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Under a question in this stack I someone commented under the answer I gave, that additional isolation work is useless (+ providing some studies about it).

The example reffered to Squats as compound a movement with Leg Extensions and Leg Curls as further isolation work for the Legs. In the provided studies, the conclusion was that the difference in muscle growth and strength between the compound-group of testsubjects and the compound-and-isolaton-group was under 1%.

Studies: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5744434/ https://www.ncbi.nlm.nih.gov/pubmed/23537028 https://www.ncbi.nlm.nih.gov/pubmed/26244600

I can't really imagine how isolation work would be completely useless, when trying to build muscle and/or get stronger. So I'm trying to get this to a wider audience.

Is it true, that isolation work does pretty much not contribute to muscle growth or strength, given you already do the compound movements (like squats, deadlifts, bench press, etc.)? Or am I misunderstanding something here?

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"Pretty useless" might be too strong a phrase. The studies you linked actually show that people doing isolation exercises did see strength gains and muscle size. (bold added by me for clarity).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5744434/

Whilst both groups significantly increased cardiorespiratory fitness and maximal strength, ... no differences were found for body composition.

Although it notes:

the improvements in MJ (Multi-joint) group were higher than for SJ (Single Joint) in VO2max..., bench press 1 RM ..., knee extension 1 RM ... and squat 1 RM. In conclusion, when total work volume was equated, RT programs involving MJ exercises appear to be more efficient for improving muscle strength and maximal oxygen consumption than programs involving SJ exercises...

https://www.ncbi.nlm.nih.gov/pubmed/23537028

There was a significant (p < 0.05) increase in MT (muscle thickness) ... and PT (peak torque) ... in both groups, but there were no between-group differences

https://www.ncbi.nlm.nih.gov/pubmed/26244600

Both groups significantly increased 1RM for elbow flexion ..., extension ..., FAC (flexed arm circumference)..., and AMC (arm muscle circumference).... Comparison between groups revealed no significant difference in any variable.

The takeaway is that you can build muscle doing solely single-joint, isolation exercises. However, there is very little carry over to multi-join exercises. Meaning, that the best thing you can do to build your squat is to squat more. There is no major benefit to adding leg presses and leg curls.

Some unilateral exercises like the lunge are also used to fix muscle imbalances in which one side of the body is stronger than the other (A different kind of imbalance that other question was asking about).

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  • I still don't quite understand this, might be because im no english speaking native. I can't really imagine a workout routine including compound and isolation exercises being just as effective (or only like a really small fraction more effective) than a workout which only includes the big compound movements. Am I misunderstanding something here?
    – Suimon
    Commented Aug 28, 2018 at 16:08
  • @Suimon More does not always mean better. There is a concept of "diminishing returns". In this context, that means that you gain less with each set. For example, the most optimal sets of squats might be 5. The sixth and seventh set does not benefit you at all. An eighth set might set you back. Adding more sets of isolation work does not necessarily benefit you as it's just adding more work. blacklabellogic.files.wordpress.com/2018/05/…
    – DeeV
    Commented Aug 28, 2018 at 18:26
  • And in these studies you can see it. People did progress with isolation work on their own. They also progressed with compound work on their own. Combining the two either meant that they reduced the volume of both (so overall volume stays the same), or the added volume didn't have any benefit.
    – DeeV
    Commented Aug 28, 2018 at 18:28
  • Okay, so I think I got it now :D You're talking about 5 squat sets and that more sets won't help me. But how does this behave when eg. only doing 3 sets of 10 reps in the squat and adding isolation exercises after that? Also, what about isolation movements of muscles, that aren't really integrated into the compound exercises. Like Calv Raises or Lateral Raises. These should be beneficial, right? Because as far as I am able to judge, these muscles aren't really "used" that much in the compound lifts.
    – Suimon
    Commented Aug 29, 2018 at 6:05
  • I also just noticed, the studies were performed on untrained individuals. So how does this apply to trained individuals (lets say 1-3 years of training already done), if it applies to them at all?
    – Suimon
    Commented Aug 29, 2018 at 7:13

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