Finally Figuring Out Treadmill Training

March was a tough marathon training grind. I finished with about 134 miles, barely more training miles than January. I only stretched my long run out to 17 miles, and each of my longest runs was a slow, very tough effort.

The key issue wasn’t a surprise: Las Vegas got warm. Winter’s over, and Vegas wasn’t going to stay cool forever. It’s not desert-hot yet, and we should avoid the worst heat before I shove off to Vancouver 2022. But temperatures got hot during stretches the law few weeks and the last weekend of March they topped 90°F. I also had trouble sleeping over the last few weeks (though I’m hoping to have nipped that). Even in the evenings, running was hot enough (temperatures in the high 70’s F) that I had to slow down and cut down the length of runs some.

I experimented with changing locations on my weekend runs, but ultimately my best options has once again become the gym treadmill. However, in the interim my research discovered some new hope for a previously hopeless training apparatus:

In recent weeks I discovered this calculator, the only one I’ve found that allows you to input both temperature and altitude with a current pace or race time, to get an adjusted equivalent time and pace.

Other calculators only do one or the other, and in many cases the conversions are coarse and broad. It was hard to figure out how running in 75°F weather at 2700′ (823m) differs from my Chicago runs that were often done in sub-60°F weather at 600′ (183m), let alone 100°F+ at 2300-2700′ (my usual Vegas summer outdoor conditions).

This calculator (while it requires metric inputs to properly work) gives a straight answer, and the results were so striking I had to first consider if the results were exaggerated or inaccurate. But then after verifying I realized that most conversions are excessively mild, typically because the formulas and factors were determined with high-level athletes, often in relatively comfortable or predictable circumstances (like flat ground, maybe a track, and reasonably temperate conditions). Most of us notice a more substantial effect, and this calculator appears to accurately measure the full effect of both.

Just to show an example, I entered a 10 minute mile, run at sea level in an ideal 53°F (converted and entered as 12°C), then entered a conversion to 73°F (23°C) at my home altitude of 2350′ (converted to 716m) at a 0.5% grade climb (26.4′ for 1 mile, adjusted to a flat 8 meters).

The converted equivalent pace is 11:44, a full 104 seconds slower! Surely, some of you reading may be thinking, that must be a mistake!

Let’s do different calculations with the same data where in each case we remove a factor so we can see how the time is affected.

Here’s one at sea level, removing the higher altitude:

Okay, similar but slightly faster pace. That’s still a 90 second difference, though it shows that the altitude while a relevant factor isn’t causing the substantial difference we saw.

Here’s another conversion, with the higher altitude but with the temperature 53°F (12°C).

In this case the adjusted time is much, much faster, much closer to the original 10:00. There’s still an altitude difference of about 24 seconds/mile, but that’s not nearly as much.

(And BTW yes, that’s a reasonable altitude adjustment. Most coaches traditionally overestimate that there’s no altitude effect on performance under 3000′. But again, that’s a product of lacking or confounded research, using high-level athletes who easily adjust to tough conditions. In truth, any altitude above sea level will cause some oxygen/gravity effect, and the effect goes from negligible to noticeable at as low as 1000-1500′. You won’t necessarily be sucking wind at 2350′, but your running there will be a bit harder than at sea level.)

So clearly, while the altitude produces a slight adjustment, any higher temperature adjustment creates a more substantial pace difference. Going off prior knowledge, once you’re above 60°F (16°C), any additional degree causes compounding difficulty with your running.

Side note: Elites experience a lesser effect at long distance from higher temperature for a simple reason: They’re very thin, due to self-selection (runners who become/remain serious runners tend to be lighter weight) and a running culture that pressures most of them to minimize bodyweight out of the simplistic, reductive belief that lighter equals faster, a belief that comes with countless caveats. But I digress.

In any case, because such runners have burned off most of their fat and adipose tissue, plus carry less overall muscle mass… these runners struggle far more with cold conditions, but also struggle far less with hot conditions. There’s less insulation that can cause overheating, and less tissue that their circulatory system needs to cool off (though that lack of insulation makes it easier for them to feel cold).

For most of us, every degree above 60°F creates quite a bit more heat that requires circulatory cooling, diverting oxygen from our running. This slows us down. If we fight against this by insisting on maintaining pace in hotter more difficult conditions, it compounds the overheating effect and often can speed us towards other health problems (heat exhaustion/stroke, etc).

Typically though, as we overheat our body’s nervous system naturally responds by further slowing and increasing the perceived difficulty of our effort to protect us by dissuading harder/faster running.

So it actually makes sense that temperatures 70°F and above would require a substantially slower pace to maintain the same effort as a faster pace in cooler conditions, that to maintain the same pace in hotter conditions requires a substantially greater effort since our circulation is also doing double-duty, not just supplying oxygen and glycogen to needed muscles but also trying to cool off our rapidly overheating bodies.

If you want to argue with the creator of this calculator about its merit, I suppose you can feel free to do so. And you would honestly be wrong to do so, plus he would be wrong to change its formulas or take it down in response. These are valid results whether you want them to be or not.


In turn, this pointed out to me several truths.

  • Once temperatures topped 65-70°F, my runs became a lot harder at the same pace, even harder after I reduced the pace on some a great deal. This is one reason why I was so exhausted last week that I stepped back my mileage a great deal, and possibly a contributing factor to why I didn’t sleep well. Even though I had run slow and maintained a similar, slightly increasing volume, I was slipping towards overtraining simply by trying to maintain my volume in slightly warmer conditions.
  • This also points out why running on a gym treadmill seems so much harder at the same pace. You are basically running in 70-75°F (21-24°F) with typical ambient indoor humidity (usually around 25-35% inside a busy gym), even with the A/C on. My original above calculation is basically the conversion to indoor treadmill pace with a 0.5% grade. To run the equivalent effort of a 10:00 mile at sea level you’d have to slow down by 104 seconds to 5.1mph (11:46 pace)!
  • In fact, working the equation backwards, to run 6.0 mph (10:00 pace) on a treadmill in those conditions is equivalent to running an 8:16 mile at sea level in 53°F weather! For someone who runs their easy runs at 10:00 pace, that treadmill effort is like running 10K pace! Even though the treadmill’s set to your easy pace!
  • What do you do about this? You go back to the old Lydiard/Hadd/Higdon advice to SLOW. DOWN. Throw mileage out the window, do your easy runs by equivalent time or calorie burn at a much slower pace than you’re used to. You work those untapped slow-twitch muscles, and you focus on matching the needed effort. Your body doesn’t strictly know miles or pace. It only knows effort, and the relative effort needed on an indoor gym treadmill requires a far slower pace than you can ideally run at that effort.
  • Because this will come up, obviously a better insulated or colder environment running on the treadmill is going to feel different, such as a treadmill in the garage during winter, which is typically not air conditioned and even with a space heater situation it can be somewhat cold. A treadmill run there will feel quite a bit easier and you can run easy quite a bit faster. But most of us have to run the treadmill in an indoor environment air conditioned to around 73-75°F, and that for this discussion is the relevant environment.
  • This lends itself far better to effort based, heart rate zone based, training than pace or defined mileage based training.
  • Since you do actually need to work on your desired goal pace for neuromuscular and bone/joint/tendon development, not to mention teaching your body to run the actual pace itself… you do pace runs outside, or you do mixed tempo runs where most of the tempo is at the same effort but equivalent but slower pace, with brief segments done at the actual pace (but of course as a result at a much higher intensity). I could and probably will write up a workout approach to this some time down the road.
  • But this kind of work usually has to be done tactically and carefully if you’re going to rely on indoor training. If you try to just run your assigned paces on an indoor treadmill, you’re not heat acclimated to 73°F or warmer, and your goal race isn’t in 73°F or warmer conditions… you’re going to basically over-train and consistently overexert yourself. If you finish your normal training plan doing that and then race in easier conditions, congratulations. You likely will crush your goal race, but mostly despite your training approach and because you managed to survive training too hard, not because you trained smart.

It’s too bad I had to learn this now, 5 weeks from Vancouver 2022 after struggling so much with training in conditions where unbeknownst to me I needed to vastly adjust-down my training paces, especially indoors on a treadmill, to successfully prepare.

It’s also why, despite running so slow in training beforehand with virtually no speedwork (and despite still recovering from a nagging bad right hamstring), I was still able to crush my efforts in the races I ran between last fall and January’s 10K. I was effectively trained to run those races in cold conditions, after training in somewhat warmer conditions. The relative heat acclimation got me ready by itself to run faster when it got colder.

So, since discovering this, I’ve gotten back on the treadmill and run at much, much slower paces, around 4.6-5.2mph. The gym is air conditioned to about 70-75°F, more like 73°F once you’re warmed up and are surrounded by other gym-goers. I run according to time, equivalent to how long it would take to run the desired miles at a converted pace (typically if I were running at 60°F at sea level with no incline). The running feels very slow, and anyway from absurdly easy to challenging but maintainable.

When I go out for outdoor runs I’m able to run comfortably fast, matching the converted expected VO2max from these shorter but warmer treadmill workouts.

This is ultimately a risky experiment. If I do a long treadmill workout at the equivalent of 20 miles but don’t actually run those 20 miles, am I still going to be ready for Vancouver? Can I run an equivalent marathon pace and effort in Vancouver next month. Traditional experts would say Hell No. I’m now curious to carry out the rest of Vancouver 2022 training with these converted treadmill workouts and see how Hell No and how far from fit and ready I turn out to be.

I’m no stranger to using myself and my own training as a guinea pig to (safely, legally) learn more about training effects and this I’ve decided is the best use of my remaining training time before Vancouver next month.

One thought on “Finally Figuring Out Treadmill Training

  1. […] have finally settled into a 3 day weekly training pattern, all brutal workouts on the treadmill. I ran 100 minute workouts on Tuesday and Thursday in a fairly humid Planet Fitness gym. These […]

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