We tend to stick to things we are familiar with and are good at performing. But when it comes to your workouts, if you want to keep making progress and improve your fitness level, you have to start changing your routine. Cardio is important but you need more than just cardio workouts.
If you have been pounding the pavement or the treadmill with nothing to show for it, perhaps it is time to change up your workout. Think about adding an incline to your treadmill routine. You can also alternate between a comfortable pace and a rapid, high intensity speed. If you have been walking outdoors on flat land, start to add some hilly terrain. Alternating between the treadmill and other cardio machines can be helpful as can adding Zumba or spinning classes.
It is also important to add strength training, preferably with hand weights, tubing, or your own body weight. Weight machines alter the way your body naturally moves and restricts your range of motion. If you want results, you need to incorporate exercises that allow your body to move naturally, with full range of motion. Machines also do not strengthen the small stabilizer muscles that help prevent injury and improve balance and coordination.