Film preview: 'Over the Limit' 

A riveting portrait of world-class Russian rhythmic gymnast Margarita Mamun, "Over the Limit" offers an at times harrowing dive into exactly what it takes to be an Olympic champion. Mamun is 20 years old, which in the world of professional athletes means she's nearly at the end of her career. But before she retires, she has one final goal to accomplish: winning an Olympic gold medal.

Rhythmic gymnastics tends to be a misunderstood sport, one that casual observers may view as simply tossing a hula hoop or twirling a ribbon. With her first feature-length documentary, Polish filmmaker Marta Prus -- a former rhythmic gymnast herself -- sets out to show her audiences that those ribbon twirls require an unwavering iron will.

Following Mamun's journey in the run up to the 2016 Summer Games in Rio, Prus's unadorned filmmaking captures the punishing regimen of grueling training sessions, a practically non-existent social life, and constant physical and emotional degradation. Cumulatively, it underlines the ways in which professional athletes are pushed beyond the limits of mere mortals in their attempts to achieve perfection. "You're not a human being, but an athlete!" Mamun's personal coach Amina Zaripova scolds her, when she dares show a hint of emotional fatigue.

Zaripova has moments of tenderness amid the harsh critiques, and she's a model of sensitivity compared to her superior. To say that Mamun's coaches tend to opt for a "tough love" approach would be a monumental understatement. "You're losing your concentration, bitch! You stupid cow! I can't stand you any longer!" screams head coach of Russia's national gymnastics team Irina Viner-Usmanova -- a larger-than-life figure in thick makeup and an endless supply of giant hats. Her endless stream of invective and verbal abuse calls to mind J.K. Simmons's tyrannical jazz instructor in Damien Chazelle's "Whiplash," though it's even more horrifying in the context of a documentary.

Watching Mamun fight through the mental and physical pressures leaves no question that it's a feat few could accomplish. She can never let emotions get the best of her, even when facing her father's cancer diagnosis and steady decline. By the end of Mamun's journey, we're able to step back and admire what Prus has been able to achieve: teaching us to admire the grace and beauty of her sport, but deepening our appreciation by never letting us forget the psychological and physical ferocity that guides it.