Exercise Performance Falls over Time in Patients with Chronic Kidney Disease Despite Maintenance of Hemoglobin Concentration

Development and Validation of an Insulin Resistance Model for a Population with Chronic Kidney Disease Using a Machine Learning Approach

Background: Chronic kidney disease (CKD) is a complex syndrome without a definitive treatment. For these patients, insulin resistance (IR) is associated with worse renal and patient outcomes. Until now, no predictive model using machine learning (ML) has been reported on IR in CKD patients. Methods: The CKD population studied was based on results from the National Health and Nutrition Examination Survey (NHANES) of the USA from 1999 to 2012. The homeostasis model assessment of IR (HOMA-IR) was used to assess insulin resistance. We began the model building process via the ML algorithm (random forest (RF), eXtreme Gradient Boosting (XGboost), logistic regression algorithms, and deep neural learning (DNN)). We compared different receiver operating characteristic (ROC) curves from different algorithms. Finally, we used SHAP values (SHapley Additive exPlanations) to explain how the different ML models worked. Results: In this study population, 71,916 participants were enrolled. Finally, we analyzed 1,229 of these participants. Their data were segregated into the IR group (HOMA IR > 3, n = 572) or non-IR group (HOMR IR ≤ 3, n = 657). In the validation group, RF had a higher accuracy (0.77), specificity (0.81), PPV (0.77), and NPV (0.77). In the test group, XGboost had a higher AUC of ROC (0.78). In addition, XGBoost also had a higher accuracy (0.7) and NPV (0.71). RF had a higher accuracy (0.7), specificity (0.78), and PPV (0.7). In the RF algorithm, the body mass index had a much larger impact on IR (0.1654), followed by triglyceride (0.0117), the daily calorie intake (0.0602), blood HDL value (0.0587), and age (0.0446). As for the SHAP value, in the RF algorithm, almost all features were well separated to show a positive or negative association with IR. Conclusion: This was the first study using ML to predict IR in patients with CKD. Our results showed that the RF algorithm had the best AUC of ROC and the best SHAP value differentiation. This was also the first study that included both macronutrients and micronutrients. We concluded that ML algorithms, particularly RF, can help determine risk factors and predict IR in patients with CKD.

Cardiorenal syndrome and the association with fitness: Data from a telerehabilitation randomized clinical trial

Aims

To investigate the associations of cardiorespiratory fitness with cardiac, vascular, renal and cardiorenal characteristics in chronic heart failure in a telerehabilitation randomized clinical trial. Secondly, to evaluate the associations of cardiorenal syndrome with the effects of exercise.

Methods and results

Sixty‐nine heart failure patients attended baseline examination, and 61 patients were randomly assigned 1:1 to 3‐month telerehabilitation or control. Data were collected at baseline and 3‐month post‐intervention, including echocardiography and vascular ultrasound, laboratory tests, exercise test with peak oxygen consumption (VO_2peak) measurement and 6‐min walk test (6MWT). Baseline VO_2peak and 6MWT distance was 0.85 mL*min⁻¹*kg⁻¹ lower and 20 m shorter per 10 mL/min/1.73m² lower estimated glomerular filtration rate (both P < 0.001). Heart failure patients with cardiorenal syndrome had 3.5 (1.1) mL*min⁻¹*kg⁻¹ lower VO_2peak and diastolic dysfunction grade 2–3, and elevated filling pressure was >50% more common compared with those without (all P < 0.05). At the 3‐month post‐intervention follow‐up, only the non‐CRS patients in the intervention group increased VO_2peak (0.73 (0.51) mL*min⁻¹*kg⁻¹), whereas VO_2peak in the CRS subpopulation of controls decreased (−1.34 (0.43) mL*min⁻¹*kg⁻¹). Cardiorenal syndrome was associated with a decrease in VO_2peak in CRS patients compared with non‐CRS patients, −0.91 (0.31) vs. 0.39 (0.35) mL*min⁻¹*kg⁻¹ respectively, P = 0.013.

Conclusions

Cardiorenal syndrome was negatively associated with VO_2peak and 6MWT distance in chronic HF, and the associations were stronger than for heart failure phenotypes and other characteristics. The effect of exercise was negatively associated with cardiorenal syndrome. Exercise seems to be as important in heart failure patients with cardiorenal syndrome, and future studies should include CRS patients to reveal the most beneficial type of exercise.

Height-adjusted lean body mass and its associations with physical activity and kidney function in pediatric kidney transplantation

BACKGROUND

Although LBM is positively associated with health outcomes, studies assessing determinants for the accrual of ht-LBM, such as physical activity, are limited. This study aimed to assess ht-LBM levels in pediatric kidney transplant recipients and test its association with baseline and contemporaneous variables, including physical activity.

METHODS

A retrospective cross-sectional review was performed on 46 pediatric kidney transplant recipients, and a longitudinal review was performed on a subset of recipients with serial post-transplant (n = 21) and pre/post-transplant (n = 11) ht-LBM measurements. Ht-LBM measurements were obtained using DXA scans.

RESULTS

This cohort was 16.0 (IQR 12.3, 17.7) years old, 56.5% male and 46 ± 45 months post-transplant with a mean ht-LBM of 15.1 ± 2.5 kg/m² . A median ht-LBM increase of 1.6 kg/m² (IQR - 0.1, 2.6 kg/m² ; p < .01) was observed, over 29.2 ± 12.0 months from the earliest post-transplant scan obtained at 46 ± 25 months post-transplant until the most recent post-transplant scan. A 1.7 ± 1.4 kg/m² (p < .01) increase was observed between pre- and post-transplant DXA scans which were taken at 12 ± 11 months pre-transplant and 13 ± 6 months post-transplant, respectively. In separate adjusted models, lower physical activity questionnaire scores (n = 17, beta = 1.55, p = .02), faster rate of estimated glomerular filtration rate decline (beta = 0.05, p < .048) adjusted for annualized change in BSA, and younger age at scan (beta = 0.32, p < .01) were each significant predictors of lower ht-LBM.

CONCLUSIONS

Physical activity and kidney function may influence ht-LBM in the pediatric kidney transplant population.

Fatigability and the Role of Neuromuscular Impairments in Chronic Kidney Disease

BACKGROUND

The combination of neuromuscular impairments plus psychosocial aspects of chronic kidney disease (CKD) may predispose these patients to greater risk for experiencing increased levels of fatigability. There has been extensive clinical and scientific interest in the problem of fatigue in CKD and end-stage kidney disease (ESKD) patients, whereas less attention has been directed to understanding fatigability. Accordingly, the primary purposes of this review are to (1) discuss fatigue and fatigability and their potential interactions in patients with CKD and ESKD, (2) provide evidence for increased fatigability in CKD and ESKD patients, (3) examine how commonly experienced neuromuscular impairments in CKD and ESKD patients may contribute to the severity of performance fatigability, and (4) highlight preliminary evidence on the effects of exercise as a potential clinical treatment for targeting fatigability in this population.

SUMMARY

Fatigue is broadly defined as a multidimensional construct encompassing a subjective lack of physical and/or mental energy that is perceived by the individual to interfere with usual or desired activities. In contrast, fatigability is conceptualized within the context of physical activity and is quantified as the interactions between reductions in objective measures of performance (i.e., performance fatigability) and perceptual adjustments regulating activity performance (i.e., perceived fatigability). We propose herein a conceptual model to extend current understandings of fatigability by considering the interactions among fatigue, perceived fatigability, and performance fatigability. Neuromuscular impairments reported in patients with CKD and ESKD, including reductions in force capacity, skeletal muscle atrophy, mitochondrial dysfunction, abnormal skeletal muscle excitability, and neurological complications, may each contribute to the greater performance fatigability observed in these patients.

KEY MESSAGES

Considering the interactions among fatigue, perceived fatigability, and performance fatigability provides a novel conceptual framework to advance the understanding of fatigability in CKD and ESKD patients. Measures of fatigability may provide valuable clinical insights into the overall health status of CKD and ESKD patients. Existing data suggest that CKD and ESKD patients are at greater risk of experiencing increased fatigability, partly due to neuromuscular impairments associated with reduced kidney function. Further investigations are warranted to determine the potential clinical role fatigability measures can play in monitoring the health of CKD and ESKD patients, and in identifying potential treatments targeting fatigability in this patient population.

Left atrial strain: A novel "biomarker" for chronic kidney disease patients?

Cardiovascular disease and chronic kidney disease are frequently inter-connected and this association leads to an exponential growth of cardiovascular risk. This risk is currently underestimated by the existing algorithms and there is a constant need for new markers to predict adverse outcomes in this special population. In general population left atrial strain has emerged as an important tool for both the diagnosis and prognostic stratification, but data regarding its role in chronic kidney disease patients is scarce. The purpose of this review is to summarize the current evidence regarding this matter. Left atrial size and function mirror the duration and severity of increased left ventricular filling pressures. Increased left atrial volume index and impaired left atrial strain parameters are independent predictors for adverse cardiovascular events. Left atrial strain is impaired before changes in volume appear, thus being able to predict both diastolic and systolic function in chronic kidney disease patients. Finally, left atrial strain can identify renal patients with impaired exercise capacity and this could have clinical applications in the rehabilitation of this patients.

Maximal Exercise Capacity in Chronic Kidney Disease Stage 4-5 Patients Transitioning to Renal Replacement Therapy or Continuing Conservative Care: A Longitudinal Follow-Up Study

INTRODUCTION

Chronic kidney disease (CKD) is associated with impaired maximal exercise capacity (MEC). However, data are scarce on the development of MEC in CKD stage 4-5 patients transitioning to renal replacement therapy (RRT).

METHODS

We explored the change in MEC measured in watts (Wlast4) with 2 consecutive maximal bicycle stress ergometry tests in 122 CKD stage 4-5 patients transitioning to dialysis and transplantation in an observational follow-up study.

RESULTS

Mean age was 58.9 ± 13.9 years and 43 (35.2%) were female. Mean time between the baseline and follow-up ergometry tests was 1,012 ± 327 days and 29 (23.8%) patients had not initiated RRT, 50 (41.0%) were undergoing dialysis, and 43 (35.2%) had received a kidney transplant at the time of the follow-up ergometry test. The mean Wlast4 was 91 ± 37 W and 84 ± 37 W for the baseline and follow-up ergometry tests, respectively (p < 0.001). The mean Wlast4 declined between the baseline and follow-up ergometry tests in patients not requiring RRT (p = 0.001) and transplant recipients (p = 0.005), but not in dialysis patients (p = 0.478). There were no differences in the ratio of Wlast4 of the follow-up to the baseline ergometry tests (∆Wlast4) between patients on different treatment modalities at the time of the follow-up test (p = 0.097). Mean capillary blood bicarbonate was significantly associated with ∆Wlast4 after adjusting for age and treatment modality in the multivariate linear regression analysis (β = 0.226, p = 0.012).

CONCLUSION

MEC declined or remained poor in advanced CKD patients transitioning to RRT or continuing conservative care in this observational study. Mean capillary blood bicarbonate was independently associated with the development of MEC.

Rate of Force Development Is Related to Maximal Force and Sit-to-Stand Performance in Men With Stages 3b and 4 Chronic Kidney Disease

Introduction: The primary aims of the present study were to assess the relationships of early (0–50 ms) and late (100–200 ms) knee extensor rate of force development (RFD) with maximal voluntary force (MVF) and sit-to-stand (STS) performance in participants with chronic kidney disease (CKD) not requiring dialysis.

Methods: Thirteen men with CKD (eGFR = 35.17 ±.5 ml/min per 1.73 m², age = 70.56 ±.4 years) and 12 non-CKD men (REF) (eGFR = 80.31 ± 4.8 ml/min per 1.73 m², age = 70.22 ±.9 years) performed maximal voluntary isometric contractions to determine MVF and RFD of the knee extensors. RFD was measured at time intervals 0–50 ms (RFD₀₋₅₀) and 100–200 ms (RFD_100−200). STS was measured as the time to complete five repetitions. Measures of rectus femoris grayscale (RF GSL) and muscle thickness (RF MT) were obtained via ultrasonography in the CKD group only. Standardized mean differences (SMD) were used to examine differences between groups. Bivariate relationships were assessed by Pearson's product moment correlation.

Results: Knee extensor MVF adjusted for body weight (CKD=17.14 ±.1 N·kg^0.67, REF=21.55 ±.3 N·kg^0.67, SMD = 0.79) and STS time (CKD = 15.93 ±.4 s, REF = 12.23 ±.7 s, SMD = 1.03) were lower in the CKD group than the REF group. Absolute RFD_100−200 was significantly directly related to adjusted MVF in CKD (r = 0.56, p = 0.049) and REF (r = 0.70, p = 0.012), respectively. STS time was significantly inversely related to absolute (r = −0.75, p = 0.008) and relative RFD₀₋₅₀ (r = −0.65, p = 0.030) in CKD but not REF (r = 0.08, p = 0.797; r = 0.004, p = 0.991). Significant inverse relationships between RF GSL adjusted for adipose tissue thickness and absolute RFD_100−200 (r =−0.59, p = 0.042) in CKD were observed.

Conclusion: The results of the current study highlight the declines in strength and physical function that occur in older men with CKD stages 3b and 4 not requiring dialysis. Moreover, early RFD was associated with STS time in CKD while late RFD was associated MVF in both CKD and REF.

Clinical Trial Registration: ClinicalTrials.gov, identifier: NCT03160326 and NCT02277236.

Left Atrial Reservoir Strain by Speckle Tracking Echocardiography: Association With Exercise Capacity in Chronic Kidney Disease

Background

Left atrial (LA) function plays a pivotal role in modulating left ventricular performance. The aim of our study was to evaluate the relationship between resting LA function by strain analysis and exercise capacity in patients with chronic kidney disease (CKD) and evaluate its utility compared with exercise E/e'.

Methods and Results

Consecutive patients with stage 3 and 4 CKD without prior cardiac history were prospectively recruited from outpatient nephrology clinics and underwent clinical evaluation and resting and exercise stress echocardiography. Resting echocardiographic parameters including E/e' and phasic LA strain (LA reservoir [LASr], conduit, and contractile strain) were measured and compared with exercise E/e'. A total of 218 (63.9±11.7 years, 64% men) patients with CKD were recruited. Independent clinical parameters associated with exercise capacity were age, estimated glomerular filtration rate, body mass index, and sex (P<0.01 for all), while independent resting echocardiographic parameters included E/e', LASr, and LA contractile strain (P<0.01 for all). Among resting echocardiographic parameters, LASr demonstrated the strongest positive correlation to metabolic equivalents achieved (r=0.70; P<0.01). Receiver operating characteristic curves demonstrated that LASr (area under the curve, 0.83) had similar diagnostic performance as exercise E/e' (area under the curve, 0.79; P=0.20 on DeLong test). A model combining LASr and clinical metrics showed robust association with metabolic equivalents achieved in patients with CKD.

Conclusions

LASr, a marker of decreased LA compliance is an independent correlate of exercise capacity in patients with stage 3 and 4 CKD, with similar diagnostic value to exercise E/e'. Thus, LASr may serve as a resting biomarker of functional capacity in this population.

Preliminary Study of the Effects of Eccentric-Overload Resistance Exercise on Physical Function and Torque Capacity in Chronic Kidney Disease

The purpose of this preliminary study was to describe changes in physical function and torque capacity in adults with chronic kidney disease (CKD) in response to a novel progressive eccentric-overload resistance exercise (ERE) regime. Participants included men (n = 4) diagnosed with CKD according to estimated glomerular filtration rate (eGFR) between 59 and 15 mL/kg/1.73 m2 and not requiring dialysis. Physical function was determined by the Short Physical Performance Battery (SPPB), five repetitions of a sit-to-stand (STS) task, and timed-up and go (TUG). Knee extensor strength was assessed using both isometric and isokinetic contractions and performance fatigability indexes were calculated during a 30-s maximal isometric test and a 30-contraction isokinetic test at 180°/second. None of the patients exhibited significant worsening in their health status after training. Participants demonstrated improvements in several measures of physical function and torque capacity following 24 sessions of ERE. Following training, performance fatigability remained relatively stable despite the increases in torque capacity, indicating the potential for greater fatigue resistance. These findings provide initial evidence for ERE as a potential treatment option to combat declines in physical function and neuromuscular impairments in people with CKD. Future research is required to determine optimal progression strategies for maximizing specific neuromuscular and functional outcomes when using ERE in this patient population.

Aerobic exercise capacity is maintained over a 5-year period in mild-to-moderate chronic kidney disease: a longitudinal study

Background

Aerobic exercise capacity is reduced in non-dialysis chronic kidney disease (CKD), but the magnitude of changes in exercise capacity over time is less known. Our main hypothesis was that aerobic ExCap would decline over 5 years in individuals with mild-to-moderate CKD along with a decline in renal function. A secondary hypothesis was that such a decline in ExCap would be associated with a decline in muscle strength, cardiovascular function and physical activity.

Methods

We performed a 5-year-prospective study on individuals with mild-to-moderate CKD, who were closely monitored at a nephrology clinic. Fiftytwo individuals with CKD stage 2–3 and 54 age- and sex-matched healthy controls were included. Peak workload was assessed through a maximal cycle exercise test. Muscle strength and lean body mass, cardiac function, vascular stiffness, self-reported physical activity level, renal function and haemoglobin level were evaluated. Tests were repeated after 5 years. Statistical analysis of longitudinal data was performed using linear mixed models.

Results

Exercise capacity did not change significantly over time in either the CKD group or controls, although the absolute workloads were significantly lower in the CKD group. Only in a CKD subgroup reporting low physical activity at baseline, exercise capacity declined. Renal function decreased in both groups, with a larger decline in CKD (p = 0.05 between groups). Peak heart rate, haemoglobin level, handgrip strength, lean body mass and cardiovascular function did not decrease significantly over time in CKD individuals.

Conclusions

On a group level, aerobic exercise capacity and peak heart rate were maintained over 5 years in patients with well-controlled mild-to-moderate CKD, despite a slight reduction in glomerular filtration rate. In line with the maintained exercise capacity, cardiovascular and muscular function were also preserved. In individuals with mild-to-moderate CKD, physical activity level at baseline seems to have a predictive value for exercise capacity at follow-up.

Genome Diversity and Signatures of Selection for Production and Performance Traits in Dromedary Camels

Dromedary camels (Camelus dromedarius) are single-humped animals found throughout the deserts of Africa, the Arabian Peninsula, and the southwest of Asia. This well-adapted species is mainly used for milk and meat production, although some specific types exhibit superior running performance and are used in racing competitions. However, neither performance nor production camels are bred under intensive genomic selection programs with specific aims to improve these traits. In this study, the full genome sequence data of six camels from the Arabian Peninsula and the genotyping-by-sequencing data of 44 camels (29 packing and 15 racing) from Sudan were analyzed to assess their genome diversities, relationships, and candidate signatures of positive selection. Genome ADMIXTURE and principle component analyses indicate clear geographic separation between the Sudanese and the Arabian Peninsula camels, but with no population-specific genetic distinction within populations. Camel samples from the Arabian Peninsula show higher mean heterozygosity (0.560 ± 0.003) than those from Sudan (0.347 ± 0.003). Analyses of signatures of selection, using pooled heterozygosity (Hp) approach, in the Sudanese camels revealed 176, 189, and 308 candidate regions under positive selection in the combined and packing and racing camel populations, respectively. These regions host genes that might be associated with adaptation to arid environment, dairy traits, energy homeostasis, and chondrogenesis. Eight regions show high genetic differentiation, based on Fst analysis, between the Sudanese packing and racing camel types. Genes associated with chondrogenesis, energy balance, and urinary system development were found within these regions. Our results advocate for further detailed investigation of the genome of the dromedary camel to identify and characterize genes and variants associated with their valuable phenotypic traits. The results of which may support the development of breeding programs to improve the production and performance traits of this unique domesticated species.

A randomized controlled trial of exercise to prevent muscle mass and functional loss in elderly hemodialysis patients: Rationale, study design, and baseline sample

Background

Elderly maintenance hemodialysis (MHD) patients exhibit muscle wasting and impaired physical function. This trial determines whether MHD patients benefit from a 12-week home-based exercise program, protein supplementation, or both.

Design

and Methods: This is a randomized, blinded controlled trial involving 60 elderly MHD patients with impaired exercise capacity and function. Patients are randomized into either a homebased exercise program or normal care over a 12-week period. Measures at baseline include peak VO₂, strength and body composition as well as cognitive and disease-specific questionnaires. Muscle biopsies are obtained and analyzed for protein signaling, expression of IGF-1, androgen receptors, and myostatin.

Results

At baseline, patient characteristics in the exercise and normal care groups were similar by age, gender and anthropomorphic measures. Peak VO₂ was impaired (14.7 ± 3.3 ml/kg/min), representing 55 ± 14% of the age-predicted value. Six-minute walk distance was 322 ± 71 m, and the mean 1-min sit to stand test was 18 ± 8 repetitions, representing 69 ± 16% and 55 ± 22% of the age-predicted values, respectively. Indices of muscle function, including upper and lower body and hand grip strength all indicate marked impairment. Quality of life (QoL) using the SF36, the Beeson cognitive test, and KDQOL all suggest marked impairments compared to age-expected reference values for non-MHD patients.

Conclusions

Patients undergoing MHD exhibit markedly reduced physical function and QoL. Thus, there are potentially significant gains to be made through a program of aerobic and resistance exercise. We anticipate this trial will demonstrate that home-based exercise improves cardiopulmonary function, protein signaling and QoL, and increases muscle mass, strength, and body composition.

Physical Activity in the Prevention of Development and Progression of Kidney Disease in Type 1 Diabetes

PURPOSE OF REVIEW

Physical activity is a fundamental part of lifestyle management in diabetes care. Although its benefits are very well recognized in the general population and in people with type 2 diabetes, much less is known about the effects of exercise in type 1 diabetes. In particular, exercise effects in relation to diabetic kidney disease (DKD) are understudied. Some uncertainties about physical activity recommendations stem from the fact that strenuous exercise may worsen albuminuria immediately after the activity. However, in middle-aged and older adults without diabetes, observational studies have suggested that physical activity is associated with a decreased risk of rapid kidney function deterioration. In this review, we focus on the role of physical activity in patients with DKD and type 1 diabetes.

RECENT FINDINGS

Hereby, we present data that show that in individuals at risk of DKD or with established DKD, regular moderate-to-vigorous physical activity was associated with reduced incidence and progression of DKD, as well as reduced risk of cardiovascular events and mortality. Therefore, regular moderate-to-vigorous exercise should become a central part of the management of individuals with type 1 diabetes, in the absence of contraindications and accompanied with all needed educational support for optimal diabetes management.

Gradual reduction in exercise capacity in chronic kidney disease is associated with systemic oxygen delivery factors

Background

The cause of reduced exercise capacity (ExCap) in chronic kidney disease (CKD) is multifactorial. The aim of this study was to investigate determinants of aerobic ExCap in patients with mild to severe CKD not undergoing dialysis.

Methods

We included 52 individuals with CKD stage 2–3, 47 with stage 4–5, and 54 healthy controls. Peak workload and peak heart rate (HR) were assessed by a maximal cycle exercise test. Cardiac function including stroke volume (SV) and vascular stiffness were evaluated by ultrasound at rest. Handgrip strength, body composition, haemoglobin level and self-reported physical activity were assessed.

Results

Peak workload (221±60, 185±59, 150±54 W for controls, CKD 2–3 and CKD 4–5 respectively), peak HR (177±11, 161±24, 144±31 beats/min) and haemoglobin level (14.2±1.2, 13.5±1.4, 12.2±1.3 g/dL) were all three significantly lower in CKD 2–3 than in controls, (p = 0.001, 0.001 and 0.03 respectively) and were even lower in stages 4–5 CKD than in CKD 2–3 (p = 0.01, 0.001 and <0.001 respectively). Resting SV and lean body mass did not differ between groups and handgrip strength was significantly lower only in CKD 4–5 compared to controls (p = 0.02). Peak workload was strongly associated with the systemic oxygen delivery factors: SV, peak HR and haemoglobin level. These three factors along with age, sex and height² explained 82% of variation in peak workload. Peak HR contributed most to the variation; the peripheral variables handgrip strength and vascular stiffness did not improve the explanatory value in regression analysis.

Conclusions

In this cross-sectional study of CKD patients not on dialysis, aerobic ExCap decreased gradually with disease severity. ExCap was associated mainly with systemic oxygen delivery factors, in particular peak HR. Neither muscle function and mass, nor vascular stiffness were independent determinants of aerobic ExCap in this group of CKD patients.

Satellite cell function, intramuscular inflammation and exercise in chronic kidney disease

Skeletal muscle wasting is a common feature of chronic kidney disease (CKD) and is clinically relevant due to associations with quality of life, physical functioning, mortality and a number of comorbidities. Satellite cells (SCs) are a population of skeletal muscle progenitor cells responsible for accrual and maintenance of muscle mass by providing new nuclei to myofibres. Recent evidence from animal models and human studies indicates CKD may negatively affect SC abundance and function in response to stimuli such as exercise and damage. The aim of this review is to collate recent literature on the effect of CKD on SCs, with a particular focus on the myogenic response to exercise in this population. Exercise is widely recognized as important for the maintenance of healthy skeletal muscle mass and is increasingly advocated in the care of a number of chronic conditions. Therefore a greater understanding of the impact of uraemia upon SCs and the possible altered myogenic response in CKD is required to inform strategies to prevent uraemic cachexia.

Size Exponents for Scaling Maximal Oxygen Uptake in Over 6500 Humans: A Systematic Review and Meta-Analysis

BACKGROUND

Maximal oxygen uptake ([Formula: see text] _2max) is conventionally normalized to body size as a simple ratio or using an allometric exponent < 1. Nevertheless, the most appropriate body size variable to use for scaling and the value of the exponent are still enigmatic. Studies tend to be based on small samples and can, therefore, lack precision.

OBJECTIVE

The objective of this systematic review was to provide a quantitative synthesis of reported static allometric exponents used for scaling [Formula: see text] _2max to whole body mass and fat-free mass.

METHODS

Eight electronic databases (CINAHL, Cochrane Central Register of Controlled Trials, EMBASE, MEDLINE, PubMed, Scopus, SPORTDiscus and Web of Science) were searched for relevant studies published up to January 2016. Search terms included 'oxygen uptake', 'cardiorespiratory fitness', '[Formula: see text] _2max', '[Formula: see text] _2peak', 'scaling' and all interchangeable terms. Inclusion criteria included human cardiorespiratory fitness data; cross-sectional study designs; an empirical derivation of the exponent; reported precision statistics; and reported information regarding participant sex, age and sports background, [Formula: see text] _2max protocol, whole body composition protocol and line-fitting methods. A random-effects model was used to quantify weighted pooled exponents and 95% confidence limits (Cls). Heterogeneity was quantified with the tau-statistic (τ). Meta-regression was used to quantify the impact of selected moderator variables on the exponent effect size. A 95% prediction interval was calculated to quantify the likely range of true fat-free mass exponents in similar future studies, with this distribution used to estimate the probability that an exponent would be above theorised universal values of [Formula: see text].

RESULTS

Thirty-six studies, involving 6514 participants, met the eligibility criteria. Whole body mass and fat-free mass were used as the scaling denominator in 27 and 15 studies, respectively. The pooled allometric exponent (95% Cls) was found to be 0.70 (0.64 to 0.76) for whole body mass and 0.90 (0.83 to 0.96) for fat-free mass. The between-study heterogeneity was greater for whole body mass (τ = ±0.15) than for fat-free mass (τ = ±0.11). Participant sex explained 30% of the between-study variability in the whole body mass exponent, but the influence on the fat-free mass exponent was trivial. The whole body mass exponent of 0.52 (0.40 to 0.64) for females was substantially lower than the 0.76 (0.70 to 0.83) for males, whereas the fat-free mass exponent was similar for both sexes. The effects of all other moderators were trivial. The 95% PI for fat-free mass ranged from 0.68 to 1.12. The estimated probability of a true fat-free mass exponent in a future study being greater than [Formula: see text] power scaling is 0.98 (very likely) and 0.92 (likely), respectively.

CONCLUSIONS

In this quantitative synthesis of published studies involving over 6500 humans, the whole body mass exponent was found to be spuriously low and prone to substantial heterogeneity. We conclude that the scaling of [Formula: see text] _2max in humans is consistent with the allometric cascade model with an estimated prediction interval for the fat-free mass exponent not likely to be consistent with the [Formula: see text] power laws.

Consequences of CKD on Functioning

Chronic kidney disease (CKD) is highly prevalent in the United States and throughout the world,(1) with approximately 13% of adults affected.(2) In addition, according to recent estimates, almost half of patients with CKD stages 3 to 5 are 70 years of age and older.(2) In the United States, the number of prevalent end-stage renal disease cases continues to increase in patients older than age 65. In light of the demographic characteristics of patients with CKD and ESRD, there has been considerable focus on associations between CKD and cardiovascular outcomes.(3) Until recently, less attention had been paid to other consequences of CKD in general and among older individuals with CKD in particular, but there is now solid evidence linking CKD with impairments of physical function, cognitive function, and emotional function and quality of life. This review summarizes available literature on these topics, focusing specifically on physical functioning and frailty, cognitive function, emotional health, including depression and anxiety, and health-related quality of life.

Prognostic value of preprocedural 6-min walk test in patients undergoing transcatheter mitral valve repair-insights from the German transcatheter mitral valve interventions registry

AIMS

The 6-min walk test (6 MWT) has been established as an important tool for functional assessment in heart failure patients. However, its prognostic impact on the outcome in subjects with mitral regurgitation undergoing transcatheter mitral valve repair is unknown.

METHODS

This present work represents a sub-analysis of the German, prospective, multicenter, Transcatheter Mitral Valve Interventions (TRAMI) registry. Of the main study cohort (n = 828) 326 patients underwent 6 MWT prior to the procedure. Patients were assigned to two groups depending on the preprocedural 6 MWT distance using the median (< 200 m [group 1] vs. ≥ 200 m [group 2]).

RESULTS

No differences regarding procedural success (97 vs. 96%; p = 0.71) and 30-day mortality (3 vs. 4%; p = 0.96) were observed between the groups. With regards to 1-year outcome, patients with a walking distance < 200 m had higher all-cause mortality (26 vs. 14%; p = 0.013) as compared to those with a 6 MWT distance 200 m. After adjustment of baseline risk factors, 6 MWT distance < 200 m still showed a strong trend towards increased 1-year all-cause mortality (HR 1.63, 95% confidence interval 0.96-2.76; p = 0.071).

CONCLUSIONS

In the present study preprocedural 6 MWT distance < 200 m showed a strong trend towards increased 1-year mortality in patients undergoing MitraClip implantation.

Cardiopulmonary Performance During Maximal Exercise in Soccer Players with Alterations in Renal Function

The aim of this study was to evaluate the curves of cardiorespiratory variables during cardiopulmonary exercise testing (CPET) in soccer players who had acute alterations in the glomerular filtration rate (GFR) after performing the pre-season training protocol. Sixteen male professional soccer players (25 ± 3 years; 179 ± 2 cm; and 77 ± 6 kg) were evaluated for oxygen uptake (VO₂), heart rate (HR) and pulse relative oxygen (relative O₂ Pulse) curves with intervals corresponding to 10% of the total duration of CPET. Athletes were grouped according to the GFR and classified as decreased GFR (dGFR; n = 8) and normal GFR (nGFR; n = 8). Athletes from the dGFR group exhibited lower VO₂ values (p < 0.05) when 90% (dGFR 49.8 ± 4.0 vs. nGFR 54.4 ± 6.1 ml·kg^-1·min^-1) and 100% (dGFR 52.6 ± 4.1 vs. nGFR 57.4 ± 5.9 ml·kg^-1·min^-1) of the test was complete; HR high values (p < 0.05) when 90% (dGFR 183.7 ± 5.1 vs. nGFR 176.6 ± 4.8 bpm-1) and 100% (dGFR 188.1 ± 5.0 vs. nGFR 180.8 ± 4.8 bpm-1) of the test was complete; and lower relative O₂ Pulse values (p < 0.05) when 70% (dGFR 25.6 ± 8.4 vs. nGFR 27.9 ± 9.7 ml·beat^-1·kg^-1), 80% (dGFR 26.6 ± 8.8 vs. nGFR 29.1 ± 10.0 ml·beat^-1·kg^-1), 90% (dGFR 27.1 ± 9.0 vs. nGFR 30.8 ± 10.6 ml·beat^-1·kg^-1) and 100% (dGFR 28 ± 9.2 vs. nGFR 31.8 ± 10.9 ml·beat^-1·kg^-1) of the test was complete. A correlation was found (r = −0.66, R² = 0.44, p = 0.00) between lower VO₂ peak and elevated levels of urinary protein excretion. In conclusion, soccer players with reduced kidney function after performing the pre-season training protocol also presented alterations in cardiopulmonary variables. We suggest that monitoring of renal function may be used to identify less conditioned soccer players.

Chronic kidney disease and sports participation by children and adolescents

Individuals suffering from chronic kidney disease (CKD) deal with major morbidity and mortality including poor exercise tolerance. A variety of factors including anemia, poor muscle mass, cardiovascular changes and limited physical activity contribute to exercise intolerance. Studies suggest that early initiation of aerobic and resistance training improves the muscle function, ability to tolerate exercise and quality of life in CKD patients. A thorough medical examination and exercise testing are recommended before initiating an exercise regimen in individuals with CKD. Though current recommendations suggest a qualified approval to contact sports in patients with solitary kidney, a proper risk assessment and counselling must be provided detailing all the risks involved. Special care must be taken to avoid infection or damage to the peritoneal dialysis catheter and hemodialysis vascular access sites. Collision sports should be avoided in individuals with kidney transplant, ectopic kidney or with other urological abnormalities (severe hydronephrosis or ureteropelvic junction obstruction) with high risk of injury.

Prehabilitation for the Frail Patient Approaching ESRD

Frailty is a distinct phenotype that is highly prevalent in chronic kidney disease (CKD) and appears to be more prevalent with decreasing glomerular filtration rate. Exercise training or intervention to increase physical activity may ameliorate poor physical functioning and frailty, and even may improve survival in patients with CKD. Although exercise interventions improve outcomes across the spectrum of CKD, including patients treated with dialysis, patients treated with dialysis face barriers to exercise that patients with predialysis CKD do not. Rehabilitation at earlier stages of CKD (or prehabilitation before dialysis) might be more beneficial than not addressing the decreasing physical functioning and low physical activity until patients are receiving dialysis. This review summarizes available literature on frailty in the CKD and end-stage renal disease population, including exercise interventions and the limited evidence for prehabilitation as a strategy.

Correlates of Physical Functioning and Performance Across the Spectrum of Kidney Function

The aim of this study was to determine the extent to which poor physical functioning, low participation in physical activity, and muscle atrophy observed among patients on hemodialysis are evident in the earlier stages of chronic kidney disease (CKD). We enrolled adults in three groups: no CKD, Stages 3 to 4 CKD, and hemodialysis. Outcomes measured were physical activity, muscle size, thigh muscle strength, physical performance, and self-reported physical function. Patients with CKD had muscle area intermediate between the no CKD and hemodialysis groups, but they had low levels of physical activity that were similar to the hemodialysis group. Physical activity and muscle size were significantly associated with all outcomes. Kidney function was not significantly associated with muscle strength or physical performance after adjustment for physical activity and muscle size. In conclusion, interventions aimed to increase muscle mass and energy expenditure might have an impact on improving physical function of CKD patients.

Insulin resistance in chronic kidney disease: a systematic review

Insulin resistance (IR) is an early metabolic alteration in chronic kidney disease (CKD) patients, being apparent when the glomerular filtration rate is still within the normal range and becoming almost universal in those who reach the end stage of kidney failure. The skeletal muscle represents the primary site of IR in CKD, and alterations at sites beyond the insulin receptor are recognized as the main defect underlying IR in this condition. Estimates of IR based on fasting insulin concentration are easier and faster but may not be adequate in patients with CKD because renal insufficiency reduces insulin catabolism. The hyperinsulinemic euglycemic clamp is the gold standard for the assessment of insulin sensitivity because this technique allows a direct measure of skeletal muscle sensitivity to insulin. The etiology of IR in CKD is multifactorial in nature and may be secondary to disturbances that are prominent in renal diseases, including physical inactivity, chronic inflammation, oxidative stress, vitamin D deficiency, metabolic acidosis, anemia, adipokine derangement, and altered gut microbiome. IR contributes to the progression of renal disease by worsening renal hemodynamics by various mechanisms, including activation of the sympathetic nervous system, sodium retention, and downregulation of the natriuretic peptide system. IR has been solidly associated with intermediate mechanisms leading to cardiovascular (CV) disease in CKD including left ventricular hypertrophy, vascular dysfunction, and atherosclerosis. However, it remains unclear whether IR is an independent predictor of mortality and CV complications in CKD. Because IR is a modifiable risk factor and its reduction may lower CV morbidity and mortality, unveiling the molecular mechanisms responsible for the pathogenesis of CKD-related insulin resistance is of importance for the identification of novel therapeutic targets aimed at reducing the high CV risk of this condition.

Performance of a Predictive Model for Long-Term Hemoglobin Response to Darbepoetin and Iron Administration in a Large Cohort of Hemodialysis Patients

Anemia management, based on erythropoiesis stimulating agents (ESA) and iron supplementation, has become an increasingly challenging problem in hemodialysis patients. Maintaining hemodialysis patients within narrow hemoglobin targets, preventing cycling outside target, and reducing ESA dosing to prevent adverse outcomes requires considerable attention from caregivers. Anticipation of the long-term response (i.e. at 3 months) to the ESA/iron therapy would be of fundamental importance for planning a successful treatment strategy. To this end, we developed a predictive model designed to support decision-making regarding anemia management in hemodialysis (HD) patients treated in center. An Artificial Neural Network (ANN) algorithm for predicting hemoglobin concentrations three months into the future was developed and evaluated in a retrospective study on a sample population of 1558 HD patients treated with intravenous (IV) darbepoetin alfa, and IV iron (sucrose or gluconate). Model inputs were the last 90 days of patients’ medical history and the subsequent 90 days of darbepoetin/iron prescription. Our model was able to predict individual variation of hemoglobin concentration 3 months in the future with a Mean Absolute Error (MAE) of 0.75 g/dL. Error analysis showed a narrow Gaussian distribution centered in 0 g/dL; a root cause analysis identified intercurrent and/or unpredictable events associated with hospitalization, blood transfusion, and laboratory error or misreported hemoglobin values as the main reasons for large discrepancy between predicted versus observed hemoglobin values. Our ANN predictive model offers a simple and reliable tool applicable in daily clinical practice for predicting the long-term response to ESA/iron therapy of HD patients.

Strategies to improve physical activity by exercise training in patients with chronic kidney disease

Decreased physical activity resulting in muscle loss is often observed in patients with chronic kidney disease and is one of the main predictors of mortality in these patients. Exercise training may improve physical activity and prevent muscle loss in patients with chronic kidney disease. Efforts to introduce exercise training to these patients may be clinically beneficial by reducing their mortality rates.

The role of physical activity in the CKD setting

A sedentary lifestyle contributes to the development of cardiovascular disease, hypertension, diabetes and probably cancer in the general population; this cluster of disease may be defined the diseasome of physical inactivity. Also in CKD/ESRD patients physical activity is strikingly low. As a result of growing evidence suggestive of cardiovascular benefit among the CKD population with exercise, the National Kidney Foundation recommended counseling by nephrologists to increase patients' levels of physical activity in their guideline about management of cardiovascular disease. Therefore, to maintain the well-being and functional capacity of renal patients attention should be directed toward maintaining strength and aerobic fitness as well as focusing on renal function and anemia or other comorbidities. All CKD/ESRD patients should be counseled and regularly encouraged by nephrology and dialysis staff to increase their level of physical activity.

Primary care physicians' own exercise habits influence exercise counseling for patients with chronic kidney disease: a cross-sectional study

BACKGROUND

The appropriate exercise counseling for chronic kidney disease (CKD) patients is crucial to improve their prognosis. There have been few studies about exercise counseling by primary care physicians for CKD patients. We investigated primary care physicians' exercise counseling practices for CKD patients, and the association of these physicians' own exercise habits with exercise counseling.

METHODS

The population of this cross-sectional study was 3310 medical doctors who graduated from Jichi Medical University from 1978 to 2012. The study instrument was a self-administered questionnaire that was mailed in August 2012 to investigate their age class, specialty, workplace, exercise habits, and practices of exercise counseling for CKD.

RESULTS

581 (64.8%) medical doctors practiced the management of CKD among a total of 933 responses. These 581 medical doctors were defined as CKD primary care physicians and their answers were analyzed. CKD primary care physicians' own exercise habits (frequencies and intensities) were as follows: frequencies: daily, 71 (12.1%); ≥ 2-3 times/week, 154 (26.5%); ≥ 1 time/week, 146 (25.1%); and ≤ 1 time/month, 176 (30.2%); intensities: high (≥ 6 Mets), 175 (30.1%); moderate (4-6 Mets), 132 (22.7%); mild (3-4 Mets), 188 (32.3%); very mild (<3 Mets), 47 (8.1%); and none, 37 (6.4%). The CKD primary care physicians' exercise recommendation levels for CKD patients were as follows: high, 31 (5.3%); moderate, 176 (29.7%); low, 256 (44.0%); and none, 92 (15.8%). The CKD primary care physicians' exercise recommendations for CKD patients were significantly related to their own exercise frequency (p < 0.001), but they were not related to their age, specialty, workplace, or exercise intensity.

CONCLUSIONS

CKD primary care physicians' exercise recommendation level for CKD patients was limited. In addition, CKD primary care physicians' own exercise habits influenced the exercise counseling for CKD patients. The establishment of guidelines for exercise by CKD patients and their dissemination among primary care physicians are needed.(University Hospital Medical Information Network Clinical Trial Registry. number, UMIN000011803. Registration date, Sep/19/2013).

A patient with CKD and poor nutritional status

Protein energy wasting is common in patients with CKD and ESRD and is associated with adverse clinical outcomes, such as increased rates of hospitalization and death, in these patients. A multitude of factors can affect the nutritional and metabolic status of patients with CKD, including decreased dietary nutrient intake, catabolic effects of renal replacement therapy, systemic inflammation, metabolic and hormonal derangements, and comorbid conditions (such as diabetes and depression). Unique aspects of CKD also confound reliable assessment of nutritional status, further complicating management of this comorbid condition. In patients in whom preventive measures and oral dietary intake from regular meals cannot help them maintain adequate nutritional status, nutritional supplementation, administered orally, enterally, or parenterally, is effective in replenishing protein and energy stores. The advantages of oral nutritional supplements include proven efficacy, safety, and compliance. Anabolic steroids and exercise, with nutritional supplementation or alone, improve protein stores and represent potential additional approaches for the treatment of PEW. There are several emerging novel therapies, such as appetite stimulants, anti-inflammatory interventions, and anabolic agents.

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.

Natural history of skeletal muscle mass changes in chronic kidney disease stage 4 and 5 patients: an observational study

Cross-sectional studies in dialysis demonstrate muscle wasting associated with loss of function, increased morbidity and mortality. The relative drivers are poorly understood. There is a paucity of data regarding interval change in muscle in pre-dialysis and dialysis-dependant patients. This study aimed to examine muscle and fat mass change and elucidate associations with muscle wasting in advanced CKD.

134 patients were studied (60 HD, 28 PD, 46 CKD 4–5) and followed up for two years. Groups were similar in age, sex and diabetes prevalence. Soft tissue cross-sectional area (CSA) was measured annually on 3 occasions by a standardised multi-slice CT thigh. Potential determinants of muscle and fat CSA were assessed. Functional ability was assessed by sit-to-stand testing.

88 patients completed follow-up (40 HD, 16 PD, 32 CKD). There was a significant difference in percentage change in muscle CSA (MCSA) over year 1, dependant on treatment modality (χ² = 6.46; p = 0.039). Muscle loss was most pronounced in pre-dialysis patients. Muscle loss during year 1 was partially reversed in year 2 in 39%. Incident dialysis patients significantly lost MCSA during the year which they commenced dialysis, but not the subsequent year. Baseline MCSA, change in MCSA during year 1 and dialysis modality predicted year 2 change in MCSA (adjusted R² = 0.77, p<0.001). There was no correlation between muscle or fat CSA change and any other factors. MCSA correlated with functional testing, although MCSA change correlated poorly with change in functional ability.

These data demonstrate marked variability in MCSA over 2 years. Loss of MCSA in both pre-dialysis and established dialysis patients is reversible. Factors previously cross-sectionally shown to correlate with MCSA did not correlate with wasting progression. The higher rate of muscle loss in undialysed CKD patients, and its reversal after dialysis commencement, suggests that conventional indicators may not result in optimal timing of dialysis initiation.

Prevention and treatment of protein energy wasting in chronic kidney disease patients: a consensus statement by the International Society of Renal Nutrition and Metabolism

Protein energy wasting (PEW) is common in patients with chronic kidney disease (CKD) and is associated with adverse clinical outcomes, especially in individuals receiving maintenance dialysis therapy. A multitude of factors can affect the nutritional and metabolic status of CKD patients requiring a combination of therapeutic maneuvers to prevent or reverse protein and energy depletion. These include optimizing dietary nutrient intake, appropriate treatment of metabolic disturbances such as metabolic acidosis, systemic inflammation, and hormonal deficiencies, and prescribing optimized dialytic regimens. In patients where oral dietary intake from regular meals cannot maintain adequate nutritional status, nutritional supplementation, administered orally, enterally, or parenterally, is shown to be effective in replenishing protein and energy stores. In clinical practice, the advantages of oral nutritional supplements include proven efficacy, safety, and compliance. Anabolic strategies such as anabolic steroids, growth hormone, and exercise, in combination with nutritional supplementation or alone, have been shown to improve protein stores and represent potential additional approaches for the treatment of PEW. Appetite stimulants, anti-inflammatory interventions, and newer anabolic agents are emerging as novel therapies. While numerous epidemiological data suggest that an improvement in biomarkers of nutritional status is associated with improved survival, there are no large randomized clinical trials that have tested the effectiveness of nutritional interventions on mortality and morbidity.

Skeletal muscle alterations and exercise performance decrease in erythropoietin-deficient mice: a comparative study

BACKGROUND

Erythropoietin (EPO) is known to improve exercise performance by increasing oxygen blood transport and thus inducing a higher maximum oxygen uptake (VO2max). Furthermore, treatment with (or overexpression of) EPO induces protective effects in several tissues, including the myocardium. However, it is not known whether EPO exerts this protective effect when present at physiological levels. Given that EPO receptors have been identified in skeletal muscle, we hypothesized that EPO may have a direct, protective effect on this tissue. Thus, the objectives of the present study were to confirm a decrease in exercise performance and highlight muscle transcriptome alterations in a murine EPO functional knock-out model (the EPO-d mouse).

METHODS

We determined VO2max peak velocity and critical speed in exhaustive runs in 17 mice (9 EPO-d animals and 8 inbred controls), using treadmill enclosed in a metabolic chamber. Mice were sacrificed 24h after a last exhaustive treadmill exercise at critical speed. The tibialis anterior and soleus muscles were removed and total RNA was extracted for microarray gene expression analysis.

RESULTS

The EPO-d mice's hematocrit was about 50% lower than that of controls (p<0.05) and their performance level was about 25% lower (p<0.001). A total of 1583 genes exhibited significant changes in their expression levels. However, 68 genes were strongly up-regulated (normalized ratio>1.4) and 115 were strongly down-regulated (normalized ratio<0.80). The transcriptome data mining analysis showed that the exercise in the EPO-d mice induced muscle hypoxia, oxidative stress and proteolysis associated with energy pathway disruptions in glycolysis and mitochondrial oxidative phosphorylation.

CONCLUSIONS

Our results showed that the lack of functional EPO induced a decrease in the aerobic exercise capacity. This decrease was correlated with the hematocrit and reflecting poor oxygen supply to the muscles. The observed alterations in the muscle transcriptome suggest that physiological concentrations of EPO exert both direct and indirect muscle-protecting effects during exercise. However, the signaling pathway involved in these protective effects remains to be described in detail.

Association of 1,25-dihydroxyvitamin D levels with physical performance and thigh muscle cross-sectional area in chronic kidney disease stage 3 and 4

BACKGROUND

Declines in 1,25-dihydroxyvitamin D (1,25(OH)₂D) levels and physical functioning follow the course of chronic kidney disease (CKD). Although the molecular actions of vitamin D in skeletal muscle are well known, and muscle weakness and atrophy are observed in vitamin D-deficient states, there is little information regarding vitamin D and muscle function and size in CKD.

OBJECTIVE

To examine associations of vitamin D with physical performance (PF) and muscle size.

DESIGN

Cross-sectional.

SETTING

CKD clinic.

SUBJECTS

Twenty-six patients (61 ± 13 years, 92% men) with CKD stage 3 or 4.

MAIN OUTCOME MEASURES

Gait speed, 6-minute walk, sit-to-stand time, 1-legged balance, and thigh muscle cross-sectional area (MCSA), measured by magnetic resonance imaging (MRI).

RESULTS

Overall, 73% were 25-hydroxyvitamin D (25(OH)D) deficient (n = 10) or insufficient (n = 9) (Kidney Disease Outcomes Quality Initiative guidelines). 25(OH)D level was associated with normal gait speed only (r = 0.41, P = .04). Normal and fast gait speed, the distance walked in 6 minutes, and sit-to-stand time were best explained by 1,25(OH)₂D and body mass index (P < .05 for all) and 1-legged stand by 1,25(OH)₂D (r = 0.40, P < .05) only. There were no associations of age, estimated glomerular filtration rate (eGFR), intact parathyroid hormone (iPTH), or albumin with any PF measures. MCSA was associated with eGFR (r = 0.54, P < .01) only. Variance in MCSA was best explained by a model containing 1,25(OH)₂D, plasma Ca²⁺, and daily physical activity (by accelerometry) (P < .05 for all). Once these variables were in the model, there was no contribution of eGFR.

CONCLUSION

These results suggest that 1,25(OH)₂D is a determinant of PF and muscle size in patients with stage 3 and 4 CKD.

Exercise in individuals with CKD

There are few studies evaluating exercise in the nondialysis chronic kidney disease (CKD) population. This review covers the rationale for exercise in patients with CKD not requiring dialysis and the effects of exercise training on physical functioning, progression of kidney disease, and cardiovascular risk factors. In addition, we address the issue of the risk of exercise and make recommendations for implementation of exercise in this population. Evidence from uncontrolled studies and small randomized controlled trials shows that exercise training results in improved physical performance and functioning in patients with CKD. In addition, although there are no studies examining cardiovascular outcomes, several studies suggest that cardiovascular risk factors such as hypertension, inflammation, and oxidative stress may be improved with exercise training in this population. Although the current literature does not allow for definitive conclusions about whether exercise training slows the progression of kidney disease, no study has reported worsening of kidney function as a result of exercise training. In the absence of guidelines specific to the CKD population, recent guidelines developed for older individuals and patients with chronic disease should be applied to the CKD population. In sum, exercise appears to be safe in this patient population if begun at moderate intensity and increased gradually. The evidence suggests that the risk of remaining inactive is higher. Patients should be advised to increase their physical activity when possible and be referred to physical therapy or cardiac rehabilitation programs when appropriate.

Elevated Levels of N-Terminal Pro-Brain Natriuretic Peptide in Patients with Chronic Dyspnea and Moderate Renal Dysfunction: Decreased Clearance or Increased Cardiac Stress

BACKGROUND/AIMS

Serum levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) are often increased in patients with impaired renal function. The objective of this study was to investigate whether the increase in NT-proBNP is predominantly due to a reduced renal clearance or an increased cardiac secretion.

METHODS

A series of 697 outpatients (age: 57.5 ± 16.4 years) referred for evaluation of dyspnea were assigned to 4 groups according to their estimated glomerular filtration rate [eGFR (ml/min per 1.73 m2)]: group 1, eGFR <60 (n = 77); group 2, eGFR ≧60 to <75 (n = 139); group 3, eGFR ≧75 to <90 (n = 191), and group 4, eGFR ≧90 (n = 289). The patients were also grouped into 2 categories based on the presence (n = 176) or absence (n = 521) of heart disease.

RESULTS

In patients with heart disease, the adjusted values for NT-proBNP were higher in eGFR group 1 than in eGFR groups 2-4 (p ≤ 0.01). In patients without heart disease, eGFR group 1 membership had no effect on NT-proBNP.

CONCLUSION

A reduced renal clearance does not explain increased NT-proBNP levels in patients with moderate renal impairment and dyspnea. Our data suggest that a moderate reduction in renal function places additional stress on the heart in patients with established cardiac disease.

Exercise as an anabolic intervention in patients with end-stage renal disease

Muscle wasting and accompanying structural derangements leading to abnormalities in muscle function, exercise performance, and physical activity are common in patients with end-stage renal disease. Therefore, several studies have been performed examining the effects of exercise in this particular patient population. Most of the studies have assessed the effects of cardiopulmonary fitness training, whereas a few have examined the role of resistance (i.e., strength) training. Despite the proven efficacy of resistance exercise as an anabolic intervention in the otherwise healthy elderly population and certain chronic disease states, recent studies in patients on maintenance hemodialysis have not been encouraging in terms of long-term improvements in markers of muscle mass. Preliminary studies indicated that a combination of simultaneous exercise and nutritional supplementation could augment the anabolic effects of exercise, at least in the acute setting. However, a recent randomized clinical trial failed to show further benefits of additional resistance exercise on long-term somatic protein accretion above and beyond nutritional supplementation alone. Further research is necessary to both understand the observed lack of obvious benefits and strategies to improve the exercise regimens in patients with end-stage renal disease.

Position stand on androgen and human growth hormone use

Hoffman, JR, Kraemer, WJ, Bhasin, S, Storer, T, Ratamess, NA, Haff, GG, Willoughby, DS, and Rogol, AD. Position stand on Androgen and human growth hormone use. J Strength Cond Res 23(5): S1-S59, 2009-Perceived yet often misunderstood demands of a sport, overt benefits of anabolic drugs, and the inability to be offered any effective alternatives has fueled anabolic drug abuse despite any consequences. Motivational interactions with many situational demands including the desire for improved body image, sport performance, physical function, and body size influence and fuel such negative decisions. Positive countermeasures to deter the abuse of anabolic drugs are complex and yet unclear. Furthermore, anabolic drugs work and the optimized training and nutritional programs needed to cut into the magnitude of improvement mediated by drug abuse require more work, dedication, and preparation on the part of both athletes and coaches alike. Few shortcuts are available to the athlete who desires to train naturally. Historically, the NSCA has placed an emphasis on education to help athletes, coaches, and strength and conditioning professionals become more knowledgeable, highly skilled, and technically trained in their approach to exercise program design and implementation. Optimizing nutritional strategies are a vital interface to help cope with exercise and sport demands (). In addition, research-based supplements will also have to be acknowledged as a strategic set of tools (e.g., protein supplements before and after resistance exercise workout) that can be used in conjunction with optimized nutrition to allow more effective adaptation and recovery from exercise. Resistance exercise is the most effective anabolic form of exercise, and over the past 20 years, the research base for resistance exercise has just started to develop to a significant volume of work to help in the decision-making process in program design (). The interface with nutritional strategies has been less studied, yet may yield even greater benefits to the individual athlete in their attempt to train naturally. Nevertheless, these are the 2 domains that require the most attention when trying to optimize the physical adaptations to exercise training without drug use.Recent surveys indicate that the prevalence of androgen use among adolescents has decreased over the past 10-15 years (). The decrease in androgen use among these students may be attributed to several factors related to education and viable alternatives (i.e., sport supplements) to substitute for illegal drug use. Although success has been achieved in using peer pressure to educate high school athletes on behaviors designed to reduce the intent to use androgens (), it has not had the far-reaching effect desired. It would appear that using the people who have the greatest influence on adolescents (coaches and teachers) be the primary focus of the educational program. It becomes imperative that coaches provide realistic training goals for their athletes and understand the difference between normal physiological adaptation to training or that is pharmaceutically enhanced. Only through a stringent coaching certification program will academic institutions be ensured that coaches that they hire will have the minimal knowledge to provide support to their athletes in helping them make the correct choices regarding sport supplements and performance-enhancing drugs.The NSCA rejects the use of androgens and hGH or any performance-enhancing drugs on the basis of ethics, the ideals of fair play in competition, and concerns for the athlete's health. The NSCA has based this position stand on a critical analysis of the scientific literature evaluating the effects of androgens and human growth hormone on human physiology and performance. The use of anabolic drugs to enhance athletic performance has become a major concern for professional sport organizations, sport governing bodies, and the federal government. It is the belief of the NSCA that through education and research we can mitigate the abuse of androgens and hGH by athletes. Due to the diversity of testosterone-related drugs and molecules, the term androgens is believed to be a more appropriate term for anabolic steroids.

Chronic kidney disease, exercise, and sports in children, adolescents, and adults

Individuals with chronic kidney disease have poor exercise tolerance and are easily fatigued compared with their healthy peers. The primary reasons for poor exercise tolerance include anemia, effects of chronic uremia and metabolic acidosis on the heart and skeletal muscles, and lower levels of physical activity. Studies suggest that regular and early implementation of both aerobic and resistance exercise programs in persons with chronic kidney disease have positive effects on muscle function, exercise tolerance, and quality of life. Before starting any exercise program, a medical assessment and exercise testing are generally recommended. No consensus exists regarding allowing young athletes with a solitary kidney who want to participate in contact or collision sports. Decisions to allow participation in different sports and leisure activities should be made on an individual basis, considering multiple factors. This article reviews factors that affect exercise tolerance in persons with chronic kidney disease, the effects of exercise, and exercise recommendations.

Is there an association between serum 25-hydroxyvitamin D concentration and muscle strength among older women? Results from baseline assessment of the EPIDOS study

OBJECTIVE

To examine whether low serum 25-hydroxyvitamin D (25OHD) concentration were associated with low muscle strength while taking into account the effects of potential confounders among a cohort of community-dwelling women aged 75 years and older.

DESIGN

Cross-sectional study corresponding to the baseline assessment of the EPIDOS study.

SETTING

Five French cities including Amiens, Lyon, Montpellier, Paris and Toulouse.

PARTICIPANTS

Randomized sample of 440 women included in the EPIDOS study.

MEASUREMENT

Maximal isometric voluntary contraction strength of the lower limb and hand with computerized dynamometers, serum 25OHD and parathyroid hormone concentration. Age at baseline evaluation, number of chronic diseases, body mass index (BMI), use of calcium drug, practice of a regular physical activity, serum calcium concentration and clearance of creatinine were used as covariables. Subjects were separated into 3 groups based on serum 25 OHD levels with the following cut-off values: < 15 ng/ml, 15-30 ng/ml and > 30 ng/ml.

RESULTS

More than 90% of women had a serum 25OHD insufficiency (i.e. < 30 ng/ml) and 40.2% had a related secondary hyperparathyroidism. The mean value of muscle strength was not different among the 3 groups of women (174.9 +/- 53.2 for serum 25OHD < 15 ng/ml versus 175.9 +/- 52.6 for serum 25OHD 15-30 ng/ml versus 173.4 +/- 53.1 for serum 25OHD > 30 ng/ml with P=0.946 for quadriceps, and 56.1 +/- 13.2 for serum 25OHD < 15 ng/ml versus 57.1 +/- 13.5 for serum 25OHD 15-30 ng/ml versus 61.1 +/- 12.7 for serum 25OHD > 30 ng/ml with P= 0.064 for handgrip). There was no significant association between serum 25OHD concentration and quadriceps strength (crude beta = 0.03 with P = 0.891 and adjusted beta = -0.04 with P = 0.837). Univariate linear regression showed a significant association between serum 25OHD concentration and handgrip strength (crude beta = 0.16 with P = 0.049) but not while using an adjusted model (adjusted beta = 0.13 with P = 0.106).

CONCLUSIONS

The findings of this study do not support the hypothesis of a relationship between low serum 25OHD concentration and low muscle strength. Further research is needed to corroborate and explain this finding.