How does stress affect muscle growth?

The role of cortisol

Cortisol is a glucocorticoid produced in the adrenal cortex. The scientific literature describes its short-term release as part of the body's physiological stress response. Review articles outline possible mechanisms by which chronic stress can affect muscular adaptations (Schakman, Teng, and Bhatt, 2012).

The evidence on chronic stress

Stults-Kolehmainen and Sinha (2014) published a comprehensive review of the relationship between psychological stress and post-exercise recovery. Their analysis found that high psychological stress was associated with slower recovery of muscle strength after eccentric training. Bartholomew et al. (2008) also showed that students under high academic stress recovered strength more slowly after a standardized resistance workout than a low-stress control group.

Important: an acute training stimulus raises cortisol briefly — that's physiologically normal and necessary. The negative effects relate to chronic elevation from ongoing psychological stress, lack of sleep, or overtraining.

Practical countermeasures

The most effective countermeasure against chronically elevated cortisol is enough sleep. Leproult and Van Cauter (2010) showed that restricting sleep to 4 hours per night raised evening cortisol levels by 37%. Other evidence-based approaches include: consistent training routines (regular exercise is often discussed in the literature in connection with better stress management), adequate calorie intake (an extreme deficit raises cortisol), and proper training management with planned deload phases.