At least where androgen levels are midnormal or better, no results have ever indicated to me that muscle is built more readily with lower cortisol levels than with mid-normal or high-normal levels.
The activities of glucocorticoids (GC’s) such as cortisol and dexamethasone have I think been misunderstood, leading to incorrect theorizing and to some ineffective supplement products.
An excellent article providing information on this is “Synergistic stimulation of myogenesis by glucocorticoid and IGF-I signaling”
Briefly, in their cell study:
“IGF-I was used at 5 nM, which is sufficient to stimulate myogenic differentiation. Dexamethasone (Dex) was used at a relatively low dose of 10 μM compared with other studies.
“Combined, Dex and IGF-I enhanced morphological differentiation compared with IGF-I alone. Quantification of morphological differentiation using the myogenic index clearly showed Dex reduced myoblast fusion. In contrast, IGF-I increased fusion, which was further exceeded by the combination of IGF-I and Dex. This not only resulted in more, but also larger, myotubes.
“As a mere restoration of protein synthesis signaling by IGF-I did not explain the synergistic effects of IGF-I and GC on myotube formation and myosin expression, muscle-specific mRNA abundance during differentiation was assessed. After 48 h of differentiation, muscle-specific mRNA was quantified. MCK expression was increased by IGF-I (90%), but surprisingly also by Dex alone (70%). Combined IGF-I/Dex increased MCK expression more than threefold compared with either IGF-I or Dex alone, indicating a synergistic interaction.”
The authors also analyzed data from a previous human study with COPD patients where low-dose Deca Nandrolone Decanoate and glucocorticoids were used. Their findings?
“Muscle powder Deca Nandrolone Decanoate administration in absence of GC did not result in significant gain of FFM or inspiratory muscle strength.
“Conversely, Muscle powder Deca administration in the presence of GC did significantly improve gain in FFM as well as inspiratory muscle strength.”
So, the right GC level can actually aid muscle growth and strength, very substantially!
Reducing cortisol, where not excessive in the first place, could actually be counterproductive. At best, I think that practical results show no benefit to reducing cortisol when levels are already normal.
My recommendation is to not worry about cortisol unless it is abnormally high.