I've been doing that tightening the actual joints down, using a 1/2" thick dowel (got that tip from your Kudzu site's videos). As much strain as you're putting on the sinew at that point, I can't see how anyone could do it with bare hands. Ouch.

Nah, my problem occurs when I'm knotting the joints off; those final eight or so knots around the rest of the lashing. I'm probably a bit more enthusiastic about getting them tight than I should be; either that, or my hands have become more accustomed to typing away at a keyboard for work. I might just start the first four or so loose like your video shows (I just noticed that, btw), and use the dowel to draw them tight, then finish the rest by hand.