We started to talk about the back step. My partner claimed that good leads make deep backsteps, which she maintained gives energy to the dance. I wasn't so sure about the depth. In any case, deep backsteps can be a health hazard.
When I got home I started to look through some videos of the old guys. Ricardo Vidort steps back occasionally, but it's rarely a formal backstep, more like a quick rebound: most of the time he seems to be running forwards and around his partners. Tete took big backsteps in demos, but he took big steps anyway. Other dancers are like Ricardo Vidort: you don't really notice the back step although it is there. I don't think you can dance without stepping back sometimes.
I remembered that Ricardo Suarez has a very quick, energetic and precise backstep. How is it possible to get so much energy into a counter-intuitive and possibly awkward step? I watched some videos, and all the answers seem there in this short clip, first in real timethen in slow motion. He dances with his weight well forwards, as is usual for his generation. Then as he steps back, his right knee bends and his body sinks onto it, a smooth, swooping movement with a rebound back up onto a straight left leg. I think the big point is that he doesn't just step back; his whole body moves back and down, and he carries his partner with him. She's drawn downwards and forwards into a positive step. & since Ricardo's whole body moves back the foot stepping back stays almost flat to the ground.
My impression is that the energy comes from the whole body movement, and the precision of Ricardo's timing itself creates energy. This flexing of the leg you are stepping away from, and landing on a straight leg, is fairly consistent across the older dancers. It's the same pattern when taking a simple step to the left.
(Ah! The parquet floor of Maipu 444, and the red and black table cloths of Cachirulo! Ricardo's partner in March 2009 was Florencia Bellozo.)
So my partner was right in one way, there's energy in the backstep, but the energy isn't the consequence of a long step. Ricardo Suarez makes clear and relatively deep backsteps, but they don't need to be big to make sure they are full of energy.