When it comes to running or training for any type of running event, you must think about your feet and how they are being used.
With advances in science and research, there's a lot of information available out there in regards to proper biomechanics.
It is critical that you find a technique and style that works for you. It has to be comfortable, efficient and sustainable over long miles and many years of training. Shoe technology has evolved to where it's possible to get a properly fitted to a shoe that meets your running style.
In my experience as a healthcare provider, when people switch to more of a mid-foot or fore-foot running style, there's less impact and stress throughout the kinetic chain, and therefore less impact to the knees, hips and lower back while running. I've also seen those that suffer from chronic shin splints have much more comfort when they switch over from a heel strike pattern.
If you have not run in this way before, I recommend meeting with a health professional who can help you through this transition. Fore-foot and mid-foot running will use your calves in a way they may have not been used before so be ready for some serious soreness!
Making the switch also requires time. Do not attempt to make changes to your running style if you have a race coming up, especially a marathon. This is something to work on when it is your off season from racing. It takes patience to be able to learn a new style and then continue with it.
Most people revert back to their old style of running as they fatigue. This is normal until you put in the hours of training with the new style and your nervous system adapts to the new movements and biomechanics.
My advice is to keep at it, your joints and body will thank you later!