Monitoring Exercise Intensity

Cardiorespiratory exercise is the method by which we are able to improve our aerobic capacity. Aerobic capacity is the determining factor in sustaining both the duration and intensity of the exercise. Thus, the benefit of training the cardiorespiratory system is to enable more oxygen to be delivered and ultimately consumed by the body, allowing the activity to continue. It is important for the fitness professional to understand and be able to monitor cardiorespiratory exercise in order to determine that it is safe as well as effective in improving aerobic capacity.

The most important application for the fitness professional to monitor cardiorespiratory activity is with submaximal exercise, in the group exercise setting. Maximal exercise monitoring is done primarily in the clinical setting, with an expanded set of objectives, and is not applicable to this writing. Personal fitness trainers must also monitor their client’s aerobic work. However, they have the clear advantage of knowledge gained through pre-exercise screening and assessment information. They will utilize the same monitoring protocols yet, unlike group instruction, are able to focus on the specific needs of the individual within a predetermined time frame and a calculated protocol of progression.

There are, however, significant challenges when monitoring the cardiorespiratory response to exercise in a group atmosphere. In any given class, group exercise instructors must deal with a large range of age, number of participants, and varying levels of physical conditioning. Furthermore, they do not have the luxury of pre-exercise screening and classes are likely ongoing so the continuity of progression is virtually non-existent. Therefore, a monitoring protocol must be in place to control the exercise environment for the benefit of the entire class.

A linear relationship exists between heart rate and oxygen uptake. At the onset of exercise there is an increase in heart rate. As the intensity increases, more oxygen is required causing the heart rate to increase as well. Because of this relationship, heart rate is often considered as an effective monitoring tool for cardiorespiratory exercise.

Calculating Heart Rate Parameters

In order to establish safe and effective heart rate parameters, it is necessary to first determine the maximum heart rate (HRmax). The most accurate way is to directly measure the HRmax with an electrocardiogram (EKG) monitoring device during a graded exercise test. Due to the impracticality of this procedure, another method is to estimate HRmax by using the prediction equation of “220 – age.” This formula was introduced as far back as the 1930s, and has been widely accepted by the health and fitness community. While simple to use, the American College of Sports Medicine (ACSM) recognizes the high degree of variability with this method stating, for example, that it underestimates HRmax for both sexes younger than 40 years of age and overestimates HRmax for both.

Another method for calculating the training heart rate range is known as the Karvonen or heart rate reserve method (HRR). The V02R is the range of oxygen consumption (V02) from rest to maximum. The ACSM cites the work of Swain and Leutholtz ( 1997) which determined that HRR and V02R reflect the rate of energy expenditure during physical activity more accurately than the other exercise intensity prescription methods.

Heart Rate Monitoring Method

AFAA recommends that the group exercise instructor guide the participants to take a pulse count or rating of perceived exertion (RPE) at three different times during a class. Five minutes after the beginning of aerobic work to determine if the participants are working within their training heart rate range. At the completion of the most intense aerobic work to see if participants have maintained aerobic training level. At the completion of post-aerobic cool-down to determine if participants have sufficiently recovered from aerobic work.

NOTE: If taking HR at these three times is not feasible, then a pulse check or RPE should be taken at the completion of the most intense cardiovascular work rather than not at all. Alternative methods such as the talk test or heart rate monitors may be used. The instructor should indicate in advance when the pulse or RPE is to be taken.

The following steps illustrate AFAA’s recommended method of pulse taking:

a. Locate the radial artery (AFAA preferred site) pulse within 2 to 4 seconds and find the beat of the heart.
b. Begin with the count of “1″ and continue counting the beats for 10 seconds. Multiply by 6 to determine exercise working heart rate.

It is important to continue moving the feet while taking the pulse in order to prevent lightheadedness or blood pooling in the extremities (especially individuals who are less fit or who may be taking antihypertension medication).

The Problems of Heart Rate Monitoring

Understandably, a great deal of emphasis is placed on heart rate monitoring. Given their relatively linear relationship to work intensity, heart rate measures are a useful guide to experiencing the training benefits of exercise. There are, however, some drawbacks in acquiring heart rate values that fitness professionals should know so as to keep the limitations in perspective.

As stated previously, ACSM recognizes a “high degree of variability” when estimating the maximum heart rate by the historical formula of 220 – age. Even though a new formula has been introduced to be more accurate, it is still an estimation. Additionally, there is no distinction between men and women in any heart rate formula when it is clearly known that, on average, a female’s heart rate is higher than a male’s.

With regard to taking heart rates during exercise, the method of palpating heart rates is flawed. The reason for this is because of the time it takes to actually complete the process. For example, after the instructor announces to the class to find a pulse, it takes 5-7 seconds for the entire class to do so, and another 3-5 seconds for the instructor to have everyone begin together. The heart rate began to drop the moment the exercise was reduced to enable the heart rate reading. By the time another 10 seconds is added for the actual reading, the true exercise value of the reading has diminished.

Of course, it should be said that with the advancement of technology, the optimal way to monitor heart rate during exercise is with a wireless telemetry device (heart rate monitor). Only then can a true real time reading be taken with “at-a-glance” convenience. They are very accurate, inexpensive, and mobile, nevertheless, the fact of the matter is that they are rarely seen on a regular basis.

Rating of Perceived Exertion (RPE)

The original scale is a 15-point system that begins at 6 and ends at 20. A more recent, simplified scale begins at 0 and progresses to 10 (Table 20-3). The terminology used with the revised scale is believed to be better understood by the participant. When using the 15-point scale, values of 12 to 13 (light to somewhat hard), and 16 (hard) correspond to 50-74% (average of 60%), and 85% of heart rate reserve, respectively (ACSM). The respective values on the 10-point scale are 4-6 and 7-8.

Perceived exertion is simply how hard each exercising individual feels they are actually working. Regardless of the pace of the group, the participants can self-evaluate and adjust the workload specific to how they feel. This serves as a two-fold benefit in that it enables the exercising individual ultimate control over the exercise intensity and reduces the potential liability of the group instructor. The only downside to effectively using the RPE scale is not teaching it properly to the participants. Keeping in mind the teaching nature of the group exercise instructor, however, it is likely to be accomplished if covered as often as palpating heart rates. Additionally, an RPE chart should be visible to the participant in every group exercise room or studio.

The RPE scale is considered a reliable guide as it has a strong linear relationship to heart rate. Although RPE has been considered an alternative to heart rate, both are uniquely valuable and should be used together. It is common to see charts on the walls of group exercise facilities that provide an at-a-glance view of where their heart rate should be according to their age. The RPE chart is equally, if not more, important and should be placed next to the heart rate chart.

The Talk Test

The talk test is another tool used to evaluate an individual during cardiorespiratory exercise. The ability to engage in conversation during exercise represents work at or near a steady rate. When oxygen supply meets demand, a person is able to breathe rhythmically and comfortably. If the work encroaches upon anaerobic metabolism, respirations increase due to an elevation in lactic acid production and the ability to talk diminishes. The talk test has been criticized to be safe “to a fault” because it can actually keep a person that could otherwise handle more intense work from doing so because the priority is slanted to the ability to talk.

Dyspnea scale is helpful for participants who have pulmonary conditions (such as asthma or emphysema) or who feel limited because of breathing difficulties. The scale should be used in conjunction with RPE and HR, and participants should reduce intensity when their breathing becomes more labored (+3). Participants with breathing difficulties should consult with their primary care physician regarding their exercise goals and methods.

There are few others in the fitness industry that face such a high degree of responsibility as does the group exercise instructor. The multifaceted nature of the “group” dictates that they are nomadic, diverse in their ability, and span a wide range of biomechanical as well as physiological capability. Furthermore, there is minimal opportunity for advanced wellness information or the continuity of progression. The instructor’s goal is to provide a choreographed workout, teaching some while leading all through issues of timing, cueing, transitions, technique, pace, and rhythm. Additionally, and even more importantly, the group exercise instructor ensures that the participant encounters a positive and fun experience while simultaneously meeting the ultimate objective of cardiovascular improvement.

With that said, the goal of this article was to provide an overview of the tools, such as estimated heart rate formulas, rating of perceived exertion, and the talk test, to monitor cardiorespiratory response to exercise such that the objective can be met safely as well as effectively. However, the calculations to determine various heart rate ranges are, at best, estimates of where each participant is physiologically. Short of actual wireless telemetry, the more important tool therefore, is probably the rate of perceived exertion (RPE). The underestimated value of the RPE, while only a perception, is that it is the “participant’s” perception of how hard they are working. This not only shifts the responsibility of the intensity to the participant, but also empowers the individual to help control their movements accordingly.

 

Leave a Reply