How much does stress affect muscle growth?
Stress is an enigmatic cowboy riding a horse that is both black and white, wearing different coloured hats under different skies. Stress is also a multidimensional stimulus that comes with a pandora’s box of implications. In some situations, it becomes a marauding bugaboo. If unchecked, it will affect a whole collection of physiological functions that can, in extreme circumstances, create a cascade of chronic conditions. While in other cases, stress wears a white hat and is a positive catalyst, increasing resilience, adaptation and is a necessary component in the process of muscle growth.
I am going to assume that you’re talking about a garden-variety strain of the former example, where stress is wearing it’s destructive, black hat.
Lots of chemical conditioning goes on during periods of stress response, including rising levels of cortisol secretion which is antagonistic to and creates negative stimulus towards muscle growth. In elevated levels, maintained for long periods of time without respite, stress becomes a rather nasty agent of catabolism and harbinger of disease states.
The primary job of many coaches and athletic trainers is to keep unnecessary stress at bay and use the positive stressors (eustressors) they have at hand to assist their players and clients in adaptation processes that benefit their skill sets. Good coaches are acutely aware of the responsibility that they carry to differentiate between pathological stress and eustress. An interesting example of this responsibility are the oyakata who run the stables of Sumo Wrestlers in Japan where these trainers’ or handlers’ reputations and livelihoods depend on their primary duty to keep athletes free of all negative stimuli (anything which may cause them stress leading to losing valuable weight and diminishing their budo).
To sum it, by keeping it close and constant, by unwisely allowing stress free reign and allowing a loss of control of its management will gobble up hard earned muscle mass, interfere with necessary tissue hygiene and repair, set you up for increased risk of injury and generally play havoc with most anabolic processes that are vital to your health and growth.