Excess Stress manifests in excess tension.
Remember that too much tension uses excess energy, and this can also make you feel tired (excess fatigue). Too much tension blocks the flow of energy inside you. Your blood vessels and other channels are too compressed and do not allow for a free flow of blood and energy throughout your body. If your abdomen is too tense all the time (because you pull the navel to the spine), e.g., you may feel the energy in your chest, but it will not be allowed to flow into your legs and feet. You switch on your sympathetic nervous system (also called the flight and fight response) if your abdomen is firm all the time and preventing the diaphragm from moving freely.
On the other hand, diaphragmatic breathing switches on the parasympathetic nervous system (the one that feels calm). So, we must learn how to switch on the core without switching on the sympathetic nervous system!
I teach in my regular weekly classes to let go of this excess stress and tension. The result: better sleep!
Never over tense, because as we have seen, over tension restricts the blood flow. The contraction should be roughly only a quarter of the muscle’s ability. If you work with strengthening joints, it can be more, but you will most likely restrict blood flow and other energetic flow.