‘GMA’ 40th Anniversary: Behind the Scenes at ‘Dancing With the Stars’ Finale Rehearsals

— -- The final four contestants on Season 21 of ABC’s “Dancing With the Stars” got in yet another practice tonight ahead of the next week’s finals, and “Good Morning America” went behind the scenes as part of the "GMA" 40-hour broadcast marathon.

Former mirror ball champion and “GMA” contributor Melissa Rycroft was joined by “Dancing” pros and mirror ball champions Tony Dovolani (Rycroft’s "Dancing" partner) and Peta Murgatroyd for an hour-long look at the grueling rehearsals leading up to the finale.

In a live interview, "GMA"'s Amy Robach asked Dovolani how hard the finalists were training at this point.

“I think the only thing that’s missing is the sleeping bags,” Dovolani replied.

During tonight’s livestream marathon, Rycroft and ABC News' Ginger Zee checked in with conservationist Bindi Irwin and her pro partner, Derek Hough; U.S. Army National Guardsman Alek Skarlatos and his pro partner Lindsay Arnold; Backstreet Boys band member Nick Carter and his pro partner Sharna Burgess, and Big Time Rush singer Carlos PenaVega and his pro partner, Witney Carson.

Zee and Cameron Bure also chatted about their most memorable on “Dancing” history, such as Kim Kardashian's low-scoring mambo to "Baby Got Back," Donald Driver's sizzling freestyle with Murgatroyd that earned them a perfect score, and Marie Osmond fainting on live TV.

Five celebrity dancers had remained when “Spy Kids” actress Alexa PenaVega was voted off last week, but that number was whittled down to four when singer/TV host Tamar Braxton dropped out because of blood clots in her lungs.

Another contestant -- reality TV star Kim Zolciak-Biermann – was forced to withdraw from competition early in the season after suffering a mini-stroke. She later underwent heart surgery.