Saido Chesto

"Saido Chesto!" originated as the Engrish adaptation of the phrase "Side Chest!" referring to the "side chest" pose in bodybuilding, as expressed in the 2016 manga ダンベル何キロ持てる？which was published with the English subtitle "How much heavy dumbbells can you lift?"

The pronunciation Danberu Nan-Kiro Moteru? means approximately the same thing: "How Many Kilograms of Dumbbell Can You Lift?" and the English dub kept pretty close to that: "How Heavy Are the Dumbbells You Lift?"

The phrase gained popularity as the manga received an anime adaptation in 2019 as the phrase "Saido Chesto!" was used as part of the opening song "Onegai Muscle!"

The phrase is used by 街雄 鳴造 (pr Machio Naruzo) with Naruzo Machio's surname being a play on the phrase "Macho": he is usually just called "Machio-san". He is a baby-faced bodybuilder who appears of normal build when clothed but when he flexes his muscles burst through his clothing and he is the largest of all bodybuilders, their humble god-king.

This happens during a scene in the one of the anime's episodes in addition to the OP:

https://www.youtube.com/watch?v=Ru2245jBzJY

The meme has taken on two forms. The most creative is the tributary form:

Fans of the song began to mine old cartoons for clips of characters normally non-muscular who had moments of becoming muscular for a brief period of time. The theme music is then overlaid with these clips in a structured way and generally the video is just titled "Saido Chesto" with the summary explaining the character/series.

The music of Onegai Muscle is played quietly in the background up until the "Saido Chesto" lyric happens, at which point the volume elevates to a loud level.

This is timed with when the character becomes muscular, for dramatic impact.

A less creative form of the meme is simply doing "reaction videos" where the audio and imagery of Machio Naruzo is inserted into various dramatic anime scenes, usually with characters reacting in horror to it. The same audio approach is used: either the music will be quiet and burst out loud, or sometimes completely silent until the Saido Chesto reveal.

Examples:

17 July 2019 for eponymous Spongebob Squarepants https://www.youtube.com/watch?v=MzqZrf1t030
19 July 2019 towards Attack on Titan characters https://www.youtube.com/watch?v=eE2pvSHmwQI
19 July 2019 toward character from Araburu Kisetsu no Otome-domo yo https://www.youtube.com/watch?v=QrTdtcypXTA
28 July 2019 for Blend-S in https://www.youtube.com/watch?v=r2hmwefPD30
>this was an overlap with https://knowyourmeme.com/memes/s-stands-for-smile-sweet-sister-sadistic-suprise-service

13 August 2019 for various characters at https://www.youtube.com/watch?v=nWgnMv41qhc
>as interpreting https://knowyourmeme.com/memes/boys-locker-room
14 August 2019 towards Jotaru Kuzo from Jojo's Bizarre Adventure https://www.youtube.com/watch?v=HyU_FI-M0N8
14 August 2019 for Shaggy Rogers from the live-action Scooby-Doo films https://www.youtube.com/watch?v=Jf8qgjrN0jM
23 August 2019 for Pillar Men from Jojo's Bizarre Adventure https://www.youtube.com/watch?v=ZZRanhyc_BI
23 August 2019 for Jojo from same https://www.youtube.com/watch?v=TOfJ5R_lTj4
25 August 2019 for Richard Waterson The Amazing World of Gumball https://www.youtube.com/watch?v=ead58L9CMgc

10 September 2019 for Rick Sanchez and Summer Smith from Rick and Morty https://www.youtube.com/watch?v=zA_0WlTTc0s
11 December 2019 for blonde guy from Attack on Titan https://www.youtube.com/watch?v=mRSjVTVZjVE
17 December 2019 for eponymous Courage the Cowardly Dog https://www.youtube.com/watch?v=Vr26locP7os
31 December 2019 for Bugs Bunny in Space Jam https://www.youtube.com/watch?v=7rqv2GET3nI

5 July 2020 for Maki Oze from Fire Force https://www.youtube.com/watch?v=y9_19q_UFwA
8 December 2020 for Gawr Gura https://www.youtube.com/watch?v=PxZrXrNdZsI

Other tributes to the memetic phrase include various artwork:
29 August 2019 https://9gag.com/gag/avogRKb
13 September 2019 https://9gag.com/gag/aj5A27G
17 October 2019 https://www.deviantart.com/soritachan/art/COMM-Atzuma-Saido-Chesto-817129987
20 December 2019 https://askbrasil.tumblr.com/post/189784936634/saido-chesto
27 April 2020 https://www.deviantart.com/serahkyu77/art/Double-Saido-Chesto-839616038
4 May 2020 https://www.reddit.com/r/VirtualYoutubers/comments/gdicvo/saido_chesto/
13 May 2020 https://www.furaffinity.net/view/36335206/
13 June 2020 https://knowyourmeme.com/photos/1862015-rwby