Walking may seem like a modest workout, but the treadmill can become a powerful tool in your weight loss exercise arsenal. It is accessible, low impact and adaptable to all fitness levels. Whether you're a seasoned gym-goer or just dusting off your sneakers, walking on a treadmill can help burn calories, improve cardiovascular health, and build muscle—the secret is in how you walk, your pace, and your chosen intensity. I've put together five of my best treadmill workouts for weight loss to speed…