BT BM 107b(48) :במלי כתפי {ניגרי}<נגדי> סגיא‏ : it should be as much as the full shoulders of the pullers
See the entire entry for kṯep̄, kaṯpā n.f. shoulder

BT BM 107b(48) :משום אמתוחי אשלא‏ : because the ropes are pulled
See the entire entry for mtḥ vb. to stretch, pull, extend