While pursuing ways to improve your body, it is very common to reach plateaus where the improvements obtained from your current process are less and less apparent. Here are some methods that will aid you in overcoming these barriers.
The more method
If you have been stuck on the same weight for several weeks, try adding 5lbs. You might not be able to do as many repetitions but that is okay. The extra weight will shock the body into building more muscle. For runners, if you are stuck at running an even 3 miles per session and feel like you cannot go any further after that, push yourself to put in an extra half mile for a few weeks then another half mile after that. Your body will build up more endurance so you can handle a longer run.
This can also be done with diet. For highly active individuals, the main problem with not seeing the gains they want can be traced to the fuel they put in the body. For example, weight lifters need adequate amounts of protein to rebuild muscle while runners will need adequate amounts of carbohydrates for easy to access running fuel.
The change method
Often times, individuals will perform the same exercise routine over and over. This can lead to the muscles becoming complacent. Try performing an exercise you have not done recently. For example, if you do bench press two times a week, try executing chest flys instead. For runners that go the same speed the entire run, change it up by adding intervals or hills to the run. It will definitely make difference in your breathing as well as how well your legs hold up endurance wise.
As far as diet is concerned, try taking a good look at what you eat on an average day. You may find that you are missing a specific macronutrient which in turn, is holding you back from reaping the full benefits of your workouts.
The break method
It is possible to push the body too hard too fast and get to the point where you are tearing it down faster than the muscles can rebuild. When this occurs, it is time for a break. You do not need to stop working out completely, perhaps one day you lift weights at 50% of your normal weight or you run half as far as you normally would. This allows the body to catch up and fully repair itself.
Einstein once said that the definition of insanity is doing the same thing over and over and expecting different results. This is completely true in the world of fitness where routine and schedules are a necessity to stay on track, just remember that you need to change up what you do during that time to keep advancing your body.