Hundreds will be breaking a sweat today to honor first responders killed in the September 11th terror attack.

Today is third annual New York City Memorial Stair Climb at the World Trade Center.

Starting around 9 a.m., members of the FDNY, NYPD and Port Authority Police Department will climb all 72 floors of the building.

They'll do the event in full gear in honor of the first responders that died in the attack.

The climb will also memorialize fallen first responders and military personnel worldwide.