I'm thinking about including some Isometric exercises into my routine, either before a TRX exercise to pre-fatigue the muscle, after the exercise like a superset, or during the exercise (i.e. holding the pike for 5 seconds during the suspended pendulum).  I have also started playing with some Isotonic contractions (i.e., "flexing" my chest and tying to maintain constant tension throughout the chest press or atomic pushup).  So far it seems like this adds a real challenge to some of the exercises, but I don't really know what I'm doing and am just gauging the effectiveness of these exercises by how tired I am after I do them.  Has anyone out there used Isometric or Isotonic exercises?  Any ideas on how to effectively incorporate them into an existing TRX program?  Thanks, any and all suggestions would be helpful!! 

 Isometrics isn't used as much these days as it was before I was born, but it has made a little bit of a comeback in the past couple years and I have made some use of them. People can hold for several seconds or more in a position and it does seem to help muscle growth. This idea pre-dates Charles Atlas who really marketed it and has been overlooked with the coming of wide use of weights and machines, but still works.

The three types of muscle contraction are concentric, eccentric, and isometric.  If we take a body row, when you pull your body towards the handles you are concentrically contracting your muscles. If you hold at the top, you are isometrically contracting your muscles. If you slowly lower yourself down, you are eccentrically contracting your muscles, also sometimes called emphasizing the negative.

 Any exercise where you stop part way, not because you are stuck, is an isometric one. Hold your shrug at the top. Stop midway down in the pushup. Hold a plank position.  Everyone of those is isometric. This you could easily place in any TRX routine.

Isometrics are a good way to vary your routine. Depending on your goal, they can be quite helpful. Primarily, they are used to stimulate muscle growth. They are also used by people who train and compete in sports involving grappling. If you ever see someone spend time trying to hold onto a choke, they are able to hold on longer thanks to the fact that they use isometrics to get their muscles more accustomed to working for longer periods without rest.

Unless you are training in some sort of grappling, isometrics are most likely a way for you to stimulate muscle growth. For muscle growth, the consensus seems to be that as little as five seconds of holding can start to stimulate it, slightly longer might be better. You can use the above mentioned methods, I would follw with stretching and a protein shake or some milk to stimulate muscle growth.

Grapplers need to be able to hold for longer with their limbs so they tend to use different methods to improve their abilities. It can be as simple as trying to hold the triangle choke on a grappling dummy for progressively longer periods. Or a variation on this is possible with the TRX, but Randy Couture used to do a barbell circuit where he never let go of the barbell of which video exists on the internet. By doing a circuit (emphasizing the upper body) nonstop where you always held onto the handles for say ten minutes, you could help not only with your grip, but your muscle endurance as well.

Awesome!  Thanks for the info.  I am not looking for anything sport-specific, just another way to keep things fresh and avoid falling into a routine.  One of the things I really love about the TRX is how easily I'm able to change up the workouts by changing my foot or hand position, altering the movement or angle, etc.  While playing around the other day with my routine, I was using a slow eccentric contraction followed by an explosive concentric movement and by tossing in a few isometric "halts" during my suspended pushups.  I was so tired by the end of it that it got me thinking that this may be something good to use in the routine to shake it up a bit.  We'll see how it goes.... 

I tried incorperating isometrics into the day 2 shoulder superset. I'd hold my arms at the end position for 5 seconds after one set, such as the Y or T. I found it caused a lot more burn in my arms. It was also really difficult to manage to keep steady, it definately added another element of fatigue to the super set, while not compromising the strength needed to perform the exercises. If you try it please let me know what you think.

 Max