Re: Swingers.
This thread slipped by me so apologies to OP who thought it would be of interest.
My 2penneth on why we swing our arms.
Essentially it happens because everything is connected. Our arms, when walking are essentially pendulums hanging loosely at our sides. It we tense the muscles at the shoulders in any way then they cease to be pendulums and are rigid limbs and stop swinging.
Whilst our arms are acting as pendulums, the simple laws of physics dictate that they will be affected by any other forces connected to them. Thus the movement of the rest of our body, the rhythm created by our gait and stride, creates forces which act on our pendulum arms.
This principle is called resonance and is best described by something called "Barton's Pendulums". See the picture below.
Here there is a heavy pendulum on the left (X) and a number of other pendulums suspended at differing heights. ALL the pendulums are suspended from one horizontal string/cable.
Now when pendulum X is set in motion what happens is that it creates forces in the horizontal string and those affet the other pendulums which being swinging themsevles but at different rates. The pendulm at the same height as X is the one that swings the most as it is in resonance with it.
In a similar way I believe our arms swing because of the motion of our main body mass and they swing in resonance with that motion.