Application slows down during Back up The Application is 24/7 up Full back up time is 4 am and back up size is 92 gb. It takes one hour to complete the back up. During those time users complain that the application freezes. 

Just wanted to know whether back up freezes or slows down the application momentarily? No other jobs are running that time.
Certainly, running a backup will have an impact on the performance profile of the machine serving the database being backed up.

For a FULL Backup, the operation consists of reading every allocated page in the entire database, and writing those pages to the backup file/device.

Since your users are complaining about the application being slow during the period of time when the backup takes place, I'd say it's obvious that the backup is having an impact.