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I'd say your pretty beastly!I can’t speak to whatever personal experience Thib has with using only overcoming isometrics, and try to only speak confidently from what I know first hand. It may be that the levels of hypertrophy he’s talking about are at the higher end of what is possible, or a different % of muscle:fat gain during a bulking phase, or he’s going on the advice of someone(s) he respects enough to take as established fact.
As a general policy, what ANYONE claims re what isometrics are or are not capable of doing, they should be speaking from direct experience, from a specific application and timeframe, from isolated usage. Otherwise everyone who’s ever picked up a kettlebell or barbell would be qualified to discuss what these tools are/are not good for, without going into specifics. Not many see the inherent logic of that statement applied to isometrics, but is obvious when applied to KB, barbell etc.
The observations from short term interventions is that isometrics work just as well as isotonics. Observations from longer term studies suggest that gains slow way down at 6-8 weeks (similar to isotonics) and you should change some variables to keep making progress.
Shorter holds will def work for hypertrophy but you will need to do more of them or combine them with some other approach.
Back in ‘21 I gained just under 3lbs a month for almost 4 months straight. I estimate I gained about 2-3lbs of fat to an overall gain of 10-12lbs, a good return. This was back when I was using jumprope or sprint in place for 10-15 seconds after every isometric hold IIRC. It worked better for hypertrophy than my current approach but made it tough to do anything on between days. Splitting it up has has made it harder to increase muscle but my overall aerobic health from the off-day intervals is much improved.
That said, isometrics of any stripe are not the best vehicle for hypertrophy because they are stingy on the metabolic stress and occlusion factors. I would not recommend them if hypertrophy is the primary goal unless there were other factors that made them a good candidate for a given individual.
But, if they worked for me as 54yr old they should work reasonably well for younger athletes. Even now I maintain at 196-200lbs at a height of 5’10”. Not beastly but that’s a lot of muscle compared a theoretical lean healthy weight of about 165lbs and comparable to what I managed doing Cluster sets with sandbags. Am pound for pound stronger as well.
Thanks for the in-depth response.
I agree about anecdotal experience being important and that's going to vary between people because we're all in different states with different goals.
I think people like to hear anecdotal experience with isometrics too, because there's enough studies showing they're effective but people seem to always ask... but can isometrics really do X?
Again, thanks for the response.