Marathon running vs cycling

I regularly do 100 mile plus rides. I run marathons only about three times a year. I'd say very roughly it's about 5 x harder per mile run to cycling. And the London 100 sounds like a major draft fest - that's more like a fast half marathon.

It's impossible to apply a hard and fast rule. Exertion in cycling is more dependent on external variables than running. Total ascent, wind direction and speed, whether you're riding in a group etc are all factors that, whilst obviously effect running to an extent, are more pronounced with cycling,

Ride London 100 is a lot easier than running a standard city marathon because it's flat and you end up riding in groups a lot. Riding 100 miles round Dartmoor or completing the Fred is a different story.

It also depends how you measure difficulty. Riding can be hard at the time but recovery is relevantly instant. The best measure of this is to look at the pros - how many 100mile+ rides does a tour rider put during the year? It's many times what a pro marathon runner would do.

For, me, a slow marathon (4hr) is way more knackering than a slow 100 bike ride (ie 8hrs). At the top end (which I certainly don't have experience of,) I'd imagine the comparison is a lot closer. I think the general advise, is that after a long distance run, it takes about a day a mile to recover properly. ie if you go flat out, most punters will take best part of a month before they should think about competing again. At the TdF, we see top performing athletes race hard over 200km/day for a fortnight - couldn't imagine pro marathon runners being able to do the same, their bodies would disintegrate.

I always thought it was simply that running was high-impact and cycling not, so you were able to sustain the relatively light load of distance cycling much more easily. Part of it I guess, but thanks for the education as above, now I get it.

I rode 180miles on the weekend, recovered in a day. if I ran a marathon right now I know my heart could do it, but muscle and joints would be trashed and I'd be a wreck for a week or more...

Anyone who runs a marathon gets my respect, I think it's mentally tougher than 14 hours on a bike at a moderate pace. But then I am a cyclist

My first thought is similar to shakebeforeusing above; the Ironman distances were chosen because they were considered equal challenges for swimmers, cyclists and runners. I generally feel as knackered after a 100 mile ride as after a Marathon and would consider them equivalent; I would say that I am as good a runner as a cyclist and spend roughly similar training time on each discipline, but Marathons take a while for me to recover from! Generally...

To answer this question properly you need to know a thing or two about muscle physiology and how this differs between cycling and running. There are two standard types of muscle contractions: concentric contractions - which occur when the muscle is lightly loaded or completely unloaded - where the muscle shortens as it generates force, and eccentric contractions - for heavily loaded activities - where the muscle actually extends when putting force in. Think of it as the difference between touching your shoulder with your hand and doing the same but holding a dumbell. The former's easy enough to do all day, the latter will start hurting pretty quickly.

Cycling, being very efficient, mainly causes concentric contractions in your legs (except when putting in hard efforts), whereas running will always cause eccentric loading. The problem with eccentric muscle wear is that it becomes exponentially worse the longer the activity goes on, and so can't be maintained for anywhere as long as concentric wear. In fact, in running races over 25km the main limiting factor to speed is the damage caused to the athletes' legs. In cycling at anything other than race pace (so including pretty much anyone's long ride), the muscle wear causes nowhere near as much damage. The only time you're causing eccentric wear when cycling is when you can really feel the pain in your legs.

Essentially, overall, the fatigue caused by cycling is much more dependent on the pace than in running. I generally feel from experience that hard cycling corresponds to about 4 times the distance as running. From this I'd say that the equivalent to running a marathon is a century ride, but at time trial race effort the whole way...

tl;dr - running a marathon is like racing a 100 mile time trial

(also, this ties in quite nicely with the cycling/running distances for an ironman triathlon, which are 180km and a marathon respectively)

The general rule of thumb is that you have to cycle 3 times further to achieve same output as running. However factors such as intensity and physical effort can alter this simple rule by quite a margin on both counts. For example I did a 109k (64miles) ride in 4hs 15mins today but this included an 9 mile uphill slog to Shap summit and the ascent of Kirkstone Pass all into a headwind. How many hills are there in London ?

I reckon maybe an Alpine Queen Stage? Or something like the L-B-L sportive yesterday?