"You cramped because of lactate build up" - that shows a remarkable insight into the cramping problem off little information. The scientific proof between lactate build up and cramping is poor. Similar with electrolyte/salt although this is a more popular line.
"Didn't cramp in training but only went into late teens although probably slower pace than the marathons" It would be good to get an understanding of training pace (or Heart Rate) and typical mileage. When you say "probably slower" does this mean you are not monitoring your pacing?
If I had cramped up in a couple of marathons I would probably focus on muscle endurance. Certainly building up the long slow runs to include a few 20's. Possibly with some general strengthing
I find this cramping thing very interesting.
I`m afraid I don`t buy into the argument that shortage of salt (and other minerals) causes cramp - although the two may be correlative.
What`s striking is that most people do not cramp during training (whether its long slow distance or speed work). They cramp in races - often long races.
That suggests to me that it`s a fitness issue. More specifically a speed/endurance issue. The body is simply not used to running at that pace over an extended distance.
The problem can undoubtedly be compounded by dehydration etc but the principal activating cause is the body not being used to it.
I used to cramp in my earlier marathons. What`s helped me are marathon paced runs - or running chunks of my long run at or near (marathon) race pace.i.e. running at speed over a prolonged distance.
Endurance runs are absolutely necessary. But - I`m personally not convinced they are sufficient.
None of the above is very scientific I`m afraid !
Would be very interested to hear what others think.