I just don't understand what the problem is.

Main Entry: 1shank
Pronunciation: 'sha[ng]k
Function: noun
Etymology: Middle English shanke, from Old English scanca; akin to Old Norse skakkr crooked, Greek skazein to limp
1 a : the part of the leg between the knee and the ankle in humans or the corresponding part in various other vertebrates b : LEG c : a cut of beef, veal, mutton, or lamb from the upper or the lower part of the leg : SHIN -- see BEEF illustration
2 : a straight narrow usually essential part of an object: as a : the straight part of a nail or pin b : a straight part of a plant : STEM, STALK c : the part of an anchor between the ring and the crown -- see ANCHOR illustration d : the part of a fishhook between the eye and the bend e : the part of a key between the handle and the bit f : the stem of a tobacco pipe or the part between the stem and the bowl g : TANG 1 h (1) : the narrow part of the sole of a shoe beneath the instep (2) : SHANKPIECE
3 : a part of an object by which it can be attached: as a (1) : a projection on the back of a solid button (2) : a short stem of thread that holds a sewn button away from the cloth b : the end (as of a drill bit) that is gripped in a chuck
4 a : the latter part of a period of time b : the early or main part of a period of time
5 slang : an often homemade knife
- shanked /'sha[ng](k)t/ adjective

Merriam-Webster Online Dictionary


stagday


but in answer to the thread's question, fatigue is only 1 probable cause but it sure is a mystery. just don't dwell on it.