T Nation

Super Beast

What % of 1 RM should be used on the isometric action exercises?

It depends on the exercise and duration.

As a rule of the thumb …

15-30 seconds: 70-80%
30-45 seconds: 60-70%
45-60 seconds: 50-60%
60-75 seconds: 40-50%
75-90 seconds: 30-40%
90-105 seconds: 20-30%

But it will be highly variable from one individual to the next. Use these guidelines as a starting point on adjust the load according to your capacities.