Meaning:
“肌肉” means “muscle,” and “博士” means “doctor.” This term, literally translated as “muscular doctor,” originally refers to someone who is a doctor (or just very well-educated, often stereotyped as wearing glasses and not good at sports) but has the looks of a personal trainer. Now, Chinese netizens use it as an umbrella term on people who have achieved surprisingly high levels of success in their chosen hobbies, which may go against people’s general impression of their type. For example, an unassuming and quiet girl could secretly be a sophisticated gamer and highest ranked on the “Kings of Glory” leader board who uses ruthless tactics to decimate her opponents.
Example:
A: 公司组织街舞大赛，我们部门谁报名参加？
Gōngsī zǔzhī jiēwǔ dàsài，wǒmen bùmén shuí bàomíng cānjiā？
The company is organizing a hip-hop dance competition. Who in our department can participate?
B: 让晓丽去。她是个肌肉博士，街舞高手。
Ràng xiǎolì qù。Tā shì ge jīròu bóshì，jiēwǔ gāoshǒu。
Ask Xiaoli to get enrolled. She’s a serious hobbyist and skillful hip-hop dancer.