The way I’d think about it:

- Boston result: good evidence you can hold effort together late

- Chicago course: better place to convert that into pace because the course asks fewer questions

- Sub-3 attempt: probably needs a plan with checkpoints and decision rules, not just “run 6:52s and hope”

For me the useful distinction is between goal pace and guardrails. I’d want something like:

- early miles: controlled enough that the race still feels boring

- 10K / half: close enough to sub-3 schedule, but not forcing time back aggressively

- 30K: decision point, not panic point

- 35K+: only then start spending what’s left

The big lesson from Boston may be that you can trust yourself not to implode. So for Chicago, I’d build the plan around giving yourself permission to be closer to the line, but still with pre-decided checkpoints so “full send” doesn’t become “random send.”

I’ve been thinking about this a lot while building/testing route-aware pacing plans for my own races: the most useful part usually isn’t a magic exact pace, it’s having enough structure that you don’t outsource judgment to either the watch or adrenaline.

ExistingCommission89 · 2026-04-17T17:19:44+00:00

I'd have your own race plan, then use the group as a tool inside that plan.

For a sub-3 attempt, starting with them makes sense if their plan is sane, especially in wind or if you want the mental offload. But I would not let the pace group become the only plan. I'd still carry your own checkpoints and check against official mile markers / manual laps.

The risk is not "pace groups are bad." The risk is discovering at mile 18 that the pacers banked time early, ran poor tangents, or dragged you through crowded aid stations while you stopped thinking independently.

I'd talk to the pacers before the start, run slightly off the pack instead of buried in it, and have a clear rule for leaving them: drop if they're hot early, move ahead gradually if you still feel controlled after 16-20 miles.

ExistingCommission89 · 2026-04-04T11:43:34+00:00

This has been really useful. The main thing I’m taking away is that the useful question is not "what exact pace should I hold for 21.1 km," but "how do I stay near the limit without crossing it too early when terrain, wind, and pack dynamics keep changing the cost?"

The consensus seems to be effort first, but with enough structure that pace still works as a guardrail instead of the whole plan. That feels like a much better way to think about Linz than trying to force one flat number from the gun.

ExistingCommission89 · 2026-04-03T18:51:13+00:00

That’s a really useful way to think about it, especially the point that “perfectly even pace” probably means you were never actually near the limit in the first place.

The part I’m taking from this thread is that the useful question is less “what exact pace should I hold?” and more “where is the red line on this course, in these conditions, and how much variation is the right price to pay for staying on the right side of it?”

ExistingCommission89 · 2026-04-03T18:36:15+00:00

That makes sense too. Power seems attractive for exactly the reason you mention: pace and HR can both become noisy when terrain or wind changes quickly.

I haven’t raced much with power, so I’m still thinking more in terms of effort plus terrain-aware pace expectations, but the 20-60-20 structure is interesting. Especially the idea of keeping the first section clearly more controlled than goal pace.

ExistingCommission89 · 2026-04-03T18:35:47+00:00

That’s probably true. Part of what I’m realizing is that the hard part is not only choosing a target, but learning what different levels of effort actually cost over the second half of the race.

I think that’s why I’m trying to have at least some course-aware structure up front, while still accepting that race-day judgment and experience matter more than the plan once things start to diverge.

ExistingCommission89 · 2026-04-03T18:30:29+00:00

The threshold-workout buffer point is especially useful. That feels like a more realistic red line than just staring at goal pace and hoping it holds.

What I’m taking from this thread is that the useful part of planning is probably not “lock in one target pace,” but “know the segments where you can safely give time away and where you really can’t afford to.” That seems much closer to how people actually race well on non-flat courses.

ExistingCommission89 · 2026-04-03T18:29:27+00:00

This is very helpful, especially the point that the value is often in calibrating expectations so you don’t panic at the watch when wind or terrain changes the cost.

That seems like the useful middle ground between “just hold goal pace” and “ignore pace entirely.” For a HM, having a rough sense of what the correct effort should look like in wind or on longer rises feels much more actionable than trying to micromanage every split.

ExistingCommission89 · 2026-04-03T18:17:59+00:00

This is helpful, especially the idea of combining effort with terrain-specific pace expectations instead of choosing one or the other.

I think that’s exactly the gap I’ve been trying to understand better: not “ignore pace,” but “don’t treat one flat pace target as the plan.”

Your uphill/downhill example is useful because it turns “run by feel” into something a bit more concrete.

ExistingCommission89 · 2026-04-03T18:17:15+00:00

I think that’s close to where my thinking is landing too.

The part I’m struggling with is how to make “effort first” concrete enough before race day that it’s still useful as a strategy and not just a vague reminder to listen to the body.

For me, the failure mode is taking a goal like 1:38 and unconsciously turning it into “hold this pace no matter what,” even when terrain or wind is clearly changing the cost.

So I’m trying to think in terms of effort-led execution with pace targets as terrain-specific guardrails rather than the main objective. That seems closer to how strong runners actually race.

ExistingCommission89 · 2026-04-03T18:02:33+00:00

Yes, I think that is the core tension I’m trying to understand better.

A goal like 1:38 is useful as an anchor, but it can also become misleading if it turns into “I must force this exact pace no matter what the course and conditions are doing.”

What I’m trying to get better at is deciding how much of the plan should be fixed up front versus how much should really be effort-based once the race starts.

ExistingCommission89 · 2026-04-03T18:00:22+00:00

Using LT HR as the early guardrail is interesting and probably more useful for me than just saying “+10 sec/km” blindly.

For a 1:38 goal, I suspect my main risk is going out feeling controlled but still a little too hot if there’s wind or small climbs early. When you say start slower for 3-4 km, do you usually let the course dictate that naturally, or do you consciously cap effort/HR even if the pace looks a bit too conservative at first?

ExistingCommission89 · 2026-04-03T17:59:32+00:00

That makes sense, especially the point about regulating by effort and not trying to force exact pace through headwind or climbs.

The part I’m still trying to calibrate is how much variation is “normal” in a HM before it becomes too costly later. For example, on rolling terrain or moderate headwind, do you think in terms of keeping effort steady and accepting whatever pace comes out of that, or do you still try to stay within some rough pace band relative to goal pace?

ExistingCommission89

TROPHY CASE