Question

3. Many tools have been recommended for identifying target exercise intensity for effective improvement of cardiorespiratory fitness. Two examples are:
A. Use of the formula “220 – Age” for estimating MHR (Maximal Heart Rate) and then using a percentage of that value (such as 60 or 70%) for training intensity.
B. Percentage of Heart Rate Reserve (%HRR) also called the Karvonen Method is one of the approaches recommended by the ACSM.
C. Based off an indicator of the “anaerobic threshold” such as lactate threshold or ventilatory threshold.
Clarify strengths and weaknesses of each approach and justify why one might be better than another.

Answer 1

It is very important to know one’s target heart rate zone, when working out so as to burn maximum number of calories and get promising results from the workout. In order to find target heart rate zone, it is important to know maximum heart rate of an individual which is defined as fastest rate at which the heart would beat in a single minute. The following are the methods used for the same:

1. “220-Age” formula

Since long times, the basic formula used for calculation of maximum heart rate (MHR) has been “220-age” method. However, there have been a lot of problems on relying on this method for extrapolating physical fitness. There are a lot of reasons associated with this problems. MHR has been found to be influenced at genetic levels. MHR has also been found to vary with age as well as gender. Older people show lesser MHR whereas women have increased MHR as compared to men Age effect is because increase in age actually depresses the sinoatrial node which is the natural pacemaker for the heart. MHR has been found to be influenced by altitudes which has nothing to do with physical fitness of an individual. Training has not been found to influence MHR and, if there is any change, it may show decreased levels as the body experiences expanded blood as well as stroke volumes. Thus, MHR is not an appropriate way to measure physical fitness as they are multiple factors which affect it.

2. Karvonen Method

Karvonen method is one of the simplest technique used to determine target training zones. This method makes use of maximum heart rate (MHR) determined using an individual’s age as well as values of resting heart rate (RHR) so as to evaluate heart rate reserve (HRR). Desirable MHR percent to be used for training is entered into the formula to calculate target heart rate, which is usually found to be in the range of 65?85% training at threshld levels.Target heart rate is calculated as follows:

MHR = 220 – Age (years)

HRR = MHR – RHR

Target Heart Rate = HRR x desired %MHR + RHR

However, Karvonen method cannot be used to estimate metabolic fitness at individual level. It is effective for health improvements as well as basic fitness in general. However, it is unable to calculate remarkable improvements in performance. This is because it is unable to assess changes in metabolic fitness as well as substrate oxidation of fats, carbohydrates, etc. RHR determined by this method has been used as an indicator of overtraining, i.e., RHR has been found to decrease proportionally as fitness increases.  

3. Anaerobic Threshold

Anaerobic threshold is defined as the heart rate above which an individual gains anaerobic fitness. It is being used for determination of short distance time trial performance associated with power output. Anaerobic threshold determines the heart rate deflection point (HRDP) as well as estimates a lactate threshold heart rate or functional threshold heart rate (LTHR or FTHR). However, reliability as well as validity of the HRDP has been found to be dependent on the method used and shows great influence upon incremental increase in workload as well as duration. Hence, the associated power has been found to be unreliable so as to predict the power output of the functional thresholds.  The HRDP, in contrast, may seem to be reliable method for assessment of heart rate changes thus relating to fitness as well as to establishing exercise intensities based on heart rates. Although the HRDP has been found to reflect a physiological threshold point in concept, it does not specify changes in terms of metabolic fitness.

Thus, even though heart rate intensities that are derived from age, maximum values as well as resting heart rates have been commonly used to for prescribing general fitness, they lack required sensitivity to improve endurance performance. Anaerobic thresholds with the heart rate deflection point may serve as an indicator of overall fitness. However, end results are open to interpretation because of limitations in metabolic fitness as well as the future directions of training. Thus, depending upon the output needed, the method for determining physical fitness should be decided.