the position and mobility of the navicular bone have more to do with [over]pronation than the tibialis muscles. there are 2 theories out there on how to fix this, wear highly supported gear or wear minimalist and non supportive gear. the supportive gear would be like wearing orthotics or inserts in all your shoes as well as wearing athletic shoes that have built in support. this would be analogous to having a short table leg and instead of replacing it with a one of the proper leg length you place a support under the short leg. the non supportive gear has you wear minimalist shoes, like nike free runners. there is mounting evidence showing that over a few years overpronation can be corrected during the gait cycle and while standing. you need to decide which one you want to focus on. the best thing you can do is go to a specialty running store and have them analyze your gait. they commonly will have you walk and or run on a treadmill and film you for detailed analysis.