Different people have different goals when it comes to exercising and working out. Some want to exercise in order to maintain a certain weight, some want to lose weight and tone, and others may want to gain a significant amount of muscle, as in body building.
If your goal is to lose weight and tone or gain a significant amount of muscle, it is important that you incorporate muscle fatigue into your workout regimen. Simply put, you must fatigue the muscles which will cause you to feel a burning sensation within the reps.
The burning sensation that I’m speaking of is actually a buildup of lactic acid in the muscles, as a result of sustained pressure due to force (squats, heavy weights, etc). Microscopic tears during this sustained rhythmic pressure causes the muscle to heal with what can be related to as muscle scar tissue, and we all know that scar tissue doesn’t go away easily.
So if you want to build those muscles then you need to lift, squat, lunge, crunch, etc. until you “feel the burn.”