Treadmill
Despite the fact that it is much nicer to run outside than inside, the treadmill is an extremely efficient way to maintain and/or improve cardio respiratory conditioning. Unlike the cycle and rowing ergometer, jogging or running on a treadmill is weight dependent: the energy expended is determined by your body weight. In addition, it is an impact sport and should not be the only form of conditioning, so joints are protected and injuries minimized. However, if you are on a ship or in another type of confined space, a treadmill could maintain your fitness!
What kind of workouts should you do on a treadmill? Three days per week is more than enough, if you do other types of exercise on off days. On a treadmill, you can mix up your pace and/or change the resistance by changing the incline. The incline and speed will determine the intensity of the workout. Remember, a strenuous workout is over 750 kcal/hr, and a moderate workout would be 450 to 600 kcal/hr.
Article Ref:
The Navy SEAL Physical Fitness Guide