Fatigue can be defined as extreme tiredness resulting from mental or physical exertion or illness. In exercise training terms, fatigue determines your ability to sustain repeated efforts of a single movement.
A distinction should be made between central and peripheral fatigue with the former being thought of as a mental fatigue and the latter a fatigue of the neuromuscular junction.
Endurance is defined as the ability of the body to resist fatigue. To improve endurance requires you to challenge both central and peripheral nervous systems. Think of a marathon runner and a weight lifter - both achieving fatigue in training but at completely opposite ends of the training systems spectrum. This week, try altering your training intensities and see if you can notice the difference between central and peripheral fatigue.