Stitch strength heresy - Lock vs Saddle

[AlZilla]

So, I'm going to commit heresy. I've had time to ponder this while spending about 8 hours hand stitching a project.  Here I go ...

I don't believe that the saddle stitch is any "stronger" than the lock stitch. We often see it said, but I just don't see any reason for it.

Hear me out - any given stitch length is the same whether it's locked by machine, or a hand sewn saddle stitch. If the thread is the same, the strength is equal. Each stitch line has the same number of stitches and, thus the same length of thread.  The bottom thread on a saddle stitch goes all the way to the other side. The bottom thread on the lock stitch goes half way, thens around and goes half way back. So, everything is equal.

I can see the argument that if I break one side of a saddle stirch, I still have the 2nd thread running end to end. That's not "strength", it's durability.

I'm willing to be wrong.

[fredk]

Its a matter of semantics

[DJole]

In the lock stitch, the threads are pulling on each other. In the saddle stitch, they are only pulling on the leather. 
I wonder if that might make a difference? Of course, it's only speculation without somebody putting the threads to a test on an industrial testing machine. 

[friquant]

In studying knots and rope, the strength of a rope is greatest with no knots at all. Adding a knot puts kinks in the rope, and the rope is weaker with the knots/kinks. I think of it as a stress concentration factor, as cutting a notch in a board would be.

For knots and rope, each particular knot has a strength rating, some percentage of the original rope strength that remains when the rope is tied with that knot. But thread being as thin as it is, I don't know if it's subject to the same rules about kinks. 

A few months ago I tried out a force tester that would record the maximum strength, and I broke a few threads with it before i sent it back. I wasn't really studying the effect of the knots at the time so I don't have any data on that front. 🤷‍♀️