Hiking is essentially walking! The best way to train is to go on as many walks, day-hikes, or shorter backpacking trips as possible. Practice putting all your gear in your pack and carrying it around. The more you make hiking a part of your lifestyle, the more enjoyable your backpacking adventure will be. Even urban hiking on city sidewalks will help with physical conditioning if you can’t get to trails all the time. Seek soft ground and natural terrain when you can (e.g. local parks, hills, or beaches). Strength training is helpful for overall conditioning and muscular endurance. Always check with you doctor before embarking on a new training program.