Hand kneading demonstrated by French baker, Simon Gosset

Nice film Graham.
Where was it ?

I cannot imagine doing that for 20 long minutes!  Couldn't you not stop and rest from time to time?  What arms that guy must have!

Actually, 20 min is theorical and is more suitable for a bigger amount of dough and a French flour. For this amount of dough and an Australian flour (with usually more gluten or a bit stronger), you should need no more than 15 min and even less.
If you are like me, lazy, you can also use an other way... Mix your flour and water, without kneading it. You just need to obtain something homogeneous enough. Let it rest for 20 min (until 40 depending of the flour). Then, add your yeast or your leaven, the salt, and knead for 10 to 12 minutes (it should be enough for a small amount of dough, especially if you use a leaven).
What is important is to get a dough which is smooth enough but if it starts to crack when you stretch it, do not knead longer. That meams you reached the limit of extensibility of you dough. If you go further, you will get something stronger, more elastic and even tenacious.

Hello Graham,

Actually, folding air in the dough during the kneading has two interests : make the yeast and bacterias breath and oxidate the gluten net.
Making the micro-organisms breathing permit to give them a bit more activity (breath is chemically more efficient than fermentation). So, the chemical processes will start quicker. The air inserted in the dough gives also more volume to the dough.
Secondly, why to oxidate the gluten ? The oxidation of the gluten constituents will promote strong links (di-sulfur gates between the molecules) in the gluten net. So, the network will be stronger and will get more elasticity.
This point is important but is also a defect. I mean if you oxidate to much your dough (with an intense kneading, without salt for example), you will make it to tight, difficult to shape : the dough will lose its extensibility and even crack during the stretching (particularly annoying for baguettes). Moreover, the oxidation will annihilate the flavor and the color of the crumb. That is why industrial bread is white and without savor (they also use ascorbic acid and soya bean flour to increase these oxidation phenomenons). That is also why, among others reasons, industrials use enzymes and other additives to give more extensibility to their doughs.
On an other side, these strong links in the gluten net are also produced during the bulk proofing. That is why it is also more interesting to reduce the kneading time and increase the proofing adding some folds if necessary.