I would advise myofascial release. No magnesium or supplement can help if the muscle is dysfunctional. Do you have a foam roller? Even tennis balls work. There are some really "deep" (anatomically speaking) muscle fibers that can cause issues. I used to suffer shin splints. No nutritional plan truly helped combat it until I started doing a lot of Active Release Techniques (ART) and started re-activating prime movers.

The issue is, there could be potentially 100 (small) reasons for your degree of suffering of them. Weak Achilles tendon, unequal ratio strength between tibialis anterior and your calve muscles. Etc.. All due to your large volume and diversity of exercise. Example: I do the squat test and glute test with my athletes to see what's function/dysfunction and needs to be correected. One of the largest issues I see is dysfunction glutes/hamstrings and dominant quads. Once I corrected this with functional exercises, ART, and stretching, a lot of major pains go away (including shin splints.)

The body works in synergy. Your heal is literally connected to your shoulders in some way. Once one muscle starts to shut down or have issues, it means more taxing on the rest of your body and muscle groups.

Here are a couple minor techniques you can do to try and release your TA and calves: http://www.youtube.com/watch?v=fWioS5N5FS4 http://bodythrive.wordpress.com/2012/02/08/using-myofascial-release-to-treat-prevent-plantar-fasciitis-and-shin-splints/ http://healthonabudget.com/self-myofascial-release-with-tennis-ball-to-release-muscle-tension/

If none of the above listed work, then it must be something more superior (Glutes/Hammies/Lower back/etc)