One of my favorite touring routs is on a rural route. It is 15 km* long, I take about an hour to complete it since a part of the first half is sandy and I need to dismount to traverse it.
At the 10 km mark there is a steady descent which is mostly between gravel and crushed stone. I don't pedal and slightly press the brakes so that I keep a safe speed between 20~30 km/h. It takes 3 min until the terrain is level again.
The thing is: After the 1st minute I start to feel some discomfort in my left foot, which is the one corresponding to the lowest pedal — for some reason I have better balance if my left foot is in the down position when coasting, and even though I want to exchange the position, I don't want to relinquish balance. After the 2nd minute the discomfort gradually becomes a light pain, and when the descent is over I am glad I can pedal again, which causes the light pain to quickly go away.
Is that discomfort and pain I experience on the down foot something expected or known between cyclists?
As far as I know I am healthy and otherwise experience no trouble when cycling, though I am no "serious" rider either, rather lazy on maintenance (e.g. no clipping pedals or special clothes, never wash my bicycle, no odometer or any GPS whatsoever, ...). I wonder if it is because of the constantly shaking on the gravel descent and the left feet having to absorb it or something else.
Further info: My saddle height is appropriately set, namely knee is only slightly flexed when my feet is in the down position. The air temperature is totally comfortable (25 °C). Shoes are definitely not tight. If I can give any more useful information, I'll be glad to edit the question.
*Time, distance and speed are all to my best estimate, they are not totally accurate.