Toning the muscles used for breathing, such as the diaphragm and the intercostal muscles, which lie between the ribs and enable you to inhale and exhale can increase your endurance. Since your diaphragm is mostly responsible for breathing, the more muscular it is, the more endurance you will have.
This approach coincides with research indicating runners whose breathing was the most strained showed the most leg weakness. Further, the researchers concluded in their study that the harder the respiratory muscles had to work, the more the legs would struggle in a race. In other words, breathing more fully is fundamental for preventing lung-and leg-fatigue. So while running or participating in cardio activities, concentrate on taking slow and deep breaths to strengthen the diaphragm.
