Your heart rate is an accurate assessment of how hard you are working during aerobic exercise. Aerobic exercise includes running, power walking, elliptical training, swimming, dancing and many other forms of exercise that you might know as cardiovascular training. As the energy demands of the exercise increase, heart rate increases proportionately. Because the exercising muscles need more oxygen and fuel, an individual’s heart rate and stroke volume (i.e., the amount of blood pumped per beat) must increase to deliver more blood to the tissues to meet the increased metabolic needs of the active muscles. It is this increased metabolic demand that overloads the cardiorespiratory system and provides the necessary stimulus to improve aerobic exercise capacity.

A normal resting adult heart rate is somewhere between 60 and 100 beats per minute, but some elite athletes can have rates as low as 40 beats per minute. When you exercise, your heart rate rises as the intensity and type of exercise increases. Fitness trainer Jacki Sorensen’s Working Heart Rate Range Chart recommends that no one under 30 exercise with a rate of over 190 beats per minute, and as you get older that number decreases (see Resources). The best way to learn your maximum heart rate is to have a doctor-supervised stress test, but formulas are out there to estimate the heart rate. The easiest way to estimate your maximum heart rate is to subtract your age from 220.

According to exercise physiologist Cedric Bryant, it is much easier to get an elevated heart rate reading during weightlifting or strength training. Bryant says that an elevated heart rate while lifting weights is due to the nervous system’s response to muscle contractions. So it is natural for you to have more of an elevated heart rate when pumping iron. The disproportionate rise in heart rate during resistance training is due to a phenomenon known as the pressor response, which is governed by the autonomic nervous system and occurs reflexively from the contraction of the skeletal muscles. It causes an increase in heart rate with a corresponding reduction in stroke volume. As a result, even though heart rates are increased during resistance training, the oxygen uptake is not increased to the same degree as it is during aerobic conditioning. This factor minimizes the metabolic overload to the muscles and, therefore, limits the aerobic training benefit that can occur as the result of resistance training. The pressor response helps to explain, from a physiological standpoint, why the heart rate is disproportionately elevated, relative to oxygen uptake, during resistance training.

A review of studies on Circuit weight training (CWT), which involves performing 10 to 15 repetitions of eight to 12 exercises, with rest periods of less than 30 seconds, indicated that they increase muscular fitness. But only modestly improve aerobic capacity (i.e., approximately 5 percent to 7 percent). Conventional aerobic exercise training programs (e.g., running, cycling, swimming) conducted over a similar period of time, on the other hand, typically result in greater improvements in aerobic exercise training (i.e., 15 percent to 25 percent).

The best training approach for optimally improving both aerobic and muscular fitness is to separately participate in aerobic- and resistance-type activities. Circuit weight training can, however, serve as a time-efficient and relatively effective way for beginners and deconditioned individuals to achieve modest-to-moderate increases in both aerobic and muscular fitness. Click if you’re considering using a stairmaster vs. a stationary bike or this article helps you decide between the best elliptical vs. a treadmill.