Meaning:
“撸” is a verb from northeastern Chinese dialect which either means to “rub something (like leaves) off from a branch” or “work hard to hone one’s skills,” and “铁” means “iron,” which in this context refers to dumbbells or other strength training equipment in gyms. While many young people love to “撸串” (eating kebabs at roadside stalls), they also love to “撸铁” (doing serious strength training sessions in gyms to lose weight and build muscles).
Example:
A: 国庆假期你去哪里玩了？
Guóqìng jiàqī nǐ qù nǎlǐ wán le？
Where did you go during the National Day holiday?
B: 和闺密一起去了西班牙。你呢？
Hé guīmì yīqǐ qù le xībānyá。Nǐ ne？
I traveled to Spain with my best friend. How about you?
A: 我天天去健身房撸铁。
Wǒ tiāntiān qù jiànshēnfáng lūtiě。
I worked out at the gym everyday, doing strength training sessions to build muscles.