Can I raise my long run mileage suddenly while still keeping my same average weekly mileage safety? ie: I currently run about 20ish miles a week with my long run being 7 miles. Is upping the ling run from 7 miles to 10 miles too drastic?
I am starting a training plan that stars out at 21mpw with a 10 mile long run, and then peaking at 31mpw with a 13 mile long run. The longest run I have run since December is 7 miles and I am training for a half marathon in April.
With so few other base or foundation miles, moving from 7 to 10 miles for the longest weekly run is possible, however, it will most likely raise your exposure to injury.
FWIW, I'm a trail runner, and back in 2009 while I was finally working my way back into running following a six year layoff, I took a wrong turn and got lost. Prior to that day my longest run in years had been like 6 miles (however, I did have a few 8 miles days split into two runs), on that particular day I ended up going 12 miles and oh geez was I beat when I finished, I mean, you could'a stuck a fork in me and called me done! I had to take three, maybe even four days after that run to rest up, my muscles and joints were that tender.
Fat old man PRs:
Well, yeah, there is some increased risk in going straight from 7 to 10. You would have to be careful and "listen to your body" on that run. An alternative would be to do your first 10-miler run/walk, maybe run 5 minutes, walk 1 or 2 minutes (repeat as necessary ). Really, though, what's your hurry? You're peaking at 13 and you have 7 or 8 weeks to get there. You could add one mile per week and still get there easily. Training plans are just plans - they're not law. You may not be used to doing so, but there is nothing wrong with making adjustments in the plan to suit your circumstances.