Heart Rate and Exercise Training

Help your clients understand the many factors that affect resting and exercise heart rate.

"I think I need to do a little more explaining about why we take exercise heart rate. Yesterday, one of my clients asked why couldn't he just drink a few cups of coffee and skip the exercise session! He was kidding, of course. But he was asking all kinds of questions about heart rate training zones. He got a heart rate monitor a few days ago, and I think he wears it everywhere. He wants me to tell him what his heart rate should be at each exercise station and just about every minute of the day. I don't think he realizes how much resting and exercise heart rates vary from person to person. Maybe if I explain this a little better, he won't be so worried about it." As you know, heart rate is a convenient way to estimate exercise intensity, since it has a fairly linear relationship to workload. Heart rate, expressed as beats per minute, is such a simple number that people new to exercise may not realize the many factors that contribute to it, or what changes in this variable indicate.

Resting heart rate

Resting heart rate is influenced by many factors. It is partly determined by genetics, and varies greatly from person to person. Lifestyle factors also affect resting heart rate. Caffeine, nicotine, alcohol, pseudoephedrine and many other drugs stimulate the sympathetic nervous system, the branch of the nervous system responsible for the fight-or-flight stress response, which increases heart rate. On the other hand, some drugs, especially those given for heart conditions (especially the beta blocker family) slow heart rate. Factors that raise metabolic rate, such as fever, illness, stress or a large meal, will raise resting heart rate. Women often experience a rise in resting heart rate during the premenstrual period. Emotional factors that increase arousal, such as fear, anxiety, excitement and sexual arousal, also increase heart rate. You may have noticed an increase in your clients' resting heart rates as they prepare to begin an exercise test. Athletes notice elevated resting heart rates before contests.

Exercise heart rate

Heart rate response to physical activity is primarily determined by the metabolic demands of exercise. As workload increases, so does exercise heart rate. The relationship of exercise heart rate to exercise intensity is somewhat specific to exercise mode. Upper-body exercise and swimming usually elicit relatively lower maximal and exercise heart rates. Target heart rates will be about 10 beats per minute lower for these forms of exercise.

Heart rate changes with exercise training

For relatively untrained individuals, several weeks of regular exercise training often decreases resting heart rate and the heart rate response to a given submaximal exercise workload. A "given submaximal workload" means a specific, measurable workload that can be reliably replicated. An example is bench stepping at a specific cadence and bench height, or riding a calibrated cycle ergometer at a specific cadence and setting. A decrease in exercise heart rate at a given submaximal workload is a good sign that cardiovascular training effects are occurring. A reduction in resting and exercising heart rate occurs, in part, because exercise training increases the output of the parasympathetic nervous system at rest. This branch of the nervous system is associated with relaxation. Parasympathetic input to the heart slows the heart rate. As the heart beats more slowly, the heart's chambers have a longer time to fill, so they have more blood to pump out with each contraction. Increased parasympathetic input also increases heart rate variability, the normal beat-to-beat changes in heart rate. For example, your clients may notice that their heart beats more quickly as they inhale, and more slowly as they exhale. This variation may become more pronounced with exercise training. Endurance athletes tend to have larger stroke volumes because their hearts adapt to exercise training. Long-term exercise training may increase the size of heart chambers, especially that of the left ventricle, which sends blood to the body. This is a healthy adaptation that is not associated with high blood pressure, unlike increases in the heart wall thickness that occur in response to hypertension.
References
American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. Lippincott, Williams & Wilkins: Philadelphia, Pa., 2006.
McArdle, W.D., F.I. Katch and V.L. Katch. Exercise Physiology: Energy, nutrition and human performance. Lippincott, Williams & Wilkins: Baltimore, Md., 2007.

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