Exercise in the End-Stage Renal Disease Population
Kirsten L. Johansen
Departments of Medicine, Epidemiology, and Biostatistics, University of California, San Francisco, and Nephrology Section, San Francisco VA Medical Center, San Francisco, California
Address correspondence to: Dr. Kirsten L. Johansen, Nephrology Section, 111J, San Francisco VA Medical Center, 4150 Clement Street, San Francisco, CA 94121. Phone: 415-221-4810; Fax: 415-750-6949; E-mail: kirsten.johansen{at}ucsf.edu
Many of the known benefits of exercise in the general populationare of particular relevance to the ESRD population. In addition,the poor physical functioning that is experienced by patientswho are on dialysis is potentially addressable through exerciseinterventions. The study of exercise in the ESRD populationdates back almost 30 yr, and numerous interventions, includingaerobic training, resistance exercise training, and combinedtraining programs, have reported beneficial effects. Recently,interventions during hemodialysis sessions have become morepopular and have been shown to be safe. The risks of exercisein this population have not been rigorously studied, but therehave been no reports of serious injury as a result of participationin an exercise training program. It is time that we incorporateexercise into the routine care of patients who are on dialysis,but identification of an optimal training regimen or regimens,according to patient characteristics or needs, is still neededto facilitate implementation of exercise programs.
The US Surgeon General issued a landmark report in 1996 thatcontained the seminal recommendation that "significant healthbenefits can be obtained by including a moderate amount of physicalactivity ... on most, if not all, days of the week" (1). Severalof the known benefits of exercise or regular physical activityin the general population are related to areas of specific concernto patients with ESRD, such as reduced risk for cardiovascularmortality, improvement in BP control among hypertensive individuals,better control of diabetes, and improvement in health-relatedquality of life as a result of enhanced psychologic well-beingand improved physical functioning (1–3). Given that cardiovascularmortality is the number-one cause of death among patients withESRD in the United States and approximately 80% of incidentESRD patients have a history of hypertension (4), there is greatpotential for mortality reduction as a result of exercise participationin this population. However, epidemiologic research recentlyuncovered a phenomenon of altered risk factor patterns, sometimesreferred to as "reverse epidemiology," that applies to manyusual cardiovascular risk factors, including body size, BP,plasma homocysteine, and total and LDL cholesterol (5–9).Therefore, caution is required when extrapolating evidence ofbenefits in other populations to patients with ESRD. However,the same type of observational data that has yielded paradoxicassociations for other risk factors supports a usual relationshipbetween sedentary behavior (10) or low cardiorespiratory fitness(11) and higher mortality among patients with ESRD (Figure 1).
Figure 1. Survival among sedentary and nonsedentary incident dialysis patients.
It has been hypothesized that many traditional cardiovascularrisk factors exhibit paradoxic associations with mortality inthe ESRD population because of associations between usuallyfavorable characteristics and malnutrition or inflammation (8,12).In other words, dialysis patients with protein-energy malnutritionor inflammation are both more likely to have low levels of traditionalrisk factors such as body weight-for-height, cholesterol, andBP and more likely to have superimposed illnesses that predisposeto morbidity and mortality; the malnutrition-inflammation-diseaseinverse associations may outweigh the more typical negativeassociations of high levels of these risk factors. Conversely,there is no such inverse association between physical activityand nutritional or inflammatory status or underlying disease.Rather, low levels of physical activity would be expected tobe associated with malnutrition, inflammation, and disease,making a typical association between sedentary behavior andhigher mortality not surprising. Figure 2 illustrates the parallelassociations of sedentary behavior and ESRD with other cardiovascularrisk factors and with inflammation, oxidative stress, and endothelialdysfunction and illustrates the areas in which exercise hasbeen beneficial in the general population. This review discussesthe extent to which these effects of exercise training havebeen demonstrated in the ESRD population.
Figure 2. Diagram of potential adverse effects of sedentary behavior and chronic kidney disease and potential beneficial effects of exercise interventions.
In addition to the possibility of improving cardiovascular outcomes,exercise has the potential to improve physical functioning andhealth-related quality of life. Low exercise capacity (maximalor peak oxygen consumption) (13–18), muscle wasting (19–21),and poor physical performance (22,23) and functioning (24–27)are also highly prevalent among patients with ESRD and potentiallymodifiable with exercise interventions (Figure 2). These problemsare associated with development of disability, loss of independence,and death among community-dwelling elderly people, again raisingthe possibility that exercise interventions could be especiallybeneficial to patients with ESRD and could improve survival.
Despite the myriad potential benefits of exercise, dialysispatients are extremely inactive (28), and nephrologists rarelyassess patients' physical activity levels or counsel patientsto increase activity (29). The lack of exercise assessment andcounseling is almost certainly multifactorial, related to suchfactors as competing medical issues that lead to limited timeavailable for exercise counseling, lack of training in exerciseprescription, and fear of adverse events related to exercisein this population. For example, it is possible that, althoughexercise participation could lead to greater benefits amongpatients with ESRD than the general population, dialysis patientsmay also incur greater risk because of underlying heart or musculoskeletaldisease. This review focuses on the available data regardingbenefits and risks of exercise among patients with ESRD.
Several studies have examined the effects of aerobic exercisetraining on peak oxygen consumption (VO2peak) in this population(16,18,30–45). Although the intensity and the durationof exercise in the studies varies, all have included initialmoderate aerobic training progressing to vigorous training for30 min or more three times per week for 8 wk up to 12 mo (moststudies 3 to 6 mo). On average, aerobic exercise training for8 wk to 6 mo improves VO2peak by approximately 17% (Figure 3),but there is considerable variability from study to study, andmany studies have been uncontrolled (16,18,30,32–36,41,43).Only two of these studies included patients who were on peritonealdialysis (35,40). Many studies were conducted before the routineuse of erythropoietin to control the anemia that is associatedwith chronic kidney disease (CKD), but the effects of aerobictraining seem to be similar among patients who receive erythropoietin(Figure 3). Therefore, although it is firmly established inthe literature that aerobic exercise training increases VO2peakin patients with ESRD, the total number of patients studiedis still relatively small, particularly when one considers onlythose for whom a control group was also assembled. Furthermore,the improvement in VO2peak is modest, and patients do not approachpredicted age-adjusted VO2peak levels even after training.
Figure 3. Change in peak oxygen consumption (VO2peak) in response to aerobic exercise training programs. Each bar represents a distinct study. The numbers to the right of the bars represent the number of exercising patients available for analysis. *Change in VO2peak was statistically significant; the study included a nonexercising control group. Studies above the black line included patients who received erythropoietin.
Studies of the effects of exercise on VO2peak have providedimportant information because they showed that patients withkidney disease could respond physiologically to exercise trainingin a manner that is similar to other patient groups. However,the qualified success of vigorous aerobic exercise trainingthat is designed to increase VO2peak should be put into perspective.First, the patients who have been studied to date have generallybeen the healthiest individuals who receive hemodialysis, usuallya small fraction of available patients (33,41), and it is notclear that more typical (i.e., less healthy) patients with kidneydisease will be willing or able to undergo vigorous exercisetraining. Furthermore, it is not clear whether such vigoroustraining is necessary to derive many of the potential benefitsof exercise. Another important caveat to be considered wheninterpreting the increases in VO2peak as a result of aerobicexercise training is that the links between change in VO2peakand improvements in physical performance, self-reported physicalfunctioning, or health-related quality of life have not beenestablished in this population. Therefore, the extent to whicha 17% increase in VO2peak actually improves the lives of patientswith kidney disease is not clear.
Although the effect of aerobic exercise training on VO2peakin selected healthy patients who receive hemodialysis has beena major focus of exercise research in the ESRD population, someadditional information is available to address other potentialbenefits of training. Several studies have considered outcomesin addition to or instead of VO2peak, including measures ofphysical functioning and outcomes not related to physical function.These other outcomes have included anemia, lipid levels, BPcontrol, endothelial function, inflammation, mental health,and health-related quality of life. Although a few small studieshave reported an improvement in anemia with vigorous aerobicexercise training (30,31), the majority of studies have notreported this benefit (32–34,36). Studies of the lipideffects of vigorous aerobic exercise training have also beenmixed, with some showing a decrease in triglyceride (30,31)or an increase in HDL cholesterol (30,31) and others not showingany changes (34–36). Given the small numbers of patientsand lack of control groups in most of these reports, the effectof aerobic exercise training on lipid metabolism remains unclear.A recent study assessed the effects of twice-weekly aerobicexercise training on arterial stiffness and insulin resistance(46). Among 11 dialysis patients who completed the 3-mo program,arterial stiffness as measured by pulse wave analysis (augmentationindex) decreased, but insulin resistance as measured by thehomeostasis model assessment method did not change among theeight participants without diabetes. Few studies have addressedthe effects of exercise on markers of inflammation, but onegroup measured C-reactive protein in 10 patients before andafter a 6-mo intradialytic exercise program and found a significantreduction after exercise participation (47).
Two studies were designed specifically to investigate the effectsof exercise on BP control in patients who were on hemodialysis(48,49). In the first, patients were nonrandomly assigned toa 6-mo cycling exercise program during dialysis (40 exercisersand 35 control subjects). At the end of 6 mo, 24 (60%) patientswere still participating in the exercise program. The patientswho completed 6 mo of training had no changes in BP before orafter dialysis but were, on average, taking fewer antihypertensivemedications to achieve that BP than before the program, whereasthe control group did not have any significant change in BPor antihypertensive medications. The second study also involvedcycling exercise during HD and enrolled 19 patients, 13 of whomcompleted at least 3 mo of training. Predialysis and interdialytic(44 h) ambulatory systolic and diastolic BP decreased after4 mo of training, a finding that persisted after 6 mo of training.The two studies to date that were specifically designed to evaluateBP control demonstrated a beneficial effect of exercise training.
A few studies have focused on the effects of aerobic exercisetraining on mental health or health-related quality of lifeamong patients who are on hemodialysis. Carney et al. (50) reportedthat patients who underwent vigorous aerobic exercise trainingthree times per week for 6 mo (n = 10) reduced their scoreson the Beck Depression Index by an average of 4.3 points comparedwith an increase of 2.5 points in patients who did not exercise(n = 7; P < 0.05). Suh et al. (41) conducted a study thatinvolved 14 patients who were on maintenance hemodialysis andunderwent moderate-intensity aerobic exercise training threetimes per week for 12 wk. They reported a trend toward a decreasein depression using a Self-Rating Depression Scale (P = 0.073).In addition, they reported a significant reduction in anxietyand an improvement in quality of life as measured using an ESRD-specificinstrument. Kouidi et al. (38) reported a significant improvementin overall quality of life and specifically in depression asmeasured by the Beck Depression Index after 6 mo of aerobicexercise training in 24 patients. In contrast, Painter et al.(51) included the Medical Outcomes Study Short Form 36-Itemquestionnaire (SF-36) as a major outcome in a much larger studyand found no improvement in the mental health components with16 wk of aerobic exercise.
The Painter study, called the Renal Exercise Demonstration Project(51), was unique in its large size and its focus on physicalperformance and health-related quality of life as the primaryoutcome measures rather than VO2peak. The study included 286patients and included an 8-wk home-based training interventionfollowed by 8 wk of cycling exercise during dialysis sessions.Home-based training included recommendations for strengtheningand flexibility exercises as well as walking or stationary cyclingof gradually increasing duration three to four times per week.Cycling during dialysis was begun for as long as tolerated atan intensity that was determined by patients' level of perceivedexertion. Patients were encouraged to increase cycling timeto a goal of 30 min per session and to increase intensity astolerated on the basis of perceived exertion. Outcomes includedphysical performance measures such as gait speed, 6-min walkdistance, and ability to stand from a chair as well as self-reportedphysical functioning using the SF-36. The authors were ableto demonstrate that physical performance and health-relatedquality of life improved with exercise training and declinedin those who were not assigned to the exercise interventions.For example, the Physical Functioning (PF) score of the SF-36increased 12% in the group that was assigned to exercise anddecreased 12% in the control group. The authors noted that theimpact of these interventions was more profound in the patientswho had worse functioning at baseline (52). The interventiondid include a recommendation to do low-intensity strengtheningexercises in addition to aerobic exercise training, but thisaspect of the program was not directly supervised even duringthe dialysis center training phase of the study, and fewer than10% of the patients reported following this recommendation.For these reasons, it seems likely that the majority of thereported benefits can be ascribed to aerobic exercise training.This study demonstrated that a broader and less heavily selectedgroup of patients who are on hemodialysis could participatein exercise training with improvements in functioning. In fact,from the point of view of physical performance and self-reportedfunctioning, it seems that patients who are less able standto benefit more from beginning an exercise program.
Other, more recent studies have also included measures of physicalfunction other than VO2peak. For example, Molsted et al. (44)conducted a 5-mo study of twice-weekly aerobic exercise training.Among the 11 patients who completed the exercise program, therewas an improvement in the PF score and the Physical ComponentSummary score of the SF-36. In a study of aerobic cycling exerciseduring dialysis in 12 patients, Storer et al. (45) reportedimprovements in muscle strength and fatigability among exerciserscompared with a nonexercising control group. This perhaps surprisingincrease in strength in response to aerobic exercise was accompaniedby changes in skeletal muscle growth factors, including a decreasein myostatin mRNA and increase in IGF-1 receptor in the eightpatients with paired muscle biopsies, suggesting that thesepatients may be so deconditioned that even aerobic trainingprovides a stimulus for muscle hypertrophy (53). However, musclehypertrophy was not actually observed among the small number(n = 5) of patients in whom fiber size was measured before andafter exercise. Finally, the exercising patients significantlyimproved their physical performance on tasks such as stair climbing,walking 10 m, and a timed up-and-go test, although these testswere not performed by the nonexercising control subjects forcomparison.
The movement away from VO2peak as a primary outcome of aerobicexercise training has been accompanied by a movement towardadministering exercise programs during dialysis treatments.There are several reasons that exercise training during dialysisis particularly attractive. First, there is the possibilityof better adherence to a regimen that does not include extravisits, a possibility that was borne out in one comparativestudy (54). Second, hemodialysis sessions typically representa period of forced inactivity and thereby may directly contributeto the poor functioning of this population. Therefore, exerciseduring dialysis represents an opportunity to reverse the potentiallynegative impact of dialysis (55). Third, it is possible thatexercise could improve solute removal during dialysis by increasingblood flow to muscle and leading to greater efflux of urea andother toxins into the vascular compartment, where they can beremoved (56). Indeed, several studies have shown that short-termbouts of exercise or long-term exercise training can increaseurea removal (47,56–58). However, these potential benefitsmust be balanced by the possibility of reduced exercise toleranceduring dialysis as a result of fluid and electrolyte shiftsand the possibility that exercise could exacerbate dialysis-associatedhypotension. Nevertheless, beneficial effects of intradialyticexercise have been observed, and exercise is well toleratedwithin the first 1 to 2 hours of dialysis sessions (17,34,39).
Muscle strength is an important determinant of physical performanceand ability to live independently in the geriatric population(59,60). Patients who receive dialysis are weak compared withhealthy sedentary control subjects (19,61–65), and itis likely that weakness is an important limitation to physicalfunctioning in patients with kidney disease. We previously showedthat muscle strength was an important predictor of gait speedin patients who were on dialysis (19), and Diesel et al. (66)showed that isokinetic muscle strength was an important determinantof VO2peak in a group of patients who were on dialysis. Therefore,it seems likely that resistance exercise training could be ofbenefit to these patients, and it is surprising that few studieshave focused on resistance exercise training or included resistancetraining as part of the program.
Headley et al. (67) reported on the results of a 12-wk resistanceexercise training program in a group of 10 patients who wereon hemodialysis. The program consisted of two supervised trainingsessions per week during which, after a 5- to 10-min warm-upperiod, patients performed eight to nine weight-machine exercisesthat were designed to strengthen the whole body. In additionto supervised training sessions, patients were given Theraband(Hygenic Corp., Akron, OH) exercise bands and instructed tofollow at home once per week a video that covered nine exercises.At the end of the training program, the patients increased theirpeak torque of the leg extensors of the dominant leg at the90°/s velocity by 12.7 ± 3.6%, but there was no significantchange in peak torque at 120°/s or 150°/s or in gripstrength in either hand. Patients improved on several physicalperformance tests after the training, including a 6-min walktest, normal and maximum gait speed, and time to complete asit-to-stand test 10 times. There were no complications or injuriesrelated to the exercise training.
Our group recently completed a randomized 2 x 2 factorial trialof resistance exercise training and anabolic steroid administrationin 79 patients who were receiving maintenance hemodialysis (68).Interventions included lower extremity resistance exercise trainingfor 12 wk during hemodialysis sessions three times per weekusing ankle weights and double-blinded weekly nandrolone decanoate(100 mg for women; 200 mg for men) or placebo injections. Sixty-eightpatients completed the study. Exercise did not result in a significantincrease in lean body mass, but quadriceps muscle cross-sectionalarea as measured by magnetic resonance imaging increased inpatients who were assigned to exercise (P = 0.01) and to nandrolone(P < 0.0001) in an additive manner. Patients who exercisedincreased their strength in a training-specific manner, andexercise was associated with an improvement in self-reportedphysical functioning (P = 0.04 compared with nonexercising groups),but there was no change in walking or stair-climbing time relatedto exercise participation. A trial of a similar intradialyticresistance training that also includes upper body exerciseswas recently completed as well (55), but the results have notyet been published. A preliminary report in abstract form suggeststhat C-reactive protein was reduced at the end of a 12-wk program(69).
Kouidi et al. (21) enrolled seven patients who were receivinglong-term hemodialysis into a 6-mo exercise rehabilitation programthat included aerobic exercise and strengthening exercise. Theprogram consisted of 90-min sessions three times per week onnondialysis days. Specifically, the training routine includeda 10-min warm-up followed by 50 min of aerobic exercises, 10min of low-weight resistance exercise, 10 min of stretchingexercises, and 10 min of cool-down. They examined the effectof this program on VO2peak and on muscle morphology. The programresulted in an average increase in VO2peak of 48%, an increasethat is greater than any program involving aerobic exercisetraining alone (Figure 2). They also reported a remarkable improvementin muscle atrophy, with a 25.9% increase in the mean area fortype I fibers and a 23.7% increase in mean area of type II fibers.Although they characterized their training program as "mainlyof aerobic type," the notable muscle hypertrophy and the stunningimprovement in VO2peak suggest that the strength training portionmay have contributed important additive or synergistic effectsto the aerobic training. It is possible that muscle atrophyin some patients with ESRD is so severe as to limit VO2peakbecause of the small mass of working muscle. Unfortunately,the design of this study did not allow the separate contributionsof aerobic and resistance training to be delineated.
The same group of investigators also examined heart rate variabilitybefore and after the same exercise training program in 30 exercisingpatients and 30 sedentary control subjects (70). They foundthat heart rate variability increased among the exercisers,suggesting improved autonomic control of the heart and reducedrisk for arrhythmia.
A couple of other studies of mixed exercise interventions includedcontrol groups. Mercer et al. (71) conducted a nonrandomized,controlled trial of an exercise rehabilitation program thatoccurred during a 12-wk period and included a combination ofintermittent aerobic exercise on a cycle ergometer and a localmuscular endurance circuit of eight exercises. A total of 212patients were potentially available to participate, but only22 volunteered and were eligible. Thirteen were slated for theexercise, but only seven completed the study. These patientsshowed improvements in performance of a 50-m walk (15 ±5.8%), stair climbing (22 ± 11%), and stair descent (18± 12%) after the exercise intervention. DePaul et al.(72) conducted a randomized trial of a mixed-exercise interventionamong patients who were on hemodialysis and were receiving erythropoietin.The intervention consisted of progressive resisted isotonicquadriceps and hamstrings exercise and training on a cycle ergometerthree times weekly for 12 wk. Cycling exercise was performedduring dialysis, and weight training took place before or afterdialysis according to patient preference. Twenty patients wererandomly assigned to the exercise group, 15 of whom were availableto be retested after 12 wk. The exercise group increased theworkload at which their rating of exertion on the Borg scale(73) was "somewhat strong" by 20 ± 18 W, compared withan increase of 6 ± 13 W for the control group (P = 0.02).At 12 wk, the intervention group also increased their combinedhamstring and quadriceps strength by 46.7 ± 49.3 lb (P= 0.02 versus control group). There were no significant or clinicallyimportant differences in disease-specific quality of life orperformance on a 6-min walk test between the study groups. Theauthors noted that the group was particularly high functioningat baseline, with scores on the PF scale of the SF-36 and onthe 6-min walk test that were close to reported values for healthygroups and significantly higher than baseline scores in theRenal Exercise Demonstration Project (51), in which it was notedthat patients with lower functioning at baseline improved toa greater degree (52). Finally, two studies focused on Tai Chiamong patients who were undergoing peritoneal dialysis (74,75).One reported an improvement in self-reported physical functioning(74), and the other reported an improvement in mental healthscores (75).
The most common risk of exercise participation in the generalpopulation is musculoskeletal injury; the most serious risksare those of cardiac origin, ranging from dysrhythmia to ischemiato sudden death. The risk of both types of adverse events ishigher with high-intensity exercise than with submaximal exercise(76).
No studies have been specifically designed to assess the riskof exercise among patients with CKD; available information comesfrom case reports and from mentions of adverse effects thatoccurred during studies of the effects of exercise. Musculoskeletalrisk may be increased in patients with CKD as a result of hyperparathyroidismand bone disease. Their bone disease may place them at higherrisk for fracture (77), and spontaneous quadriceps tendon ruptureshave been reported (78–80), probably as a result of poorlycontrolled secondary hyperparathyroidism. However, it is possiblethat weight-bearing or strengthening exercises could, in thelong run, decrease the risks for falls and increase bone density,further lowering the risk for fracture. The up-front risks forinjury can be minimized by including a warm-up period in exercisesessions, by avoiding high-impact activities, and by beginningtraining programs at lower intensity and progressing graduallyas tolerated. These strategies have been used in many of thestudies reviewed in this article with great success, becausethe number of adverse events that were associated with exercisetesting and training has been extremely low. Furthermore, improvedmuscle strength and overall fitness that are achieved throughan appropriately prescribed program of progressive exercisecould reduce the likelihood of injury during exercise and associatedwith falls, possibly lowering the overall risk for musculoskeletalinjury (76). Specific studies that are designed to assess thebalance of risks and benefits of exercise training among patientswith CKD would be of great value.
The risk for cardiac events during maximal exercise testingis low, on the order of 0.5 per 10,000 tests for death and 3.6per 10,000 tests for myocardial infarction, estimates that arebased on tests that were conducted in healthy and diseased populations(76,81–83). No data specifically address the risks inpatients with kidney disease. It is likely that their risk ishigher than in the healthy general population because of thehigh prevalence of risk factors for cardiac disease and knowncardiac disease, but their risk is probably not significantlyhigher than the risk in populations that undergo diagnostictests for cardiovascular disease. Again, no untoward cardiacevents have been reported in any of the published studies ofexercise testing in patients with ESRD, and, although thesepatients were a highly select group, the risk seems to be low(76). The risk for cardiac events during submaximal exercise(i.e., training) is even lower than that for maximal testing(84). Although the risk for a cardiac event is transiently increasedduring exercise, overall, that risk is attenuated in individualswith higher levels of habitual physical activity (76).
A major purpose of medical screening before exercise participationis to determine which patients are at increased risk for cardiovascularevents. However, all patients with ESRD or advanced CKD areat increased risk for cardiopulmonary disease. Therefore, theexisting guidelines provide little assistance in determiningwhether exercise testing should be performed before initiationof an exercise program or which patients should be tested (76,85).The necessity for testing should be related to the proposedintensity of training and the patient's symptom or disease status.Patients with symptoms suggestive of cardiac disease or withknown disease should undergo exercise testing before participationin vigorous training programs (85). However, many of the reportedstudies of moderate-intensity exercise training in patientswith kidney disease have relied on history, physical examination,and, in some cases electrocardiographic testing to determinewhether patients may participate in exercise training programswithout adverse events, suggesting that this strategy is appropriatewhen moderate-intensity training is involved.
In addition to proper medical screening, some disease-specificconsiderations may reduce risk. Attention to patients' volumestatus and BP control is important in this population. Patientswith ESRD should have their dry weight assessed frequently toavoid volume overload and may tolerate exercise best eitherduring dialysis or on a day after a dialysis session.
There is an ever-expanding body of literature related to theeffects of exercise among patients with ESRD, and, recently,the quality of studies is improving. Returning to Figure 2 andthe potential benefits of exercise in this population, thereare now ESRD-specific data to suggest that exercise can improvemany indicators of physical functioning, such as fitness, musclemass, physical performance, and self-reported physical functioning.Fewer data are available to address cardiovascular indices.However, preliminary evidence suggests that exercise can enhancethe management of hypertension, reduce inflammation, and improveendothelial function.
Why, then, has exercise not been broadly applied in this population?Until recently, lack of published position statements aboutexercise in this population may have limited enthusiasm fora focus on exercise. However, the recently published KidneyDisease Outcomes Quality Initiative (K/DOQI) clinical practiceguidelines on management of cardiovascular disease state that,"all dialysis patients should be counseled and regularly encouragedby nephrology and dialysis staff to increase their level ofphysical activity" (guideline 14.2) (86). The lack of randomizeddata on outcomes such as survival is also often cited as a reasonthat physical activity has not been incorporated into the routinecare of dialysis patients (87,88). Although there is no doubtthat larger studies of the effects of exercise interventionson survival and quality of life are needed, there is now morecompelling evidence to support the benefits of exercise in thedialysis population than there is to support several other commonlyused therapies, such as "statins" (87). Perhaps a larger barrierto implementation of exercise programs in the dialysis populationis the lack of a clearly defined "best" program. This reviewhas synthesized results from a myriad of different exerciseprograms of varied intensity, duration, and exercise modality.Given this remarkable variety, it seems that almost any methodof increasing activity in this population is likely to be beneficial,but the nephrology community is desperately in need of comparativestudies to determine the extent to which less vigorous activityis beneficial and to set forth a regimen or counseling programthat can be broadly applied and incorporated into the routinecare of our patients.
In the meantime, we should strive to follow the K/DOQI guidelinesand encourage our patients to increase their level of physicalactivity. The first step toward increasing patients' activitylevel is assessment. Clinicians should determine whether patientsare performing at least 30 min of moderate activity on threeor more days per week. If not, then barriers to increasing activityshould be investigated, including specific questions about musculoskeletallimitations and potential cardiac limitations such as dyspneaor chest pain. Musculoskeletal limitations can be further assessedand addressed through referral to a physical therapist. Cardiovascularsymptoms warrant dry weight assessment and/or stress testing.Once these potential contraindications to exercise have beeneliminated, patients should be encouraged to begin a walkingprogram, starting with 10 to 30 min/d, 3d/wk at a moderate difficultylevel as tolerated. Patients should then be encouraged to increasetheir walking time to at least 30 min on 3 d/wk or more, keepingthe intensity at a moderate level (or a perceived exertion of"somewhat hard") (73). The success of such a program is likelyto be enhanced by regular and ongoing physician or dialysispersonnel assessment and encouragement of participation in physicalactivity. In addition, use of pedometers may increase participationby facilitating goal setting and providing tangible evidenceof progress (89,90). Physical activity programs within the dialysissetting have the potential to be of great benefit as well, andthe principles of implementation are similar to those outlinedfor a walking program (initial assessment, starting at a lowlevel as tolerated, and gradual progression toward goals). However,it is impractical to consider such a program without universalsupport of dialysis staff, because the burden of maintainingan in-center exercise program falls largely on the clinicalstaff.
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[Abstract][Full Text][PDF]
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Abstract
Why Consider Exercise in...
8 wk up to 12 mo (most studies 3 to 6 mo). On average, aerobic exercise training for 8 wk to 6 mo improves VO2peak by approximately 17% (Figure 3), but there is considerable variability from study to study, and many studies have been uncontrolled (16,18,30,32–36,41,43). Only two of these studies included patients who were on peritoneal dialysis (35,40). Many studies were conducted before the routine use of erythropoietin to control the anemia that is associated with chronic kidney disease (CKD), but the effects of aerobic training seem to be similar among patients who receive erythropoietin (Figure 3). Therefore, although it is firmly established in the literature that aerobic exercise training increases VO2peak in patients with ESRD, the total number of patients studied is still relatively small, particularly when one considers only those for whom a control group was also assembled. Furthermore, the improvement in VO2peak is modest, and patients do not approach predicted age-adjusted VO2peak levels even after training. 
the study included a nonexercising control group. Studies above the black line included patients who received erythropoietin.