Reason for some variations in doing crunches or other ab exercises

Question

In fitness classes I have often seen that crunches were done in a specific pattern, for example:

10 normal crunches
10 crunches in 2 steps (i.e. up hold 1 count, up hold 1 count, down, down) 10 mini pulsing crunches on the top
hold it 10 seconds

Or when doing bicycle crunches for example:

Do 15 very slow bicycle crunches and then do 15 very very fast ones.

What's the reason for the described variations concerning body-sculpting effects and body performance?

Answer 1

Apart from preventing boredom, interval training also helps in achieving better results. If you follow the same pattern of training after a certain time the body will get used to it and new muscle is not created.

Interval training shocks the muscles boosting the metabolism which leads to fat loss and a better body. It also helps in improving your cardiovascular strength and increases the amount of lactic acid that the body can cope up with.