I used to run backwards - normally just for a rest from going forwards at a fast walk - I never thought about any of it - I'm pretty sure that my arms were held high - not in the low swing position.
I also did a fair bit of sideways - don't know what one would call it - not walking or running - kinda sideways skip
I consider when I was doing that - back when we were talking - that I reached a pretty fit stage - walked 50 km at 6km/hr
biked 40 on mountain tracks one day, then did a 20 km next morning - could have gone again easily in the afternoon
got a gf - don't do so much now and have developed a real thing about french food and wine - doesn't do a lot for the waistline
Interestingly, I can still just pop out and do 20 k without a lot of bother - whereas most of my friends think that 3 k is a big walk
I think there's probably a lot to the walking backwards thing - it resonates with me for muscles and brain