If it was a video then I would assume it's talking about the point in the video at which the triple axel occurs. Videos can be split up into many "frames" which are like photos of a specific moment. In this case, the triple axel lasts for a total of 58 frames in the middle of an "elegant split". I'm not sure exactly what that's referring to but a split is when your legs are widely separated, usually in dance/gymnastics, so I'm assuming it's that. At the heart of = in the middle/at the centre Bloomed in that context means started/began and developed. It's a metaphor for how a young flower "blooms" and develops into a mature one. Another common metaphor similar to this is to say that a relationship is "budding", meaning "starting", in the same way that a flower "buds" (when the petals start to show). Hopefully that's helpful :)

BLOOM in that text means that the rivalry has begun a while ago, but it also could mean that the rivalry has recently begun depending on the context.