As a soon to be 67 yr old runaholic (34 yrs running over 71, 500 miles) I was "forced" to get back on a bike after a 12 yr hiatus due to an Achilles problem. First injury in over 12 yrs--actually, the last time I was on a bike was because of a Plantar Facia problem in 1997.
Bought a Trek 7.3 hybrid on 5/5/10 and have ridden over 2,100 miles. Didn't run for 6 weeks. Now back to running and decided to keep the biking going. I have gradually increased my every other day runs from 3-4 miles to 8-10 miles. The AT seems "healed".
Being an endorphin addict I now have started doing bricks (defined in title ). Ran 7 miles this AM--0630. Temp 79/hummidity 94%. Returned to the house and changed to bike gear--slow transition time (15 min) then headed out for a 30 mile bike ride--felt great so I extended the ride to a 50 miler. Finished 3 1/2 hrs+ later with temp at 86/hummidity 76%-heat index 108! Felt great. I marvel how quick I recover from an extended bike ride compared to when I use to run 20-30 mile ultra marathon training runs (in my 30's, 40's and 50's).
I present this for several reasons. #1 my ego and #2 --more importantly-- that most of us can do a lot more than we think we can. So get out there and start doing some bricks. If you do, your fancy spandex bike outfits will look a lot better on you.
Remember, a body in motion tends to stay in motion. Nick