Endurance training is characterized by exercise bouts where the body maintains an elevated heart rate for an extended period of time; usually 20 minutes or more. The goal of this type of training is to increase cardiovascular endurance and stamina in order to achieve a goal. Goals for endurance training include, but are not limited to, completing road races, decreasing body fat and cholesterol, decreasing blood pressure or increasing energy and mobility. Whatever the goal, the heart rate plays an important role in the success of endurance training.
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Resting Heart Rate
Resting heart rate is a benchmark for overall cardiovascular fitness. The resting heart rate is the number of heart beats per minute during true rest which is most effectively measured after sleep, while still lying down. The average resting heart range is 60 to 80 beats per minute. Those that participate in regular endurance training are on the low end of the range, and it is not uncommon to see resting heart rates even lower. In fact, some elite endurance athletes have measured resting rates in the low 30s. Due to other physiological changes in the heart like increased stroke volume and cardiac output, the heart can beat less and still pump an equal volume of blood. Therefore, endurance training progressively decreases resting heart rate.
Maximal Heart Rate
There are many methods of how to accurately determine the maximal heart rate. Most methods use age as a primary determining factor, but using age does not take into consideration individual health and fitness levels. The most accurate method for determining maximal heart rate is through cardiac testing using a graded exercise test, or GXT. However, due to the time it takes to administer the GXT, and the required equipment, it is not economical for the majority of the population. Maximal heart rate, or the closest possible estimate, is used to prescribe endurance training heart rate zones. While cardiac output increases and resting heart rate decreases with endurance training, there is no real associated variation in maximal heart rate in response to endurance training; however, it has been estimated that maximal heart rate decreases by one beat per minute every year.
Endurance Training Heart Rate Zone
The purpose of discovering a maximal heart rate is so that a target training zone can be prescribed. The target zone is usually between 60 and 85 percent of the maximal heart rate. It is the range in which the exercise activity can be continually performed for the designated time period. In order to train aerobically for endurance, and for the positive physiological adaptations to take place, the exerciser needs to stay within the range. If the intensity is too low, the benefits will be limited, and if it's too high, the workload becomes anaerobic in nature and will lead to faster fatigue.
Heart Rate as a Health Risk Factor
Just as a low resting heart rate can be a fitness benchmark, so can a high resting heart rate. As the resting heart rate increases, it becomes more of a risk factor or warning of potential health conditions. High heart rates are closely associated with other health conditions such as high blood pressure and high cholesterol. If the heart is beating faster to deliver oxygen and nutrients to the body, it simply won't last as long. In January of 2009, a study published in Aging Research Reviews, titled "Heart Rate, Lifespan, and Mortality Risk," outlined a direct correlation with resting heart rates above 70 and a linear relationship with the occurrence of heart attacks.
Conditions that Affect Heart Rate
There are some important conditions that need to be evaluated and considered before beginning any endurance training program. They are tachycardia, bradycardia and arrhythmia. Tachycardia is a medical condition that is characterized by high resting heart rates. It is not as serious in children as it is in adults as children have higher rates. Bradycardia is characterized by lower than average resting heart rate. It is not as dangerous a risk factor as tachycardia but should be evaluated prior to endurance training to determine if it is due to fitness or another factor. Arrhythmia is characterized by an irregular beat. A doctor should determine the cause before starting a fitness program because there are potential dangerous side effects such as light-headedness, fainting, dizziness and nausea.