Is it OK to run twice a day?

Richmond Park is full of lovely old oak trees

Hubby and I ran around the edge of Richmond Park today - a beautiful run, stunning setting, great hilly trails, a bit hot even at 8 am this morning so we  had to stop a couple of times to let the dog have a swim in the ponds to cool down.  Never in my life has a dirty pool of water strewn with the type of stringy pond weed that I've always had a phobia of ever been so appealing.  I envied our dog lolling around, lapping up the cool clear murky brown water.

Anyway, the run itself transpired to be a couple of kilometers shorter than we'd hoped.  I was also a bit behind my weekly quota as I had not run on Saturday run due to a twingy hip that I mysteriously woke up with, and that just as mysteriously wet away overnight.  As I pondered how to make up a few more K, the obvious answer was to get another run in today.  

So far we've not seen any deer and  therefore not
had a 'Fenton' moment. Thank God!!

As I had to visit my mums place and water the plants while she's out of town, I seriously considered running  there and back, which is 3 miles each way, but the 30+ degree heat coupled with my ignorance about the bodies reaction to running twice in one day forced the decision to do some research first.

I Googled the question for a while, and there are a couple of schools of thought about this.

The first is, by running more often, you reap the same fitness benefits you get when you boost the duration and intensity of any one run: reduced body fat, increased VO2 max, and improved muscle tone. You just get those benefits sooner when running more than once a day.  Advocates of running twice a day do stress that one workout needs to be an easy, low intensity session, and you should build up to it slowly.  For example, go out twice a day twice a week, but at first keep the second session to 15-20 minutes long.

The second view is that its a bad idea, as once you come back from a run your body starts to rest and repair any damage. It then has a good 24 hours to recover (including a nights sleep) before you go out for your next run (assuming you go out each day). If you run twice your body will have less time to recover and could cause injury.

I personally believe this is one of those issues where listening to your body becomes the main factor.  For some one who's been running a while, who's fit and uninjured and has the energy, I can't see it being an issue.

 I run almost every day (even if its just a couple of kilometres) and also go to yoga at least twice a week, and the gym twice a week too, so am used to working out twice in a day, so I don't think running twice can hurt me,provided I'm sensible and don't overdo it.

  I waited for the temperature to drop to a balmy 29 degrees, and drive to a kilometre away from my mums place, and have a lovely little run along the towpath to her place and back.  It's upped my quota just enough that I don't feel I've under achieved this week.

I decided to do this extra 2K in my Merrells, and I'm not if it was poor running technique in these or the simple act of running twice in a day, but my shins really complained immediately following the end of the run. After a few minutes rest they're absolutely fine, but it's something I'll have to keep my eye on. I suspect the heat today has wearied me and I've been a bit sloppy.  I'll try this again and will see how I get on.