i've been out there with cross training swimmers. a number of all americanswimmers. but we didnt run far. 2 to three miles 3 days a week. the 3 miles was a long day, not an average day. honestly we were working out more than 5 hours a day so im not embarassed. when the cross country coach/ step aerobics coach told me that if i wanted to get better at running i should throw in a longer day, like 5 miles, i told her i thought she was insane. i'd never run 5 miles straight. never jog walked 5 miles except that one half marathon i did all cocky, without really training. my first half marathon. it was a long jog walk. after getting second in the swim... anyway it is very common for pretty decent swimmers not only not to be able to break 6 min in the mile. but not to break 8 min pace in the 5k. i would guess the cardio might work against us to some degree since we might do for example 20 x 200 frestyle with 20 seconds rest. but the cardio is better than our ability to withstand the impact forces of running. all the landings. so you cant just go by cardio feel. you still have to work into the ability to handle all the landing impact. so for example when i was rehabing this last injury. there was a time where i was only at a 2 mile jog-walk range. i just had to deal with that for a while. now im back to 6 miles. but you have to work within the parameters you are able to deal with. ... read for example bowermans book on jogging. tell me his 10k time after he wrote that book. look how easy his plans are. i had to make an easier plan to climb up from this injury. i have no doubt that plenty of people can do sub 6;20 in a mile and have no business whatsoever trying a 10k. until they gradually work up to the impact forces of the landings. and i can tell you only a handful of swimmers were sub 5;30 on my team very few could break 40 in 10k.... i did on my first 10k. and i also got a groin injury that lasted for a week. no doubt this season will be much better. already is really.