Finishing a mountain stage in the Tour De France vs running a marathon: Which is harder?

I did some pretty intense training in my 12-year journey from a 4:09 to a 2:29 marathon.

But I never suffered during a run like I suffered riding up a single mountain - the Angliru from Santa Cristina village. The first half is reasonable - the second half (6 km at 13.5%) is absolutely savage! I actually thought I might die, and had to stop for a 5-minute break.

IMX most TdF mountain stages are much harder than a marathon. Millions of people (even when only semi-trained) can run a marathon. But maybe 5% of those people could do a TdF mountain stage - riding up 3-4 mountains for 30-60 minutes each is no joke.

Riding down mountains isn't for the faint-hearted either. You have a choice of 60-100 km/hr while wearing wispy lycra and relying on a few centimeters of rubber, or simply destroying your brake pads at 20 km/hr.

They have to bike the next day. All out marathon effort and then hit the roads again tomorrow, not happening.

Depends on the pace. Just to finish either isn't really that hard with the right gearing for the climbs. If you need to hit the time cut without cycling specific training/drafting skills, it might be impossible for a fit runner. With an equivalently difficult time cut pace in the marathon, likely impossible for a cyclist.

Thousands of cyclists climb Mt Baldy every year. It’s challenging but achievable.

Mt Baldy is a single climb topping-out at about 2,000m. It's about the equivalent in length and gradient of Cime de la Bonnette in TdF 2024 stage 19 - except Bonnette tops-out at a much nastier 2,800m. That mountain stage also included 2 other difficult mountains plus some savage downhills and a total length of 145 km.

I come from a running background with a 2:35 marathon. Been cycling for 5 years. Rode the Col Du Tourmalet, Col d'Aspin, and Pla d'Adet (three climbs during stage 14 this year) two weeks ago. The marathon is much more difficult on the body. That being said, I would not have made the time cut. Mostly because Niels Pollet is a truck pulling at 51 km/h in the valley leading to Luz-Saint-Sauveur

Running is harder on the mechanical system of the body (joints, ligaments, etc.)

Cycling is harder on the metabolic system (your body will get to a point where you might have to walk up a mountain)

The biggest issue with the post is that OP didn't indicate time cutoff or not for Mountainous TDF stage and also omitted time cutoff for marathon. If each has 15% time cutoff from the winner, it's a more interesting question.

My body breaks down mechanically before it does metabolically, so a marathon type effort is harder. I can do 100 mile rides with lots of elevation on a saturday and do a bike workout on tuesday and I won't be very dead.

I think many would generally have a really hard time metabolically being within 33 percent of TDF. One of the stages this year, the leaders rode >100 miles at >30mph and I think the percentage of people on the forum who could do 100 miles at >20mph is low.

This is very much an apples to oranges comparison.

Most serious runners underestimate the level of fitness is takes to ride at a high level because they see a bunch of unfit looking cyclists on group rides. Maybe they've even done one 40 mile ride with 2.5K feet of elevation and averaged 18mph and don't feel as beat up as they would running 18 miles at 550 pace. But to be at the local competitive level in cycling, never mind the pros, is a whole different ball game for all the various reasons already mentioned in this thread. Bonking while on a long run feels very different than bonking on a long ride and so does the fatigue afterwards, so I think these comparisons are fraught with asterisks and false extrapolations.

Cyclists probably respect running more than runners respect cycling. I'm a runner through and through but dabbled in cycling during bouts with injuries, so understand what it takes to do well at both sports. For sure I think that running is the more beautiful sport, but I'm sure there are many that feel the opposite.

Tens of thousands of people run marathons. Maybe millions at this point have run at least one? I am not much of an athlete, and I ran a marathon. I'm a woman over 40, and it still was very achievable. Old men and women and unfit people run marathons every year.

Very few people could complete a TdF stage. I mostly cycle these days due to a knee injury, and I have averaged around 100 miles of cycling per week, not a ton but not nothing. I couldn't even dream of completing a mountainous TdF stage. If I dedicated my life to training, I think I could probably do it, but it would be an existential struggle to complete one of the "queen" stages.

Completing a flat TdF stage is probably on par with running a flat marathon.

TDF mountain stage, walking the bike is far more embarrassing than walking in a marathon.

This is untrue. Modern gearing (11 or 12 speeds) can easily give you a 1:1 gear or even lower. You can spin up 10% no problem.

a 34 ain't gonna get a average person over a sustained 10% climb, no? Yeah, the gearing has changed on modern bikes but we're talking not great cyclists going up a really steep climb.

I'm a fit cyclist and am far from spinning easily up all the hills in my location. Granted, there's short 15% climbs all over where I'm at.

Yes, but in a mountainous TdF stage, they climb multiple mountains . . . and first they cycle 10s of miles to "warm up." In stage 20, the cyclists cycled up 4600 m.

We actually have a race like this in Washington state, RAMROD. It's very similar to a TdF stage. 800 people do it every year. Compare that to the thousands who run the various marathons in Washington state.

I have 1:1 gearing and at 10% I am in the red. I can manage 10% for only a short period of time and there is no "spinning". Only grinding.

My only marathon, done as a woman over 40, was sub 4, so I'm not super fit, but I'm not a couch potato.

You are either a very good cyclist or you have never climbed any kind of sustained 10% grade. My Garmin tells me the grade as a cycle up a hill, and 10% HURTS. Way easier to run up 10%, by the way, than cycle up.

Generally, you can walk/jog a marathon and still get done in 6 hrs. In a mountain stage, there is no respite going uphill, and if you start to walk, you are screwed and it may turn into an ultra.

Advantage - mountain stage

A big difference is that in some stages, you can pretty much pedal along with very low power output for much of that time. If you are in a line of cyclists and are the 4th rider, you are expending about 70% less energy than the person on the front to go at the same speed.

100% TDF mountain stage. any waddler can walk 26.2, but try to turn a crank at 6-10% incline for an hour.

There is a world of difference between a half and a full!

The wording of the question is ambiguous. I read it as which is harder in and of itself.