James wrote “who is interested in discussing the varied effects of loadless max intensity isometrics (eg pulling or pressing/squatting an empty bar against a pin in the power rack) vs max intensity loaded yielding isometrics in which the duration of effort of exertion is the same in both cases.”
Just from personal experience and thought, when doing an Iso hold with a weight as compared to an iso push against a weight does one not learn to create more muscle tension via the pushing against pins method??The reason I think this is cause when one pushes against an immoveable object they teach themselves to really strain and maybe if they strain hard enough teach the body to activate more MU’s…now in a basic iso hold the weight is not really being forced up(with max muscle tension) but rather absorbed ((maybe??)…when you reverse a weight from eccentric to concentric, the initial isometric reversal part of the lift seems to be the one where the most tension is needed, once that tension is created and the weight starts to move I seem to feel a bit of lost tension in my muscles due to acceleration and momentum of the bar, this is where Comp.Accel.Training (CAT) is supposed come inhandy!!!I think? 
, so if I am correct here in my idea of what is going down when you lift a barbell in a basic movement like a bench, then iso pushes against a pin at or close to the area of weight reversal may be most efficient, ,if you can learn to create major tension at that point of the lift then you should be able to accelerate the bar through the entire range of motion much easier! I think Yessis spoke of something similar, called Dynamic Isometrics, by having an athlete push against and immovable force (usually at the area of weakness) for a couple seconds and then releasing it that should teach the muscles to activate more powerfully at that specific spot and hopefully drive the bar through the sticking points above…I do not think that basic iso holds without pushing against something would produce the same kinds of results but I could be wrong 
…not sure of all of my statements here but I like the topic!!!
Pushing against pins is harder on the joints and also harder to quantify. The bar will often have a tendency to jump around against the pins as well. Yielding Isos are really more like slow eccentrics. As for volume I’ve used them with at least 15 people including myself and simply used them as what could be called max effort work…we’ve used anywhere from 4 sets to 8 sets of 10 seconds or less per hold in weakest joint range once per week. They have worked just fine everytime. Huge strength increases are not uncommon. I’d equate a 10 second hold approximately equivalent to the volume of a 2 repetition set, but obviously with greater intensity.
As for the excessively longer holds I base my opinons on personal experience as I tried using them but found them useless and then looked to the research to find out why. For example I tried one leg squats, pushups and dips for time and sure they hurt like hell when you’re doing them but the load is not enough to create enough tension and the fatigue (assuming one has a decent level of strength) and failure occurs to lack of blood flow. After talking with a few others who experienced the same I reached my own conclusions.
Having said that, I have found that longer yielding isos in the stretch range (not excessively long) can still be of benefit for strength and particularly hypertrophy stimulation yet one has to be able to use load sufficient to create the necessary tension. This means loads of ~70% + should be used and time can range anywhere from 10 seconds all the way up to around 1 minute. The ideal loading and time scenario will vary depending on the bodypart and whether one is using a compound or isolation movement. Compound movements do not respond particularly well to longer holds. For example, what you will find if you try to do a 1 minute split squat hold is that the weight you use will be so ridiculously light you might as well be in the aerobics class with the fat chicks. A preacher curl or overhead tricep movement, on the other hand, respond particularly well to 40-60 second holds.
For compound movements I tend to restrict the prescription of yielding isometrics to 10 seconds or less, UNLESS they are prescribed as part of a combination set. For example we might prescribe a 5 rep set with a 3-5 second pause at the bottom.
Now, all this is not to say that I see no value in using isometric pushups, single leg squats, etc. but I disagree with the excessively long isometric holds. I do in fact use those exact movements with beginners, but I keep the isometric hold to 10 seconds or less and work up from there and/or use a combination set.
Kelly, my experience is similar to yours. I have, however, found somewhat extended duration holds (up to a 30s total per complex set) to be useful with compound lifts for wrestlers/MMA.
I initially was experimenting with some of my clients programming and the results yielded in isometric strength endurance were evident in their increased performance during competition by way of reduced fatigue in static lock ups as well as a diminished tendency for the biceps, in particular, to get ‘pumped’.
I have successfully experimented with both single position holds in the stretched position for extensor chain movements and fully contracted positions for flexor chain movements as well as complex sets, as you referred to, in which one set incorporates 2-3 holds at different joint angles.
James wouldn’t the extreme angle isos be good for wrestlers also because they often get pulled and pushed in extreme positions, if they become stronger in these positions they could overcome them if ever encountered with em’!!!
Yes, my view is to prepare an athlete for the articulations and stressors they are likely to encounter under extreme resistance during sport.
If an athlete is able to tolerate high stress at extreme joint angles in training, then they are likely to be more resilient to similar situations during sport.
I am not stating that I address SPP in the weight room, I am simply stating that there are situations in which GPP can become somewhat specified in order to correlate more highly to sport skill.
I like the longer yeilding iso’s after my workout. I use them like the EQI description in the end of Thibaudeau’s book. I have found tremendous improvements in mobility both static and dynamic. Of course I’m not using them for “strength” or “hypertrophy” gains. EQI’s are definitely a favorite mobility drill of mine. I usually perform 2 at the end of each workout.
As far as in the workout for performance, I like yeilding isometric contractions, and the “isomio” method as kelly has mentioned. I have tried the overcoming iso’s but, in terms of intensity, they are very hard to quantify. when you stop do you know if you were pressing 315lbs or 185, or 45.
I can see where the 30-60 holds would benefit fighters definitely.
Also loaded stretching is great and a lot of these bodyweight movements can be great for that. I kind’ve think the name and popoular explanations for “eccentric quasi isometric”, falls into the “trying to be cutting edge” group I was talking about above, because people like Siff talked and recommended that same active flexibility work via loaded stretching years ago, but at least it makes more people aware of it.
Flexibility-Strength
A very simple and natural way of enhancing flexibility in the gym is to carry
out one’s normal exercises over a progressively increasing range and then use
a progressively heavier load over a progressively increasing range in
combined static and dynamic patterns of action. Why is it at all necessary
to execute flexibility exercises before strength exercises? Why not train in
such a way that the qualities of strength, power and flexibility are all
trained in integrated fashion at the same time? For example,I have had
many athletes who could barely manage a half squat and within a few months,
using this type of training, they have managed full squats without blocks
beneath their heels.Quasi Isometrics
The use of quasi-isometric activity can be especially useful in developing
active flexibility (see Ch 1.9). This requires one to exercise a limb
through a full range of movement against a resistance which is allowed to
stretch a joint gently beyond its limit of static flexibility without
producing any sudden movement which may recruit the myotatic reflex. Free
weights, pulley and other functional training machines can be particularly
versatile in allowing one to execute natural patterns of movement against
resistance (see Ch 4.2.7). In addition, longer periods of progressive
isometric or quasi-isometric activity in full range movement produce greater
gains in active flexibility…