Is it pure speed?
Legolas, in the movies, is shown casually walking across deep snow that the others need to slog through (going across the mountains). He doesn't sink into it. So, is it by pure speed that he jumps from rock to rock as they fall, or is it a combination of speed and this special ability that allows him to push off the rocks so long as he can touch them?
And does that make him faster than human eyes can even follow?