Yes, ISOMETRICS is a Scrabble word!

Letter values in Scrabble US: I 1, S 1, O 1, M 3, E 1, T 1, R 1, I 1, C 3, S 1.

Is it a valid word?

ISOMETRICS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

muscle-building exercises (or a system of musclebuilding exercises) involving muscular contractions against resistance without movement (the muscles contracts but the length of the muscle does not change)
a line connecting isometric points

Also: isometric exercise, isometric line.