I have ridden 165-170mm cranks on 26-29" wheels for the past three years, averaging three to four rides per week, typical ride time 1-2 hours during the week, 3-4 hours on the weekend rides, max distance ~20 miles, riding 90% single track/ 10% double track, no road riding. In general, other than sore shoulder, quads, and taint, I have been pain free. I do warm up before rides and stretch when I take breaks from riding.
This past summer I decided to gradually decrease the crank length on my primary muni, KH 29, to improve efficiency. First I went down to a 160’s and rode those without much problem, though I did notice I needed to use more brake on downhills and I was out of the seat more for both up and downhills.
About one month ago my left knee started to get “twingy” at the end of long rides. This feeling did go away between rides and wasn’t a problem during shorter rides, though at times I did notice some shin pain when walking/hiking. Fast forward another week and I was riding a twenty mile race, when I started having significnat knee pain ~ten miles into the event and it persisted until the end, even after taking ibuprophen.
Intending to further improve pedaling efficiency and thinking that a shorter crank might reduce knee stress, I reduced my crank length to 150’s on the 29er. In the meanwhile I let my legs rest for a few days, then gradually increased my mileage to pre-race levels. I didn’t notice any knee pain until this past weekend when I rode ~ ten miles (three hours) of tough single track.
I have a fair amount of experience with endurance sports and have dealt with chronic use related injuries such at piriformis syndrome, compartment syndrome, shin splint, ITB issues, etc…but this problem seems to be completely isolated to my left knee, only bothers me during long ride, and seems to be at it’s worse on downhills when my knee is unable to straighten; yes, on uphills where my leg is more extended, my knee feels fine.
I have already done ICE, stretching, NSAIDs, etc…so my conundrum is whether by running a shorter crank am I overstressing my knee as a result of having to work harder to control the uni?
Note: I don’t want to hear about stretching, physical therapies, meds, or anything that I can do to treat the “injury”. I’m asking about experiences and theories relating to
crank length and leg stress.