Learn Italian: Terrò i muscoli forti con l'esercizio quotidiano. - I will keep the muscles strong with daily exercise.

Tenere (to keep/to hold) is one of a few verbs that have a special double-R stem in the future tense. Instead of just dropping the final 'e' to make 'tenerò', it drops the whole '-ne-' and adds an extra 'r'. The stem becomes terr-, and you add the regular io ending to get terrò.

I learned that tenere means 'to hold'. Can it also mean 'to keep'?

Yes! While tenere is often used for holding a physical object, it is equally common for keeping something in a certain state or condition. In this sentence, you are 'keeping' the muscles strong (terrò i muscoli forti).

Why is the adjective forti ending in -i instead of -o or -a?

The singular Italian word for 'strong' is forte. Adjectives that end in -e in the singular do not have separate masculine and feminine forms. Instead, they always change their ending to -i in the plural. Since we are describing plural muscles (i muscoli), forte becomes forti.

What kind of word is quotidiano?

Quotidiano is an adjective that means 'daily' or 'everyday'. It matches the masculine singular noun it describes, which is l'esercizio (the exercise). You might also recognize this word used on its own as a noun to mean a daily newspaper.