Training is critical for comfort and success for a long distance walking to complete a full or half marathon. Your training should concentrate on building a base of walking, then increasing your mileage in a systematic fashion. You should also train wearing the gear you will be wearing during your long distance walk or race.
To reduce your risk of training injuries. increase your total mileage per week or the distance of your longest walk per week by no more than 10 percent.
This means you will likely spend a few months training. By being methodical, you give your body time to build new muscle, blood supply, and endurance.