Processor Time taken by threads

I have an application in which the main thread of the application calls the RunUserInterface, whereas another thread does the update of all the controls in the screen periodically.  On analysis of the processor time utilised by the application, I am finding that, with just the periodic update of screen, the main thread takes more than 80% of the processor time out of the total time taken by the application/process.  Is this an expected behaviour of Labwindows?  My expection is that the thread on which update is done should take the maximum process time.  And that's how I want it.  Can someone comment on this?