I thought this could be boring but was a little interested, as I have placed a toe in the water of "endurance" with a few marathons over the years and an ironman at 70. These efforts are a 50 metre jog compared to what Diana Nyad attempted in the proposed swim from Cuba to Florida (110 miles). She had failed when younger but decided to try again at 60.
The subject matter is not intrinsically exciting but the film is saved by good direction from Chai Vasarhelyi and Jimmy Chin (Free Solo), a clever script and excellent acting throughout, - especially from the 2 leads Annette Bening and Jodie Foster. I have met a few of these "ultra" people, utterly consumed by their current passion, the latest gruelling masochistic challenge, which has blotted out their view of anything or anyone else around them. Bening has wonderfully captured this character (- ?psychopathology). The single purposed mania to achieve 'this' - leavened by the occasional sobering insight of the selfishness and, maybe, craziness of it all. The friendship between the 2 ladies was well drawn and affecting.
I found the film surprisingly absorbing. To witness a great athlete with inspiring self-belief, the drama of the swim(s) and to see 2 talented actors at the height of their craft, was worth seeing.