App for fitness videos requiring merging, trimming, changing audio and speed adjusting in Instagram videos for iPhone?
Working in progress, community effort.

Clipper due to its fast speed and Videoshop due its customisation capabilities are recommended for recreational fitness videos like the video in the question. Please notice that Clipper loses your edits and can only edit one production at a time!

Full-scale almost-desktop-feeling with all kind of bells-and-whistles


iMovie (loading, big product...meant for Movie/Hollywood level stuff, overkill -- so much unnecessary adjusting!)
Videoshop (speed adjusting for each clip, audio for the whole production, possible to work with many productions at a time, unstable and slow to use)


Improvisation producs that make uploading super fast


Clipper (missing speed adjusting, only possible to work on one production at a time -- and clears up memory so you lose your production after a while, bad)
Replay (speed adjusting over the whole production, imposible to specify, example here)