Biologically speaking, what you report is not a fault.
When you run, your body is adapting to an alarm state. The blood supply is diverted to your muscles and away from functions such as digestion. as your digestive system takes a break it is sensible for it to jettison any unfinished business to avoid problems later.
This is common throughout the animal kingdom. Try chasing a herd of cows and see what you run through.
Adapting to becoming a runner may see a reduction in this response. Do be aware of the effect though, as dehydrating a bit on a hot day and then rehydrating at the end of a run can have some rather startling effects.
I'm making a comeback after three months in the Pyrenees followed by three months getting over some kind of sinus cold virus thing. Anyway It's seven months until the marathon that I've targetted. Two years ago I was nicely trained on long runs and felt pretty confident until I slipped on a muddy bank and broke my fibula.
I'm doing the Daniels' marathon plan. The first four weeks are thirty minute easy runs. My old easy pace, which didn't give me knee pain, was a nice easy to calculate ten minute mile. I used to run sixteen miles at that pace and still feel ready for more.
As it turns out, I can keep it going for a bit more than 5k, but it's a lot harder than trundling along at 6mph going 'Hello clouds, hello sky!'.
Gideon. I think that may be a very important measurement. To keep my speed down to what I reckoned ought to be my easy pace, I have had to shorten my stride until it really isn't a stride at all. I reckon I could do it with my shoelaces tied together. I walk at about 4mph on the flat, so my old 6mph jog seemed a reasonable step up.
I have been doing some corrective weight work to balance out my quads.
tricialitt: Yes, that's my quandary. Do I bin the slow runs and work on pace until my cruising pace is in the non painful region (only one minute a mile faster) or do I try to build endurance slowly at a pace that feels too fast for distance building ? I upped my speed a bit last year by binning long distance for a bit and doing track intervals.
It starts to sound like an insane idea I had when I started out (before finding the wisdom of this forum) of running a mile as fast as I could and then extending it by fifty yards each week until I could do it 26.4 times. A course in sports physiology put that idea to rest.
I'll see if I can get out of bed for a Park run tomorrow. I'd reckon on about a 25 minute time.
I was getting some knee pain after easy runs, so I eased back more.
The other day I was in a hurry, so when I found I'd let my pace get above easy, I thought "Oh the heck with it, Ill suffer for this later".
The extra speed shortened my run, so I figured that might be why I had less pain.
I went out again and again found I'd set out faster than I should have. I decided to see if I could keep the pace up and managed to for my whole scheduled run by taking the scenic route home. No pain. Next day, just fine.
This pace feels too fast to sustain for much more than 5k at the moment.
Should I train so that what currently feels like it should be fast pace feels like an easy pace ?
I was going to start increasing distance, but maybe I should wait until I can do the longer runs at this less painful speed.
I'm using the Marathon completion plan in Daniels' Running formula and had myself figured for about a 39ish VDOT.
As others have said, don't push too hard. A lot of programs seem to be geared to weekly increases of mileage. I found it was nice to repeat a week a couple of times and feel how much easier a route was second time round.
The 10% rule is a limit, not a target.
Don't worry too much about targets in the short term. If you see a race, set up a plan based on a calendar date and try to keep to a computer calculated schedule, you may be overtraining. the worst thing about overtraining is that you stop enjoying it.
I think it's generally reckoned that it takes about two weeks for the carbon monoxide to leave your bloodstream so you may start to feel a bit better in the next few days. 38" for a 5k from a standing start is not bad at all.