Muscle hypertrophy (growth) is triggered by a variety of factors. Unfortunately, many of those same factors that trigger growth have downsides -- and the downsides accumulate as time goes on. Muscle hypertrophy is actually very complex and for significant muscle mass to occur for the average person, multiple things have to occur including (but not limited to) increased blood supply, cellular power (mitochondrial changes), fiber recruitment, microtrauma and subsequent overcompensation.

Not all of these triggers are linear and not all of them operate on the same time scale. In fact, the time scale can change based upon your genetics, age and other environmental factors. Unless your genetics are particularly "good" for building muscle -- it's pretty difficult to actually collapse it all into a workable, sustainable program.

If you peruse body builder magazines (which actually I don't suggest) you will see many of the "pros" suggesting extremely high-volume routines and really high protein diets.  A volume routine is one which involves many sets and repetitions. New guys want to "be like the pros" so they jump onto the training routine.  New lifters grow right away - their muscles are fresh and untrained.  So they grow as soon as they touch a weight. 

You'll see comments from these people strewn about the web, extolling the virtue of the really high volume routine.  They write as soon as they see the results start. They start seeing results pretty quickly so there's a lot of these comments.

So word spreads about the great routine -- unfortunately, this is why this approach continues to carry on.  Usually the new lifter's enthusiam dims and quiets after about 4-6 weeks because they get hurt or feel run down or they just stop growing.

But people don't like to post about how the "great routine" now sucks so the "old information" continues to sit out on the web and the bad info lures in other guys, and this cycle repeats.

Why Does Volume Work at First - and then Stop Working?

Growth occurs when the muscle is exposed to more than it can handle and the damage inflicted is able to be repaired fully by the body. Given sufficient time and resources, the body may over-repair and further strengthen the muscle. Each time this occurs, the body requires "follow-up" work to keep the muscle at this level. And this is not an easy thing for the body to do. Training causes damage. If the damage occurs again before the body has finished repair, it sends a "hurry up" signal (to put it crudely) and repairs are hastened. However, there's a fine line -- you're "putting the pedal to the metal".  This commitment of resources has trade-offs.  Soon the body has to start fixing the reserves its been using instead of hitting them to fix the muscles.  And that slows your ability to repair down.  More damage (training) occurs.   

Repairs start to slow down even more. The initial boost in muscle growth flat out stops. Then the worn-out body starts to fail to recover prior to the next onslaught of damage. Muscle and body tissue gets damaged and isn't repaired prior to the next damage.  This is overtraining.

Overtraining is an enemy - it stops you from reaching your goals.

How Come Pros Don't Overtrain?

Now you may ask -- how come the pros keep succeeding with this high-volume routine?  The answer: recovery time is genetic and pros have great genetics.  And there's something they don't talk about a lot -- in the case of a pro their existing ability is vastly improved by use of steroids and other compounds.  Most normal bodies don't have such supplies naturally -- therefore they cannot tolerate the extreme training.

And actually...pros DO overtrain if they aren't careful.  Even with amazing genetics.  Even with crazy amounts of drugs.

So -- no matter how you look at it, volume eventually is counterproductive. And when the gains stop or reverse, many guys figure out that "this routine isn't working any more".  They keep switching from routine to routine, sometimes with some time off - so they lose some muscle, start over and the cycle repeats.  Grow/shrink, grow/shrink. For many, it leads to zero overall progress - and eventually to injury.

Some are more fortunate and dig deeper. They recognize that things aren't always "black and white" and guess that "volume routines work -- but they can't be used for long".  So either they resort to drugs or else they abandon volume, switch to short and intense routines and get better results (for a while) and don't return to volume again.  Short and intense has its own issues - but we'll return to this later.