Pre-exercise Screening for Minimizing Cardiovascular Risk During Testing

Exercise testing can pose a risk to the patient, so exercise testing must have clear indications, and any contraindications must be ruled out. On the other hand, earlier guidelines for exercise testing in patients, particularly those with cardiac conditions, were too conservative.¹ Patients can be exercised aggressively provided that the indications are based on a comprehensive assessment and a judiciously selected exercise test and protocol and provided that the patient is appropriately monitored throughout testing. The American College of Sports Medicine (ACSM)² has developed an algorithm (Figure 19-1, A) to determine the risk for cardiovascular events during exercise testing (Table 19-1) as well as guidelines for test selection and level of supervision required based on the risk assessment (Figure 19-1, B). As shown in Figure 19-1, A, patients with known cardiovascular, metabolic, or pulmonary disease are classified as having a high risk for sustaining a cardiovascular event during exercise. For these individuals, a comprehensive medical examination and physician-supervised exercise testing is recommended before starting a moderate or vigorous intensity exercise program (see Figure 19-1, B). For individuals who do not have the conditions listed above, the remainder of the algorithm describes how patient signs and symptoms and coronary artery disease risk factors determine the risk classification and exercise testing and supervision requirements. Physical therapists need to screen patients systematically before exercise testing or prescription.

Table 19-1

Cardiovascular Risk Factor Threshold for Risk Stratification

	Risk Factors	Defining Criteria
Positive	Age	Men ≥45 years; Women ≥55 years
	Family history	Myocardial infarction, coronary revascularization, or sudden death before 55 years of age in father or other male first-degree relative, or before 65 years of age in mother or other female first-degree relative
	Cigarette smoking	Current cigarette smoker or those who quit within the previous 6 months or exposure to environmental tobacco smoke
	Sedentary lifestyle	Not participating in at least 30 minutes of moderate intensity (40% to 60% ) physical activity on at least 3 days of the week for at least 3 months
	Obesitya	Body mass index: ≥30 kg × m2 – or – Waist girth:  >102 cm (40 inches) for men  >88 cm (35 inches) for women
	Hypertension	Systolic blood pressure ≥140 mm Hg and/or diastolic ≥90 mm Hg, confirmed by measurements on at least two separate occasions, or on antihypertensive medication
	Dyslipidemia	Low-density lipoprotein (LDL-C) cholesterol ≥130 mg × dL-1 (3.37 mmol × L-1) – or – High-density lipoprotein (HDL-C) cholesterol <40 mg × dL-1 (1.04 mmol × L-1) – or – On lipid-lowering medication If total serum cholesterol is all that is available, use ≥200 mg × dL-1 (5.18 mmol × L-1)
	Prediabetes	Impaired fasting glucose (IFG) = fasting plasma glucose ≥100 mg × dL-1 (5.50 mmol × L-1) – or – Impaired glucose tolerance (IGT) = 2-hour values in oral glucose tolerance test (OGTT) ≥140 mg × dL-1 (7.70 mmol × L-1) but <200 mg × dL-1 (11.00 mmol × L-1) confirmed by measurements on at least two separate occasions
Negative	High-serum HDL cholesterol	≥60 mg × dL-1 (1.55 mmol × L-1)

Note: It is common to sum risk factors in making clinical judgments. If HDL is high, subtract one risk factor from the sum of positive risk factors, because high HDL decreases CVD risk.

^aProfessional opinions vary regarding the most appropriate markers and thresholds for obesity; therefore allied health professionals should use clinical judgment when evaluating the risk factor.

Modified from the American College of Sports Medicine. (2010). Guidelines for exercise testing and prescription, ed 8. Philadelphia: Williams and Wilkins.

Evaluative Submaximal Exercise Tests

Step tests, an example of a fixed-rate exercise test in that the load and rate remain constant, emerged as practical field tests several decades ago. With the emergence of a range of field tests since then, step tests are being used less commonly. Nonetheless, when well standardized and selected appropriately for a given person, step tests can provide valuable information about aerobic fitness because they can elicit vigorous exercise intensities. People who are obese and/or physically deconditioned may require supervision when performing a step test.²²

The 12-minute walk test and its variants, 6-minute and 3-minute walk tests, were designed to test patients with lung disease.¹² These tests have been favored clinically, because they are functional and do not require exercise equipment. However, these tests are often used for patients who have extremely impaired exercise capacity and are unable to tolerate being tested on an exercise modality. A major disadvantage, therefore, is that the patient cannot be as comprehensively monitored. Thus patients who are to undergo a 12-minute walk test or one of its variants must be selected with care.

When the 6-minute walk test is applied to healthy older adults, it has been shown to be reliable; two familiarization tests are needed to minimize arousal and the learning effect.²³ In the same trial, the subjects walked, on average, at 80% of . Based on a comparison with the performance of patients with chronic obstructive pulmonary disease (COPD) to an “encouraged” 6-minute walk test and a standard incremental cycling test, the prognostic value of the walk test was reported to be high.²⁴ Patients achieved a high steady-rate in the walk test. No differences were reported in , HR, and arterial blood gases between the two tests at peak. However, and were lower in the walk test. When performance was “encouraged,” the 6-minute walk test was reported to have good prognostic value.

The 6-minute walk test has been favored as an expedient and inexpensive means of evaluating the functional capacity of older adults with multiple comorbidities. A short distance walked by this cohort is associated with having a low level of education; being non-Caucasian; having a reduced capacity to perform activities of daily living; self-reporting poor health; having a history of heart disease, stroke, or diabetes; and showing abnormal levels of C-reactive protein, fibrinogen, and white blood cell count.²⁵

The 6-minute walk test can provide a useful measure of the distance an individual can walk. Because it fails to account for body weight, which is a determinant of exercise capacity, the validity of the 6-minute walk test has been questioned.²⁶ To enhance its usefulness, Carter and colleagues (2003)²⁷ proposed the use of the product of the distance of the 6-minute walk and the body weight, to yield the work involved in the 6-minute walk. This measure provides a more valid measure of exercise performance and, in addition, can be converted to provide an index of calorie expenditure, hence serving as a standardized basis of comparison across exercise modalities.

Recently, the 6-minute walk test has been conducted on a treadmill. Although there are advantages of treadmill tests over field tests, the results of the two types of test may differ, at least in people after cardiac surgery.²⁸

The shuttle test has been another commonly used exercise test for patients with disabilities. When performance on this test is compared with the 6-minute walk distance in patients with COPD, the two tests appear to assess different pathophysiological processes.²⁹ The shuttle test is considered a more accurate predictor of maximal exercise capacity than is the 6-minute walk test.

Predictive Submaximal Exercise Testing

One application of exercise testing in patient populations that has been of interest is to predict .¹⁶ Prediction of involves a large margin of error in healthy populations, and that margin could be expected to be greater in patients who are likely to be more deconditioned, have comorbidities, and are prone to greater variations in their exercise responses. The Astrand-Ryhming Cycle Ergometer Test continues to be one of the most frequently used submaximal tests for exercise prescription as well as for prediction of .³⁰ Prediction of is obtained from a nomogram in which the is estimated from the submaximal HR. To improve its accuracy, an age-correction factor is used to adjust for the age-dependent decrement in HR_peak.³¹ This ergometer test has the clinical advantage of being applicable to less ambulatory people.

Three equations have been compared to predict in patients with hypertension and fibromyalgia:³² one equation is from the ACSM; one equation is from the Fitness and Arthritis in Seniors Trial (FAST); and the third equation was developed by Foster and colleagues (FOSTER). Predicted for all equations was different from the actual measured values. However, the FAST and FOSTER equations predicted values within 1 MET for both patient groups; the ACSM equation predicted values that were different by more than 2 METs.

The distance walked in the 6-minute walk test can provide valid information regarding the functional capacity of elderly patients with chronic heart failure.³³ The results are highly correlated with and can differentiate between classes III and IV of the New York Hospital Association classification of functional capacity.

The heart rate index has recently been described as a means of predicting energy expenditure with the equation METs = 6 × HR_index − 5.³⁴ This equation was based on secondary analysis of 220 data sets (n = 11,257 of multiple ages, pathophysiology and presence/absence of beta blocker therapy) from 60 published exercise studies. These studies reported resting HR (HR_rest), a measured-activity HR (HR_absolute), and measured oxygen consumption (mL O₂/kg/min) associated with the HR_absolute. HR_index (HR_absolute/HR_rest) was calculated. Regression analysis of oxygen consumption (expressed as METs) was performed against HR_index to derive the equation to predict METs. Simple tools are compelling for clinical use and warrant further study.

The oxygen uptake efficiency slope (OUES), which is based on a submaximal test, has been proposed as a valid and reliable index of exercise performance in patients with congestive heart failure.³⁵ This method was tested on older healthy individuals and on patients on the basis of the rationale that maximal testing is not always valid, feasible, or safe. The OUES involves plotting against the logarithm of total ventilation at submaximal work rates. On repeated tests, the OUES is less variable than endurance or . Thus the OUES is an objective and reproducible measure of cardiorespiratory reserve based on submaximal effort. The measure reflects ventilatory-circulatory-metabolic coupling and is influenced primarily by pulmonary dead-space ventilation and exercise-induced lactic acidosis.

Maximal Exercise Testing

With respect to exercise capacity in patient populations, maximal aerobic performance has been of primary interest for diagnosis, assessment, evaluation, and prognosis. Maximal incremental exercise tests (graded exercise tests, or GXTs) can be highly useful in patient populations as long as consideration for the higher level of motivation required to achieve a maximal response is taken. In addition, because maximal exercise testing inherently involves a higher risk for cardiovascular complications than does submaximal testing, it should be used judiciously.

studies (also called cardiopulmonary exercise tests, or CPETs) have become a primary component of the workup of patients with abnormal exercise tolerance for diagnostic and assessment purposes and for exercise prescription. Metabolic measurement carts are used to conduct these studies. To ensure valid and reliable data, the gases used by the cart must be calibrated and testing procedures tightly standardized before the test as well as during it. A practice session is recommended to reduce learning effects and sympathetic arousal.³⁶ Before the commencement of the test, a couple of minutes of baseline measures are taken, against which the acute exercise responses and the recovery responses can be compared. The metabolic measurement cart can be programmed to display a variety of exercise variables and graphs of interest. The exercise test results are interpreted according to an evaluation of the resting baseline values, the responses of the exercise variables to changes in the exercise test protocol (qualitatively and quantitatively appropriate), the interrelationship of these changes, and whether they achieve some peak value, such as HR or perceived exertion. Beforehand, a decision is made with respect to whether the test is sign- or symptom-limited. Any unusual responses or events during the test are documented. The full impact of the test may not be manifested for several hours or even the next day; thus the patient is followed so that these changes or effects can be evaluated as well. In some patients, lactate measures that require invasive blood work or, minimally, a finger prick, may be indicated.

From the results of CPETs, there are several important variables that can be used clinically. First, determination of the exercise limitation(s) can be made. As described in Chapter 18, the normal limitation to aerobic exercise performance is usually considered to be cardiac output, more specifically, stroke volume. In this case, subjects will exhibit a near maximal heart rate (>90% of age predicted maximum), evidence of a high metabolic demand involving anaerobic energy (respiratory exchange ratio – – >1.1; or blood lactate levels >8 mmol/L), and near maximal perceptions of effort (rate of perceived exertion >8/10 or >17/20). If these factors are present, a cardiovascular limitation is presumed. In this case, if values are well below the predicted maximal values, the patient may have some degree of underlying cardiovascular pathology or may simply be deconditioned. Examination of the pre-exercise history, the exercise ECG findings, and the levels of O₂ saturation can determine whether the cardiovascular limitation is due to disease or deconditioning. Another common limitation to aerobic exercise observed in clinical exercise testing is due to an inadequate ability to achieve an appropriate level of ventilation. Ventilatory limitations can be detected by the use of pre-exercise spirometry and exercise tidal flow volume loops; or may be detected by comparing the achieved at maximal exercise to the predicted or measured maximal voluntary ventilation (MVV). /MVV >90% is considered to indicate a ventilatory limitation. The interested reader is referred to the ATS/ACCP Statement on Cardiopulmonary exercise testing³⁷ for more information on these topics.

Second, CPETs provide a range of exercise performance data, including anaerobic threshold, which is often ignored. Recently, however, the anaerobic threshold has been considered an important marker of cardiovascular insufficiency and exercise performance that has importance in evaluating the performance of individuals with low functional work capacity, such as older adults and patients with left ventricular dysfunction, and in prescribing exercise for them.38,39 In addition, examining the anaerobic threshold may have particular relevance to individuals in these groups, who may be ill-advised to undergo maximal stress tests. From CPET, anaerobic threshold can be determined by the following criteria:

Third, CPETs can provide valuable information related to the cardiovascular health and fitness of an individual. is considered by many to be the gold standard for determination of fitness. Although this point is debatable, reference values that are specific to age and gender are widely used to determine an individual’s level of fitness. In terms of prescribing exercise training, values at peak exercise such as HR_max and work rate maximum can be used to help set appropriate levels of intensity.

In the case of a practitioner who wishes to perform maximal testing, but who does not have access to the required equipment and/or expertise to measure respiratory gases (and ), a maximal GXT may be conducted. A maximal GXT without respiratory monitoring holds the same level of risk associated with CPETs, but it will still provide valid information on maximal work rate attained and also on a subject and modality specific maximal heart rate. In this case, an achieved maximal heart rate or maximal work rate can be used to prescribe exercise training intensity more accurately than using an age-predicted maximal heart rate or a predicted maximal work rate based on submaximal testing. In addition, if all of the monitoring requirements other than are maintained (ECG, SpO₂, dyspnea, etc.), the safety of using vigorous to high-intensity exercise as a training technique can be ascertained.

General Testing Considerations

Reproducibility of exercise test results is a particular concern in patient populations whose status may change from day to day. When tested weekly for 4 weeks, patients with stable COPD have been reported to have reproducible submaximal physiological exercise responses and ratings of perceived exertion in response to a constant work rate.⁴⁰ Exercise performance at a constant work rate is a functional indicator of endurance. On serial exercise testing of patients with chronic heart failure, the mechanical efficiency of walking markedly improves, giving rise to an apparent placebo effect, which has been reported to be independent of motivation and changes in conditioning.⁴¹ This factor can invalidate the findings of a single test. Highly trained individuals show a more marked neuroendocrine (sympathoadrenal and hypothalamopituitary adrenal) response in a second bout than in the first bout of exercise performed on the same day.⁴² Study is needed on the implications of neuroendocrine changes with repeated exercise tests in patient populations.

Knowledge of the patient’s functional ability based on verbal report is useful and serves as a guideline for selecting the type of exercise test, its parameters, and the test termination criteria. Although these verbal reports do not replace an exercise test, they can be used as an adjunct. The diagram of oxygen cost is shown in Figure 19-3. This visual analog scale is constructed of a 100-mm line with physical activities hierarchically sequenced based on oxygen cost; the high end of the scale represents strenuous activity (walking briskly uphill) and the low end of the scale represents no activity, or sleep. The patient crosses the line at the point where breathlessness does not allow continuation at the patient’s best (see Figure 19-3). Figure 19-4 shows incremental workloads associated with step increments in metabolic cost—that is, multiples of resting or near resting metabolic rate (resting metabolic rate = 1 MET, or 3.5 mL O₂/min/kg of body weight). Metabolic costs of activities range from very light to very heavy activities. One limitation of such charts in indicating the metabolic costs of various activities and exercises is that they can be used only as a general guide in patients with cardiopulmonary compromise, as they do not take into consideration the increased work of breathing and the work of the heart that is observed in patients with cardiopulmonary dysfunction, or the increased energy cost associated with abnormal biomechanics as observed in patients with neuromuscular and musculoskeletal conditions.

Exercise testing and training can be challenging in individuals with physical disabilities, such as those with stroke. Because of this limitation, many patients are denied the potential benefits of diagnostic exercise testing and exercise training. The use of external body supports is one means of providing support during standardized exercise testing on a treadmill. One study examined the metabolic effects of a 15% body-weight support in individuals without impairments.⁴³ End-expiratory gas variables were not affected, except for maximal V_T, which was lower with body support; however, time to achieve peak values was increased. The responses of patient populations who would require variable levels of body support have yet to be determined. Another dimension of exercise testing in people with disabilities is the assessment of gait speed, which is associated with physical independence and in activities such as crossing an intersection safely. In addition, gait speed has been proposed as a means of predicting discharge for people with acute stroke. Within the first 5 weeks following stroke, the 5-meter walk test at a comfortable pace (as opposed to the 10-meter walk test, the timed up-and-go test, and other common functional assessment indexes) is the measure of choice for detecting change in walking ability.⁴⁴ Finally, movement economy can be compromised in people with physical disabilities, given that their movements are biomechanically inefficient (e.g., people with the residua of poliomyelitis).⁴⁵ Abnormal postural alignment and movement asymmetry need to be considered in patient populations because these impairments can increase the energy cost of a given work rate based on norms.

Exercise testing has a role in preoperative assessment. In combination with other tests and examination, exercise testing in patients as a component of the workup for abdominal aortic aneurysm repair with measurement of P can identify patients at risk for perioperative complications.⁴⁶ Exercise testing has been used to define a gas-exchange threshold for patients with COPD who are being considered for thoracic surgery.⁴⁷ A of less than 20 mL O₂/kg/min has been recommended as the threshold for predicting perioperative complications. Routine preoperative exercise testing has been advocated. Exercise testing has also been recommended to assist in determining the operability of a patient with lung cancer.^48,49 Patients may be excluded from lung resection surgery based on conventional medical criteria, yet included based on their . These patients have shown survival benefit.

Monitoring

Common variables measured during an exercise test include HR, ECG, systolic and diastolic BP, rate pressure product (RPP), RR, SpO₂, and subjective responses such as perceived exertion, breathlessness, discomfort, pain, and fatigue (see Chapter 18). Assessment of dyspnea is central to monitoring individuals with breathing and exertional impairments. The Borg scale and the visual analog scale are applicable to individuals with dyspnea, and if assessed in a systematic manner, they can provide valid and reliable measures when used in the patient groups for which they were designed, so they should be used routinely.⁵⁰ Measures are taken every few minutes after the patient has been exercising at a given intensity for a few minutes when a response to steady-rate exercise is being assessed. This allows for relative stabilization of oxygen kinetics during dynamic exercise. Subjective responses to exercise and daily activities are often the most important to the patient because these typically interfere with their social participation and its composite activities.

Pulse pressure (SBP − DBP) is known to be influenced by aging and arterial wall elasticity.⁵¹ Pulse pressure is also influenced by lifestyle interventions, including exercise and diet. Therefore it may serve as an index of changes in arterial wall stiffness with exercise training.

More detailed analysis can be done, depending on the testing or training goals. Noninvasive measures, including transcutaneous oxygen and carbon dioxide tensions, can be readily used to assess gas exchange during testing.⁵² Invasive monitoring can be done in conjunction with metabolic testing. Such monitoring requires blood sampling through an intraarterial line to examine serial changes in oxygen and carbon dioxide tensions, acid base balance, and arterial saturation, as well as to provide a means for conducting the thermodilution method that yields an index of CO.

The short- and long-term recovery responses, both quantitative and qualitative, in patient populations are important components of the exercise testing profile. The physical therapist must have a thorough understanding of normal physiological recovery responses in order to benchmark abnormal and atypical responses. Sustained elevated BP after cessation of exercise, for example, has been reported to be more sensitive than ECG for detecting myocardial insufficiency. Further, systolic BP after exercise is a strong predictor of hypertension, coronary artery disease, and cardiovascular mortality. An increase in systolic BP and the percent maximum systolic BP 2 minutes after exercise is directly and independently related to risk for stroke.⁵³

Exercise Prescription for Health and General Fitness

The components of exercise training for patients for general physical conditioning are the same as those for healthy people: selection of the type of exercise; its intensity, duration, and frequency; and the course of training and its progression. An individualized, rather than standardized, exercise prescription is essential to maximize outcomes in the same way that a physician individualizes a drug prescription.⁵⁴ The word prescription implies individualization to a person’s needs and goals, including his or her social participation and its composite activities. The selection of the type of exercise used for training and the type used in the exercise test is based on the specific objectives of training.

Several expert organizations provide general guidelines for exercise prescription for health and general fitness. Arguably, the foremost of these organizations is the American College of Sports Medicine. The ACSM guidelines are well established and updated frequently; they provide enough guidance to give a comprehensive prescription, but allow enough flexibility to suit the demands of each individual patient. Table 19-6 provides a wide array of examples of how to approach exercise prescription for patients based on their individual level of habitual activity and physical fitness. The FITT approach (frequency, intensity, time, type/mode) to providing exercise prescription ensures that each prescription is detailed enough to be performed by each patient. Although guidelines are just examples, they provide a good starting point from which to design an exercise prescription. These principles are purposefully vague in terms of the exact numbers to use. This range of potential values, particularly for intensity, reflects the fact that improvements in cardiovascular health and fitness can occur with almost any type of exercise prescription within the designated ranges.

Table 19-6

Recommended FITT Framework for the Frequency, Intensity, and Time of Aerobic Exercise for Apparently Healthy Adults^a

Habitual Physical Activity/Exercise Level	Physical Fitness Classificationc	Frequency		Intensityb			Time
		kcal/week 1	days/week1	HRR/ where R is reserve capacity	% HRmax	Perception of Effort	Total Duration Per Day (min)	Total Daily Steps During Exercised	Weekly Duration (min)
Sedentary/no habitual activity or exercise/extremely deconditioned	Poor	500-1000	3-5	30%-45%	57%-67%	Light-moderate	20-30	3000-3500	60-150
Minimal physical activity/no exercise/moderately highly deconditioned	Poor-fair	1000-1500	3-5	40%-55%	64%-74%	Light-moderate	30-60	3000-4000	150-200
Sporadic physical activity/no or suboptimal exercise/moderately to mildly deconditioned	Fair-average	1500-2000	3-5	55%-70%	74%-84%	Moderate-hard	30-90	≥3000-4000	200-300
Habitual physical activity/regular moderate to vigorous intensity exercise	Average-good	>2000	3-5	65%-80%	80%-91%	Moderate-hard	30-90	≥3000-4000	200-300
High amounts of habitual activity/regular vigorous intensity exercise	>Good-excellent	>2000	3-5	70%-85%	84%-94%	Somewhat hard-hard	30-90	≥3000-4000	200-300

kcal, Kilocalories; , oxygen uptake reserve; HRR, heart rate reserve; %HR_max, percentage of age-predicted maximal heart rate.

Note: These recommendations are consistent with the U.S. Department of Health and Human Services Physical Activity Guidelines.

^aThe various methods to quantify exercise intensity in this table may not necessarily be equivalent to each other.

^bFitness classification based on normative fitness data categorized by

^cPerception of effort using the ratings of perceived exertion (RPE), OMNI, talk test, or feeling scale.

^dTotal steps based on counts from a pedometer.

Exercise Training to Improve Tasks or Performance

Contrary to the wide range of variables listed above related to exercise prescription for general health and fitness, performing exercise training for improvements in tasks or performance requires the use of a much more specific prescription. This specific prescription needs to be tailored to each individual patient and usually requires the use of specific exercise or functional tests. The use of the physical therapy history or interview, then, represents a crucial aspect of determining the tests and training program design. If there is a specific functional task or performance goal that is identified by the patient or the physical therapist, the exercise test(s) should attempt to, as closely as possible, reflect the requirements of the task or performance. Exercise training program design should then reflect the task/performance, as well as the results of the exercise test. For example, in a private practice setting, a worker who is recovering from a low back injury due to fatigue which caused abnormal lifting mechanics might have the goal of reducing fatigue so that he may maintain proper lifting mechanics throughout his day. Exercise testing, then, should mimic the movement pattern used (lifting) and attempt to determine his endurance in performing lifting related tasks. The training program should be suited to his current level of performance and progressed appropriately to allow optimal adaptation.

Another example of how training programs are designed might be a patient with obesity who needs to increase her sustained walking speed. An appropriate test might be to perform a graded exercise test with measurement to allow the estimation of this individual’s anaerobic threshold (as a marker of maximal sustainable pace). The exercise training program would be designed to have the patient increase her anaerobic threshold (using an intensity of exercise at or around anaerobic threshold).

A significant difference between exercise prescription for health and training program design is that training programs often require long-term periodization in order to address multiple needs. Usually, this type of training design involves structuring periods of training that progress from more general to more task- or performance-specific. In the example of the patient wanting to increase anaerobic threshold, the physical therapist would usually begin the program with some lower intensity aerobic exercise for 3 to 8 weeks designed to increase overall endurance and tolerance to walking. After this initial period of “aerobic base” training, the physical therapist would progress the program by prescribing training to increase anaerobic threshold. This type of training program design is complex, and a full description is beyond the scope of this chapter; however, physical therapists working with patients requiring improvements in specific tasks/performance should be competent in comprehensive program design.⁶⁴

Emerging Alternate Types of Exercise Prescription

For many patients, continuous aerobic training as described above is either ineffective, inefficient, or intolerable (see Chapters 18, 34, and 35). There are a few promising methods of altering aerobic exercise prescription techniques that help to minimize these limitations. One example is the use of single-limb training (as opposed to double-limb). As mentioned in Chapter 18, patients who exhibit inability to exercise at high enough intensities to elicit significant physiological benefit due to impairments of central cardiovascular or respiratory responses can increase their muscle specific peripheral load by restraining exercise in one limb. Dolmage and Goldstein (2008)⁶⁵ found that single-limb cycling in patients with COPD allowed patients to rapidly progress single-limb workload, resulting in a significantly greater increase in than the group who trained using two-legged cycling (22% versus 1%, respectively). This increase in was achieved during a double-legged cycling GXT. What is most striking about this study is the fact that the overall training time between the two groups was the same. The double-legged training group cycled for 30 minutes continuously, whereas the single-limb group exercised one leg for 15 minutes, then switched legs for the remaining 15 minutes. There are two main conclusions that can be made in regard to the physiological adaptations achieved with single-limb training. First, it appears that progression of overall intensity beyond what is capable through double-legged training in this population is much more important than overall training time. Second, because increased in the single-limb group on a double-limbed test, the mechanisms for increases in are likely due to peripheral adaptations. It has been proposed that adaptations at the level of muscle mitochondria are most apparent with maximizing the amount of tissue oxygenation to minimize the circulating PO₂.^66,65

Another example of a promising method of exercise training is the use of high-intensity interval training. Although typically thought of as an “athletic” type of training, high-intensity interval training has been used successfully in patients with cardiovascular and respiratory disease. In patients with COPD, for example, ventilatory limitations prevent continuous exercise performance at high intensities.⁶⁷ As such, interval exercise models can be used to attempt to increase overall workload during exercise and to enhance muscular adaptation.^68,69 Interval exercise involves alternating periods of higher intensity work bouts (termed work phase) with those of lower intensity (termed recovery phase). The results of training studies reported to date in COPD indicate that high-intensity interval training (at a work phase of 90% to 100% of peak aerobic power) increases muscle performance and exercise tolerance to a similar degree as continuous training, with less ventilatory limitation and dyspnea.^68,69 In addition, the adaptations achieved in skeletal muscle are comparable to those achieved by continuous training. Meyer and colleagues (1996)⁷⁰ used high-intensity interval training at a work phase of approximately 120% of peak aerobic power compared with a continuous exercise protocol at 75% of peak power in patients with chronic heart failure. The interval exercise protocol resulted in greater exercise times, with reduced levels of ventilatory and cardiac stress and reduced symptoms of fatigue and dyspnea. After only 3 weeks of training at this high intensity, these patients achieved remarkable increases in maximal aerobic power and leg muscle performance, with reduced symptoms and stress during training.⁷⁰

Recovery and Overtraining

The prescription of the parameters for optimal physiological recovery has not been described in detail. However, the practice of progressive, decremental exercise intensity in the form of a warm-up is supported. Such activity facilitates venous return and the return of HR and other exercise parameters to baseline values.⁷¹ In addition, light activity after exercise promotes the degradation of circulating catecholamines. Priming exercise in athletes improves performance,⁷² and this result can be expected in nonathletes as well. However, the parameters (i.e., exercise type, intensity, and duration) of an optimal warm-up have yet to be defined, and they may depend on the individual, general health and fitness, weight, age, and morbidity.

New advances in athletic training may have application to clinical populations, including titrating, or periodizing, training day by day, week by week, or month by month. Periodization has two primary goals: to structure a training program to achieve optimal, multiple physiological adaptations and to prevent overtraining. An overtraining phenomenon has been described in healthy people. Athletes whose performance has dropped off may improve performance outcomes with several weeks of rest.⁷³ Prevention of overtraining is achieved through a detailed analysis of the responses to and recovery from the previous exercise session. This method is based on modeling the effects of training, detraining, and overtraining.^74,75 This method does not assume that the interval between exercise sessions is the same across individuals or the same for a given individual from one day to the next. The proponents of the model believe that training is optimized by the avoidance of under- or overtraining and that training effects are better if they are accumulated over time, rather than according to the conventional methods that subscribe to a rigid exercise intensity, duration, and frequency over some interval (e.g., 6 to 8 weeks).

The role of overtraining in people with underlying pathology, whether induced by the pathology or resulting from an excessive therapeutic exercise prescription, is not well understood. The extent to which some severely compromised patients are, in fact, overtrained as a mere consequence of their activities of daily living is not known. It is possible that the syndrome of inability to maintain work performance, persistent fatigue, frequent illness (in particular upper respiratory tract infections), disturbed sleep, and altered mood states may reflect overwork in patients that is analogous to overtraining in athletes.76,77 With respect to immunity, reduced neutrophil function may be implicated in both situations. In athletes, this overtraining syndrome due to excessive physical exertion and inadequate recovery has been related to autonomic dysfunction and increased cytokine production. Because regular intense exercise can suppress mucosal immunity and because saliva is the most commonly used secretion for assessing mucosal immunity, monitoring the saliva of athletes during critical training periods provides an index of risk status. The usefulness of mucosal assessment in clinical populations warrants investigation. Relaxation has been shown to offset the exercise-induced suppression of secretory immunoglobulin associated with upper respiratory tract infection in healthy people.⁷⁸ The role of relaxation and its immune protection warrants exploitation in clinical populations. Immunity may be optimized with an appropriate balance of exercise, rest, and recovery. Achieving an optimal balance of exercise and rest or recovery warrants study in patient populations as a means of maximizing a patient’s social participation.

Prescriptive rest periods between bouts of exercise and optimal sleep in patient populations, comparable to the training of athletes, should be considered as carefully as the prescriptive parameters of exercise itself to maximize functional performance.

Specific Procedures

In a supervised setting, the general procedures used in exercise training are comparable to those used for testing. Specifically, the patient prepares for the training session in a standardized manner and is monitored according to his or her condition. The components of the session are the same with respect to warm-up, cool-down, and recovery. The main part of the exercise program, however, will usually be steady-rate or interrupted exercise. Varying work rates may be indicated for some patients.

In the majority of situations, the goal is to transfer the responsibility of surveillance and monitoring from the physical therapist to the patient. Depending on the patient’s pathology and ability to learn how to monitor exercise responses accurately, this process takes varying amounts of time. Planning of transition to home and the community is considered from the beginning. The patient’s daily needs at home serve as the basis for the exercise program; his or her skills need to be transferred from the physical therapist and clinic to the home environment.

Monitoring

For safety reasons and to ensure that the patient is within the target training range of the variables selected to set exercise intensity, the patient must be closely monitored. This is particularly true if the patient has any risk for untoward or adverse reactions to exercise. If a patient is considered to be at any risk, exercise training should take place only in a supervised setting. A stable patient may begin an exercise program in a supervised setting, but with training and education can usually be transferred to an unsupervised setting. Education includes self-monitoring of exercise responses, maintaining exercise intensity within the appropriate limits, and keeping a record of the details of their exercise sessions. When the patient is safely carrying out the exercise program independently in the community, some mechanism is needed to follow up on the patient’s progress. If the objective is continued conditioning, the patient should be rescheduled for a retest. If the patient is on a maintenance program, the physical therapist is responsible for reminders about exercise and injury precautions and about notifying the physical therapist or physician if significant adverse effects are observed.

The HR, BP, RR, and other measure are taken according to standardized procedures. Electronic equipment and mechanical devices must be calibrated. A break point in the double product (HR × systolic BP) and work-rate relationship can provide a good estimate of the anaerobic threshold in patients with exercise intolerance as well as in healthy persons.⁸¹

Patients on sympathomimetic drugs or with various pathologies will have abnormal exercise responses. Thus knowledge of these factors is essential to determine whether a measure is valid.

The World Health Organization recommends repeated BP measurements be performed in the sitting or supine position followed by standing⁸² and that the cuff be positioned at the level of the right atrium, irrespective of body position. One concern about this recommendation is that systolic and diastolic BP is lower in a sitting than in a supine position, so the two readings are not equivalent.⁸³ Blood pressure may be under- or overestimated if the level of the cuff is not at the level of the right atrium, regardless of body position. Further, this effect may be amplified in patients with autonomic dysfunction such as that found in patients with diabetes.

Nutritional status and rest/sleep status must be assessed in patient populations by physical therapists to maximize exercise capacity and function comparable to competitive athletes. Mobilization and exercise must be prescribed to maximize these effects during acute and chronic long-term exercise.

Most evidence related to exercise and health has focused on cardiovascular conditioning. The relationship between other dimensions of health is being increasingly studied—for example, immunological status⁸⁴ and mental health.⁸⁵ With respect to mental health, little is known about the parameters of exercise that are optimally antidepressive, other than benefits may be associated with regular physical activity, preferably engaged in with other people. Although there is an association between depressive symptoms and reduced activity in community-living older adults, research is needed to establish the role of exercise training in preventing or attenuating these symptoms.⁸⁵