Thanks for the replies guys, appreciate the advice!

I'm not sure exactly how one could "mash" that would hurt the knee. I find when I'm going up a hill that's too steep for my gearing, I end up standing on the forward pedal and pulling up with the rear foot- most of my effort going to the rear foot. Your forward pressure is fairly limited by your weight. So, it's more of a tension stress to the knee than compression. I think what hurts the knee is heavy loading and impact, which causes the mating surfaces of the bone to be scarred like a bearing race and wears out soft tissue which normally prevents this from happening. I don't see this happening during any part of my normal riding.

It is definitely possible to hurt the muscles around the knee without compression, but I concur that this would be mostly a cleat adjustment and fit thing.

I think maybe the idea is something like this: mashing in a huge gear tires out (puts large stress on) the leg muscles. Do too much of that too soon, without enough rest and you can get overtraining injuries...

I mean that could happen with any kind of riding without recuperation, but high gear + low rpm = higher intensity (from the muscles' point of view)

When I 'mash', i feel it in my quads, not my knees. If you're feeling it in your knees, then there's a fit issue IMO.

One end of the quadriceps is attached to the knee cap...

Edit: https://www.exrx.net/Muscles/Quadriceps.html

Doing to much too soon of any type of exercise can hurt

"attached to" still isn't the knees

True. I don't know enough about the physiology. I was thinking damage to the muscle might cause pain in the joint.

I have a suspicion that spinning at the edge for extended periods can also be bad for the knees vs. keeping muscles engaged and coordinated properly.

Spinning is "keeping muscles engaged and coordinated properly". Trust me. You cannot do this without proper muscle coordination:

I mean spinning on the road, especially downhill.

Same thing applies. I do cadence drills at 90, 100, 110, 120, 130, and 140 RPM on the road and it requires concentration (till it's learned) and proper muscle recruitment. Butt-hops show up around 120-135 rpm without proper technique. I can spin over 215-220 RPM on rollers for 15 second efforts similar to that in the video. I've done lots of cadence work.

Many road riders that use gears are only comfortable in a certain self-selected cadence range. For example 85-95 RPM and select a gear that puts them there depending on the terrain. Many fail to extend their cadence comfort zone upwards.

Again, high cadence won't hurt you. Even for the relatively untrained cyclist. For knee issues: The key is bike fit with an emphasis on saddle height, saddle for/aft adjustment, and cleat placement.

I think you missed my point. Key descriptor was 'at the edge' - the point where the rider is pushing their spin capability limit and the coordination becomes a bit off. Technique is sloppy which adds tensions to the muscles/joints and the breakdown of spinning faster - with the added forces spin above this capability (such as downhill) and I suspect there is potential for injury to knees.

Doubtful downhill as the cyclist isn't really applying any force to the pedals (almost spinning idly). Might make more sense in a sprint or even uphill...

Only if their spin is perfect and perfectly matched to the cranks, but if not there are forces being applied to the cyclist.

On a related note:

Many (and I would venture to guess, most) serious injuries come from skidding on big-ish gears. The violent snap that is required to break the friction of the tires is hard on some people. This is especially bad if the person isn't properly warmed up.

I believe that this can happen even if the person does have a good fit. But it can be exacerbated by bad fit, untrained leg muscles, poor technique, large gear ratios, heavier riders (relative to gear ratio), and/or stopping from high speeds. This is the equivalent of having never been to a gym and jerking to lift a very heavy box of books without bending one's knees.

...or doing stunts with your cheerleader girlfriend because she talked you into it. I did this in college. My back was jacked up for over a week.

re: knee pain...

i also ride a fair bit, and have been professionally fit to a bike more than once. not to the sputnik, but the measurements were translated with the assistance of the fitter. brakes, not skids.

when in form, 46x15/16 is not an issue. in my rolling hills, it does come with a bit of high torque/low rpm grinds. i have done centuries w/6k+ ft of climb with zero knee issues.

that said, with too much time off my 40yr old knees do forget how to cope, and i get a bit of knee pain if i grind too much.

OK, first off I am 64 years old, and have been riding and racing fixed for 35 years. I have never had serious knee problems, not even tendinitis. On the road I have always ridden between 60 and 72 gear inches. On the track I warm up in ~80 gi and race in ~90gi. Some of the events that I race involve a starting start at full power at zero rpm in said ~90gi. If anything will tear up your knees, it's doing standing starts in a big gear. The reason I have not had problems, even at my advanced age is that I have built up my leg muscles, tendons and ligaments through weight training and other exercises, have proper fit and technique, and always warm up with stretching, followed by lower gear riding before changing to the higher gear. On the road I'm never mashing and can always maintain a decent cadence, because I'm not overgeared. Also, I'm not too proud to break out the geared road bike on really windy days like today when I want to get a productive workout. Tomorrow, it's back to the gym.

I've got to try rollers. I find spinning to be one of the most rewarding parts of riding fixed. It's nice when you can see your smooth cadence range edging upwards over time. That video was absurd.

46x17 here.

Stand up when you need to. Walk your bike when you need to.

I've only ever had knee pain with poor fit. My first road bike was a bad fit, my first 60 miler hurt and I was diagnosed tendonitis the following day. The other time was due to poor cleat positioning. I felt fine on short rides but on the first long ride the pain set in.

This is one of those statements that should be in big flashing letters somewhere. Couldn't be more true.

FIFY
A cheerleader asked me on a date once and I wasn't interested. I'm really regrettin' that now.

Yeah, man. *EVERY* girl that I know who was a collegiate cheerleader still has a banging body well into their 30s.

You make 30s sound so old! I know girls in their 50s who are totally hot.