Custom Thread Pool Profile maxPoolSize

Hi,

I have set Custom Thread profile and i could see there are 20 threads
created from the below configuration.

<threadPoolProfile id="apthreadprofile" defaultProfile="true" poolSize="20"
maxPoolSize="50" maxQueueSize="500" rejectedPolicy="Abort"/>

But i could never see that the thread count getting increased above 20 but
the max pool size is configured to 50.
When will the max pool size be used?

We tried doing a load test with 50 concurrent users with concurrent
sessions, which means there will be 50 concurrent requests but could see
only 20 threads at any given time.

Thanks,
Arthanarisamy