Daily physical exercise training (daily PET): Just do it!

According to the World Health Organization, physical activity is defined as any movement of the body resulting in energy expenditure. Physical exercise is a form of planned and structured physical activity with the aim to improve or maintain physical fitness. Both are considered to be beneficial for health and well-being. ¹ However, physical inactivity and muscle wasting are major concerns for individuals on dialysis. The typical lifestyle associated with kidney disease, combined with the physical demands of dialysis treatments, can worsen comorbidities, such as cardiovascular disease, obesity, and frailty. In addition, dialysis itself often increases fatigue and physical deconditioning, leaving patients with limited ability to participate in daily life. In this context, physical exercise may offer one of the most effective non-pharmacologic interventions to address these challenges.

Most exercise interventions have been conducted within dialysis units during hemodialysis. However, since peritoneal dialysis (PD) is a home-based therapy, it is ideal for exercise to be done at home. Despite this, studies examining the effects of home-based exercise for individuals receiving PD are limited. Recently, Chen et al. conducted a systematic review and meta-analysis to assess the impact of home-based exercise for people with kidney failure undergoing dialysis. ² They showed that a 3- to 6-month period of home-based exercise significantly improved walking speed as measured by the 6-min walking test (p < 0.001). Additionally, this study showed that home-based exercise significantly enhanced patients’ exercise capacity, as measured by peak O₂ consumption (p = 0.007).

It should be noted that only 6 of the 12 identified randomized controlled trials (RCTs) (partially) included patients receiving PD. Furthermore, studies had a small sample size. Finally, none of the studies used residual kidney function (RKF) as an outcome measure, a key determinant of long-term outcomes in persons receiving PD.

In this issue of Peritoneal Dialysis International, Uchiyama and colleagues present the results of a feasibility study examining the impact of home-based exercise on RKF in individuals beginning PD treatment. ³ Participants from three centers were randomly assigned to either an exercise intervention group or a control group. The exercise program consisted of aerobic exercise three times a week and resistance training twice a week for 24 weeks under the guidance of a rehabilitation doctor and physiotherapist. The control group received no specific intervention. The primary outcome was the preservation of RKF, measured by residual glomerular filtration rate (rGFR). Secondary outcomes included urinary protein levels, distance covered in the incremental shuttle walking test, and glycated hemoglobin (HbA1c) percentages.

A total of 63 participants were randomly assigned to either the exercise (n = 31) or control (n = 32) group. Of these, 25 participants in the exercise group (mean age = 65.8 ± 14.6 years, 88% male) and 30 participants in the control group (mean age = 68.4 ± 11.1 years, 83% male) were included in the final analysis. Groups were comparable regarding baseline characteristics.

They found that, using adjusted linear mixed models, rGFR in the exercise group changed from 6.98 ± 0.61 mL/min at baseline to 6.17 ± 0.62 mL/min at 24 weeks. In contrast, the control group showed a change from 6.71 ± 0.57 mL/min to 5.25 ± 0.59 mL/min after 24 weeks. However, the difference in rGFR between the two groups at 24 weeks was not statistically significant (0.65; 95% CI: −1.15, 2.45; p = 0.48). No significant differences were observed between the groups in either the continuous ambulatory peritoneal dialysis (CAPD) or automated peritoneal dialysis (APD) groups.

There was a trend toward improvement in mean urinary protein level (in grams per day) in the exercise group at 24 weeks (−1.07; 95% CI: −2.29, 0.15; p = 0.09) compared to the control group. The results of the incremental shuttle walking test did not differ significantly between the groups. However, the mean HbA1c showed a significant decrease in the exercise group compared to the control group (−0.57; 95% CI: −0.97, −0.18; p = 0.005).

RCTs investigating the beneficial effects of exercise in individuals receiving PD are limited. Furthermore, preserving RKF is a key outcome, as it is associated with improved health-related quality of life, reduced morbidity, and better survival. It should be noted that this study was conducted during the COVID-19 pandemic, which posed several challenges. Given these difficulties, Uchiyama et al. deserve praise for their efforts in completing the trial, which provides valuable insights for the PD community.

Nevertheless, some limitations have to be acknowledged. First, sample size was small and follow-up period relatively short. Furthermore, PD prescription and blood pressure treatment were left to the discretion of the centers, which resulted in a significantly higher systolic blood pressure in the control group compared to the exercise group at 24 weeks (152.2 ± 21.4 mmHg vs. 136.1 ± 22.4 mmHg; p = 0.03). Finally, no information about ultrafiltration volume and peritoneal protein loss was available. This might have impacted RKF and level of proteinuria. However, it is unclear whether remnant proteinuria in dialysis patients is an important endpoint in dialysis trials.

Although no significant differences were observed in the preservation of RKF between the exercise and control groups, the exercise group did show a trend toward reduced urinary protein levels and significant reductions in HbA1c compared to the control group. These findings suggest that while home-based exercise may not dramatically alter RKF in the short term, it may mitigate some of the metabolic effects associated with PD and potentially contribute to the preservation of RKF over the long term. This underscores the importance of incorporating exercise programs early in PD care.

Although many persons receiving PD recognize the benefits of exercise for both their physical and mental health, and perhaps these endpoints may be more relevant ones in clinical trials, there are still significant gaps in knowledge about how to safely engage in exercise. MacRae et al. conducted a survey to examine differences in perceptions and exercise practices among individuals receiving PD. ⁴ Common areas of confusion included whether exercise should be performed with or without intraperitoneal PD fluid, the maximum weight a patient should lift, and regarding the safety of swimming.

Harasemiw et al. conducted a qualitative content analysis from an international survey to explore clinicians’ perspective regarding exercise programming for persons receiving PD. ⁵ They concluded that exercise prescriptions should be individualized and the program accessible for patients of different ages, comorbidities, and physical abilities. In addition, four key priorities were identified: promoting specific exercises, addressing barriers to exercise, defining key components of exercise prescriptions, and focusing on patient-relevant outcomes.

These surveys underscore that more education for both patients and health care providers is crucial to reduce variability in recommendations to ensure that persons receiving PD can safely incorporate exercise into their care routines. To guide widespread implementation and acceptance of exercise programming, the International Society for Peritoneal Dialysis (ISPD), in collaboration with the Global Renal Exercise Network (GREX), has recently published a set of clinical practice recommendations based on the available evidence. ⁶ Additionally, it may be valuable to conduct safety studies themselves with safety as a specific endpoint, to further ensure that physical exercise is both effective and secure for individuals receiving PD.

Nevertheless, further well-designed RCTs with larger sample sizes and longer follow-up are needed to explore the impact of physical exercise on patients’ physical and mental health and clinical outcomes and to provide the field with evidence-based recommendations. Until then, we should emphasize the benefits of exercise.

To take the first step, we propose a daily physical exercise training (daily PET) program for everyone receiving PD. The daily PET can be simple, light, and tailored to each patient's preference. Although physical exercise can be performed at every moment of the day, it might help patients if they incorporate the daily PET into their daily PD routine. For example, by lifting hand weights to train arm muscles during each manual PD exchange, while waiting during the inflow and outflow of PD fluid. Or by using a resistance band to train arm, leg, and core muscles at the beginning and end of every automated PD treatment. We believe that a daily PET can improve patient's physical condition and empower them to take control of their well-being, ultimately enhancing their health-related quality of life.

With this editorial, we urge the PD community to embrace and implement daily “PET” as an essential part of PD treatment, and we would like to reinforce our call with the slogan of a well-known sports brand: Just Do It!