Pedometer-assessed physical activity in children and young adults with CKD

Patient-Centered Quality Measures for Dialysis Care: A Report of a Kidney Disease Outcomes Quality Initiative (KDOQI) Scientific Workshop Sponsored by the National Kidney Foundation

Providing high-quality patient-centered care is the central mission of dialysis facilities. Assessing quality and patient-centeredness of dialysis care is necessary for continuous dialysis facility improvement. Based predominantly on readily measured items, current quality measures in dialysis care emphasize biochemical and utilization outcomes, with very few patient-reported items. Additionally, current metrics often do not account for patient preferences and may compromise patient-centered care by limiting the ability of providers to individualize care targets, such as dialysis adequacy, based on patient priorities rather than a fixed numerical target. Developing, implementing, and maintaining a quality program using readily quantifiable data while also allowing for individualization of care targets that emphasize the goals of patients and their care partners provided the motivation for a September 2022 Kidney Disease Outcomes Quality Initiative (KDOQI) Workshop on Patient-Centered Quality Measures for Dialysis Care. Workshop participants focused on 4 questions: (1) What are the outcomes that are most important to patients and their care partners? (2) How can social determinants of health be accounted for in quality measures? (3) How can individualized care be effectively addressed in population-level quality programs? (4) What are the optimal means for collecting valid and robust patient-reported outcome data? Workshop participants identified numerous gaps within the current quality system and favored a conceptually broader, but not larger, quality system that stresses highly meaningful and adaptive measures that incorporate patient-centered principles, individual life goals, and social risk factors. Workshop participants also identified a need for new, low-burden tools to assess patient goals and priorities.

Comparison of effectiveness of Nintendo Wii-based exergaming and home-based fun video exercises in pediatric patients with chronic kidney disease

Functional capacity and quality of life (QoL) are reduced in children and adults with chronic kidney disease (CKD). Aerobic, strengthening exercises, and exergames are reported as effective in the treatment of symptoms associated with CKD. Unlike adult patients, there are insufficient studies investigating the effects of exercise on disease-related symptoms in pediatric CKD. This study aimed to compare the effects of Nintendo Wii-based exergaming and home-based fun video exercises on functional capacity, muscle strength, physical activity (PA), depression, fatigue, and QoL in pediatric patients with CKD. Twenty-three pediatric patients with CKD were included in the study and randomized to group I (Nintendo Wii Fit) and group II (home-based fun video exercises). Patients in both groups underwent exercise programs twice per week for 6 weeks. Functional capacity, muscle strength, PA, QoL, fatigue, and depression of the patients were evaluated before and after the treatments. Sixteen patients completed the study. After treatment, significant differences were observed in both groups on 6MWT, muscle strength, average daily steps, PedsQoL Child Self-Report PHSS, and the Visual Fatigue Scale. Left knee flexor muscle strength and average step counts were found to be superior in group I. Both exergaming and home-based fun video exercises provide positive effects on functional capacity, muscle strength, fatigue, PA, depression, and QoL in pediatric patients with CKD. We think that these exercise methods can help to protect physical and mental health of patients and should be included in treatment from the early stages of the disease.

An ethical analysis of obesity as a contraindication of pediatric kidney transplant candidacy

The inclusion of body mass index (BMI) as a criterion for determining kidney transplant candidacy in children raises clinical and ethical challenges. Childhood obesity is on the rise and common among children with kidney failure. In addition, obesity is reported as an independent risk factor for the development of CKD and kidney failure. Resultantly, more children with obesity are anticipated to need kidney transplants. Most transplant centers around the world use high BMI as a relative or absolute contraindication for kidney transplant. However, use of obesity as a relative or absolute contraindication for pediatric kidney transplant is controversial. Empirical data demonstrating poorer outcomes following kidney transplant in obese pediatric patients are limited. In addition, pediatric obesity is distributed inequitably among groups. Unlike adults, most children lack independent agency to choose their food sources and exercise opportunities; they are dependent on their families for these choices. In this paper, we define childhood obesity and review (1) the association and impact of obesity on kidney disease and kidney transplant, (2) existing adult guidelines and rationale for using high BMI as a criterion for kidney transplant, (3) the prevalence of childhood obesity among children with kidney failure, and (4) the existing literature on obesity and pediatric kidney transplant outcomes. We then discuss ethical considerations related to the use of obesity as a criterion for kidney transplant.

Preliminary Evaluation of Sedentary Lifestyle in Italian Children after Solid Transplant: What Role Could Physical Activity Play in Health? It Is Time to Move

BACKGROUND

Advances in the medical-surgical field have significantly increased survival after solid organ transplantation in the pediatric population. However, these patients are predisposed to the development of long-term complications (e.g., cardiovascular disease). The therapeutic role of physical activity (PA) to counteract these complications is well known. The purpose of the study was to investigate the level of PA in a pediatric population after solid organ transplantation.

METHODS

In the first 4 weeks at the beginning of the school year, the Physical Activity Questionnaire for Older Children and Adolescents was administered to young patients who had previously undergone solid transplants at our institute.

RESULTS

Questionnaires of 49 patients (57.1% female, mean age 13.2 ± 3.5 years) were analyzed and 32.7% of subjects did not perform any exercise during school physical education classes. Only 24% practiced a moderate quantity of exercise in the previous week (2-3 times/week) and 72% engaged in sedentary behaviors during weekends.

CONCLUSIONS

Preliminary data confirmed that young recipients are still far from meeting the minimum indications of the World Health Organization on PA and sedentary behavior. It will be necessary to increase their involvement in PA programs in order not only to increase their life expectancy but also to improve their quality of life.

Physical activity and the 'pediatric inactivity triad' in children living with chronic kidney disease: a narrative review

The ‘paediatric inactivity triad’ (PIT) framework consists of three complex inter-related conditions that influence physical inactivity and related health risks. In those living with chronic kidney disease (CKD), a multi-factorial milieu of components likely confound the PIT elements, resulting in a cycle of decreased physical functioning and reduced physical activity. In this review, we explore and summarize previous research on each of the three principal PIT components (exercise deficit disorder, dynapenia, and physical illiteracy) in the pediatric CKD population. We found those living with CKD are significantly physically inactive compared to their peers. Physical inactivity occurs early in the disease process and progressively gets worse as disease burden increases. Although physical activity appears to increase post-transplantation, it remains lower compared to healthy controls. There is limited evidence on interventions to increase physical activity behaviour in this population, and those that have attempted have had negligible effects. Studies reported profound reductions in muscle strength, physical performance, and cardiorespiratory fitness. A small number of exercise-based interventions have shown favourable improvements in physical function and cardiorespiratory fitness, although small sample sizes and methodological issues preclude the generalization of findings. Physical activity must be adapted and individualized to the needs and goals of the children, particularly those with acute and chronic medical needs as is the case in CKD, and further work is needed to define optimal interventions across the life course in this population if we aim to prevent physical activity declining further.

Relation of Anxiety, Depression, and Behavioral Problems With Time Allocated to Television, Computer, and Smartphone in Children Receiving Renal Replacement Therapy

OBJECTIVES

Children and adolescents with chronic diseases have more screen exposure time compared with their healthy peers. In this study, we investigated screen exposure time of children who received renal replacement therapy, which included kidney transplant and dialysis treatment, versus a healthy control group.

MATERIALS AND METHODS

Our study included 55 children and adolescents between the ages of 8 and 18 years. Although 28 participants did not have any chronic disease, 27 had chronic diseases and received renal replacement therapy. Among these patients, 17 had kidney transplant and 10 were receiving dialysis. A sociodemographic information form and the Conners Short-Form Parent Rating Scale were given to parents. Pediatric and adolescent patients completed the Children's Depression Inventory and Spielberger State-Trait Anxiety Scale-2. We analyzed differences between the groups with and without renal replacement therapy and examined relations between continuous variables.

RESULTS

Duration of television screen time was significantly higher in children and adolescents receiving renal replacement therapy. Patients in the renal replacement therapy group showed a positive correlation between the Conners Short-Form Parent Rating Scale anxiety subscores and duration of smartphone use. In the kidney transplant recipient group, smartphone and computer durations were positively correlated and television duration was negatively correlated with the Conners Short-Form Parent Rating Scale behavioral problems subscores.

CONCLUSIONS

Children on renal replacement therapy may be at risk in terms of excessive television exposure. Children who are on dialysis and have had a kidney transplant may be more prone to the negative effects of screen exposure than healthy peers who do not have chronic illnesses. These children and adolescents should be closely monitored to avoid the negative effects of excessive screen exposure.

Daily Step Counts in Patients With Chronic Kidney Disease: A Systematic Review and Meta-Analysis of Observational Studies

Background

Physical inactivity is an essential factor in the prognosis of patients with chronic kidney disease (CKD). Daily step count is a straightforward measure to assess physical activity levels. Understanding the step counts among different CKD stages is essential to change sedentary behavior.

Objectives

This systematic review and meta-analysis aimed to investigate the daily step counts in patients with CKD at a different stage.

Design

A systematic review and meta-analysis.

Data Sources

The literature search was performed in PubMed, Embase, and Web of Science from inception to November 3rd, 2021.

Review Methods

Observational studies (cross-sectional, case-control, or cohort studies) reported specific values of step counts in CKD patients by the wearable device were included. A random-effects model was used to pool the data. Subgroup analysis explored differences in outcomes by stage of CKD. Heterogeneity between studies was assessed using the χ2 test of Cochrane's Q statistic. A contour-enhanced funnel plot was conducted to investigate publication bias. Univariate and multivariate meta-regression was conducted to examine possible sources of heterogeneity.

Results

Twenty-eight articles were identified and used for quantitative analysis. The result showed that the daily step count in patients with CKD was 4642.47 (95% CI: 4274.18–5010.76), and significantly lower than the healthy population. Subgroup analysis revealed that the step counts decreased before dialysis, dropped to a freezing point at the hemodialysis phase, and increased after kidney transplantation. Meta-regression analysis showed that daily step counts were relatively higher in the Americas or younger than 60 or kidney transplant recipients.

Conclusion

The status of daily step counts in patients with CKD decreases with CKD severity and increases after kidney transplantation. Although studies have begun to focus on strategies to improve step counts in patients with CKD, future studies should focus more on step counts in pre-dialysis patients and changing their physically inactive lifestyle early to alleviate deteriorating renal function.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=291551, identifier: CRD42021291551.

Assessment and management of obesity and metabolic syndrome in children with CKD stages 2-5 on dialysis and after kidney transplantation-clinical practice recommendations from the Pediatric Renal Nutrition Taskforce

Obesity and metabolic syndrome (O&MS) due to the worldwide obesity epidemic affects children at all stages of chronic kidney disease (CKD) including dialysis and after kidney transplantation. The presence of O&MS in the pediatric CKD population may augment the already increased cardiovascular risk and contribute to the loss of kidney function. The Pediatric Renal Nutrition Taskforce (PRNT) is an international team of pediatric renal dietitians and pediatric nephrologists who develop clinical practice recommendations (CPRs) for the nutritional management of children with kidney diseases. We present CPRs for the assessment and management of O&MS in children with CKD stages 2-5, on dialysis and after kidney transplantation. We address the risk factors and diagnostic criteria for O&MS and discuss their management focusing on non-pharmacological treatment management, including diet, physical activity, and behavior modification in the context of age and CKD stage. The statements have been graded using the American Academy of Pediatrics grading matrix. Statements with a low grade or those that are opinion-based must be carefully considered and adapted to individual patient needs based on the clinical judgment of the treating physician and dietitian. Research recommendations are provided. The CPRs will be periodically audited and updated by the PRNT.

Longitudinal outcomes of body mass index in overweight and obese children with chronic kidney disease

BACKGROUND

Longitudinal changes in body mass index (BMI) among overweight and obese children with chronic kidney disease (CKD) are not well characterized. We studied longitudinal trajectories and correlates of these trajectories, as results may identify opportunities to optimize health outcomes.

METHODS

Longitudinal changes in age-sex-specific BMI z-scores over 1851 person-years of follow-up were assessed in 524 participants of the Chronic Kidney Disease in Children Study. A total of 353 participants were categorized as normal (BMI > 5th to < 85th percentile), 56 overweight (BMI ≥ 85th to 95th percentile) and 115 obese (BMI ≥ 95th percentile) based on the average of three BMI measurements during the first year of follow-up. Studied covariates included age, sex, race, CKD etiology, corticosteroid usage, household income, and maternal education.

RESULTS

In unadjusted analysis, BMI z-scores decreased over time in elevated BMI groups (overweight: mean = - 0.06 standard deviations (SD) per year, 95% CI: - 0.11, - 0.01; obese: mean = - 0.04 SD per year, 95% CI: - 0.07, - 0.01). Among obese children, only age was associated with change in BMI z-score; children < 6 years had a mean decrease of 0.19 SD during follow-up (95% CI: - 0.30, - 0.09). Socioeconomic factors were not associated with change in BMI.

CONCLUSION

Overweight and obese children with CKD demonstrated a significant annual decline in BMI, though the absolute change was modest. Among obese children, only age < 6 years was associated with significant decline in BMI. Persistence of elevated BMI in older children and adolescents with CKD underscores the need for early prevention and effective intervention.

Group-Based Care in Adults and Adolescents With Hypertension and CKD: A Feasibility Study

Rationale & Objective

Group-based care provides an opportunity to increase patient access to providers without increasing physician time and is effective in the management of chronic diseases in the general population. This model of care has not been investigated in chronic kidney disease (CKD).

Study Design

Randomized controlled trial in adults (n = 50); observational study in adolescents (n = 10).

Setting & Participants

Adults and adolescents with CKD and hypertension in the Bronx, NY.

Intervention

Group-based care (monthly sessions over 6 months) versus usual care in adults. All adolescents received group-based care and were analyzed separately.

Outcomes

Participant attendance and satisfaction with group-based care were used to evaluate intervention feasibility. The primary clinical outcome was change in mean 24-hour ambulatory blood pressure. Secondary outcomes included physical activity, medication adherence, quality of life, and sodium intake as assessed by 24-hour urinary sodium excretion and food frequency questionnaires.

Results

Among adults randomly assigned to group-based care, attendance was high (77% of participants attended ≥3 sessions) and most reported higher satisfaction. Mean 24-hour ambulatory systolic blood pressure decreased by −4.2 (95% CI, −13.3 to 5.8) mm Hg in group-based care patients compared with usual care at 6 months but this was not statistically significant. Similarly, we did not detect significant differences in health-related behaviors (such as medication adherence, sodium intake, and physical activity) or quality-of-life measures between the 2 groups. Among the adolescents, attendance was very poor; self-reported satisfaction, although high, did not change from baseline compared with the 6-month follow-up.

Limitations

Small study size, missing data.

Conclusions

Group-based care is feasible and acceptable among adults with hypertension and CKD. However, a larger trial is needed to determine the effect on blood pressure and health-related behaviors. Patient participation may limit the effectiveness of group-based care models in adolescents.

Funding

National Institutes of Health R34 DK102174.

Trial registration

https://clinicaltrials.gov/show/NCT02467894.

Endurance training during maintenance hemodialysis in pediatric and adolescent patients-theory and best practice suggestions

Patients on maintenance hemodialysis (HD) spend significant sedentary time traveling to and receiving dialysis, which leaves little time for social or sport events. Also, chronic HD patients are not physically fit, too exhausted after HD, and are not necessarily motivated to perform sports. There is increasing evidence that endurance training during HD can both increase dialysis efficacy and improve the ability of patients to participate in social life. With limited spare time, how can we motivate patients to train? Would that training improve endurance and modify leisure activity choice? Since HD patients would be a captive audience, we would suggest that endurance training during HD would be a preferred solution, if pediatric and adolescent patients could be persuaded to participate. There are few data on how training should be organized, as well as which parameters are best markers of safety and efficacy. And, most importantly, motivational aspects for performing endurance training on a regular basis clearly have to be considered. It is therefore in any case important to assess whether training improves endurance and, thus, quality of life or also quality of care parameters.

Physical fitness and health-related quality of life in pediatric renal transplant recipients: An interventional trial with active video gaming

BACKGROUND

Pediatric renal transplant recipients are at increased risk for cardiovascular diseases, one contributing factor is reduced cardiorespiratory fitness. The purpose was to evaluate cardiorespiratory fitness, motor coordination, muscle strength, daily physical activity, and health-related quality of life and to find out, if active video gaming is effective for improving these items in this patient population.

METHODS

Twenty renal transplant recipients (13.5 ± 3.4 years) and 33 matched healthy controls (13.1 ± 3.2 years) performed a spiroergometry, a motor coordination test, and a maximal handgrip strength test. Quality of life was determined with a validated questionnaire, and daily physical activity was recorded with a physical activity monitor. Thirteen patients (12.9 ± 3.4 years) participated in a 6-week home-based exergaming intervention (3×/week for 30 minutes) and repeated all tests after that.

RESULTS

The renal transplant recipients exhibited a substantial impairment compared with the controls in peak oxygen consumption (-31%, P < .001), motor competence (-44%, P < .001), daily physical activity (-33%, P = .001), and quality of life (-12%, P = .017). Handgrip strength was similar in both groups. Despite of low compliance in the intervention group, steps per hour were significantly increased after 6 weeks of exergaming (+31%, P = .043); however, all other measures remained unchanged.

CONCLUSION

Cardiorespiratory fitness, motor competence, and quality of life are reduced in pediatric renal transplant recipients. Home-based exergaming is not appropriate to improve these items, probably due to a substantially impaired motor competence. However, it provided a stimulus for an increased daily physical activity.

Physical activity and somatic symptoms among hemodialysis patients: a multi-center study in Zhejiang, China

BACKGROUND

Somatic symptoms are commonly reported by patients on maintenance hemodialysis. Based on evidence that exercise can improve psychological state among the general population, we aimed to evaluate the effects of physical activity on somatic symptoms specifically in this clinical population.

METHODS

This was a multicenter, cross-sectional study that included patients receiving hemodialysis treatment ≥3 times per week for > 3 months, aged 18 years or older, and who were willing to complete our study questionnaires and wear a pedometer; they were recruited from four hemodialysis centers in Zhejiang, China. Physical activity was quantified using pedometer data, with somatic symptoms quantified using the Symptom Checklist-90 (SCL-90). Hemodialysis information and blood laboratory tests were obtained from patients' medical record. The score on the somatic dimension of the SCL-90 (S1-score) subdivided into tertiles for analysis: ≤1.17 (Q1), 1.17-1.58 (Q2) and ≥ 1.58 (Q3). A multivariate logistic regression analysis was performed to estimate the crude and adjusted odd ratios (ORs) and 95% confidence intervals (CIs) for the S1- somatic score according to the physical activity level during the last week. For this analysis, patients were stratified in a high and low exercise group using a cutoff of 3000 MET-min/week. Model 1 was adjusted for skinfold thickness of the triceps, upper arm circumference, grip strength, 5-m walking time, and 30-s sit-to-stand test. In model 2, we further adjusted for the leukocyte count, high-sensitivity C-reactive protein level, and albumin level.

RESULTS

After screening, 320 patients were enrolled into the study group (37.50% male, average age of 58.60 ± 14.2 years and mean average number of steps per day of 3725.92 ± 2663.47). The S1-score (1.51 ± 0.39) was significantly higher for patients than for the normal reference population (P < 0.001). As the S1-score increased, the average number of steps per day decreased, both on dialysis and non-dialysis days. Total physical activity, measured by pedometry, showed the best correlation to S1 scores (r = - 0.813; P < 0.01). The OR of a high S1-score was 1.97 [95% CI, 0.63-4.08] for patients in the low physical activity group.

CONCLUSION

Higher S1 (somatic symptom) score was related to low physical activity among patients on maintenance hemodialysis.

Validity and Reliability of the International Physical Activity Questionnaire in Chinese Hemodialysis Patients: A Multicenter Study in China

Background

This study aimed to assess the reliability and validity of the International Physical Activity Questionnaire (IPAQ) in Chinese maintenance hemodialysis (MHD) patients. These findings could help increase the validity of future MHD physical activity (PA) studies, both within China and throughout the world.

Material/Methods

A multicenter prospective cohort study including 320 patients was conducted in Zhejiang, China. Patients’ PA was assessed by analyzing answers to the International Physical Activity Questionnaire Chinese version (IPAQ-C) during hemodialysis, and comparing the results with 1 week of pedometer data.

Results

The IPAQ-C had good internal reliability and test-retest stability (total ICC=0.84, 95%CI 0.76–0.89), and all PA-related variables correlated significantly between the IPAQ-C and pedometer data (r=0.280–0.561). When stratified by sex, there was a significant correlation for total PA (Spearman r=0.468 p<0.01 for women; Spearman r=0.603 p<0.01 for men) and intensity between pedometry and IPAQ-C. After adjustment for several factors, no relationships were observed among women, but significant relationships existed for men (total partial r=0.486 p<0.05, moderate PA partial r=0.358 p<0.05, walking partial r=0.465 p<0.05, vigorous PA not significant).

Conclusions

This is the first study to test the reliability and validity of the IPAQ-C in Chinese MHD patients. Overall, we conclude that IPAQ-C is a simple and reliable instrument for measuring PA in Chinese MHD patients, but possible sex and age bias should be considered when interpreting these results.

Effects of a Structured Physical Activity Program on Serum Adipokines and Markers of Inflammation and Volume Overload in Kidney Transplant Recipients

BACKGROUND Kidney transplantation (KTx) reverses most abnormalities related to chronic kidney disease (CKD), but sedentary lifestyle persists in most kidney graft recipients. Physical inactivity has been associated with altered adipokine profile and inflammation in CKD. We postulated that increased physical activity achieved through an individually-tailored program can reverse these changes. MATERIAL AND METHODS We included 25 clinically stable KTx recipients at least 12 months after transplantation and with eGFR >30 mL/min and 15 age-matched non-dialysis patients with CKD stage 3. Body composition, pattern of daily physical activity, and serum concentrations of leptin, adiponectin, NT-proBNP, and hsCRP were assessed at baseline. All patients in both groups participated in a 12-week supervised exercise program with short cell phone text reminders. All measurements were repeated after 3 months. RESULTS Active energy expenditure increased significantly during the 3 months in both the KTx and CKD patients, compared with baseline by 47% (p<0.001) and 20% (p=0.01), respectively. Time spent daily on physical activity was also increased (129±83 vs. 194±142 and 81±56 vs. 124±57 min, respectively, p<0.001). Adipose tissue mass decreased significantly in the KTx group (from 40.8±11 to 38.5±10.3 kg, p=0.01). Serum leptin decreased significantly in both KTx and CKD patients (from 11.5±7.0 to 10.0±5.6, p=0.03 and from 14.1±8.3 to 12.2±6.1 ng/mL, p=0.01, respectively). Serum adiponectin increased only in the KTx group (from 1900±953 to 2015±1133 ng/L, p=0.004). Serum CRP decreased in both groups (from 15.1±5.2 to 14.0±5.6 mg/L, p=0.01 in the KTx group and from 16.5±3.9 to 15.4±4.3 mg/L in the CKD group p=0.05). NTpro-BNP was unchanged during the study. CONCLUSIONS Increased physical activity induces beneficial effects on adipokine profile and inflammation but does not seem to affect volume overload in kidney transplant recipients and CKD patients.

The effects of intradialytic resistance training on muscle strength, psychological well-being, clinical outcomes and circulatory micro-ribonucleic acid profiles in haemodialysis patients: Protocol for a quasi-experimental study

BACKGROUND

Intradialytic resistance training (IRT) protects patients' muscle mass and functions against protein-energy wasting, malnutrition and cachexia. However, the evidence of the effects of such an intervention in haemodialysis patients is limited and not conclusive. To improve the applicability of such interventions, we need a better understanding of molecular, functional and psycho-social adaptation in dialysed patients following a physical training. Therefore, the aim of this study is to investigate the effects of IRT on lower extremity muscle functions, quality of life, and anxiety and depression, clinical outcomes and circulatory micro-ribonucleic acid (miRNA) profiles in patients on chronic haemodialysis therapy.

METHODS

We will perform a quasi-experimental study in 3 dialysis centres. Patients will be recruited via their nephrologists and will be allocated to an experimental and a control group based on the location of the patients' dialysis centre. Patients allocated to the experimental group will undergo a 12-week IRT, while the control group will remain physically inactive during dialysis. The primary outcome is the change in the maximal force produced during an isometric contraction of lower extremity muscles. Secondary outcomes regard quality of life, anxiety and depression, clinical outcomes and circulatory miRNA profiles. Patients' level of health literacy defined as the ability to get and understand health information will be also measured in the study as a potential modifier of effects.

DISCUSSION

This quasi-experimental study can add in an important way to our understanding of the effects of resistance training on dialysis patients' muscle strength, quality of life and disease-specific outcomes.

Exercise Science and Child Health: A Tale of Many Journeys

Children are the most naturally physically active human beings; reduced physical activity is a cardinal sign of childhood disease, and exercise testing provides mechanistic insights into health and disease that are often hidden when the child is at rest. The physical inactivity epidemic is leading to increased disease risk in children and, eventually, in adults in unprecedented ways. Cardiopulmonary exercise testing (CPET) biomarkers are used to assess disease severity, progress, and response to therapy across an expanding range of childhood diseases and conditions. There is mounting data that fitness in children tracks across the life span and may prove to be an early, modifiable indicator of cardiovascular disease risk later in life. Despite these factors, CPET has failed to fulfill its promise in child health research and clinical practice. A major barrier to more accurate and effective clinical use of CPET in children is that data analytics and testing protocols have failed to keep pace with enabling technologies and computing capacity. As a consequence, biomarkers of fitness and physical activity have yet to be widely incorporated into translational research and clinical practice in child health. In this review, the author re-examines some of the long-held assumptions that mold CPET in children. In particular, the author suggests that current testing strategies that rely predominantly on maximal exercise may, inadvertently, obfuscate novel and clinically useful insights that can be gleaned from more comprehensive data analytics. New pathways to discovery may emanate from the simple recognition that the physiological journey that human beings undertake in response to the challenge of exercise may be far more important than the elusive destination of maximal or peak effort.

Patients receiving dialysis do not have increased energy needs compared with healthy adults

BACKGROUND

Patients receiving dialysis are thought to have increased energy needs due to stress from the dialysis process or uraemic toxins. However, certain conditions may induce hypometabolic states potentially leading to unwanted weight gains when increased calorie intake is recommended.

OBJECTIVES

Since there is conflicting research, this study aims to assess total energy expenditure (TEE) of patients receiving dialysis through analysis of resting energy expenditure (REE) and physical activity levels.

DESIGN

Comprehensive review of the current literature on REE and physical activity levels.

METHODS

Two electronic databases (PubMed and CINAHL) were searched using keywords to find papers published within the last 10 years for physical activity studies and within the last five years for REE.

INCLUSION CRITERIA

Adults undergoing long-term dialysis treatments who do not have comorbidities that influence energy expenditure such as inflammation, hyperthyroidism or cancers. Participants were also required to ambulate without assistance.

RESULTS

Only seven of the 325 studies found were included in this review. Most studies were controlled trials with one being a prospective study. Patients receiving dialysis had rest energy expenditures comparable to healthy adults. There was not a consensus between studies as to which predictive energy equation produced accurate energy recommendations. Overall, patients receiving dialysis were significantly less active compared with healthy adults and this related to muscle mass.

CONCLUSION

Patients receiving dialysis tend to be sedentary or lightly active and do not have increased energy expenditure compared with healthy adults. Therefore, stable patients should not be prescribed increased calorie intake.

Protective effect of regular physical activity on major depressive episodes in patients with early stages of chronic kidney disease

Previous studies have demonstrated an association between physical activity (PA) and depression in diverse population. The purpose of our study is to examine if PA within the recommended level over time is associated with major depressive episode (MDE) in patients with early stages of chronic kidney disease (CKD) in Mainland China. Patients with stages 2–5 CKD not receiving dialysis were enrolled from a nephrology outpatient clinic between May 2014 and February 2016. Based on the patterns of PA over time, all patients were divided into four groups: persistently active, from inactive to active, from active to inactive, and persistently inactive. An MDE was diagnosed by using the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition)-based the Mini International Neuropsychiatric Interview. Among 150 patients, 34 had a current MDE (22.7%) and 116 did not (77.3%). After multivariable adjustment, patients being persistently active had significantly lower odds of having an MDE (odds ratio 0.102, 95% confidence interval, 0.022–0.467, p = .003) compared with those who were persistently inactive. Additionally, patients with diabetes mellitus had significantly higher odds of having an MDE (odds ratio 4.287, 95% confidence interval, 1.473–12.483, p = .008) compared with those without diabetes mellitus. Our results suggest a protective effect of regular PA on MDE in patients with early stages of CKD in Mainland China.

Influential factors on serum albumin concentration in hospitalized chronic kidney disease patients

BACKGROUND

Serum albumin concentration (SAC) is a prognostic factor that is affected by many factors such as postural change, liver function and food intake. Chronic kidney disease (CKD) patients excrete proteinuria, have low-protein diet, and receive glucocorticoid therapy. No one has evaluated the most influential factors on SAC in CKD patients.

METHODS

A retrospective study. Hospitalized CKD patients with less than 1 g/gCreatinine proteinuria receiving glucocorticoid therapy (n=28), with 1 or more g/gCreatinine proteinuria not receiving glucocorticoid therapy (n=36), and with 1 or more g/gCreatinine proteinuria receiving glucocorticoid therapy (n=39) were enrolled. SAC, hemoglobin, proteinuria and blood pressure at the last outpatient check-up before hospitalization, on the second day of hospitalization, at the last laboratory examination before discharge, as well as at the first outpatient follow-up after discharge were analyzed.

RESULTS

SAC decreased on the second day of hospitalization and increased at the first outpatient follow-up significantly in all groups. Unexpectedly, the change of SAC was irrelevant to the amount of proteinuria.

CONCLUSIONS

SAC was affected by not only proteinuria, but also postural change, physical activity, and food in CKD patients. SAC should be analyzed by standardizing a patient's condition during phlebotomy. J. Med. Invest. 64: 146-152, February, 2017.

Cardiovascular Phenotypes in Children with CKD: The 4C Study

BACKGROUND AND OBJECTIVES

Cardiovascular disease is the most important comorbidity affecting long-term survival in children with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Cardiovascular Comorbidity in Children with CKD Study is a multicenter, prospective, observational study in children ages 6-17 years old with initial GFR of 10-60 ml/min per 1.73 m2. The cardiovascular status is monitored annually, and subclinical cardiovascular disease is assessed by noninvasive measurements of surrogate markers, including the left ventricular mass index, carotid intima-media thickness, and central pulse wave velocity. We here report baseline data at study entry and an explorative analysis of variables associated with surrogate markers.

RESULTS

A total of 737 patients were screened from October of 2009 to August of 2011 in 55 centers in 12 European countries, and baseline data were analyzed in 688 patients. Sixty-four percent had congenital anomalies of the kidney and urinary tract; 26.1% of children had uncontrolled hypertension (24-hour ambulatory BP monitoring; n=545), and the prevalence increased from 24.4% in CKD stage 3 to 47.4% in CKD stage 5. The prevalence of left ventricular hypertrophy was higher with each CKD stage, from 10.6% in CKD stage 3a to 48% in CKD stage 5. Carotid intima-media thickness was elevated in 41.6%, with only 10.8% of patients displaying measurements below the 50th percentile. Pulse wave velocity was increased in 20.1%. The office systolic BP SD score was the single independent factor significantly associated with all surrogate markers of cardiovascular disease. The intermediate end point score (derived from the number of surrogate marker measurements >95th percentile) was independently associated with a diagnosis of congenital anomalies of the kidney and urinary tract, time since diagnosis of CKD, body mass index, office systolic BP, serum phosphorus, and the hemoglobin level.

CONCLUSIONS

The baseline data of this large pediatric cohort show that surrogate markers for cardiovascular disease are closely associated with systolic hypertension and stage of CKD.

Walking, Sedentary Time and Health-Related Quality Life Among Kidney Transplant Recipients: An Exploratory Study

OBJECTIVES

The primary objectives of this study were to: 1) establish walking and physical activity prevalence and sedentary time estimates; and 2) determine associations of health-related quality of life (HRQoL) with objectively assessed walking, self-reported physical activity, and sedentary time among kidney transplant recipients.

METHODS

Using a cross-sectional design, kidney transplant recipients received a survey package containing measures of sedentary time, moderate-to-vigorous physical activity, and HRQoL, and a step pedometer.

RESULTS

Thirty-two participants returned a completed survey, for a response rate of 82% (32 of 39 interested participants). The average steps per day were 9752 steps (SD = 3685) and 59% achieved public health guidelines of at least 150 minutes of moderate-to-vigorous physical activity per week. Total sedentary time during the week was 11.6 h/d whereas total sedentary time during the weekend was 8.9 h/d. Compared to those not achieving at least 10,000 steps/d, respondents who were achieving at least 10,000 steps/d had a significantly higher physical component score for HRQoL (Mdiff = 7.8, P = .018). Similar patterns emerged for meeting physical activity guidelines and sedentary time.

CONCLUSION

For kidney transplant recipients, greater participation in walking, overall physical activity, and lower engagement in sedentary activity, was associated with better HRQoL.

Physical activity and screen time in adolescents in the chronic kidney disease in children (CKiD) cohort

BACKGROUND

Self-reported physical activity (PA) and screen time exposure in adolescents with chronic kidney disease (CKD) has not been evaluated.

METHODS

We performed a cross-sectional analysis of PA and screen time in 224 adolescents at entry into the Chronic Kidney Disease in Children (CKiD) cohort. We compared proportions of CKiD vs. healthy 2012 National Health and Nutrition Examination Survey (NHANES) participants reporting the recommended 60 min of PA 7 days/week or ≤ 2 h/day of entertainment screen time (binomial probability test). Within CKiD, we assessed correlates of PA and screen time using multivariable logistic and linear regression and examined longitudinal data for 136 participants.

RESULTS

Median age of CKiD participants was 15 years, and 60 % were male. Median estimated glomerular filtration rate (eGFR) was 41.3 (IQR 30.8, 52.3) ml/min/1.73 m(2). Only 13 % of CKiD participants met recommendations for PA vs. 25 % of NHANES (p < 0.001), while 98 % in CKiD exceeded the recommended screen time vs. 73 % in NHANES (p < 0.001). Within CKiD, obesity (p = 0.04) and lower eGFR (p = 0.02) were independently associated with greater screen time.

CONCLUSIONS

Adolescents with CKD engage in significantly less PA and greater screen time than healthy youth in the United States, and this may worsen over time.

Role of the endogenous nitric oxide inhibitor asymmetric dimethylarginine (ADMA) and brain-derived neurotrophic factor (BDNF) in depression and behavioural changes: clinical and preclinical data in chronic kidney disease

BACKGROUND

Patients with chronic kidney disease (CKD) exhibit a high prevalence of neuropsychiatric alterations, including depression and behavioural changes. CKD is also associated with decreased physical activity not fully explained by co-morbidities. In patients without CKD, the brain-derived neurotropic factor (BDNF) as well as the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) had been suspected to be involved in major depression. The aim of our study was to examine the role of ADMA and BDNF in the behaviour of haemodialysis patients (CKD5D) as well as in a rat model of 5/6 nephrectomy and chronic ADMA infusion alone.

METHODS

Eleven (5F/6M) CKD5D patients underwent Beck Depression Inventory (BDI) testing along with analysis of ADMA and BDNF. Male Sprague-Dawley rats were randomly assigned to four groups: (i) saline infusion; (ii) ADMA (250 µg/kg/day) infusion via osmotic mini pumps; (iii) 5/6 nephrectomy; (iv) untreated controls. After 28 days, the animals underwent behavioural tests measuring anxiety, locomotion and investigative behaviour. Animals were sacrificed, blood samples were drawn and analysed and hippocampal immunohistology for BDNF was performed.

RESULTS

In CKD5D patients, decreased BDNF levels correlated with higher scores of depression (Pearson r = -0.8156, P = 0.002). ADMA infusion led to a significant decrease of BDNF while the decrease of BDNF in 5/6 nephrectomy was not significant. However, an attenuated hippocampal BDNF expression could be detected in 5/6 nephrecomized animals. Decreased spontaneous locomotor activity was shown in ADMA-infused rats [15.9 (13.5-26.1) lines crossed/min] and 5/6 nephrectomy [14.6 (6.1-20.2) lines crossed/min] when compared with controls [32.5 (15.3-42.4) lines crossed/min]. Anxiety-like behaviour tested by hole investigation time was significantly more pronounced in 5/6 nephrectomy [24 (6-44) s] when compared with ADMA infusion [64 (28-93) s] and controls [33 (26-65) s].

CONCLUSIONS

Progressive renal failure in rats is accompanied by a marked increase of ADMA and a decrease in BDNF. 5/6 nephrectomy leads to significantly decreased exploratory behaviour and locomotion. Both behaviours could be reproduced by ADMA infusion alone. Indicators of anxiety were more pronounced in ADMA-infused animals when compared with 5/6 nephrectomized rats. Furthermore, an inverse relationship of BDNF and BDI in 11 CKD5D patients was shown.

Light-intensity physical activities and mortality in the United States general population and CKD subpopulation

BACKGROUND AND OBJECTIVES

Sedentary behavior is associated with increased mortality in the general population. Whether replacing sedentary behavior with low- or light-intensity activities confers a survival benefit in the general or CKD populations is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This observational analysis of the 2003-2004 National Health and Nutrition Examination Survey examined the associations of low- and light-intensity activities with mortality. On the basis of the number of counts/min recorded by an accelerometer, durations of sedentary (<100/min), low (100-499/min), light (500-2019/min), and moderate/vigorous (≥2020/min) activity were defined and normalized to 60 minutes. The mortality associations of 2 min/hr less sedentary duration in conjunction with 2 min/hr more (tradeoff) spent in one of the low, light, or moderate/vigorous activity durations while controlling for the other two activity durations were examined in multivariable Cox regression models in the entire cohort and in the CKD subgroup.

RESULTS

Of the 3626 participants included, 383 had CKD. The mean sedentary duration was 34.4±7.9 min/hr in the entire cohort and 40.8±6.8 in the CKD subgroup. Tradeoff of sedentary duration with low activity duration was not associated with mortality in the entire cohort or the CKD subgroup. Tradeoff of sedentary duration with light activity duration was associated with a lower hazard of death in the entire cohort (hazard ratio, 0.67; 95% confidence interval, 0.48 to 0.93) and CKD subgroup (hazard ratio, 0.59; 95% confidence interval, 0.35 to 0.98). Tradeoff of sedentary duration with moderate/vigorous activity duration had a nonsignificant lower hazard in the entire cohort and CKD subgroup.

CONCLUSIONS

Patients with CKD are sedentary nearly two thirds of the time. Interventions that replace sedentary duration with an increase in light activity duration might confer a survival benefit.

Effects of acute exercise on markers of inflammation in pediatric chronic kidney disease: a pilot study

BACKGROUND

Children and adolescents with chronic kidney disease (CKD) are chronically exposed to high levels of inflammation, placing them at an increased risk of secondary health complications. Regular exercise may represent an effective therapy to reduce inflammation. The aims of this pilot study were to determine the effects of acute exercise on inflammation and immune cell counts in CKD.

METHODS

Nine children and adolescents (4 males) with CKD stages III-V performed a graded exercise test to determine peak oxygen uptake (VO2peak). Following a 10-min break, participants cycled for 20 min at 50 % of VO2peak. Blood samples were collected before and after the exercise period for the determination of complete blood counts, natural killer cells (NK(bright), NK(dim)) and circulating progenitor cell (CPC) counts, as well as interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) concentrations.

RESULTS

Complete blood counts and NK(dim) cell and CPC counts were unchanged with exercise. Following exercise, NK(bright) cell counts increased (7.4 ± 4.3 vs. 12.2 ± 8.3 × 10(6) cells/L; p = 0.02), while trends were observed for an increase in IL-6 (2.1 ± 2.2 vs. 2.7 ± 2.6 pg/mL; p = 0.08), decrease in TNF-α (4.5 ± 1.2 vs. 4.2 ± 1.0 pg/mL; p = 0.08) and an increase in the IL-6:TNF-α ratio (0.6 ± 0.7 vs. 0.8 ± 0.8; p = 0.07).

CONCLUSIONS

Our findings suggest that acute exercise may create an anti-inflammatory environment in children and adolescents with CKD stages III-V.

Sedentary Behavior in Individuals With Diabetic Chronic Kidney Disease and Maintenance Hemodialysis

OBJECTIVE

The objective of this study was to examine whether more advanced kidney failure is associated with sedentary behavior and whether demographics, comorbidity, nutritional, and inflammatory markers explain this association.

DESIGN

Observational study.

SETTING

Outpatients recruited from outpatient clinics and dialysis units.

SUBJECTS

One hundred sixty patients with chronic kidney disease (CKD) or receiving maintenance hemodialysis (MHD).

METHODS

Standardized questionnaires including Baecke physical activity questionnaire, standardized anthropometry examination, and blood draw.

MAIN OUTCOME MEASURE

Sedentary behavior (defined as answering "very often" for "during leisure time I watch television" or answering "never" for "during leisure time I walk") and being physically active (top 25th percentile of the total Baecke score).

RESULTS

Nineteen percent of CKD and 50% of MHD patients were sedentary (P < .001) and 38.8% of CKD and 11.3% of MHD patients were physically active. In separate multivariable logistic regression models, compared with CKD patients, MHD patients were more sedentary (odds ratio 3.84; 95% confidence interval, 1.18-12.51) and less physically active (odds ratio 0.07; 95% confidence interval 0.01-0.40) independent of demographics, comorbidity, smoking, body size, serum high sensitivity C-reactive protein (hsCRP) and albumin. Congestive heart failure, peripheral vascular disease, and higher body mass index were independently associated with sedentary behavior, whereas younger age, lower body mass index, lower serum hsCRP, and higher serum albumin were associated with being physically active.

CONCLUSIONS

Sedentary behavior is highly prevalent among diabetic CKD or MHD patients. The strong association of MHD status with sedentary behavior is not explained by demographics, smoking, comorbidity, nutritional, and inflammatory markers. Interventions targeting obesity might improve sedentary behavior and physical activity, whereas interventions targeting inflammation might improve physical activity in these populations.

Impact of chronic kidney disease on quality of life, lung function, and functional capacity

OBJECTIVES

To evaluate the impact of the chronic kidney disease (CKD) on quality of life, from the children's and their parents' perspective, respiratory muscle strength, lung function, and functional capacity in children and adolescents.

METHOD

Cross-sectional study of children with CKD aged 8 to 17 years. Those incapable of taking the tests were excluded. After an interview, quality of life by Pediatric Quality of Life Inventory) (PedsQL(TM)), muscular strength, pulmonary function tests, and the 6-minute walking test (6MWT) were applied. Student's t-test, ANOVA (difference in means), and Pearson's coefficient of correlation were used. The level of significance was set at 5%.

RESULTS

Of the 40 patients, the mean distance walked at the 6MWT was 396 meters, and the mean final score at the quality of life test as perceived by the children and parents was 50.9 and 51, respectively. From the children's perspective, the transplanted patients had a higher quality of life score when compared to those undergoing hemodialysis (p<0.001); those who practiced physical activity had better quality of life when compared to the sedentary children (p<0.001). From the children's and the parents' perspectives, the male gender had a higher quality of life score (p<0.05). There was a positive correlation between the distance walked at the 6MWT and age, height, final PedsQL(TM), forced vital capacity (FVC), and forced expiratory volume in the first second (FEV1), as well as a negative correlation between FEV1/FVC and the distance walked.

CONCLUSION

A significant reduction in the quality of life and the functional capacity was observed in children with CKD, influenced by the type of treatment, gender, and sedentary life style.

Daily physical activity and physical function in adult maintenance hemodialysis patients

BACKGROUND

Maintenance hemodialysis (MHD) patients reportedly display reduced daily physical activity (DPA) and physical performance. Low daily physical activity and decreased physical performance are each associated with worse outcomes in chronic kidney disease patients. Although daily physical activity and physical performance might be expected to be related, few studies have examined such relationships in MHD patients, and methods for examining daily physical activity often utilized questionnaires rather than activity monitors. We hypothesized that daily physical activity and physical performance are reduced and correlated with each other even in relatively healthier MHD patients.

METHODS

Daily physical activity, 6-min walk distance (6-MWT), sit-to-stand, and stair-climbing tests were measured in 72 MHD patients (32 % diabetics) with limited comorbidities and 39 normal adults of similar age and gender mix. Daily physical activity was examined by a physical activity monitor. The human activity profile was also employed.

RESULTS

Daily physical activity with the activity monitor, time-averaged over 7 days, and all three physical performance tests were impaired in MHD patients, to about 60-70 % of normal values (p < 0.0001 for each measurement). Human activity profile scores were also impaired (p < 0.0001). MHD patients spent more time sleeping or in marked physical inactivity (p < 0.0001) and less time in ≥ moderate activity (p < 0.0001). These findings persisted when comparisons to normals were restricted to men or women separately. After adjustment, daily physical activity correlated with 6-MWT but not the two other physical performance tests. Human activity profile scores correlated more closely with all three performance tests than did DPA.

CONCLUSIONS

Even in relatively healthy MHD patients, daily physical activity and physical performance are substantially impaired and correlated. Whether training that increases daily physical activity or physical performance will improve clinical outcome in MHD patients needs to be examined.

Use of pedometers to increase physical activity among children and adolescents with chronic kidney disease

BACKGROUND

Children and adolescents with chronic kidney disease (CKD) are inactive relative to their peers.

METHODS

Forty-four children and adolescents aged 7-20 years with CKD, end-stage renal disease (ESRD) on dialysis or a kidney transplant participated in a 12-week pedometer-based intervention to increase physical activity. Patients recorded daily step counts and reported them weekly. Pediatric Quality of Life Inventory (PedsQL) and 6-min walk (6 MW) were administered at baseline and after 12 weeks.

RESULTS

Age was 15.1 ± 3.4 years; 27 % had CKD, 16 % were receiving dialysis, and 57 % had received a kidney transplant. Mean daily step count did not change significantly (+48, 95 % CI -48 to +145 steps/day per week). Transplant recipients and patients with CKD increased their activity by 100 steps/day (95 % CI -14 to 208) and 73 steps/day (95 % CI -115 to 262) each week, respectively, and patients on dialysis decreased by 133 steps/day (95 % CI -325 to 58; p value for interaction 0.03) in multivariable analysis. Change in physical activity was associated with change in 6 MW distance (r = 0.74, p < 0.001) and change in physical functioning (r = 0.53, p = 0.001).

CONCLUSIONS

Youths with CKD did not significantly increase their activity over 12 weeks of a pedometer-based intervention. However, changes in physical activity were associated with changes in physical functioning and performance.

Metabolic syndrome in children with chronic kidney disease and after renal transplantation

Visceral obesity and metabolic abnormalities typical for metabolic syndrome (MS) are the new epidemic in adolescence. MS is not only the risk factor for cardiovascular disease but also for chronic kidney disease (CKD). Thus, there are some reasons to recognize MS as a new challenge for pediatric nephrologists. First, hypertensive and diabetic nephropathy, the main causes of CKD in adults, both share the same pathophysiological abnormalities associated with visceral obesity and insulin resistance and have their origins in childhood. Secondly, as the obesity epidemic also affects children with CKD, MS emerges as the risk factor for progression of CKD. Thirdly, metabolic abnormalities typical for MS may pose additional risk for cardiovascular morbidity and mortality in children with CKD. Finally, although the renal transplantation reverses uremic abnormalities it is associated with an exposure to new metabolic risk factors typical for MS and MS has been found to be the risk factor for graft loss and cardiovascular morbidity after renal transplantation. MS is the result of imbalance between dietary energy intake and expenditure inducing disproportionate fat accumulation. Thus, the best prevention and treatment of MS is physical activity and maintenance of proper relationship between lean and fat mass.

Aging and chronic kidney disease: the impact on physical function and cognition

Evidence has recently been building that the presence of chronic kidney disease (CKD) is an independent contributor to decline in physical and cognitive functions in older adults. CKD affects 45% of persons older than 70 years of age and can double the risk for physical impairment, cognitive dysfunction, and frailty. To increase awareness of this relatively new concept of CKD as a risk factor for accelerated aging, we review studies on the association of CKD with physical function, frailty, and cognitive function. We also present a summary of the proposed mechanisms for these associations.

Inflammatory factors and exercise in chronic kidney disease

Patients with chronic kidney disease frequently present with chronic elevations in markers of inflammation, a condition that appears to be exacerbated by disease progression and onset of haemodialysis. Systemic inflammation is interlinked with malnutrition and muscle protein wasting and is implicated in a number of morbidities including cardiovascular disease: the most common cause of mortality in this population. Research in the general population and other chronic disease cohorts suggests that an increase in habitual activity levels over a prolonged period may help redress basal increases in systemic inflammation. Furthermore, those populations with the highest baseline levels of systemic inflammation appear to have the greatest improvements from training. On the whole, the activity levels of the chronic kidney disease population reflect a sedentary lifestyle, indicating the potential for increasing physical activity and observing health benefits. This review explores the current literature investigating exercise and inflammatory factors in the chronic kidney disease population and then attempts to explain the contradictory findings and suggests where future research is required.