good to run on fatigued legs?

Here's my take.  Training is beneficial, sometimes we are tired when we train.  That is different than thinking that training tired is beneficial -- if you get what I mean.

To the extent that fatigue doesn't compromise the quality of your key sessions; the speed of your recovery from your key sessions... then training tired is OK.  As well, there will be periods in your athletic development where it may make sense to get quite tired -- there are endurance and mental gains that stem from learning to cope with fatigue.

 That said, with the athletes that I advise... the ability to get tired, isn't a key limiter.  Most often, we can increase performance (on a lower average training load) by improving recovery (mainly sleep) as well as enhancing nutrition.

 Kind of a long version of... "it depends".  

What I ask myself is "did I get tired the right way".  

Hope this helps,

g

The real question is, are you following a plan or just making it up as you go along?  If that is what the plan prescribes, then there should be some logical reasoning.

If it is not a plan and you are just making it up, maybe you should get a plan .......

I'm following Hal Higdon's training plan (Intermediate II) for the National Marathon (March 22) but also keeping a swimming + running base for my 09 tris (esp for IM Cozy).

I'm running: Tuesday and Thursday (3-5 mi), Saturday (5-10 mi), and Sunday (long run_ 10-20 mi).

I'm swimming: Monday and Wednesday (30-60 min)

I'm biking: Monday, Wednesday, Saturday (45-60 min)

I normally recommend that you listen to your body.  The main risk you have is that you are more likely to incur an injury when you're fatigued.  Especially when running.  What usually happens is that your body is tired, so form could become poor, and that can lead to injuries.  I'm not saying it will every time, but the possibility is there.

But, like others have said, sometimes we need a tougher workout like that for the mental boosts it can bring to our training.

Either way, just listen to your body - it will tell you when it needs a break, usually.  Good luck with your training!!

It probably did not hurt you.

So you're tired after a big day, and you run slower.  Nothing wrong with that; it's to be expected, really.

At least you ran slow, and didn't try to push the pace.