We can become very fit exercising moderately. Measured Variation is the key.
Keep track of the distance you are traversing, the difficulty level of your path, and the time that it takes to complete it. To increase your fitness level, keep two of these the same and try to increase one. Continue to do this for a week or so and then try using a different variable etc.. If you want to keep everything the same, add some resistance training for variation and strength.
You will gradually increase your fitness level, continue to boost your immune system and be injury free.
For more information, contact Sheena with Living Lean personal training and eating for elite fitness at 925-360-7051 or www.thelivingleanprogram.com.