Heart Rate During Aerobics

Q: Why is an elevated heart rate alone not always a valid indicator of an effective aerobic-training stimulus?

A: During aerobic exercise, an individual’s heart rate is a reliable indicator of how hard that individual is working. 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.

With resistance training, heart rate is disproportionately elevated relative to oxygen uptake. At any given level of oxygen uptake, heart rates are much higher for resistance training than for aerobic conditioning. 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.

The misperception that resistance training can increase aerobic exercise capacity is not new. In fact, it was popularized in late 1970s and early 1980s in a form of exercise known as circuit weight training (CWT), which involves performing 10 to 15 repetitions of eight to 12 exercises, using 40 percent to 60 percent of one-repetition-maximum. During CWT, individuals rapidly move from machine to machine, with very brief (less than 30 seconds) rest periods between exercises. A review of studies involving CWT indicates that such training programs are effective at increasing 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).

Despite marketing claims to the contrary, exercise products and programs that focus predominantly on resistance training do not provide a sufficient stimulus to produce meaningful aerobic training benefits even though exercisers’ hear rates are elevated during such training. It is important to understand that although a regular, sustained increase in heart rate is widely recognized as critical to achieving increased aerobic fitness, the heart rate merely serves as a monitor for the real training stimulus (i.e., increased energy expenditure or oxygen uptake). 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.

Source: Bryant, Cedric X. ACE FitnessMatters, March/April 2004

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• Tip of the Month

  June 2010

  Abdominal Workouts: Frequency, Intensity, and Duration

  Over the past 15 years, there has been countless advice on how to “properly” train your abdominals, or core.  There isn’t a fitness magazine out there that doesn’t publish a different abdominal workout each and every issue.  Opinions and research may change over time, but there are a few things you should look at before you alter your workout with each Fitness Magazine you read!
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• Recipe of the Month

  June 2010

  Ham and Cheese Breakfast Casserole

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  4 large eggs
  4 large egg whites
  1 cup nonfat milk
  2 tablespoon Dijon mustard
  1 teaspoon minced fresh rosemary
  1/4 teaspoon freshly ground pepper
  5 cups chopped spinach, wilted (see Tip)
  4 cups whole-grain bread, crusts removed if desired, cut into 1-inch cubes (about 1/2 pound, 4-6 slices)
  1 cup diced ham steak, (5 ounces)
  1/2 cup chopped jarred roasted red peppers
  3/4 cup shredded Gruyère, or Swiss cheese
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