Change and decay of one's own body. How fast is it? We all know that we get sick and get old but i have heard that "Abhidhamma" talks about a faster version of decay and change.As i have heard there is a change that is happening every fraction of a second but we are unable to recognize it with our senses.

Does anyone have knowledge to share about this?

And how can we use this to our personal practice?
With vipassanā-ñāṇa you can recognise this change perhaps not to the clarity as in the Abhidhamma.

In p 39 of Process of Conciousness and Matter by (Aggamahāpaṇḍita) Bhaddanta Dr. Rewata Dhamma (Writen as a supplement to Comprehensive Manual of Abhidhamma), gives an idea at what rate phenomena arises and passes away.

For personal practice if will be sufficient recognise:


Arising
Passing
Change, i.e., what has arisen is what has not arisen before 


Also see my other answer on similar subject matter: https://buddhism.stackexchange.com/a/12392/295

Following two articles by Piya Tan might be of interest:


Dhamma and Abhidhamma
The Radiant Mind