I think the appeal to distance is that it's very concrete. Go out and run three miles and everyone knows what that means. If you have a car or GPS watch or run on a marked trail, access to a computer and know how to use an online map to do it, or heck even just have a good feel for distances you can just plot that distance out and run it. Also people set goals with races, like I want to run a 5k. You don't ever hear anyone say I wan to run a 45m (minute). Apparently one of the drawbacks to setting distance goals is that not all three mile stretches are the same. If I say to someone at work that I'll be running three miles, those three miles are way different than the three miles around my house.
Let's take two very similar distanced runs
|About three miles near my house|
|About three miles near where I work|
The home run has a change in elevation of 45 feet the whole time. So when you look at that graph, if you change the numbers on the right side you could say I started at zero, over the next mile I climbed 20 feet, and then over the next 2 miles I descended 40 feet. Let's put that in context; a flight of stairs is about 15 feet of climbing. So over the course of 8 minutes I want you to climb one and a half flights of stairs, and then over the course of 16 minutes I want you to walk down two and half flights. Take note about how your feeling at the end.
The work run has a change in elevation of 72 feet the whole time. The deal here though is that it's basically done twice on the same run. So if we say I started at zero, I climb about 15 feet over about half a mile, then descend 72 feet over the next 1/2 mile. Then about 1 mile later I do it in reverse. Back to the stairs (you're going to need a taller building.) In four minutes I want you to climb one flight of stairs, in the next four minutes I want you to descend five flights. Take a 8 minute rest. In four minutes I want you to climb five flights of stairs and then immediately run around and descend one flight, take your time on that you have four minutes. Now compare how you're feeling to the first time.
So a popular answer to this seems to be time. If three miles one day is going to feel substantially different than three miles on another day due to terrain or weather or general body feelings, maybe it's better to set a time goal. I've heard a variety of explanations, but basically it comes down to the idea that 45 minute is 45 minutes. If you are feeling cruddy that might mean 2 miles, or if you're feeling great maybe it will mean 8 miles. The common concern I've heard about this is that if you're training for a marathon and you've never done one you might be concerned that you're not going to get the miles in. I think for most training plans though they are designed for a particular skill level and if they say run 30 minutes they know about how far you might cover on average.
Four years ago I started with couch to 5k. It's totally time based. If I remember correctly the longest amount of time you run is about 45 minutes, and that's 15 minutes per mile which should mean that at the end of that I should feel comfortable finishing a 5k. The main problem I had that year was that 20 minutes out was not the same distance as 20 minutes back. So I often ended up 5 minutes from my house.
Three years ago I just "did whatever" and it was all distance based. At this point we had two kids, and were living in Florida, and so I tried to make sure I was staying on a schedule. The problem I ran into then was 1.5 miles out was not the same time or effort as 1.5 miles back, so I often found myself disappointed with my performance.
Two years ago I took a slightly more methodical approach and had a more steady schedule, but again it was basically distance based. This time we were back in Minnesota, and our kids were a little older so my schedule was less rigid. I was also in better shape, so now 1.5 miles back is roughly the same time as 1.5 miles out.
This year I'm back to time based. Because my first big goal is to accomplish the longest race I've ever done I went out and found a training program and modified it slightly to fit my needs, but it's all time based. There are some very long times on there. And here's the rub, if you're going to be going for a long enough time even on a run, you need to have some sort of plan on where you're going. For instance near my house if I turn right at the end of my street and try to run for 30 minutes in one direction (60 minutes total,) after about 20 minutes I'd start running into dead-ends or highways. If I run around the lake, as long as I don't need to run longer than 90 minutes I can do that loop twice, but that's going to get boring. I mean I don't mind running for 45 minutes in one direction and then running back, but I'm not super excited about running a big loop twice, it'd be super tempting to stop as I passed my house.
So I've started mapping out my runs with an approximate distance. And that leads to the next problem - this year I'm gaining speed much faster than I have in previous years, and the times are getting longer. For a 30 or 40 minute run I can basically just go out and then turn around and come back half way through. For a 60 minute run though unless I start running into problems where I'd need to re-run portions of a course two or three times if just did that. Some of it is the area's I'm running in; the longest trail I can easily get my hands on is about 6 miles.
Back to the mapping. Let's take yesterday for example. The prescribed set was an hour and fifteen minutes, 20 minutes warm up, 35 minutes of 3 minutes hard, 2 minutes recovery, 20 minutes warm down. I figured about 8 miles would cover it assuming nine minute miles.
|I potted a 8ish mile course|
So I get it, the time based thing has it's benefits. This is even more clear on a bicycle where environment can really wreak havoc. Try peddling into the wind for 10 miles one day and compare it to the same distance on the way back. I don't really have a problem with it, I'm just struggling with the logistics of it. In the end I suppose I could hop on a treadmill or track and do it, but seriously, an hour on a 400 meter track would be like 30 laps. I'm pretty sure I'd be dizzy :) I really want a hybrid model - similar to car warranties. Today's run is 7 miles or 60 minutes, whichever comes first. I think it would give some sort of scope so if I was feeling junky I'd just do 60 minutes, but if I was feeling great I could push for the seven miles and be happy with that.