"Research is contradictory as to whether or not the post-exercise anabolic hormonal response associated with metabolic stress plays a role in skeletal muscle hypertrophy.
Given the inconsistencies between studies, any attempts to draw definitive conclusions on the subject would be premature at this time.
Based on limited cellular signaling data, it is conceivable that the primary effect of post-exercise hormonal elevations is to increase satellite cell activity as opposed to mediating acute increases in muscle protein synthesis. If so, this could favor greater long-term increases in muscle hypertrophy without significantly impacting short-term gains. This hypothesis requires further study.
What seems relatively clear from the literature is that if a relationship does in fact exist between acute systemic factors and muscle growth, the overall magnitude of the effect would be fairly modest. The ~8% figure reported by West and Phillips (95) would seem to be a reasonable upper estimate as to a potential contribution from transient hormonal elevations, but further research is required to quantify any potential impact. Whether such modest effects are meaningful is a separate issue and would be dependent on individual goals and needs.
For the recreational gym participant, slight increases in muscle mass might not have much practical importance. However, for the athlete or bodybuilder, it could mean the difference between winning and losing a competition. There also may be practical implications for the elderly, where even small morphological improvements could lead to an enhanced functional capacity.
Another possibility to consider is that genetic factors may influence a person’s response to post-exercise hormonal elevations. It has been estimated that genetic differences can account for approximately half of the variation in athletic performance (16). This is consistent with studies showing that the hypertrophic response to resistance training displays tremendous variance between individuals (7, 58).
It is therefore conceivable that acute hormonal responses may be more relevant to certain lifters as opposed to others. There is some evidence to support this contention as a strong trend for a significant association has been shown between IGF-1 and those who respond favorably to hypertrophy-type training (95).
Finally and importantly, studies in trained individuals on the topic are lacking and it remains to be determined whether training status influences the morphological response to acute exercise-induced hormonal elevations.
Some researchers have proposed that post-exercise hormonal fluctuations may be permissive for untrained individuals but follow a dose-response relationship in those with considerable training experience.
Indeed, hormonal levels following resistance exercise were shown to be significantly more pronounced in strength athletes compared to endurance athletes and sedentary individuals (83), suggesting that such elevations may play a greater role in hypertrophic adaptations as one gains resistance training experience (38).
This hypothesis warrants further investigation."