is over 50 .. and more fit than stars half her age!

The Queen of Pop kicked off her MDNA tour today in Tel Aviv, Israel -- where she showed off her impressive bod in a number of new costumes.

The 53-year-old superstar flexed some seriously buff arms while playing the guitar and later changed into a flirty cheerleader uniform that showed off her muscular derriere.

The singer's set list included new songs like "Girl Gone Wild" and "Give Me All Your Luvin'" as well as classic hits like "Express Yourself," "Like a Virgin" and "Like a Prayer."

From Tel Aviv, Madge is off to Abu Dhabi, Istanbul, Buenos Aires and the US.

Check out her performance pics above!

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