Effects of regular running on cycling performance?

Cougie, d'you think there's any truth in the argument that cycling is better for general fitness as you can do it for longer?
For example, I'll enjoy a 3, 3.5 hour bike ride and maybe think I could go further, but a 2 hour LSR is pretty much the limit of my endurance - do they have equal effect?

Yes Cougie - I think that was what i was trying to say. I am finding that cardio-vascular fitness is established through running OR cycling. They dovetail nicely. But to reach a peak of performance in either discipline, then you must have intense, function specific training to accompany.

The muscles used in cycling and running are different, so although your cardio system will have good ability to supply oxygen to them, the muscle fibres themselves are still required to burn the fuel and oxygen (create power). If you train hard on one discipline and then try to perform hard in the other, with little cross-training, you will quickly find those muscle weaknesses for yourself

I had a knee-op 3 months ago and am running a mara this w/e. I've really cut back on running training (only done 360kms in prep for this mara - usually I would do 1,500+ kms), but I have thrown in 900kms on my new bike.

My observations.
1) Hard to get same sustained HR intensity when cycling. Every uphill has a downhill.
2) It is easier to go for longer on the bike and re-fuelling is much easier when sitting down.
3) I get much more DOMS in my quad muscles after running now, as they are less used to/ adapted to, the impact stresses from running.
4) The cycling is strengthening my hamstrings more than running does (because you pull upwards in the pedal stroke when wearing cleats)
5) My neck/ shoulders/ back have been really painful after riding, suggesting I need to get some set-up work done. Running tends to cure any back pain but does nothing for my neck and shoulders.
6) I get a buzz from the different training approaches. It's more interesting to ride than simply to run 6-7x week. But I really appreciate being able to run in quieter/ more beautiful places than road cycling gives me access to.

All sorts of opinions on this I'm sure.

For most people, from beginner to elite, cycling can be sustained at a higher speed for a longer than running and hence I conclude that it requires less effort to cycle than to run.

Whether 4 hous of cycling makes you "fitter" than 2 hours of running? Hmm, that is very dependant on what your definition of "fitness" is.

As a runner who recently took up cycling for commuting purposes, my experience tends to:

• cycling is not a replacement for running training if you want to be a faster runner
• it does build up your aerobic fitness because you can do it on days you cant run
• use it as a supplement to training, alongside core work and weights etc., and you will benefit

What I find (I dont train by HR) is that is has improved my leg turnover and my recovery times in terms of breathing from fast running and reps, but on the downsides, it makes my knees ache and makes my perceived effort when easy running out of whack (so I run harder than I should because I am used to increased leg turnover and the higher effort level for cycling).

Singleton wrote (see)

All sorts of opinions on this I'm sure.

For most people, from beginner to elite, cycling can be sustained at a higher speed for a longer than running and hence I conclude that it requires less effort to cycle than to run.

It depends on how much effort you are putting in.   I agree it's harder to put in full effort on a bike and harder to run easily - but both can be done if you have put the time in to get fit enough to do them - in other words you just need to be conditioned for it.  

A cyclist should be able to ride a ten mile effort in 20 minutes or a touch over and be absolutely wiped out as much as you would be from a 5k running race.  One of the hardest sessions I do on a bike is 10*30 seconds on a turbo with a good recovery interval in between - I can do that so hard that I still feel wiped out the next day - but I probably need to be fairly bike fit to get that kind of effort out.

The reasons running is typically seen as harder are you get more muscle and soft tissue damage so feel more beaten up for a few days after a hard effort, and there is a higher minimum effort threshold for running so new runners are working quite hard just for relatively short runs.