What would happen if I did nothing but tempo runs?

You eventually would get hurt or be unable to hit pace from not enough recovery. If you manage to not get hurt and still hit pace you would likely just race poorly.

You'd stagnate at about 85 percent of your potential.

This and every single run would hurt along the way.

Are you capable to run 6:30 on your 1st mile of every run? If so, you are probably a 34 minute 10k guy who isn't trying hard enough.

i know guys who train like this. they run mileage at 7:00 and race at 6:30. and have an injury 80% of the time.

I did this in high school. Every day was 8-10 miles at 5:40-5:55 pace. My mentality was 'I have to work hard!'... I didn't know any better. I ran 9:12 3200 first meet of the year and 9:05 last meet of the year. You can run fast off that type of training, but you plateau, you don't reach a true peak. And I had pretty much no kick since I was just used to grinding all the time, so if anyone could sit on me long enough they'd out kick me.

I used to do this years ago because I didn't know any better. Now I struggle to hit the paces I ran at every day, but I race a lot faster.

Seemed to work out pretty well for CJ Albertson

2:55 mary

You don't understand tempo runs. There is no such thing as a pace to "hit."

He went from 1st to 13th. Clearly he didn't run a smart race by pacing himself properly.

can't always trust a distance runner to go by feel either. many seem to have a mindset that any effort that is not a TEN is "easy"

im one of them. i mostly go by heartrate to keep myself honest. though i know there are enough people who will say this is flawed as well.

He clearly stated a goal pace for his tempos.

And that's the problem.

i'm not surprised if there are so many definitions about "tempo runs" like shoe brands. anyway, if a moderate run is a 4 or 5/10, then the (lightweight) tempo run starts from 5.5/10, depending on the duration. it's "comfortably hard" and you can run a few per week. the result would be a solid distance runner.

and of course, there is also the "hard tempo" (8/10) with an ambitious given pace. this is a real workout (like the legendary "hard 10-miler"). some try to run pretty close to race pace (8,5-9/10) to test themselves or to shape up prior an important race. and you will be glad when a "hard tempo" is finished. we all know that nobody could do that for a few weeks.

If you can run a 36:50 10K, then 6:30/mi is about your estimated marathon pace. (If your "real" 10K race pace is faster, then 6:30 will be proportionally slower than your marathon pace).

So the theoretical question becomes, what improvements can 40mpw of training at marathon pace, with nothing faster or slower, bring?

One thing you don't mention is the range of training distances in a single day. Are some sessions shorter, e.g. 30 minutes, and others longer, e.g. 90 minutes, or are they all the same, like 1 hour a day, 7 days a week? Also, is the terrain flat or undulating? Changing these will provide a broader range of stimulation.

At a simple level, I like to think of training with three variables: endurance, stamina, and speed.

If you follow Jack Daniels, marathon pace is in the middle of a no man's land where it is not very effective at improving either endurance or speed.

Assuming 40 miles per week is not enough volume to get injured, you will become very efficient at marathon pace, but unless some of the runs are longer than 90 minutes, you won't have developed the endurance to run at that pace for much longer.

You might see some marginal improvements at 10K, and maybe even run a sub-3 hour marathon, but at some point you will stagnate, and you won't get the "bang for buck", that a variety of paces, distances, and terrain could bring.

You will get so fast until you can't handle it anymore.

You would get incredibly efficient at burning fat as a fuel source and likely get much faster if aerobic base is your true limiter and if that is actually your correct tempo pace and you're staying under 2.0 mmol on these runs.

Possibly repeatable but your intensity control would have to be near flawless.

No one knows. Why don't you try it and find out?

If I remember correctly, Brian Sell ran all his miles at or below 6:00 pace. Worked out pretty well for him...