Isometric Duration has two different applications. In the first, it can mean, “hold the top position”. In this case, the exercise will be prefixed with the phrase “Top ISO-D”. Isometric Duration may also mean hold the bottom position, in which case the exercise is prefixed with the phrase “ISO-D”.
In the first case, Top ISO-D works a bit like Concentric Duration (C-D) because it helps reprogram coaptation. It’s like saying to the fascia, “hold together more than you already were holding together.”
In the second case, Isometric duration is actually misnomer, because the isometric part infers that there is to be no movement, and there is always movement occurring in kinetic action.
There are two possible scenarios that exist in an ISO-Duration exercise. The trainee is not yet at the bottom, despite a significant amount of Eccentric Duration (E-D) training. In this case, ISO-D works like a specialized form of E-D: the trainee goes to their best current bottom position and begins holding position across the 1-minute period. If this is the case, they are actually going to end up in a true E-D phase, and they will express more range of motion and improve progression toward the bottom of the range.
The other possibility is that the trainee already actually expresses the full range of motion of the exercise trajectory. When this happens, ISO-D functions to cortically map the bottom position of the range so that the conscious (brain) and unconscious (enteric nervous system) minds can function in synchronicity to produce upward movement. This point is the threshold of power development in the kinetic chain.