Introduction

Chronic kidney disease (CKD) is a prevalent global health issue, affecting approximately 850 million individuals [1]. CKD significantly contributes to the development of cardiovascular diseases, hypertension, anemia, and bone disorders, while also increasing the risks of mortality [2]. Although many patients with CKD remain in stages 1–4 and do not require dialysis or renal replacement therapy, they often experience reduced physical function and lower levels of physical activity, which are associated with a substantial symptom burden [3].

Reduced physical activity in CKD patients can exacerbate muscle loss [4], increase cardiovascular risk [5], and worsen inflammation and oxidative stress [6]. It may also lead to higher insulin resistance [7] and contribute to poorer mental health [4], further lowering quality of life [5]. Regular physical activity is essential for mitigating these risks and slowing CKD progression.

Despite these challenges, engaging in regular physical activity such as aerobic and resistance activities offers significant benefits for CKD patients [4,7]. Prior research has shown that physical activity provides multiple advantages for patients with CKD Additionally, physical activity has been shown to reduce blood pressure [8,9], improve health-related quality of life (QoL) [10,11], and increase exercise tolerance by boosting maximal oxygen uptake [6,10]. Physical activity may also help reduce certain inflammatory markers [12,13] and has potential cognitive benefits, though more research is needed in this area.

Although the recognized benefits of physical activity, it remains a significant challenge for patients with CKD. A study conducted on 5,656 patients across all CKD stages in England found that physical inactivity worsens as the disease progresses. In CKD Stages 1 and 2, 66% of patients were inactive, and this figure increased significantly to 83% in Stage 3. By Stages 4 and 5, 89% of patients were physically inactive, highlighting the growing prevalence of inactivity as kidney function declines [14]. Similarly, a study encompassing all stages of CKD in South Korea reported that out of 36,732 participants, approximately 42% were classified as physically inactive, based on the criteria of engaging in at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity physical activity per week [15].

Several studies have highlighted a range of factors that impact physical activity among individuals with CKD. These factors can be grouped into five primary categories. Demographic factors, such as age [14,16], sex [14], education level [14,17], and employment status [17,18], play a crucial role in influencing physical activity. Physiological factors are also significant, including glomerular filtration rate (GFR) [19,20], hemoglobin (Hb) [14], calcium levels [16], insulin sensitivity [21], body mass index (BMI) [21]. Additionally, physical health factors, including physical functioning, bodily pain, general health [22], as well as the presence of comorbidities [14,17], direct impact patients’ ability to engage in physical activity. Lifestyle factors, particularly smoking [18] and drug use [16], also influence overall physical activity levels in CKD patients. Lastly, psychosocial factors, such as mental health [22], social functioning [22], and self-efficacy [14,18], are critical for understanding the motivations and barriers to physical activity in this population. Although factors influencing physical activity in CKD patients have been identified, there is a lack of studies that accurately assess physical activity levels. Therefore, this study aims to evaluate the physical activity levels in CKD patients and explore associated health outcomes.. Recognizing the impact of physical activity on CKD management is critical for developing effective interventions To address this, we conducted a cross-sectional study among community-dwelling CKD patients in South Korea.

Methods

Participants

This study analyzed data from the 6th and 7th cycles of the Korea National Health and Nutrition Examination Survey (2016–2020). Among 39,728 participants, 31,811 individuals aged 19 years or older were identified, and 844 participants with an eGFR below 60 mL/min/1.73 m² were selected. After excluding cases with missing data, a final sample of 690 participants was included (Fig 1).

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Fig 1. Flow chart for study population.

eGFR = estimated Glomerular Filtration Rate; KNHANES = Korea National Health and Nutrition Examination Survey.

https://doi.org/10.1371/journal.pone.0332604.g001

Results

General characteristics and differences in eGFR according to general characteristics

The mean age of participants was 71.0 years, the majority aged ≥60 years. Slightly more than half were male, and most had an education level of middle school or below, were unemployed, and had a BMI ≥ 25 kg/m². Most participants were non-smokers, reported no activity limitations, and were receiving CKD treatment. eGFR differed significantly by age (p < .001), BMI (p < .001), and self-rated health (p < .001) (Table 1).

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Table 1. General characteristics of individuals with CKD.

https://doi.org/10.1371/journal.pone.0332604.t001

The bivariate association of each variable and physical activity in CKD

Physical activity levels in CKD patients varied significantly by sex, education, employment, treatment status, and activity limitations (Table 2).

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Table 2. The bivariate association of each variable and physical in CKD.

https://doi.org/10.1371/journal.pone.0332604.t002

Men were more likely to achieve recommended activity levels than women (about 32% vs. 19%), and the proportion increased with education, reaching nearly 38% in those with a college degree. Employed individuals were more active (about 32%) than those not working (23%). Patients receiving treatment and those with activity limitations showed lower adherence (about 25% and 17%, respectively) compared to their counterparts.

The associated factors of physical activity in CKD

As shown in Table 3, unadjusted analyses indicated that male sex, higher education, employment, absence of treatment, and no activity limitations were associated with a higher likelihood of meeting physical activity recommendations.

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Table 3. Factors associated with physical activity in individuals with CKD.

https://doi.org/10.1371/journal.pone.0332604.t003

After adjusting for sociodemographic and clinical variables, four factors remained statistically significant. Men were more than twice as likely as women to achieve sufficient physical activity (OR = 2.56, 95% CI = 1.39–4.70, p = .003). Current smokers had substantially lower odds of being active compared with non-smokers (OR = 0.41, 95% CI = 0.18–0.93, p = .034). Participants reporting activity limitations were less likely to meet activity recommendations (OR = 0.52, 95% CI = 0.28–0.95, p = .033). Furthermore, individuals with moderate CKD (eGFR 30–59.9 mL/min/1.73m²) had significantly lower odds of sufficient physical activity than those with advanced CKD (<15 mL/min/1.73m²) (OR = 0.26, 95% CI = 0.07–0.98, p = .047). Education level, employment, and treatment status were not significant in the adjusted model. The eGFR 15–29.9 (mL/min/1.73m²) group showed a non-significant trend toward lower activity (OR = 0.22, p = .057).

Discussion

This study analyzes the characteristics of individuals with CKD across eGFR stages (Table 1) and finds that most participants were aged 60 or older, with the majority classified in Stage 3. CKD is a chronic condition, with many patients remaining in stages 1–4 without requiring dialysis or renal replacement therapy. Although the number of participants in Stage 5 was small, older adults (≥60 years) represented the majority, emphasizes the prevalence of advanced CKD among the older people. These findings are consistent with previous studies. Wilkinson et al. [14] reported that the median age increased with CKD progression, from 72 years in Stage 3–73 years in Stages 4 and 5, with over 70% of patients aged above 61 in these stages. Similarly, Hara et al. [19] found that the mean age of participants across Stages 3, 4, and 5 was approximately 61 years, with more than 70% being in their 60s across these stages. These results highlight the significant impact of aging on CKD progression.

The distribution of BMI categories differed significantly across CKD stages. A higher BMI (≥25 kg/m²) was prevalent in Stage 3 (45.0%) and Stage 4 (47.3%) but decreased markedly in Stage 5 (15.5%). In contrast, underweight patients (BMI < 18.5 kg/m²) were rare in G3 (2.0%) and G4 (1.8%) but increased significantly in G5 (23.8%). Similarly, Navaneethan et al. [27] found that the number of patients with higher BMI decreases, whereas those with lower BMI increase as CKD stages advance, indicating potential associations with declining renal function and malnutrition.

As CKD progresses, patients tend to rate their health more poorly. A higher proportion of participants in earlier stages (G3) reported good self-rated health, while those in advanced stages (G4 and G5) were more likely to report poor health. This is consistent with findings by Lee et al. [28] and Ko et al. [29], both of which highlighted the link between advanced CKD stages and lower self-rated health. These findings suggest that worsening health perceptions in later CKD stages may reflect functional decline, highlighting the need to address both physical and psychological well-being in CKD care.

In this study, only 20.5% of patients met the recommended physical activity levels, while 79.5% engaged in insufficient activity (Table 2), whereas 44.9% of the general adult population in South Korea were reported to meet the recommended physical activity levels [24]. Consistent with the findings of this study, Chu et al. [20] reported that 78.5% of participants had low physical activity levels. Notably, in their study, only 44.6% of the non- CKD comparison group demonstrated low physical activity levels. Wilkinson et al. [14] reported that 89–94% of participants in CKD stages 4–5 had low physical activity levels, whereas 35–43% of adults in the general population were classified as ‘inactive’. According to previous studies, patients with CKD generally exhibit lower rates of physical activity compared to the general population, highlighting the importance of identifying factors associated with this gap. In addition, male, non-smoking, fewer activity limitations, and lower eGFR were significant factors associated with higher physical activity levels in patients with CKD (Table 3).

Sex is a strong predictor of physical activity in CKD. Men were more likely than women to meet sufficient physical activity criteria. Peng, Han, and Xu [30] also found gender differences in physical activity, with a higher proportion of men being ‘Extremely Highly Active’ at 55.5%, compared to 44.5% in women. Similarly, being female was associated with a higher likelihood of low physical activity, with women being over four times more likely (OR = 4.05) according to Bahadi et al. [16] and nearly twice as likely (OR = 1.668) according to Wilkinson et al. [14]. This difference can be explained by several reasons. Men benefit from elevated testosterone levels, which support cardiovascular health [31]. In contrast, women, particularly those who are middle-aged or postmenopausal, face physiological changes such as declining estrogen levels, impaired autonomic function, and decreased cardiac relaxation, which contribute to difficulties in maintaining regular exercise [30]. Furthermore, societal influences play a significant role, as traditional gender roles encourage men to be more active, while women face cultural barriers that limit their participation [32]. These societal expectations contribute to a higher self-efficacy and greater awareness among men, while women, lacking social support, often experience lower participation [33]. Despite these gender differences, time constraints remain a shared challenge for both men and women, limiting their ability to engage in physical activity [34].

Current smoking status is significantly associated with reduced physical activity levels among patients with CKD in this study. Current smoking reduced the likelihood of physical activity participation by 59% in our study (Table 3), consistent with the 12% reduction reported by Chiang et al. [11]. However, there were few studies on the direct relationship between smoking and low physical activity in patients with CKD. Based on prior research on the health effects of smoking in patients with CKD, it is possible to understand how smoking may influence their physical activity, as follows. Smoking has been shown to induce oxidative stress and inflammation, contributing to impaired muscle function and increased fatigue in patients with CKD [15]. Additionally, the associated decline in pulmonary function and exercise-induced dyspnea further exacerbates limitations in physical activity [35]. Smoking, while used for stress relief, can lead to mental health issues like anxiety and depression, reducing motivation to start and increasing the likelihood of discontinuing physical activity due to physical discomfort [36,37].

The present study found that activity limitation emerged as a key factor influencing physical activity, although it has been infrequently explored in previous research. Variables similar to activity limitation as predictors of physical activity have been used in other studies, including the quality-of-life subdomains ‘physical function’ or ‘role physical’ [17,22,38,39]. Activity limitation in CKD patients is closely associated with chronic musculoskeletal issues, fatigue, and metabolic abnormalities, all of which hinder PA [21,40]. Particularly, dialysis directly exacerbates this limitation by inducing fatigue and muscle weakness, while promoting a sedentary lifestyle due to the extended and repetitive nature of treatment sessions [17,22,39]. The findings suggest that dialysis is a variable that can directly or indirectly influence physical activity levels in patients undergoing hemodialysis.

This study observed an inverse association between eGFR and physical activity, with lower eGFR levels linked to higher activity. This finding contrasts with prior studies that generally reported a positive relationship between kidney function and physical activity [22,41,42]. According to prior research, the influence of eGFR on physical activity is generally explained by the following: higher kidney function is linked to increased physical activity, likely due to reduced inflammation and improved physical capacity [19,43]. In contrast, lower kidney function is associated with greater symptom burden, including fatigue and muscle weakness, which are factors known to reduce physical activity levels [14]. Direct cross-sectional evidence showing higher physical activity among individuals with lower eGFR is limited. However, several observational and programmatic studies indicate that exercise counseling, structured rehabilitation, and group-based interventions can increase activity among patients with advanced CKD. These findings suggest that some patients with lower eGFR in community settings may have increased activity levels in response to clinical advice or participation in local programs [44–46], which may help explain the observed inverse association in our study. Several factors could underlie this unexpected association. Survivor bias may have affected the findings if patients with severe illness and low activity were underrepresented. Self-reported measures could also have introduced misclassification. In addition, patients with lower eGFR levels may have been more likely to adopt healthier behaviors, including physical activity, as part of disease management or in response to clinical advice. Given these considerations, the observed inverse association should be interpreted with caution. Further longitudinal and interventional studies with diverse CKD populations are needed to confirm and better understand this relationship.

Although education, employment, and treatment were significantly associated with physical activity in the unadjusted analysis, they lost statistical significance after adjustment (Table 3), whereas they remained significantly associated with physical activity in the bivariate analysis (Table 2).

Higher education levels were positively associated with physical activity participation in this study, with a higher percentage of patients with college or higher education (38.1%) engaging in physical activity compared to those with lower education levels (21.3%). This is consistent with findings from Peng, Han, and Xu [30]. Lower education levels are often linked to higher physical inactivity, due to limited health awareness and lack of exercise guidance in healthcare settings [16,46].

This study found that the employed (32.2%) were more likely to meet the recommended physical activity levels than the unemployed (22.6%). However, other studies, such as those by Chiang et al. [11] and da Costa Rosa et al. [39], found no significant differences in physical activity based on occupation. While employment alone may not guarantee higher activity levels, job type plays an important role [19]. Sedentary jobs may limit physical activity, while physically demanding jobs may encourage more activity [19,39]. Further research is needed to explore these varying results and the role of different job types in physical activity.

Patients with CKD not receiving treatment were more likely to engage in sufficient physical activity, with 38.5% of them compared to 24.5% of those undergoing treatment. The findings of this study indicate that patients with CKD undergoing treatment encounter multiple barriers to engaging in physical activity, such as demanding therapy schedules, inadequate guidance from healthcare professionals, insufficient exercise counseling, and feelings of powerlessness [18,40]. So, effective communication, information sharing, and the attitudes of healthcare professionals are crucial in promoting physical activity among CKD patients receiving treatment [3,18]. Although treatment status was associated with physical activity in the univariate analysis, this association was no longer significant after adjustment. The use of the self-reported GPAQ may have led to overestimation of physical activity, which should be considered when interpreting the results.

This study revealed that female gender, current smoking, activity limitations, and higher eGFR were associated with lower physical activity in CKD patients. Tailoring physical activity interventions is crucial, considering the patient’s clinical condition, physical performance, and demographic factors [18]. A personalized exercise plan should encourage daily activities, particularly for patients with multiple comorbidities, and adjust treatment schedules and medications to manage fatigue, pain, and emotional distress [40].

Conclusions

In patients with CKD, female gender, current smoking, activity restrictions, and high eGFR were associated with decreased physical activity. Since reduced physical activity in CKD patients negatively affects quality of life by accelerating muscle loss and increasing cardiovascular risk, individualized physical activity strategies should be implemented based on clinical status, physical function, and demographic characteristics. These findings highlight the need for tailored interventions and counseling in both public health programs and clinical practice to promote physical activity among vulnerable subgroups of the CKD population.

Limitations

This study has several limitations. First, the small sample size, particularly the limited number of patients with eGFR < 15, may have introduced sampling errors and limit the generalizability of the findings to the broader CKD population. Second, the use of secondary data from the Korean National Health and Nutrition Examination Survey restricted the inclusion of key variables, such as external motivators for physical activity (e.g., medical advice), as well as dialysis status. Because dialysis treatment is known to substantially impact physical activity levels among CKD patients, the absence of this information may have introduced confounding and affected the interpretation of associated factors. In addition, dialysis status was not identified in the dataset, as it is known to significantly influence physical activity in CKD patients and may have affected the interpretation of related factors. Third, physical activity was measured using self-reported data, specifically the Global Physical Activity Questionnaire (GPAQ). Self-reported measures are subject to recall and social desirability biases, which may lead to misclassification of activity levels, thereby influencing the accuracy and validity of the findings. These limitations underscore the need for future research utilizing objective physical activity measurements and inclusion of dialysis status to improve data accuracy and interpretability.

Despite the study’s limitations, this research provides a comprehensive analysis of physical activity among Korean CKD patients using a nationally representative dataset. By examining patients across different eGFR stages, it highlights variations in physical activity and associated factors, addressing gaps in prior research. Furthermore, it identifies modifiable factors, such as smoking and activity limitations, offering practical insights for targeted interventions to improve patient outcomes.

Supporting information