Fatigue: What Is Stress?
If the stress on the body is persistent over a prolonged period of time then the individual will enter the resistance phase (phase 2). The defence mechanisms in response to stress will be constantly elevated leading to potentially negative consequences i.e. increased blood pressure, increased heart rate, heightened anxiety and other psychological issues. As a result, the immune system may become suppressed.
As the body remains in the resistance phase, and the stress on the body isn't suppressed or removed, then there is the potential to move into the exhaustion phase (phase 3). Due to being exposed to hormone production long term (specifically cortisol and epinephrine), the body can no longer deal with these metabolic adaptations. This leads to increased susceptibility to illness and disease during this phase.
It's Thursday night training, still no sign of footballs, must be running again. Being the warrior that you are you get on with it and say nothing, placing more (similar) stress on the body. Hello resistance phase!
This cycle continues for several days and weeks (trust me I've seen/experienced it myself), and it's a week away from the start of the season and you're run down, have the flu and your hamstring feels like guitar string. Exhaustion phase has crept up on like those last minute assignments that you forgot to do and now you're out of action for a couple of days/weeks.