33 pairs of nerves are connected from spine to the organs of the body and practice of every asana influences spine as well as the abdomen. As a result every organ receives the required quantity of vital energy. With practice of asanas muscles expand and contract enhancing flexibility. Blood circulation improves and the nervous system does not experience excessive pressure.
During physical exercise muscles experience pressure and blood vessels break down and reform in a way that makes them rigid. During exercise, breathing becomes faster, heart rate and blood pressure rise and this exerts extra pressure on lungs and heart. Exercises excite the sympathetic nervous system whereas practice of asanas controls the reflexive activities along with activating them. Hence brain experiences less pressure. This is why practice of asanas is more beneficial than practice of physical exercises.