What is the role of exercise in chronic kidney disease?

INTRODUCTION

Physical activity consists of all body movements during daily living, is supported by skeletal muscles and results in energy expenditure. Exercise is a subset of planned, structured and repetitive physical activity aimed at improving body and organ/system fitness. Basically, being physically active and performing physical exercise have many benefits, and health organizations strongly recommend that healthy adults engage in at least 150 min of moderate-intensity [3–6 metabolic equivalent units (METs)] or 75 min of vigorous-intensity (6–9 METs) aerobic physical activity along the week to reduce cardiovascular risk factors, diabetes, depression and mortality.

In the worldwide population, physical activity levels are much lower than recommended, and it has been estimated that inactivity is responsible for 6% of coronary heart disease, 7% of Type 2 diabetes, 10% of breast cancer and 10% of colon cancer [1]. Physical inactivity is also highly prevalent in patients with established chronic diseases and is associated with lower functional capacity and physical performance, poor rehabilitation and unfavourable outcomes.

Reducing inactivity could greatly improve health and, theoretically, physical activity could be easily increased in the general population by promoting awareness and developing specific programmes [2]. Yet, in some subjects, recommended targets may be hard to achieve and may become themselves a barrier for activity. Nevertheless, there is a dose–response relationship between physical activity and health outcomes; thus, also small amounts of activity may be associated with clinically relevant health benefits, as performing physical activity only once weekly reduces the incidence of some chronic diseases [3].

PHYSICAL ACTIVITY DURING CHRONIC KIDNEY DISEASE

Chronic kidney disease (CKD) is associated with inactivity along the whole course of the disease [4]. In non-dialysis-dependent phase, physical activity worsens with the glomerular filtration rate (GFR) lowering and is associated with frailty and disability; in dialysis, patient inactivity is highly prevalent and is associated with poor outcomes; and in kidney transplanted patients, physical activity is still reduced and a complete recovery is unusual. Several comorbidities (diabetes, coronary artery disease, peripheral artery disease and heart failure) and pathological conditions (reduced muscle mass/function, fatigue and depression) contribute to low physical functioning along CKD [5–7].

Reported barriers to participation in exercise programmes in pre-dialysis CKD include excessive tiredness, low muscular strength/power, pain in bones/joints and shortness of breath [8]. In patients on dialysis, both physical and psychological barriers are common, including fatigue, perception of burden of comorbidities, lack of time or access to facilities, fear of getting injured, pain, depression and lack of motivation [9]. In renal transplanted patients, major barriers to exercise seem to be the fear of draft injury, pre-existing pathological conditions, and low energy levels and fatigue [5, 7].

During CKD, increasing physical activity (both supervised and home-based exercise programmes) improves physical performance, functioning and quality of life [10]. In non-dialysis CKD, a combined aerobic and resistance training schedule, with a moderate to vigorous intensity level, may provide a greater improvement in physical performance as compared with aerobic training alone, while there is no conclusive evidence indicating a clear-cut advantage for a specific strength or balance training programme. In any case, symptom burden is significantly decreased in patients enrolled in aerobic or combined aerobic–resistance training programmes. No major cardiovascular or traumatic adverse events have been reported in most studies [10]. Yet, in non-dialysis-dependent CKD, since the issue of potential cardiovascular acute adverse effects is insufficiently explored, there is a need for tailored prescriptions of exercise programmes, with respect to intensity and type (i.e. aerobic versus resistance or a combination of both), according to individual level of deconditioning. Notably, no conclusive data on the effects of exercise on hard outcomes are available. Retrospective data in a heterogeneous CKD cohort, also including dialysis and transplant patients, suggest that the ability to complete a training programme and the related improvement of physical performance may be associated with a lower risk of cardiovascular morbidity and mortality [11].

In patients on haemodialysis (HD), a large body of evidence points to favourable effects of exercise training, both during dialysis sessions and on non-dialysis days, on increasing aerobic capacity and muscular function, decreasing depression, improving quality of life and also increasing the dialytic efficiency. Most of the available data come from trials that implemented intradialytic aerobic training, although a few studies also included resistance exercises. In general, the greatest benefits of exercise were observed in the studies that offered extended (≥4 months) programmes with moderate-to-vigorous activity levels. Importantly, supervised intradialytic exercise training is apparently safe, as no major traumatic or cardiovascular adverse events were reported [10]. A smaller body of evidence is available in patients on peritoneal dialysis, yet without suggesting lower efficacy or safety as compared with patients on HD. In general, peritoneal dialysis patients should perform moderate-to-vigorous exercise without dialysis fluid within the abdominal cavity, while less vigorous activity (i.e. walking) can also be performed with dialysis fluid present [12]. A home-based, low-intensity exercise programme may safely improve physical performance and quality of life in patients on either HD or peritoneal dialysis [13]. No evidence exists to show that exercise training impacts on hard cardiovascular outcomes in dialysis patients [10], only retrospective, observational data, which suggest that HD patients who increase their level of physical activity may have a lower risk of all-cause death than patients who reduce it [14].

In kidney transplant patients without major comorbidities, an aerobic, resistance or combined exercise training improves cardiorespiratory fitness, aerobic capacity, muscle performance and strength. In overweight or obese patients, body weight may improve, and in hypertensive patients, arterial blood pressure decreases. In all patients, exercise intervention improves several domains of quality of life and no adverse short-term effects are reported [15]. Low muscle strength has been associated with all-cause death in renal transplant recipients; however, no direct evidence for a relationship between exercise training and hard outcomes in these patients is available [16].

EXERCISE PRESCRIPTION DURING CKD

A patient-centred approach should be used in the prescription of exercise in CKD, taking into account disease stage and patients’ goals, and tailoring exercise schedules according to individual needs and ability. A special effort should be devoted to identify and overcome patients’ barriers to exercise, especially in those with end-stage kidney disease (ESKD) on HD.

A thorough preliminary evaluation of comorbidities, pharmacologic treatments and actual physical capacity is mandatory [17–19]. As CKD patients have a high or very high cardiovascular risk, a symptom-limited stress test needs to precede participation in exercise training involving vigorous activity [18]. Stable cardiovascular disease does not preclude a rehabilitation programme, whereas unstable angina, arrhythmias or decompensated heart failure are contraindications to starting a structured exercise programme [18].

Exercise prescription in all CKD patients should be performed ideally with a multidisciplinary team-based approach involving the referring nephrologist together with other healthcare professionals such as physiotherapists and exercise physiologists. Aerobic training includes walking, cycling or cross-training with specific machines at gym facilities, while resistance training encompasses several types of exercise with weights or elastic bands. Specifically, in non-dialysis CKD, moderate-to-vigorous jogging, swimming or rowing and resistance exercises with free weights or machines can be suggested; in HD patients, recumbent stationary cycling and exercise with light weights and elastic bands can be implemented during the intradialytic period with special care taken to avoid using the fistula arm and to perform the exercise routine during the first 2 h of the dialysis session. In transplanted patients, the most common interventions are aerobic or resistance or combined exercise programmes comprising 20–60 min sessions, with two to three times per week repetition.

All fit patients should follow the recommendation for the general population. Patients who cannot tolerate the minimum recommended amount of physical activity because of health conditions should be as physically active as their conditions allow. Moving more and sitting less will benefit everyone, and also the most sedentary patients will benefit from even small increases in aerobic and muscle-strengthening physical activity. In any case, the need for a gradual increase in the level of aerobic and resistance exercise should be stressed, with a final goal of attaining the target for healthy individuals (150 min/week, in three 30-min sessions of aerobic training at moderate-to-high rating of perceived effort on a Borg scale and two 30-min resistance training at 60–70%, one-repetition maximum for a given exercise) using a FITT (Frequency, Intensity, Time and Type of exercise) approach [17].

CONCLUSIONS

Nephrology care providers should facilitate awareness and implementation of physical activity (Table 1) and development of specific exercise programmes (Figure 1) across all CKD stages as a basic intervention within the comprehensive treatment of renal disease. Patients should be monitored during the exercise programme.

FIGURE 1

Exercise prescription according to conservative, dialysis and transplant stages of CKD. Suggested target levels of exercise [signified as a percentage of target exercise levels for healthy subjects (left y-axis) or as a rating of perceived exertion on the Borg scale (right y-axis)] for renal patients in non-dialysis CKD, dialysis and kidney transplant (KT) care. M = moderate (3.0–5.9 METs) and V = vVigorous (6.0–8.9 METs) are suggested training intensity according to METs [i.e. M: cycling (slow pace), walking (5 and 6 km/h), swimming; V: jogging, cycling (climbing), rowing, trekking and tennis]. In CKD, dialysis and KT, target intensity levels of aerobic training are 60–75%, around 60% and 50–80% peak oxygen consumption or 40–90% maximum heart rate (only KT), as assessed by stress testing, or rating of perceived exertion (RPE) 15–17, 12–14 and 15–17 on the Borg scale, respectively. Target duration and frequency of training should be 30 min/day for 3–5 days/week for all patients. Target amount of resistance training are three sets of 10–15, two to three sets of 8–15 and three sets of 10–15 repetitions of flexion/extension motion of different muscle groups, respectively, at 70%, 50–60% and 70–80% of one-repetition maximum, respectively.

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CONFLICT OF INTEREST STATEMENT

None declared by all authors.

REFERENCES