Sometimes(like recent times) we talk about “Stress” and “Stressors” as factors that disrupt our homeostasis. So fighting with your girlfriend is stress, and training is stress and missing a meal is more stress on your body.
Other times (like in my childhood) we talked about “Stress” as the result of the disruptions. Like so much aggravating stuff has happened to me that I’m “stressed” and now I’m irritable and can’t think straight.
If you’re irritable and can’t think straight (like you’re “stressed out” in the old sense of the word) it can be useful to Stop Thinking, or Turn Off Your Brain, or Forget Your Troubles for Awhile.
Exercise can be good to help you get to this “relaxing” or “meditative” or “stress reducing” mindset. You focus on your muscles, or your breathing or whatever and forget your troubles for awhile.
The problems is that Training is not Exercising. Especially if you’ve been doing it for awhile. You’re not going into the gym for some moderate, de-stressing physical activity, with no pressure to perform. You’re going to rip shit up, you know what constitutes a “good” or a “bad” workout, and you’re going to try hard to have a “good” one.
And if you’re really “stressed”, like you’re homeostasis is already thrown off, your performance is likely to be impaired or lowered. So you’re pushing hard when you’re already messed up. You just add to the stress.
Easy, calm stuff works better for mental clarity or stress relief for me. Like walking through the woods or by the water helps me relax after my stressful curls and tricep kickbacks.