Featuring Kevin Pearce and Shaun White. Unrated.

What begins as an adrenaline-fuelled ode to extreme sports, and the rivalries among the privileged boys (and some girls) who practise them, morphs into something much deeper and darker in Lucy Walker’s provocative new documentary.

The filmmaker, who did a similarly subversive number on Brazilian garbage pickers turned artists in her Oscar-nominated Waste Land, here starts with long-time frenemies Shaun White and Kevin Pearce, now still in their mid 20s, who for years alternated between the top two positions at all major snowboarding competitions.

A seamless blend of home movies, TV coverage, and footage shot for The Crash Reel gives us a swift overview of two remarkably similar lives, with White starting as a sickly, redheaded child in California and Pearce growing up one of four generally cheerful blond brothers in Vermont. Leaders of a furry snowboarding gang that called itself FRENDS (“Because there’s no ‘I’ in friends,” one explains, unironically), both were preparing outrageous new tricks for the 2010 Olympics when Pearce had a spectacular accident in a massive Utah halfpipe.

With Pearce languishing in a coma temporarily, the ESPN world fades, modern medicine steps forward, and Pearce’s exceptional family comes into highly emotional focus. His Irish-born father (a successful glass blower), gritty New England mom, and two snowboarding brothers all put pressure on the recovering athlete not to hit the powder anytime soon.

Their influence pales before that of the other brother, David, who has Down syndrome. His awareness of perceived disability truly torments him. This existential dilemma mirrors Kevin’s determination to do things denied him, but the likelihood of repeat injuries for those who’ve had serious head trauma—as in football and other increasingly risky sportutainments—is great, as is the tendency to misread their own weaknesses. Pearce remains an adrenaline junkie as long as he can, but it’s hard to ignore his brother’s pleas. “When you talk about doing double corks,” says David, wiping away tears, “I get very anxious.” So does the viewer.