Sasquatch is right, but you have yourself referred to 'excessive pressure'. It is not a strength exercise, but is really about technique.
Cancon has also given you some sound advice. Play a note repeatedly, barely touching the string at first and then gradually increasing the pressure until you find the minimum pressure that generates a clear tone. Learn what that feels like and make sure you don't keep holding strings down long after you need to.
Best wishes, V
"There are only two things worth aiming for, good music and a clean conscience." Paul Hindemith