Meaning:
“秀” means to “show off,” and “肌肉” means “muscles.” This term, commonly seen in media reports and widely used by Chinese people today, likely originated in English as the direct translation of the idiom “flexing one’s muscles.” Literally it means to “contract one’s muscles, especially to demonstrate their size and strength.” By extension, it means to “demonstrate one’s influence, power or strength.”
Example:
A: 今年赌城的消费电子展有哪些亮点？
Jīnnián dǔchéng de xiāofèi diànzǐ zhǎn yǒu nǎxiē liàngdiǎn？
Are there any highlights in this year’s CES in Las Vegas?
B: 非常多，比如一群芯片行业的头部公司在人工智能和自动驾驶领域秀肌肉。
Fēicháng duō，bǐrú yīqún xīnpiàn hángyè de tóubù gōngsī zài réngōng zhìnéng hé zìdòng jiàshǐ lǐngyù xiùjīròu。
Quite a lot. For example, many leading chip manufacturers flexed their muscles in AI and self-driving technologies.