Ugh, ya'all's laymen assessment of what's causing what is missing the mark. Yes there are various ways each person may find better leverage and ease, but its not the actual loads on leg muscles and joints that gives these surprise injuries, often not discovered till next day or so. IT All About The Nerves, and not the local ones but the central nervous system one wtf up at top of neck in brain stem.
Its the same exact thing that happens to sports runners that suddenly pull a hamstring, yet did not hit a hole or get tackled, just pow! out of the blue down.
What is happening is a nerve mis-firing, muscle balance contracting conflict. Same as if ignition sparks hits too soon on piston rise BANG. In runner's case there are 6 big strong hip flex/forward muscles-the Quad's etc, and 6 big strong extension-backwards muscles, hamstrings. So when all 6 flex mm's at full force, one of the 6 hamstrings mm's mis-fires POW!, simply over powered so pulls apart or off attachments-tendons. Where the mis-fire happens in in CNS-spinal level, brain is not smart or fast enough to allow normal walking or running or kicking, just like music performance, spine must be programed by practice till patterns can be triggered automatically by brain commands to spine to go this way or that and at what speed/power.
What upsets the nerve firing is usually a physical and or chemical stress that finally reaches a threshold to break down, all of a sudden first use or after some repetitions. The almost universal common physical source of upper cord 'impingement' is old neck injury and habits finally wearing out to bump nerves directly or its blood supply, then Owie. Long term fix is re-growing neck via stretches and traction and what ever allows easiest stretching and traction.
The chemical side of nerve muscle joint equation are the minerals which is what nerves are moving in and out mm cells to contract and reset. BTW it takes no energy to contract a mm, think Rigor mortis , its takes energy to relax a muscle or reset nerve to fire. Think cocking pistol then slight trigger pull to fire a bullet, can't fire again till shortened up hammer spring is stretched out again. If not enough alkaline mineral reserves on hand right now, cramp and tear and cry city. Identical to most heart attacks too. Sugars/booze suck down these reserves, usually over hours for a hang over or surprise injury w/o undo stress. Come on man 10's of 1000's of folks kick off old hard start bikes for eons and don't get nothing but pissed off and tired. The mineral complex is also what is used to build joints and connective tissues and resist over inflammation too.
Third elements enters here too, state of mind while making excess efforts. If frustrated, pissed off it changes the mm tone of jaw and neck to add tension over what's required to get the job done, sometimes just enough for a OWie.
But once spark timing puts hole in piston, or upper neck bounce injures a joint, ya have to deal with the resultant damage. I highly recommend the soft flexible rubbery magnet sheets put over local boo'boo's, impacts to slices to burns. Baylar College found the mechanism, keeps capillary beds opening and closing instead of just filling up swollen or closing shut keeping blood flow out. Can take hours to kick in but effect last hours/over night once removed. When I break stuff like my R knee off in avatar event, I wear magnetic a couple weeks or else can't hardly move it. Broken end of 5th finger a week ago, needed 4 days magnet wrap to keep in from throbbing or lingering after a new bump to it, now merely puffy achy to grip hard, otherwise ignored.
Keep in mind as yo'al age and get new injury, if not for the above I'd not be able to live and work fine, let alone expect to ride again after next bad crash.
