I know Lyle's written about this issue, but I liked how organized and simple this article was in explaining it:
The Fall of The Greatest Theory of Muscle GrowthBeginner | May 09 2010
The recent study was the final nail in the coffin for one of the greatest theories of muscle growth-the hormone theory - proposed by the prominent researcher William J Kramer.
What is the hormone theory of muscle growth?
Growth & Development: Hormones like testosterone, growth hormone, & IGF-1 are important for growth & development.
Injection of hormones: Injection of hormone,s especially testosterone has shown increase strength and muscle mass while suppression of testosterone has shown to decrease in muscle mass & strength.
Acute Increase after exercise: These same hormones are elevated acutely after resistance training. The magnitude of increase depends on rest times between sets, the weight used and so on.
For example, the large rises in these hormones are observed after high intensity exercises with short rest periods using big muscle groups (multi-joint exercises).
Based on the above hormone hypothesis , it is assumed that
1. Exercise induced muscle growth is primarily due to an acute increase in these hormones.
2. Hence workouts should mainly use multi joint exercises with short rest periods to raise the hormone levels.
3. Small exercising muscle groups (e.g., biceps), which are incapable of causing large increases in anabolic hormones when used in isolation, should be trained concurrently with large exercising muscle masses like squats or leg press that can elevate testosterone and GH.
The fall of the hormone hypothesis
Local factors in muscle growth: The recent discovery of local factors like MGF,muscle IGF-1 showed that it is local factors that are mainly responsible for muscle growth and not systemic hormones.
The discovery of these local factors, which are found inside the muscle, showed why muscle growth is specific to the exercised muscle. If systemic hormone were indeed responsible, you would have seen an increase in muscle growth in the non-exercised muscle too.
No effect of GH administration: Injection of high doses growth hormone to raise resting levels resulted in little increase in muscle growth or strength.
So the benefits of these tiny spikes in GH after exercise which do not even change the resting levels are questionable.
Unilateral exercises: Increase in muscle growth has been observed with unilateral exercises like biceps curl without any increases in systemic hormones.
For example, unilateral exercise like biceps curl and leg extensions which do not cause a spike in systemic hormones have shown to increase muscle growth and strength.
No Increase in protein synthesis: There was no significant increase in protein synthesis due to an acute increase in systemic hormones after the workout.
BUT the question can these spikes in systemic hormones play a small role if not a major role in muscle growth which might have been overlooked in the above studies . All the above were indirect studies until the recent study.
What was the study design?
•Twelve healthy untrained young men trained their biceps independently for 15 wk on separate days.
•In one training condition, participants performed isolated biceps curl exercise designed to maintain basal hormone levels.
•In the other training condition, participants performed identical biceps curls followed immediately by a high volume of leg resistance exercise to elicit a large increase in these hormones .
•If the hormone hypothesis were true, the biceps curl plus leg pres group should see greater muscle growth & strength, right.
What were the results of the study
Unfortunately, at the end of 15 weeks there was no significant difference between groups in strength, muscle cross sectional area, & Type 1 or Type 2 fiber area.
Simply put, the increase in testosterone, growth hormone or IGF-1after your workout do not help in muscle growth/strength.This study was the final nail in the coffin and clearly drops the curtain on one of the best known theories of muscle growth .
•Don’t perform multi-joint exercise like deadlifts, squats, 20 resp squats or leg press for the sake of increasing hormones.
•Don’t keep rest times short or perform high intensity workouts for the purpose of raising hormone levels.
•If your trainer says the program works by increasing hormones, send this article to him