One of the most important aspects of the Overload Principle is that of volume vs intensity. The most simplistic version of the rule being:
High intensity = low volume
Low intensity = high volume
Some examples are as follows:
• Running is relatively low in intensity and can therefore be done for an extended duration. Alternatively when running at a high speed the intensity is increased and your ability to continue is greatly reduced.
• Jumping. You can manage to do many little jumps for an extended period of time, but when you start jumping from greater heights the load on the legs increases and if you continue you will end up injuring yourself.
The trick here is to listen to your body and learn your limits. As your strength and conditioning increases your ability to sustain activity at high or low intensity increases as well. So comparatively a seasoned traceur could get to a point where what he considers being low intensity is high intensity for a beginner.
There and a multitude of ways to vary volume and intensity, the different ways that you utilise it can change the effects you get from the training. A perfect example is the differences you gets in training effect when you vary the rest, weight and repetition when doing weight lifting. The variances that you choose can effect whether your muscles get bigger, stronger or more powerful.
An even more complex and long term variance on intensity vs volume is the concept of periodization.