msparks

as for general fitness, i think you can acheive the same cardio benefits from either although a little more easily with running - i.e. with a little less time out of your week. In general you need to be out on the bike a little longer than you would out running, primarily b/c when cycling you generally don't go at such a constant pace as when running b/c of hills, corners or just being lazy and coasting which you can't do when running. if you compare running with spinning (cycling in the gym in aerobics-like classes) or cycling on a trainer, i think the cardio benefits are quite close (OK, i'm not a specialist here, but just my view)

i'm mostly a cyclist but i have done lots of triathlons and adventure racing and multisport stuff with running and cycling, and used to train 3-4 days a week running, 4 days a week on the bike and 2 days a week swimming (about 2-3 years ago when i was competitve in tri and multi-sport). i currently cycle about 10,000 miles per year, but only run about 2-4 times a month because i've had knee and lower back problems from too much running (knee tendonitis and bulged disc in my back)... i simply can't run more than about 8 miles a week, week after week, without developing some impact/overuse injuries (i'm 31 - at 18 or 25 i could run all i wanted)

BUT, cycling is much easier on the body, particularly on preventing injury to the joints - shin splints, back problems, knee injuries are all common with high-volume running and some people just can't run more than about once a week without really damaging their bodies. For example, about half of the serious triathletes and multisport athletes i have known have had to cut back on running b/c of injuries when they're running 20-40 miles per week and now train by swimming and cycling more.

plus, i find cycling great fun and running i only sort of like...

on the other hand, for your case where you are tested in running: running will better prepare you for running than cycling. cycling will make you fit but even training double the amount of time on the bike i think would be less effective than running because you use different muscles and your body will adapt to the stresses of cycling and some of these will cross over into running but not all... you have to train by running at least some and then can supplement the minimum with time on the bike

i would say, if your only goal is to pass the test, run most of the time and cycle a little. If you hate running and love cycling or have some injuries do it the other way around and cycle a lot and run maybe only twice a month - since you need at least an 8:45 min/mile speed for 2 miles, run like twice this distance (4 miles) twice a month and see if you're meeting it. if not, then cut back on cycling time and add more running. I know that for me, i could probably run only once a month and with all my cycling training i would be able to run 2 miles in less than 8min/mile pace, but then maybe you're inherently not as talented at running...

i would say the main advantage for running is what you can do with little time; say you're working a lot and travelling - you can bring along your running shoes and get in a 30-minute jog 3 times a week which will keep you from getting totally out of shape with very little time committment. trying to bring a bike with you on a business trip and then getting all your gear on and then doing a ride takes much more time and effort and hassle and most 'busy' people i know are not able to get on the bike more than once a week if even that...