EXERCISE INTENSITY

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EXERCISE INTENSITY Intensity of cardiorespiratory exercise is measured as percent of maximal capacity, more specifically, as a percent of VO2max.
Intensity Percent VO2max Very Light Light Moderate Hard Very Hard Maximal <20% 20-39% 40-59% 60-84% >85% 100%	The box to the left summarizes the ACSM classification system for exercise intensity.
There are three primary steps in prescribing exercise intensity; and there are three sub-steps to the first two: Determine the target intensity Sliding scale based on existing fitness 10% below the end point of the exercise test 10% below the intensity that elicits an abnormal response Provide the client/patient with a means of monitoring intensity Heart Rate RPE METs Translate the prescribed intensity to actual work rates for the exercise session Determining the Target Intensity There are three basic ways to determine the intensity of cardiorespiratory exercise. The first is based on the existing fitness; the second is modified for submaximal testing; and the third is based on an abnormal response to exercise. These are: Sliding scale based on existing fitness 10% below the end point of the exercise test 10% below the intensity that elicits an abnormal response When prescribing exercise intensity, a range of intensities is recommended rather than a single intensity. A range of exercise intensities can be effective for most health or fitness outcomes. These ranges are often quite broad. An example is the 60-85% intensity range for improving fitness. Even though the range spans 25%, it will be easier for the client/patient to use a 10% range somewhere within the 25% range. The Sliding Scale Based on Existing Fitness: Individuals with lower cardiorespiratory fitness can improve fitness with lower exercise intensities, whereas individuals with higher cardiorespiratory fitness require higher exercise intensities to make improvements. Karvonen {Karvonen, 1957 #302} reported the minimal exercise intensity required to improve fitness in the apparently health population was 60% of capacity or VO2max. The sliding scale was developed to estimate effective exercise intensity for low and high fit individuals. Target Intensity = [60 + Max METs]/100 This formula estimated higher exercise intensities for individuals with higher exercise capacities and lower exercise intensities for individuals with lower exercise capacities. For example, according to the sliding scale, an individual who exhibits a 5 MET capacity should exercise at 65% of capacity: Target Intensity = [60 + 5]/100 = 65% Whereas an individual who exhibits a 12 MET capacity should exercise at 72% of capacity. Target Intensity = [60 + 12]/100 = 72% Target intensities are given in range, usually 10% wide. The target intensity determined by the sliding scale can be used as the bottom, top or middle point of the prescribed intensity range. See the discussion below on choosing the prescriptive range of exercise intensity. 10% Below the End Point: Whether it is a 12 minute walk or a maximal graded exercise test, an assessment of exercise capacity is given prior to exercise programming and prescription. For safety, exercise intensity should not be prescribed above the intensity used in the exercise assessment. According to the work of Cumming and colleagues, 50% of the individuals who exhibited a positive electrocardiographic response to maximal graded exercise testing would have been missed had the test terminated at 80% of heart rate max. Had these individuals been tested to 80% heart rate max, yet prescribed exercise intensity above the 80%, they may have been in danger of an adverse event during exercise. It is safer to prescribe exercise intensity below the intensity of exercise that has been evaluated. Prescribing the intensity 10% below the end point assures a more normal heart rate, ECG, and blood pressure response during training. If submaximal graded exercise is utilized for the exercise testing, choosing the stage below the end point would assure a margin of error between the prescribed intensity and the end point intensity. If the exercise assessment involves 12 or 15 minute walk/run, choose a speed below the average speed or a heart rate below the highest heart rate exhibited during the assessment. When using the 10% below the end point to determine target heart rates, knowledge of the corresponding exercise intensity is not possible. It can only be estimated. 10% Below an Abnormal Response: Abnormal cardiovascular responses to exercise are often reproducible. That is, an ischemic response to exercise will occur at the same double product for patients who exhibit stable angina. An ischemic response can be exhibited as a drop in blood pressure, dysrhythmia, and/or angina. Prescribing the exercise intensity below the ischemic response decreases the incidence of an abnormal response compromising the exercise or resulting in an adverse event. When using the 10% below the abnormality to determine target heart rates, knowledge of the corresponding exercise intensity is not possible. It can only be estimated. Providing the client/patient with a means of monitoring intensity The duration of exercise is measured by minutes and the frequency of exercise is measured by days. Minutes and days are easy for the client/patient to monitor. Intensity of exercise, on the other hand, is measured by percent of VO2max and is much harder for the client/patient to monitor. If a client is instructed to exercise between 60 to 70% of VO2max, it may be difficult for them to figure out how hard to work. Therefore, other variables that reflect the intensity of exercise must be monitored to estimate the intensity of exercise. These variables must exhibit a linear relationship with exercise intensity and be simple for the client/patient to monitor. The three most common linear variables used to monitor intensity are Heart Rate (HR) Ratings of Perceived Exertion (RPE) METs or Energy Expenditure As exercise intensity increases, so does heart rate, perceived exertion, and energy expenditure (METs or VO2). These variables can be used alone or in combination. Heart rates and RPE are most often used in the health and fitness setting whereas all three are more often used in exercise treatment. Using Heart Rate to Guide Exercise Intensity. There are several ways to choose target heart rates to guide exercise intensity. The three primary target heart rate methods are: Percent Heart Rate Max (%HRmax) Heart Rate Reserve (HRR) Direct Determination Before using heart rate to guide exercise intensity, there are some principles to remember regarding the heart rate VO2 relationship. To explore these relationships go to the K561 web site. Heart rate has a liner relationship with VO2. This relationship varies with Mode of exercise Calculation of target heart rates The linear relationship between heart rate and VO2 is best in cardiorespiratory exercise for guiding exercise intensity. Within the spectrum of cardiorespiratory exercise, the more muscle mass involved in the exercise, the better target heart rates reflect exercise intensity. A target heart rate calculated from one test mode may not be as accurate for other modes of exercise. If a heart rate:VO2 graph can be created for each mode of cardiorespiratory exercise, target heart rates will better reflect target intensities. The two most common calculations for target heart rate are Percent Heart Rate max (%HRmax) and Heart Rate Reserve (HRR). The Figure to the right illustrates the %HRmax and %VO2max relationship. These two formulas show different relationships. As the intensity approaches maximal capacity, the two formulas appear to predict exercise intensity similarly. However at the lower intensities found in most health and fitness exercise prescriptions, there is a larger discrepancy between the two methods. Without corrections, 60% of %HRmax appears to be comparable to a significantly lower percentage of VO2max. Thus, %HRmax overestimates exercise intensity. The difference is between 10-15% in the light and moderate exercise intensities. If %HRmax is to be used, 10-15% higher than target percentages should be calculated for the target heart rate. For example, for a target intensity 50-60%, a target heart rate between 65-75% of heart rate max should be calculated. Target Heart Rate = HRmax x (%Intensity +15%) Heart Rate Reserve Heart rate reserve more accurately estimates energy expenditure because the range of the working heart rate (rest to max) is considered in the calculation. In the %HRmax formula it is assumed that heart rate goes down to zero. This is not true. Resting heart rate is significantly different than zero. The heart rate reserve formula considers the true resting and maximal heart rates. Target Heart Rate = [(HRmax – HRrest) x %Intensity] + HR rest Caution should be taken when using equations to estimate maximal heart rate. These formulas have large standard deviations; some formulas can be off +12 to 15 beats per minute. If the formula, 220-age were used to estimate maximal heart rate, the range of variation for the target heart rates for 60% intensity can exhibit a significant variation. For example: What is the target heart rate at 60% intensity for a 50 year old man with a resting heart rate of 70 beats per minute. To estimated his HRmax: Estimated HRmax = 220 – age = 220 – 50 = 170 beats per minute If the standard deviation for this equation is +15 beats per minute, his maximal heart rate can be anywhere between 155 to 185 beats per minute. The resultant target heart rate at 60% can range between 121 and 139 beats per minute. Thus, caution should be taken when estimating maximal heart rates to calculate target heart rates. The client/patient may find it too easy or too difficult to achieve the target heart rates. If so, the target heart rates should be modified in the field, according to the response of the client/patient. RPE is a good adjunct to help modify target heart rates calculated from estimated maximal heart rates. The Direct Determination of Target Heart Rates. The direct method of determining target heart rates does not need target heart rate formulas or calculations. Exercise test data is required for the direct method. The direct method is used more often in cases when the intensity is chosen as 10% below the end point or 10% below the abnormality. The direct determination of target heart rates can be accomplished several ways. One way is to choose the heart rates that correspond to the stage of the exercise test that is at the target intensity. A second way, illustrated to the left, is to graph the heart rate:VO2 response and draw a line from the target intensity to the heart rate. Another way is to choose the heart rates of the stage below the end point of a submaximal graded exercise test. Or, in the case of an abnormal test, choose the heart rates of the stage below the presentation of the abnormality. If a 12 minute walk/run is used for assessment, choose a heart rate below the highest heart rates taken during the walk/run. When using the direct determination of target heart rates, knowledge of the exact exercise intensity is not possible. It can only be estimated. Using Rated Perceived Exertion to guide Exercise Intensity Rating of perceived exertion (RPE) is a subjective rating system for exercise intensity based on general fatigue. RPE can be used in conjunction with target heart rates. RPE is often used as a substitute for target heart rates when The ability to monitor heart rate is compromised No exercise test heart rates exist Applying effort to physical activities other than cardiorespiratory endurance (i.e. playing tennis or gardening) The heart rate-VO2 relationship has been modified and new target heart rates cannot be calculated. For example, medications such as Beta-Blockers alter the heart rate – oxygen consumption. Target heart rates calculated in the non Beta-Blockade condition cannot be used when taking Beta-Blockers. RPE is more often used in the clinical setting than in the health and fitness setting. Two scales of RPE now exist. Both scales are illustrated below. Category Scale Category-Ratio Scale 6 7     Very, very light 8 9     Very light 10 11     Fairly light 12 13     Somewhat hard 14 15     Hard 16 17     Very Hard 18 19     Very, very hard 20 0         Nothing at all             “No, Intensity” 0.3 0.5     Extremely weak         “Just noticeable” 0.7 1         Very weak 1.5 2         Weak                         “Light” 2.5 3         Moderate 4 5         Strong                         “Heavy” 6 7         Very strong 8 9 10      Extremely strong          “Strongest Intensity” The first is called a Category Scale which has a linear relationship with cardiorespiratory exercise intensity. In fact, the scale, which ranges from 6 to 20, was developed to estimate exercise heart rates by multiplying the RPE by 10. Word description anchors every odd number on the scale. The Category-Ratio Scale has a non-linear relationship which mimics the blood lactate or minute ventilation response to increasing exercise intensities. The word anchors were improved for better understanding with more common phrases used to describe exercise. Onset of blood lactate is between 4 and 5 on the Category-Ration Scale and represents 12 to 16 on the Category Scale. The target RPE can be chosen in a similar manor as the direct method to determine target heart rates. If both target heart rates and RPE are to be used to guide intensity, take the RPE from the exercise test that corresponds to the target heart rate. The instructions for RPE are important to guide the individual to focus on general fatigue: “During the exercise test we want you to pay close attention to how hard you feel the exercise work rate is. This feeling should reflect your total amount of exertion and fatigue, combining all sensations and feelings of your physical stress, effort and fatigue. Don’t concern yourself with any one factor such as leg pain, shortness of breath, or exercise intensity, but try to concentrate on your total inner feelings of exertion. Try not to underestimate or overestimate your feelings of exertion; be as accurate as you can.” These instructions should be given before the exercise test as well as when giving the exercise prescription. Additional orientation to the RPE scale during exercise helps the individual focus on the feelings of exertion. After an exercise prescription is given and before the individual begins to exercise have the individual walk on a treadmill or ride a cycle ergometer at the target exercise intensity. This intensity should also elicit the target RPE. Instruct the individual to remember that this effort is the target RPE. Occasional orientations ensure proper use of the RPE to monitor exercise intensity Using METs to guide Exercise Intensity Prescribing exercise intensity with METs is the truest method to guide intensity. METs and VO2 are both measures of energy expenditure and can be converted to the other, using the following relationships. 1 MET = 3.5 ml/min kg 1 MET = 1.05 kcal/kg hr METs are often easier for the individual and non-exercise physiology clinician to understand because the energy the expenditure is measured in multiples of one MET. For example, an exercise that is 10 METs has an energy expenditure 10 times greater than that of rest. Exercise intensities are easier to understand based on METs. Keep in mind the principle of specificity of exercise. The desired outcome of the cardiorespiratory exercise program is an increase in cardiorespiratory energy. METs are energy expenditure. There is no purer form of estimating energy expenditure. Therefore the formula to determine target METs is: Target METs = max METs x % Intensity The energy expenditure of physical activities, exercise, occupational activities, leisure activities and sports has been determined. Choose those activities in which the energy expenditure is within the target MET range. TRANSLATING EXERCISE INTENSITY FROM THE PRESCRIPTION TO THE WORKOUT Whether you are prescribing exercise intensity by METs or suggesting a workrate for your client to exercise, the exercise intensity needs to be translated from percent intensity, heart rates, perceived exertions, and METs to actual work rates for each activity. The ACSM metabolic equations can be used to estimate the work rate for Group 1 activities recommended in the exercise prescription. Using the prescribed intensity, calculate the VO2. Calculate approximate work rates for the individual to try on the treadmill, cycle ergometer, arm crank, and/or stepper.

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