here are a couple ideas I've had for the icon:
1. Mg represented in an icon which is reminiscent of a stylized period table of elements, using a sans serif font similar to gil sans (doesn't have to be this, i'm totally open to other fonts, just want to provide a suggestion).
2. We use heart rate interval tracking to do what we do. As such, i also imagine a play on the heart rate interval graph, in a box, to create an icon of the M. I've sketched this below.
Beside or below the M or Mg Icon, I envision Melogram in some kind of simple script typeface. Because I know there are many kinds of script, I've uploaded examples of the kind of script logos I like.
Above all else, we need Melogram to be unique. The icon and logo shouldn't be confused with something else.
Be creative, these are just suggestions, and you're the designers!