A. There are plenty of things you need to be aware of as you make the transition from walker to runner and first and foremost is being mindful of slow and steady. You didn't mention your age, but the older we get the more careful we have to be when it comes to adding activities that require more effort from the body.
Before you start training, it's a good idea to get a complete physical. Once your doctor has assured you everything is in check, you can forge ahead without any worries.
If you've been walking, then I would strongly suggest you begin with walk/run cycles to see how your body responds. Some body types seem naturally built to run; these bodies can run forever and rarely experience injuries. Then there's the other group -- that would be me -- whose bodies are not designed to run and who must use plenty of common sense in order to avoid injury.
That said, if you're currently walking four to five times per week for 45 minutes at about a 15-minute mile, break your walk/run up as follows:
Week 1: Monday, Wednesday and Saturday: Walk four minutes, run two minutes. For the last five minutes of your walk/run, stick to a brisk walk to cool down.
Tuesday and Thursday: Walk seven minutes, run three minutes. Last five minutes cool down.
Week 2: Monday, Wednesday and Saturday: Walk 10 minutes, run five minutes. During the last segment, walk five minutes, run five minutes; Last five minutes walk for cool down.
Tuesday and Thursday: Walk five minutes, run three minutes. Continue that cycle and walk for last 10 minutes for cool down.
You can see the progression that will allow your body to acclimate to running. I would alternate the programs for week one and week two for about four weeks, then see how you're doing. Eventually you'll be walking less and running more until you work your way up to running the entire distance. It's generally suggested that you never increase your running mileage by more than 10 percent each week.
Also, it's crucial to stretch after your activity. I typically encourage my clients to warm up before they head out by doing a brisk walk or an easy jog. Listen to your body, see how it feels, and as you transition into running never skip your post exercise stretch. Good luck!
Trainer tip: Whether you're a walker or a runner, make sure your shoes are in good shape and provide the support that you need. I encourage you to visit a specialty store for help in finding the perfect shoe for your feet. Injuries can occur simply from wearing poor fitting or worn-out shoes.