Isometrics and Gravity

by Darren
(Worcestershire uk)

I have been using a gravity force trainer which uses your body weight for every exercise.

I have made some gains but not much.

How can I implement isometrics in my training routine; leg extensions, chest press, shoulder press, lat pull downs, tricep dips, and barbell curls?

Is it simply a matter of holding a contraction for longer? I would be gratefull for some feed back thanks.