The most common cause of vascular obstruction is a blood clot, also known as a DVT. This type of vascular problem usually occurs in one leg (not both), and leads to swelling of the soft tissues throughout the foot and ankle. The swelling can also extend further up the leg.
The hypothalamus is a part of your brain that controls body temperature. When you exercise, your body temperature increases, causing the hypothalamus to signal the brainstem to further increase your heart rate.
When you exercise, your respiratory rate increases. This is true regardless of whether you exercise by stationary methods such as weight lifting, or by a traveling method such as jogging or biking. Clearly, an active body needs more oxygen than a body at rest.