http://www.dangerousdecibels.org/edu...me-guidelines/

Ear exhaustion is a real thing. If I mixed my projects at loud levels, they'd come out sounding like manure as the high-frequency response of my eardrums would become less and less sensitive with high-dB exposure. When I hear mixes that are far too bright and tinny, I can be almost dead sure that the engineer was either up late at night mixing and/or mixing at loud levels.

I haven't personally taken a dB-meter out on rides, but I would not be surprised at all if wind noise on descents or headwinds reached 90-95 dB or even higher, well above the "safe" limit of exposure. (Remember that dB is a logarithmic scale!)

I don't think OP was ever talking about feeling exhausted in the legs due to wind noise, but exposing your ears to unsafe levels of sound for long periods of time can be very tiring for your ears and for your mind, which is constantly trying to filter out white noise.