Posted: 18/06/2013 at 16:42
Short answer: What johnas said.
Full answer: I reckon cycling will give you alot of the aerobic benefits if you work at same intensity so intervals of 400m for example would have to be the same time but obviously give you a longer rep distance. As 400m on bike won't really stress you because it'll be over so quick. I love my turbo trainer because if its ever snowing or I'm injured I can always use that. Injurys always seem aggravated buy impact for me. Cycling removes this problem. ultimately though nothing trains you for running like running. Over time the miles strengthen up all the things that are stressed ie bones (metatarsals, ankle, heel, shin, hip ect) tendons, ligaments and muscles. no substitute I don't think.
Not a swimmer I'm afraid so can't really help there. Sure the tri people can help.