"This claim appears again and again, and [I hope I may be forgiven for pointing this out] it is false.

If you had a mosquito [even a heavy one] jumping up and down on a sturdy, thick aluminum frame [a Santa Cruz Bullet, for example], the frame would not reach its fatigue limit in your lifetime, my lifetime, or all of our lifetimes put together, or within any other reasonable time frame -- and not within most wildly unreasonable time frames."

I'm no engineer, but I know in cycles to failure tests they will do cycles of 10% of the tensile strength, and that these apparently low levels cause material failures. So it is somewhere above the level of a helium atom. The 10 percent test is taken as important because, for instance, a boat just gently tipping back and forth in it's slip may experience a demasting when the spar clumples, even though nothing in it's service life could explain such a failure. So I guess the issue for Al might be something like carrying it around on the back of your car for eons just in case you want a ride, a lot of low impact cycles on the bike rack might prove damaging.