It's the regular movement that's the most important.

"And if you have little experience with injury and are comfortable with your stride, then by all means, stick with it, as is. The best running form, Mr. Kulmala said, is any that keeps you moving regularly."

In this Well blog post about runners striking on the front of their foot or heel first, Gretchen Reynolds discusses how the recurring argument about which is best is moot. The most important factor is sticking with the activity, using whichever stride and strike minimizes injury and potential for future injury. She includes some rough results from recent studies - in short, they show that both methods of running, heel-striking vs. forefoot-striking, put pressure and strain on the body just in different places. 

Forefoot-strikers are more likely to feel the pressure and suffer injury in the ankles and achilles'. Heel-strikers are more likely to feel it in the knees. 

Wherever you feel it, minimize the potential for injury by smartly adjusting your exercise so you can keep on moving. Once the habit's broken it can be tough to return to. And the most important habit we can all get more of is moving our bodies.