Are frequent muscle twitches normal? throughout the day a muscle (arm, leg, thigh, or stomach) twitches/pulses for like a second im 18 not exercising

Get checked out: Start with some blood tests ( thyroid function, electrolytes, kidney function etc.) If you have muscle pain or weakness be sure to tell the doctor who orders the tests.

Normal: without other symptoms to go along with it these twitches would probably be considered normal

Check blood Ca, Mg: Muscle twitching could be a sign of low calcium or magnesium in the blood. This can easily be checked with a blood test. Mg deficiency is fairly common. You could take magnesium oxide 400mg/d (available over the counter) and see if it helps.