Complex sentence: The distinction is that in a yielding isometric, one is pressing roughly the exact amount of pressure needed to negate the resistance, neither dropping nor lifting it, whereas in an overcoming isometric, one can be exerting more force and simply unable to move it.
Split into simpler sentences: The distinction is that in a yielding isometric, one is pressing roughly the exact amount of pressure needed to negate the resistance, neither dropping or lifting it. Whereas in an overcoming isometric, one can be exerting more force and simply unable to move it.