During training, the need for oxygen increases, and your breathing has to adjust to it. Therefore, lung work becomes faster, so your breathing will be deeper and more frequent. The costal pressure changes have a sucking effect on the vena cavae system (veins). This effect is parallel with the breathing movements. When inhaling, your chest cavity grows and air pressure decreases in the lungs. When exhaling, your chest volume decreases, air pressure in the lungs increases, and in parallel your blood pressure increases in your veins. During training, the pressure on the obturator muscle increases as it does during complete lung...