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.
Positive adaptations occur in as little as three months of aerobic training. Enhancing cardiac output allows you to maintain lower heart rates during physical activity. For example, at the start of a program you may have a heart rate of 150 beats per minute while running at a 6 mph pace. After three or more months of training increased cardiac output enables you to sustain the same running intensity at a lower heart rate such as 125 beats per minute.