Laila Ali and Cody Simpson guest star on 'The Biggest Loser'

Trainers motivate kid participants to "Lead By Example," with Simpson joining teen ambassador Lindsay in giving an emotional anti-bullying speech to her peers

World Champion Fighter Laila Ali and Australian pop singer and teen phenomenon Cody Simpson make special appearances on an inspirational episode of "The Biggest Loser: Challenge America," that airs on Monday, Feb. 4 (8 p.m.), marking the halfway point for season 14.

First, the contestants find out from host Alison Sweeney that the weight of only one player on each team will count this week, but they won't know who it will be until the weigh-in. The trainers - and a roll of the dice - will determine who will represent each team. With this week's theme of "Leading by example," trainers Bob, Jillian and Dolvett Skype with kid participants Biingo, Sunny and Lindsay, and motivate each one to do just that. While Sunny creates a circuit training routine for her fellow classmates, Biingo tries to recruit more friends to his after-school sports club. And Lindsay bravely gives an emotional anti-bullying speech to her peers at school, joined by popular singer Cody Simpson, who also talks about his experience being teased before performing for the kids.

Back at the ranch, the adult contestants compete in a crazy challenge requiring them to avoid three swinging pendulums while walking on a balance beam to retrieve calorie-coded plates matching five specific dishes. And Jackson opens up to Dolvett about his experience being bullied as a child. Later, Dolvett's team has a special visit with four-time undefeated world champion fighter Laila Ali, who puts them through a fun and challenging boxing workout. Finally, it's time for the weigh-in and the roll of the dice to determine who will weigh in from each team before another player is sent packing. Also this week, the eliminated contestant makeover segments continue, with Pam Geil's transformation photo shoot featured in the first half hour of the show.

Ali is a world-class athlete, fitness and wellness expert, cooking enthusiast, founder of the Laila Ali Lifestyle Brand and mother of two toddler-aged children. The daughter of the legendary Muhammad Ali, she is also a four-time undefeated world boxing champion, whose stellar record includes 24 wins (21 of which were knockouts) and zero losses. In addition to appearing as a cast member on NBC's reality series "Stars Earn Stripes" where she competed to raise money for a charity that supports veterans and their children, Ali is currently the host of "Everyday Health" and a former co-host of "American Gladiators" alongside Hulk Hogan.

With more than 4 million Twitter followers, 4 million-plus Facebook likes and more than 152 million YouTube views, 16-year-old pop star Simpson is already a teen phenomenon. He recently released his debut album "Paradise," and is currently on tour supporting Justin Bieber on Bieber's "Believe Tour." The year 2012 proved to be a banner one for Simpson, having kicked things off with his own sold-Out "Welcome To Paradise Tour," being named "Favorite Aussie Superstar" at the Nickelodeon Kids' Choice Awards and releasing a new interactive film, "Finding Cody," via Warner Music Group's original YouTube channel, "The Warner Sound."

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