"All in My Head (Flex)" is a song recorded by an American group Fifth Harmony, featuring vocals by rapper Fetty Wap, for their second studio album, 7/27 (2016), which was released on May 27, 2016.

The song's accompanying music video, set on a tropical beach, was directed by Director X and premiered on the Vevo platform on June 23, 2016.

[1] Prior to the release of their second studio album 7/27, Fifth Harmony member Dinah Jane shared her thoughts on her favorite album track "All in My Head (Flex)" on Instagram: "The vibe and rhythm to this I feel represents me best as a South Pacific Islander [...] This is just one of those feel-good songs that you can't help but jam to, no matter where you're at or who you're with!

"[4] "All in My Head (Flex)" was written by Fifth Harmony's members,[5][6][7] with Stargate, Benny Blanco, Fetty Wap, Tory Lanez, Sir Nolan, Julia Michaels, and Brian Garcia.

[17] Following the rap performed by Fetty Wap, Ally Brooke belts out the first verse: "Curtains like waves closing in all around us, dimming the lights just so that they don't blind us," backed by the percussion and guitar chords.

[19] Concerning his collaboration on "All in My Head (Flex)", Fetty Wap told Billboard that during the recording, his voice "wasn't as mature as it is now" and described it as "impossible" to perform on stage; "Like, I smoke way too much now.

"[20] Peter Meister of website Sputnikmusic described the song as "sassy and badass, Fetty Wap flexes his muscle with might within the funky, glowing synths crashing with the industrialized percussion which breaks free and explodes at all angles".

[21] Digital Spy's Lewis Corner described the song as having an "urban-pop undertone, which is brought to life with light reggae guitar plucks and crisp clicks".

[17] Christopher R. Weingarter of Rolling Stone felt that the Caribbean rhythms hinted at in Reflection's track "Them Girls Be Like" "burst forth" in "All In My Head (Flex)" and "Gonna Get Better".

"[23] Describing the song as "reggaeton-inflected" the Los Angeles Times Gerrick D. Kennedy believed that "All In My Head (Flex)", as well as another 7/27 track, "Not That Kinda Girl," "are the album's most infectious offerings".

[25] However, Spencer Kornhaber of The Atlantic felt that "All In My Head (Flex) brings in the most exuberant rapper of our times, Fetty Wap, to very catchy effect.

Gil Kaufman from Billboard said that the group is "dancing and serving up their best surfside poses while singing the reggae-tinged song on a picturesque beach".

The camera fades to Lauren, who sings the bridge as she stands next to a background of rocks, as a take of another man is shown.

The group is then scattered in different spots standing in a large rock formation, where shots of Dinah alone are spliced as she sings the chorus.

Each girl is dressed in beach draps and dance with a man as the scene interchanges with Fetty Wap's rap verse.