As you row, the pulse quickens. The heart is pumping more blood to the lungs for the removal of impurities and the addition of more oxygen. The heart is also pumping more blood from the lungs throughout the body to deliver oxygen and nutrients. The rate of blood flow to the body increases. The body attempts to direct flow to the areas that are working. But as the heart pumps harder and faster, more blood also tends to go to the extremities of the body, to the organs, to areas of potential infection, and to the brain.

Each of these examples of enhanced delivery of blood provides a mechanism to improve health. For example, maintaining highly efficient blood flow through the brain will tend to keep the blood vessels of the brain healthier and support the brain with better delivery of oxygen and nutrients.

Technical Note: The heart pumps blood throughout the body using miles of arteries and veins. This includes a lengthy system of microscopic, single-cell–carrying capillaries that deliver nutrients to and remove wastes from each cell of the body. Exercise improves oxygen delivery to the cells because it leads to “increased maximal blood flow and increased muscle capillary density in the active tissues,” according  to Jack Wilmore and David Costill (Physiology of Sport and Exercise, page 229). Blood is pumped away from the heart at a relatively high speed, and slows down as the arteries branch off and ultimately separate into millions of capillaries. At any given time, while nearly three-fifths of your blood is returning to the heart in your veins, five percent is moving through your capillaries, almost one-sixth is in your arteries, twelve percent is moving between heart and lungs to be regenerated, and approximately nine percent is in your heart. (See Know Your Body: The Atlas of Anatomy, introduced by Emmet B. Keeffe, MD, page 95.) This highly complex system both expands and becomes more efficient as you exercise.

We usually think of the blood vessels as if they were HVAC vents in a building: They are there. They are open. When the heart pumps, the blood flows everywhere. This simplified image is fundamentally flawed for at least three reasons:

• First, blood vessels can expand or constrict, affecting blood flow to particular areas.
• Second, when we are sedentary, our remaining in one position and our worsening posture both tend to limit blood flow to some areas.
• Third, unless we get the heart pumping more powerfully as it does when we row, the blood pressure does not tend to deliver blood to all areas in a sufficient flow for optimum health.

Imagine your system of blood vessels is like a highway (the main veins and arteries), with a network of feeder roads and local streets eventually branching off to one lane roads and driveways (capillaries). If traffic on the highway is not moving (whether because traffic is stalled or simply because there is little traffic), then the flow of vehicles to the local streets and eventually to the individual driveways is minimal or non-existent. If the highway flow is increased (as the flow of blood increases during moderate full body exercise), that increases the flow along the highway to all destinations and, thus, to the local roads. Imagine the difference between having limited or restricted blood flow that may not reach all parts of your body effectively versus having a period of increased blood flow each day. Which do you think would be better for your overall health? Which would you prefer?