After a bit of advice.
I am coming to the end of C25K but, have just failed W8D1 due to arch pain. I have been running in shoes fitted by a specialist a couple of years ago (150 miles). Is it worth trying some insoles flat feet before I try new shoes?
I doubt it is the shoes unless they are a stability shoe which should very rarely if ever be used.
I expect this is just a standard running issue fork the fact you are increasing volume and intensity but your muscular-skeletal system has not adapted sufficiently for the increased stresses. You gain fitness very quickly starting to run, and as you run more and faster you increase stress on joints. However, getting bones and ligaments to strengthen takes much longer than the cardio fitness gains so ti si common to basically be able to outrun what your body can handle. You need more recovery time and just be patient while your body adapts.
I would also check that your running form, foot-strike and cadence are at least close to desirable. Some people run with a very low cadence and strike their heals, this increase stresses a lot.
Similarly, you probably aren't running your easy runs slow enough. The faster you run the greater the impact stresses. Moreover, as a beginner any kind of speed-work or intervals has a very high risk, but most C25k programs seem to put a lot of emphasis on weekly workouts etc. If you can run with a phone in your hand and have a proper conversion with someone without struggling for breath or pausing to speak then you are running at the right pace. Most beginners run far too fast. I also woudln't do any kind of intervals, fartleks, threshold runs in weekly training until you have been running for 6 months. he odd faster run now and again is fine, but not tryign to put 2 hard works in each week.
