Exercise plateaus are based on the physiological principle that the body is lazy, or just misunderstood. Or better yet, efficient.
In other words, if you don’t change your exercise patterns, your body will find an easier way to do them. Consider, for example, if you walk or run a 2 km route 3x/week over and over again, the body will figure out a way to cheat. However, in this case, cheating is fair because this newly acquired efficiency allows the body to progress to the next level.
Bust your plateaus with change – i.e. by incorporating variety into your workout. One way to incorporate variety is to balance aerobic with anaerobic exercise. Aerobic training develops fat burning for quicker recovery from anaerobic exercise. Usually people prefer aerobic OR anaerobic training but ultimately limit their results by not doing both.
If you start an exercise session with a lot of strength and/or speed but fade quickly, you may need more aerobic exercise (ex. 20-60 minutes of running, cycling, rowing, etc.). On the other hand, if you start an exercise session slowly but improve with time, you may be anaerobically challenged. In this case, you may need to work on more interval sessions (1-3 minutes of higher intensity/speed with active recovery) and/or do more strength training.