I have 8 hours a week to devote to running. For which distance should I train?

800 meters

You could do anywhere from 5k-10k reasonably well with 8 hours.

8 hours at 8minute pace = potential maximum of 60 miles per week. That is more than enough for the 5K and probably 10K.

At age 40+ the 5K is probably too fast for you now, and so I would focus on the 10K.

Don't get bogged down in structured training since you are so pressed on time. Just make sure each week you are doing each of the following:

-Intervals of 1000m repeats (shoot for 5 repeats)

-1 tempo run of 4 or so miles at between HM or marathon pace

-1 long slow run of at least 10 miles

Just doing the above each week will result in increases to your 10K time, and that's ONLY 3 days of running each week. The rest of the days, if you're short on time, fine to go for a hobby jog or not even run at all. By hobby jog, I mean short 4-6 mile hobby jogs whenever you have time.

5k

One session a week plus 6 days of easy running. 8 hours is a lot. 40-50miles for 5k is plenty

How much of the 8 hours do you plan to spend trolling letsrun?

marathon on a track

You should do cross fit brah! Give up on the running if you don't want to be SKINNY FAT.

Ramp up your pace to 5:00/mile. That will give you 96 miles a week in your 8 hours. Make you a 10K - half marathon monster.

Literally any distance you want. That is more than most 5k-10k guys spend actually training at the college level.

800-1500 takes less time still.

And you can achieve modest/solid marathon goals on that 60-70 mpw.

Lol what college are you talking about?

For me it was a minimum of 3 hours a day on weekdays and about 2 hours a day per weekend.

Typical weekday:

AM: Easy 5-8 miles, untimed (~45 minutes)

PM:

-Warm-up jog (8 minutes or so)

-Stretching (15 minutes)

-Plyos/biomechanical work (15 minutes)

-Workout (45-60 minutes)

-Cooldown jog (10 minutes or so)

-Stretching (10 minutes)

-More plyos/biomechanical work (15 minutes)

-Core exercises on the track (10 minutes)

-Weights (30-45 minutes)

Typical Saturday (if not racing)

AM: 3-5 mile hobby job (30 minutes)

PM: 8 mile steady pace run (45 minutes)

Typical Sunday:

10-15 mile long run (60-90 minutes)

This is not even including time to travel to the track, changing, showering, ice baths, massages. Minimum 4 hour daily commitment save for weekends.

Good advice on the 40 mile per week training plan, but I have to question the time put in per day that you listed.

You were not doing workouts 6 days a week and you were not likely doubling 6 days a week. My guess is you were doing workouts 2 days most weeks, plus a race. Maybe 3 workouts if no race that week.

I was able to manage a fair amount of success at th4 Steeple/5k/10k on about 8-10 hours a week of training (including stretching time and some treatment time). My mileage ranged from 40 to 55 miles most weeks, with a rare 70 mile week here and there.

Admittedly, I am a dinosaur and this was in an era before doing tons of drills and active warm ups and weight training were as prominent as they are today. But if you are trying to maximize your return on hours invested because of the demands of real world living, I am guessing that most people would elect to focus on the core part of training - running miles with a light to medium stretch after your run (or after a light jog warm up on your quality days).

I started training again this year and have gotten to about 8 hours a week of cardio (1-2 hours is cycling). D1's advice is right on the money, but for me it's either-or on the 1000m repeats or tempo run each week. Some guys 40+ can handle 5K focus and anyone doing this level of training can certainly run them. This volume feels like bare bones for a decent half marathon but it's a possibility.

25 minutes a day of stretching? Are you training to be a gymnast?

Some additional thoughts/expansions on D1's suggested training approach (which I agree with):

Consider running your tempo runs a bit shorter (20 minutes rather than 4 miles) and at a bit of a faster pace. The rule of thumb that I go by is that they should be run at the pace that you would be able to race for an hour at. That is likely to be around 15k pace or faster for many people. Another measurement is usually around 5k pace plus 25 or so seconds. The subjective rule of thumb is that by a few minutes into the run, you should be able to speak a sentence at a time, but not able to maintain a conversation.

On the intervals, I would try to vary the distance from week to week so that you don't get stale or bored. Depending on your 5k race pace, you might go from anywhere between 800m to 1600m on your intervals. Generally, you should shoot to keep your intervals to between 3 and 5 minutes in duration. So if you are a sub 18:00 5k runner, you may not do the 800s, and if you are much above 17:00 for the 5k, you may not do the 1600s. Rest should be no longer than the duration of your interval (I tend to shoot for about a minute or so less than the duration of the interval). It should also be active rest (jogging) to the extent possible so that you heart rate stays up some so that when you start your next interval, you get into the target heart rate zone more quickly (thus maximizing the benefits of the workout).

30 seconds per stretch. Calves, glutes, hams, quads, groin, more hams, arms, shoulders, neck...that's a minimum of 20 stretches (10 x 1 for each side). Do the math.

We also did a fair amount of dynamic stretching. Plus, it takes time to gather the team together, shake things out between stretches, etc. We took injury prevention seriously.

We did double every single day (except Sunday). Saturdays were on our own, but during XC season we were expecting to put in at least 8 miles. My body couldn't handle that in a single run so I broke it up into a double. Some guys just did it as a single run.

My weekday training schedule wasn't all "workouts." I meant "training run/workout." Some of those days, depending on where we were in the season, we would either go for a regular steady and fast run, or do a more specific track or tempo workout. We did hard hard workouts 3 days a week (2 if there was a race).

We were also pretty good about using a lot of the more meaningless races as tune-ups. We'd send All-Americans to out of conference open races to run unattached to get race fitness, or save them and have them do a track workout instead of running some stupid invitational.

I would kick it up to a 50k trail race. Over 40yo, time for a change of scenery, plus plenty more glory to be had on the ultra scene.