Not wishing to flog a dead horse, but how can the rear wheel push anything without using energy generated by your legs? You pedal, the chainset turns that rotational energy into forward momentum. If forward momentum is then diverted back through the chainset to push your pedal through its dead spot, then that momentum is turned back into rotational energy and is not available to make you go faster. In fact, if the pedal is pushing against resistance at your foot (i.e. would go faster if your foot wasn't there), then you are braking.
The effect of all this over time is to smooth out the energy transfer, which should make you a more efficient cyclist.
Richard Ballantine's Richard's 21st Century Bicycle Book has a long, regretful section on the knee damage he suffered. There may be no scientific evidence, but equally that may be because no one has looked for it. For decades there was no evidence of a link between smoking and lung cancer, but that didn't stop smokers dying of it.
If anyone does start looking, obviously the first thing they would find is a wide variation in what knees can handle: big for one person may be easy for another. 42*21 is about 54 inches - not a big gear at all. Imagine doing the hills you did using 42*21 with a 70-inch ratio instead, say 42*16 - with no option to change down when you find you're not spinning well any more. The temptation with a fixie is to fit a ratio that won't slow you down when going downhill, but that can lead you into pushing your knees too hard on an uphill.
None of us has any evidence - we are just exchanging opnions. There is stuff on the web if you look for it - e.g. http://www.sportsinjurybulletin.com/archive/1044-cyclists-knee-injuries.htm "Training factors linked with patellofemoral pain include hill training, cycling with high gears at a low cadence, and a sudden increase in training volume." But this technical stuff needs expert interpretation and I'm no expert.
This is something to think about when going fixed, that's all - especially in the stop-start environment of an urban commute.
The effect of all this over time is to smooth out the energy transfer, which should make you a more efficient cyclist.
Richard Ballantine's Richard's 21st Century Bicycle Book has a long, regretful section on the knee damage he suffered. There may be no scientific evidence, but equally that may be because no one has looked for it. For decades there was no evidence of a link between smoking and lung cancer, but that didn't stop smokers dying of it.
If anyone does start looking, obviously the first thing they would find is a wide variation in what knees can handle: big for one person may be easy for another. 42*21 is about 54 inches - not a big gear at all. Imagine doing the hills you did using 42*21 with a 70-inch ratio instead, say 42*16 - with no option to change down when you find you're not spinning well any more. The temptation with a fixie is to fit a ratio that won't slow you down when going downhill, but that can lead you into pushing your knees too hard on an uphill.
None of us has any evidence - we are just exchanging opnions. There is stuff on the web if you look for it - e.g. http://www.sportsinjurybulletin.com/archive/1044-cyclists-knee-injuries.htm "Training factors linked with patellofemoral pain include hill training, cycling with high gears at a low cadence, and a sudden increase in training volume." But this technical stuff needs expert interpretation and I'm no expert.
This is something to think about when going fixed, that's all - especially in the stop-start environment of an urban commute.
