Robert OHara / KPgirl / Louey - my ears are burning!
First of all, they're sandals, not flip flops! (Xero Shoes to be specific). I've been running in sandals for four years now and back/hip/knee pain is a thing of the past for me - I'll never go back to clodhoppers
This was indeed my first marathon (been putting it off for 20 years) and I really enjoyed it. Thought it was a very well run event overall, and a pleasantly flat course.
Nice to meet you Rob, and well done on smashing the 4hr mark.
I agree with the comments about giving it a few months. You will get there if you stick with it, and you'll learn quite a bit along the way.
I'm also a rugby player, and had a double fusion at the bottom of my back (L4-L5-S1) last year. I'm now running half-marathon distance regularly without any back issues whatsoever.
Some thoughts on technique...
Think about short forward stride (don’t overstride), and higher cadence (foot turnover). It feels odd at first, but you get used to it very quickly.
Don’t think too much about staying “on your toes”. That will overwork the calves and cause all sorts of issues. Think about landing flat footed and you should still instinctively land of the ball of the foot. Try rocking back slightly towards the heel until you feel you are heel striking – it is pretty obvious when you cross the line and are landing on the heel. On each landing the ball should come down first, then the foot loads fully, then the heel gently touches down. This last part is what many people neglect. It really makes it a lot easier on the calves.
If your calves are sore, wait until they feel better before going out again. Don’t “work through the pain”. Even though it is only muscle pain, overly tight calves will cause achilles soreness and plantar problems (the sole of the foot). Make sure you do both the regular calf stretch (here) and also/especially the soleus stretch (here).