Exercise for patients with chronic kidney disease: from cells to systems to function

Chronic kidney disease (CKD) is among the leading causes of death and disability, affecting an estimated 800 million adults globally. The underlying pathophysiology of CKD is complex creating challenges to its management. Primary risk factors for the development and progression of CKD include diabetes mellitus, hypertension, age, obesity, diet, inflammation, and physical inactivity. The high prevalence of diabetes and hypertension in patients with CKD increases the risk for secondary consequences such as cardiovascular disease and peripheral neuropathy. Moreover, the increased prevalence of obesity and chronic levels of systemic inflammation in CKD have downstream effects on critical cellular functions regulating homeostasis. The combination of these factors results in the deterioration of health and functional capacity in those living with CKD. Exercise offers protective benefits for the maintenance of health and function with age, even in the presence of CKD. Despite accumulating data supporting the implementation of exercise for the promotion of health and function in patients with CKD, a thorough description of the responses and adaptations to exercise at the cellular, system, and whole body levels is currently lacking. Therefore, the purpose of this review is to provide an up-to-date comprehensive review of the effects of exercise training on vascular endothelial progenitor cells at the cellular level; cardiovascular, musculoskeletal, and neural factors at the system level; and physical function, frailty, and fatigability at the whole body level in patients with CKD.

Association between vitamin D deficiency and exercise capacity in patients with CKD, a cross-sectional analysis

BACKGROUND

Evidence is growing for a role of vitamin D in regulating skeletal muscle mass, strength and functional capacity. Given the role the kidneys play in activating total vitamin D, and the high prevalence of vitamin D deficiency in Chronic Kidney Disease (CKD), it is possible that deficiency contributes to the low levels of physical function and muscle mass in these patients.

METHODS

This is a secondary cross-sectional analysis of previously published interventional study, with in vitro follow up work. 34 CKD patients at stages G3b-5 (eGFR 25.5 ± 8.3 mL/min/1.73m2; age 61 ± 12 years) were recruited, with a sub-group (n = 20) also donating a muscle biopsy. Vitamin D and associated metabolites were analysed in plasma by liquid chromatography tandem-mass spectroscopy and correlated to a range of physiological tests of muscle size, function, exercise capacity and body composition. The effects of 1α,25(OH)2D3 supplementation on myogenesis and myotube size was investigated in primary skeletal muscle cells from vitamin D deficient donors.

RESULTS

In vivo, there was no association between total or active vitamin D and muscle size or strength, but a significant correlation with V̇O_2Peak was seen with total vitamin D (25OHD). in vitro, 1α,25(OH)₂D3 supplementation reduced IL-6 mRNA expression, but had no effect upon proliferation, differentiation or myotube diameter.

CONCLUSIONS

Vitamin D deficiency is not a prominent factor driving the loss of muscle mass in CKD, but may play a role in reduced exercise capacity.

Association between Vitamin D Level and Muscle Strength in Patients Undergoing Hemodialysis

INTRODUCTION

Identification of the risk factors and treatment of the decrease in muscle mass or strength are important to improve the prognosis of patients undergoing hemodialysis (HD). Previous studies have investigated the association between vitamin D level and muscle mass or strength in patients undergoing HD. However, there are conflicting results regarding this association.

OBJECTIVE

To evaluate the association between vitamin D level and muscle mass indices, strength, or physical performance in patients undergoing HD.

METHODS

This study was performed in a tertiary medical center. We included patients undergoing HD aged ≥20 years. A total of 84 patients were enrolled. The patients were divided into tertiles based on the 25-hydroxy (25-OH) vitamin D level as follows: lowest tertile (Lowest T, n = 28), middle tertile (Middle T, n = 28), and highest tertile (Highest T, n = 28). We evaluated the association between the tertiles and clinical outcomes including nutritional status, muscle mass, muscle function, handgrip strength (HGS), physical performance, and health-related quality of life (HRQoL) scales.

RESULTS

There were no significant differences in the muscle mass indices and nutritional markers according to tertiles of 25-OH vitamin D level. However, 25-OH vitamin D level as a continuous variable or the tertile of 25-OH vitamin D level as a categorical variable was positively associated with HGS. Logistic and linear regression analyses showed a consistent superiority of the Highest T in HGS compared with the Lowest or Middle T. Although the statistical significance was weak, the scores of various physical performance tests and the HRQoL scales were highest in the Highest T among the 3 tertiles.

CONCLUSION

The present study demonstrated that serum vitamin D level is associated with HGS in patients undergoing HD regardless of muscle mass indices or nutritional status.

A more precise, repeatable and diagnostic alternative to surface electromyography - an appraisal of the clinical utility of acoustic myography

Acoustic myography (AMG) enables a detailed and accurate measurement of those muscles involved in a particular movement and is independent of electrical signals between the nerve and muscle, measuring solely muscle contractions, unlike surface electromyography (sEMG). With modern amplifiers and digital sound recording systems, measurements during physical activity both inside and outside a laboratory setting are now possible and accurate. Muscle sound gives a representation of the work of each muscle group during a complex movement, and under certain forms of movement even reveals both concentric and eccentric activity, something that sEMG is incapable of. Recent findings suggest that AMG has a number of advantages over sEMG, being simple to use, accurate and repeatable as well as being intuitive to interpret. The AMG signal comprises three physiological parameters, namely efficiency/coordination (E-score), spatial summation (S-score) and temporal summation (T-score). It is concluded that modern AMG units have the potential to accurately assess patients with neuromuscular and musculoskeletal complaints in hospital clinics, home monitoring situations as well as sports settings.

Interleukin-6 and vitamin D status during high-intensity resistance training in patients with chronic kidney disease

Background. The aim of this study was to investigate IL-6 and 25-hydroxyvitamin D (25-OH D) associations with muscle size and muscle function in dialysis patients. Methods. Patients were included in a 16-week control period followed by 16 weeks of high-intensity resistance training thrice weekly. IL-6 and 25-OH D were analysed after an over-night fast. Muscle fibre size was analysed in biopsies from m. vastus lateralis. Muscle power was tested using a Leg Extensor Power Rig. Results. Patients (n = 36) with IL-6 ≥ 6.49 pg/ml (median) were older and had decreased muscle power and a reduced protein intake (P < 0.05) compared with patients with IL-6 < 6.49 pg/ml. IL-6 was not associated with muscle fibre size. Vitamin D deficiency (25-OH D < 50 nmol/l) was present in 51% of the patients and not associated with muscle power. IL-6 remained unchanged during the training period, whilst muscle power increased by 20-23% (P < 0.001). Conclusion. Elevated IL-6 values were associated with decreased muscle power but not with decreased muscle fibre size. Half of the patients were suffering from vitamin D deficiency, which was not associated with muscle power. IL-6 was unchanged by high-intensity resistance training in dialysis patients in this study.

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.