Exercise training is a prominent and critical component of early outpatient cardiac rehabilitation (CR), providing impressive patient benefits for cardiorespiratory and metabolic indices, quality of life, and cardiovascular disease management as shown in Table 1.1–7 It is estimated that exercise training alone reduces total and cardiovascular mortality by 27% and 31%, respectively, for patients with cardiovascular diseases.4 Improving cardiorespiratory fitness (CRF) is a crucially important element in the secondary prevention of cardiovascular disease adverse outcomes.6 , 8 , 9 , 10 For example, in a cohort of 5641 patients who participated in CR in Canada, for each 1-MET increase in estimated CRF during CR, total mortality was reduced by 25% over 1 y.11 Similarly, previous studies have reported a decrease in cardiac or total mortality ranging from 8% to 34% for each 1-MET improvement in CRF.12 , 13
Medically directed exercise training in CR is prescribed using established guidelines, is based on recommendations for apparently healthy adults, and generally results in an improvement in CRF and skeletal muscle fitness.5 , 14 The primary components of the exercise prescription (Ex Rx) are frequency, intensity, time, type, volume, and progression and are given by the acronym FITT-VP. The specific ranges for most of the exercise prescriptive factors for aerobic and resistance exercise training for patients with cardiovascular diseases are well established.3–5 , 14 However, an often understated and the least well-defined component of Ex Rx is the rate of progression of the exercise volume over the course of CR. This is the most difficult component of Ex Rx for CR health care professionals to master in clinical practice. An appropriate progression in exercise program volume is essential to optimize the gains in CRF and skeletal muscle strength while minimizing potential adverse complications.
The purpose of this position statement is to provide concise, clinically relevant recommendations for progression of exercise training in CR. The recommendations are appropriate for essentially all patients who do not have contraindications to exercise training who participate in CR, including the elderly and patients with severe forms of cardiovascular diseases. The primary focus will be aerobic exercise training, the dominant form of training in early outpatient CR. A secondary focus will be general resistance training. Topics addressed in this statement are (1) an overview of the general principles of Ex Rx for patients with cardiovascular diseases including exercise volume, also referred to as the dose of exercise that correctly identifies the importance of exercise as a medical treatment, overload, training effect, and components of the exercise prescription; (2) a review of the literature regarding the rate of progression of the exercise dose in CR, including the combined extensive clinical experience of the authors; and (3) patient case examples of the progression of aerobic and resistance exercise.
EXERCISE DOSE, THE CONCEPT OF OVERLOAD, AND THE TRAINING EFFECT
The exercise dose is commonly defined as the total amount of energy expended during exercise training over a period of 1 wk.4 For aerobic exercise training, it is the combination of frequency (sessions per wk), intensity (how hard), type (modality), and time (total duration). In terms of kilocalories (kcal) expended per wk in aerobic exercise training as a means of quantification of the dose of exercise, guidelines recommend at least 1000 kcal/wk for the general population.5 However, for CR participants with the goal of substantially improving CRF and halting the progression of coronary atherosclerosis, 1500 kcal/wk appears to be required.7 Another method of quantification of the exercise dose is to calculate metabolic equivalents per min (MET-min) of exercise. For example, if a patient performs 10 min of exercise at an intensity of 3 METs, the volume equals 30 MET-min. Although the precise exercise volume to produce health benefits is difficult to determine, it appears that 500 to 1000 MET-min of exercise per wk produces substantial health benefits such as lower rates of coronary heart disease and premature mortality.5 Table 2 provides an example calculation of MET-min and kilocalories for a typical patient, using methods described by the American College of Sports Medicine5 and Kaminsky et al.15 An automated spreadsheet calculator for kcal per session and MET-min per session is available online (http://links.lww.com/JCRP/A22). For resistance exercise training, the dose is given by the frequency, resistance amount, number of repetitions per set, and the number of sets for each exercise.
Overload is defined as an exercise dose which is above and beyond the accustomed amount of exercise for a given individual.16–18 For aerobic exercise training, overload may be accomplished by increasing any 1 of the components of the exercise dose: frequency, intensity, time, or type (eg, moving patients from non–weight-bearing to weight-bearing modes of exercise or to combination upper and lower extremity exercise devices resulting in greater energy expenditure). For resistance exercise training, either increasing the frequency of sessions, the amount of resistance, the number of repetitions per set, the number of sets per exercise or decreasing the rest period between sets provides overload.5 , 17 Overload results in physiologic and anatomic adaptations to exercise training, within the capacity of the individual patient, which result in improvement in CRF for aerobic exercise training and increased skeletal muscle strength and endurance for resistance exercise training.7 , 17 These physiological improvements in the components of fitness are defined as the training effect. The degree of adaptation to exercise training with progressive overload varies between persons due to multiple factors as shown in Table 3.16 , 18
It is not possible to specifically predict the magnitude of the training effect for a given patient. The ranges of improvement for CRF and skeletal muscle strength in patients with cardiovascular diseases who participate in exercise training for a period of 12 wk or longer in clinical trials conducted under near-ideal circumstances are usually given as 5% to 40% and 24% to 90%, respectively.17 , 19 , 20 Gains in CRF assessed by exercise testing are usually greater for estimated than for directly measured peak
O2.21 , 22 Not all patients in CR will exhibit improvement in CRF measured by cardiopulmonary exercise testing, but almost all patients will demonstrate improved aerobic submaximal exercise endurance for a given exercise heart rate or rating of perceived exertion.21
There is some overlap in the benefits of aerobic and resistance exercise. For example, resistance exercise training without concurrent aerobic exercise training may induce small improvements in CRF in some individuals.17 , 23 In addition, resistance exercise training may result in improvement in glucose metabolism, blood lipids, and aerobic exercise endurance.17 Conversely, aerobic exercise training may improve skeletal muscle strength, bone mineral density, and basal metabolic rate.17 However, in the end, aerobic exercise training is superior to resistance exercise training for improving CRF and cardiovascular risk factors while resistance exercise training results in greater gains in skeletal muscle strength and muscle mass. Thus, for patients to experience an optimal training effect in terms of improving CRF and skeletal muscle strength, a gradual increase in the exercise dose for both aerobic and resistance exercise training is required during CR.
Example of a patient with improved submaximal exercise endurance without an improvement in CRF
A 62-y-old man with severe chronic heart failure treated with a left ventricular assist device completed CR. The primary mode of aerobic exercise was treadmill and track walking. His 6-min walk distance increased substantially from 221 m (42% of normal) to 537 m (104% of normal), but directly measured peak
O2 did not significantly improve (11.1-11.4 mL/kg/min, 40% of normal).
SPECIAL CONSIDERATIONS FOR EXERCISE PRESCRIPTION FOR PATIENTS IN CR
The components of FITT for both aerobic and strength training developed for patients participating in CR have been provided by the American College of Sports Medicine (ACSM) and are presented in Table 4.5 Symptom-limited graded exercise testing before beginning CR is the optimal method for determining the most precise Ex Rx for an individual patient. However, graded exercise testing at the start of CR rarely occurs in clinical practice for a variety of reasons. A 6-min walk test may be performed as a surrogate measure of exercise capacity.3 In addition, performance of the 1-repetition maximum test for each resistance exercise is the gold standard for prescription of resistance exercise intensity, but many programs do not routinely perform this test because of time constraints or other reasons. Ratings of perceived exertion (RPE) are a useful and practical method for prescribing exercise intensity for both aerobic and resistance exercises, particularly for patients without formal graded exercise or strength testing.24
Aerobic exercise training intensity is the most important variable in improving CRF during CR for most patients. Moderate-intensity continuous aerobic training (MCT) is defined as 60% to 85% of peak heart rate and/or RPE of 12 to 14 on the 6 to 20 scale.5 In contrast, high-intensity aerobic interval training (HIIT) involves alternating 10 sec to 5 min of more intense training (85%-95% of peak heart rate, RPE 15-17) interspersed with 1 to 3 min of MCT during an exercise session.5 , 14 , 25 , 26 Periodic assessment of exercise intensity using heart rate and/or RPE should occur during each supervised exercise session. A recent meta-analysis of trials comparing HIIT and MCT in patients with coronary artery disease reported a greater improvement in mean CRF (+1.8 mL/kg/min in peak
O2) with HIIT.27 Various progression models for using HIIT in the CR setting based on patient fitness are provided by Ribeiro et al.28 Using MCT and HIIT during alternate exercise sessions is a common approach recommended by the authors of this statement. Although using HIIT in CR has become more accepted in recent years and is contained within the ACSM guidelines,5 there remains a concern regarding the safety of prescribing exercise at a higher intensity than has been traditionally recommended. However, investigators in Norway evaluated the safety of exercise training using the records of 4826 patients who participated in CR and performed a combination of MCT and HIIT.26 They reported 1 fatal event in 129 456 patient-hours of MCT and 2 nonfatal adverse events in 46 364 patient-hours of HIIT and concluded that both forms of training were associated with low risk of adverse events. For programs limited to 12 to 18 supervised sessions by local reimbursement policies, adequate progression of the exercise dose, including HIIT, may be shifted to “maintenance” or community-based, longer duration programs after completion of early CR.
The need to individualize the exercise prescription for optimizing risk reduction or patient-specific factors is an important consideration. For example, a critical aspect in prescribing exercise for obese patients in CR is to gradually increase the exercise dose to facilitate fat mass loss. Ades et al29 reported greater fat mass loss (5.9 kg vs 2.8 kg, P < .01) for patients who exercised 45 to 60 min at 50% to 60% of capacity, 5 to 7 d/wk (energy expenditure of 3000-3500 kcal/wk) than for patients who exercised in the usual manner for CR: 25 to 40 min at 65% to 70% of capacity 3 d/wk (800 kcal/wk or less). To achieve weekly exercise energy expenditures of 3000+ kcal, a steady progression in the dose of exercise over several weeks is required. In addition, patients with extremely low baseline fitness, including the frail elderly, benefit from an initial intermittent approach to aerobic exercise training (alternating short periods of tolerable MCT with rest periods) as shown in Table 5.
PROGRESSION OF THE DOSE OF EXERCISE TRAINING IN CR
The ACSM position statement defines progression of exercise dose for aerobic training as: “...gradual progression of exercise volume by adjusting duration, frequency and/or intensity is reasonable until the desired goal (maintenance) is attained.”; resistance training as: “...gradual progression of greater resistance and/or more repetitions per set, and/or increased frequency is recommended.”18 (p1336)
In addition, there are a limited number of more specific recommendations regarding the topic made by preeminent exercise physiologists, such as Astrand16 and Pollock,30 as well as by the ACSM guidelines document.5 A summary of these recommendations, as well as considerations made by the authors of this article, is provided in Table 6. However, there are no clinical trials comparing methods or rates of progression of the dose of exercise training for patients in CR to precisely guide CR health care professionals. Also, there are multiple potential factors that may affect progression of the dose of exercise, as indicated in Table 7. The effects of these considerations are not trivial. Failure to adequately progress the dose of exercise may limit the benefits of exercise training for the patient. Unfortunately, in this scenario, the patients may perceive futility in attending CR, surmising that they can perform more effective exercise training on their own versus attending the program. Alternatively, programs that fail to progress the dose of exercise may give patients the impression that they are fragile and that higher doses of exercise should be avoided. Conversely, progression at too rapid a rate may result in adverse effects, such as orthopedic injury, delayed muscle soreness, or cardiovascular symptoms (angina pectoris, dyspnea, extreme fatigue with failure to recover from an exercise session, lightheadedness).16 , 31 However, there is no evidence that an overly cautious approach to progression of the exercise dose in CR is prudent.
PATIENT CASE EXAMPLES OF THE PROGRESSION OF AEROBIC AND RESISTANCE EXERCISE TRAINING
Patient case example 1: Using RPE and HIIT to progress the dose of aerobic exercise with exercise volume estimated by kilocalories per session and MET-min per session.
Clinical information: Summarized in Box 1.
Progression of exercise prescription: Summarized in Box 2.
This case illustrates progression of exercise time and intensity in an obese cardiac patient using RPE and HIIT with a substantial improvement in directly measured CRF. Despite the high volume of training, there was no change in body weight. Included in the case are estimates of energy expenditure in kilocalories and MET-min to illustrate the increase in exercise dose over time. The case also illustrates the discrepancy between estimated peak METs based on treadmill test time and/or peak workload versus directly measured peak METs with cardiopulmonary exercise testing.
Patient case example 2: Progression of resistance exercise training with RPE using hand weights and weight machines
Clinical information: Summarized in Box 3.
Progression of exercise prescription: Summarized in Box 4.
This case illustrates beginning resistance exercise training relatively soon after cardiothoracic surgery in a patient with normal sternal healing, following the 6-wk upper extremity lifting restriction requested by the surgeon and gradually progressing the dose of exercise using RPE and patient tolerance for 5 exercises, including both upper and lower extremities.
Patient case example 3: Progression of aerobic exercise in a very deconditioned patient using RPE and adding weight-bearing exercise as fitness improved.
Clinical information: Summarized in Box 5.
Progression of exercise prescription: Summarized in Box 6.
Patient case example 3 illustrates a gradual rate of progression in exercise time and intensity in a patient with multiple comorbid conditions and extreme deconditioning using RPE as an indicator of intensity. The patient transitioned from non–weight-bearing exercise only to 30 min of a combination of weight-bearing and non–weight-bearing modes of exercise. She returned to ambulation without the aid of a walker.
Two additional patient case examples are shown in the Supplemental Digital Content 1 Appendix, available at: http://links.lww.com/JCRP/A74.
SUMMARY AND CONCLUSIONS
Exercise training in the setting of CR provides multiple benefits including improved CRF, a crucially important marker of prognosis. Guidelines for the prescription of aerobic and resistance exercise training for patients with cardiovascular diseases have been developed and widely disseminated. The most challenging and least well-defined aspect of the exercise prescription for patients in CR is the progression of the dose of exercise. Cardiac rehabilitation health care professionals' confidence and ability to guide progression of the dose of exercise for their patients to the recommended goal of 1500+ kcal/wk are the product of having a working knowledge of the principles of exercise progression and clinical experience in working with a variety of patients. This position statement provides specific recommendations, including patient case examples, for the progression of exercise training in CR to help fulfill that need. An appropriate progression in exercise program volume is essential to optimize the gains in CRF and skeletal muscle strength while minimizing potential adverse complications.
The authors appreciate the contribution of Rebecca C. Toth, MS, Cardiovascular/Pulmonary Rehabilitation and Preventive Cardiology, Peninsula Regional Medical Center, Salisbury, Maryland, for preparation of patient case example number 3.
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Keywords:Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
cardiac rehabilitation; exercise prescription; progression of exercise training