Why Does Exercise Make Your Heart Rate Go Up?

Your heart rate increases with physical activity to provide your working muscles with the increased oxygen necessary for continued exercise. At the onset of exercise, certain physiological responses, such as blood redistribution and increased stroke volume, work with increased heart rate to maximize the amount of available oxygen reaching your muscles. Your age, sex and level of physical conditioning determine the intensity and efficiency of this response.

The Exercise Response

As soon as you begin to exercise, your brain senses that your working muscles will need more oxygen. To supply extra oxygenated blood to your muscles, your central nervous system signals your cardiovascular system to increase your heart rate and channel blood flow away from your internal organs and toward your exercising muscles. Your heart's stroke volume--the amount of blood pumped with each beat--increases as well, allowing your heart to work more efficiently.

Response Within the Muscle

Working muscle fibers consume increased energy to power exercise, resulting in increased carbon dioxide, hydrogen and potassium ions and increased osmolarity, or tendency to take in water. These chemical reactions trigger the small blood vessels supplying the muscles to dilate, increasing blood flow to the muscle fibers to allow effective gas exchange and solute removal. The University of Washington notes that these effects can lead to as much as a twentyfold increase in blood supply to working muscles. Your heart rate and stroke volume increase in response to this increased demand for blood supply.

Aerobic Capacity

Untrained individuals normally experience a greater increase in heart rate compared to highly conditioned athletes. With regular physical exertion, the heart becomes larger, stronger and more efficient. This results in an increased aerobic capacity, allowing your heart to pump more blood with each stroke. According to Michigan State University, increased aerobic capacity allows highly trained athletes exercising at a comfortable pace to experience heart rate increases of 12 to 15 fewer beats per minute compared to untrained individuals.

Gender Considerations

On average, women have a lower stroke volume compared to men in similar states of physical conditioning. In a 2005 statement published in the journal "Medicine & Science in Sports & Exercise," authors Fu and Levine found that women and men tend to experience heart rate increases that are roughly proportional to body size and level of perceived exertion. An average woman may need to work harder than an average man to perform a given task, but when faced with exercise that is of equivalent intensity relative to size, both experience roughly the same increase in heart rate.

Age Effects

According to Fu and Levine, aerobic capacity appears to decline universally with age, regardless of physical conditioning. As you age, the maximum heart rate you are able to comfortably achieve with exercise will gradually lessen. Men tend to experience this change more significantly than women, and highly trained athletes usually see a proportionately greater difference in aerobic capacity over time than sedentary individuals.