flexing one's muscles

Verb

flex one's muscles (third-person singular simple present flexes one's muscles, present participle flexing one's muscles, simple past and past participle flexed one's muscles)

1. (literally) To tense and bend one's flexor muscles.
2. (figuratively) To show off one's strength or skills.
   • But at a time of a growing perception in the West that China is flexing its muscles [...], countries closer to China’s shores also worry that it might be getting more assertive.2010 January 21, “Choppy waters”, in The Economist