Courtesy of the Oxford English Dictionary (OED)...
α. OE sceanca, scanca, scance, ME scanke, ME (Ormin) shankk, ME–16 schank(e, shanke, ME sschanke, MEschanke, 15 shainke, shankke, sanke, shaunck, 15–16 shanck(e, ME– shank.
β. OE sconca, sconc, ME sconke, shonke, (soncke), ME schonke.
Etymology: Old English sc(e)anca weak masculine corresponds to Low German schanke leg, thigh, Flemish schank bone (Swedish, Danish skank, Norwegian skonk thigh, probably < Low German) < West Germanic *skankan-; also, with difference of declension, to Middle Low German schenke, Dutch schenk leg-bone ( < *skanki-); a derivative from the same grade of the root is Middle Low German, Middle High German, modern German schenkel thigh (West Germanic *skankila-). From other grades of the root (*skink-: *skank-:*skunk-) are Old Saxon scinka, gl. Latin ‘basis’, ‘tibia’ (Middle Low German schinke thigh, ham), Old High German scinko (masculine),scinka (feminine), leg-bone, thigh (Middle High German schinke (masculine), thigh, ham, modern German schinken (masculine), ham); Old Frisian skunka, sconck (modern Frisian skonk, schunk), Low German (Koolman) schunke thigh, ham, Dutch schonk bone. The Old English strong form sconc neuter may belong to either the a or the u grade.
The root agrees formally, and may be identical, with that of Old Norse skakk-r wry, distorted ( < Germanic *skanko-), which is probably cognate with Greek σκάζειν ( < pre-Hellenic *sq'ngy-) to limp. Even assuming the identity of the root, however, the etymological meaning of the Germanic nouns remains obscure.
a. That part of the leg which extends from the knee to the ankle; the tibia or shin-bone. Also (now jocularly) the leg as a whole; chiefly pl. one's legs.
**This is the usage that is particularly relevant and applicable to my running adventures…
b. Shanks' (or Shanks's) mare, pony , etc.: one's own legs as a means of conveyance.
- a1774: R. Fergusson Poems (1785) 224
- “And auld shanks-nag wad tire, I dread, To pace to Berwick.”
- a1795: S. Bishop Poet. Wks. (1796) I. 204
- “I'd rather‥ride on Shanks's Mare.”
- 1823: Scott Fam. Lett. 11 Feb. (1894) II. xix. 167,
- “I found shanksnaigie‥the only way of moving by which I could get out to dinner.”
- 1898: T. Watts-Dunton Aylwin xii. iii,
- “I'll start for Carnarvon on Shanks's pony.”