Muscle power and physical dysfunction: A model for tailoring rehabilitation in chronic kidney disease.

INTRODUCTION: Chronic kidney disease (CKD) is characterized by adverse physical function. Mechanical muscle power describes the product of muscular force and velocity of contraction. In CKD, the role of mechanical muscle power is poorly understood and often overlooked as a target in rehabilitation. The aims of this study were to investigate the association of mechanical power with the ability to complete activities of daily living and physical performance. METHOD: Mechanical muscle power was estimated using the sit-to-stand-5 test. Legs lean mass was derived using bioelectrical impedance analysis. Physical performance was assessed using gait speed and 'timed-up-and-go' (TUAG) tests. Self-reported activities of daily living (ADLs) were assessed via the Duke Activity Status Index. Balance and postural stability (postural sway and velocity) was assessed using a FysioMeter. Sex-specific tertiles were used to determine low levels of power. RESULTS: One hundred and two non-dialysis CKD participants were included (age: 62.0 (±14.1) years, n = 49 males (48%), eGFR: 38.0 (±21.5) ml/min/1.73m2 ). The mean relative power was 3.1 (±1.5) W/kg in females and 3.3 (±1.3) W/kg in males. Low relative power was found in 34% of patients. Relative power was an independent predictor of ADLs (ß = .413, p = .004), and TUAG (ß = -.719, p < .001) and gait speed (ß = .404, p = .003) performance. Skeletal muscle mass was not associated with any outcomes. CONCLUSION: Knowledge of the factors that mediate physical function impairment is crucial for developing effective interventions. Incorporation of power-based training focusing primarily on movement velocity may present the best strategy for improving physical function in CKD, above those that focus on increasing muscle mass.

Utility of Ultrasound as a Valid and Accurate Diagnostic Tool for Sarcopenia: Sex-Specific Cutoff Values in Chronic Kidney Disease.

OBJECTIVES: Patients with chronic kidney disease (CKD) have aberrant changes in body composition, including low skeletal muscle mass, a feature of "sarcopenia." The measurement of the (quadriceps) rectus femoris (RF) cross-sectional area (CSA) is widely used as a marker of muscle size. Cutoff values are needed to help discriminate the condition of an individual's muscle (eg, presence of sarcopenia) quickly and accurately. This could help distinguish those at greater risk and aid in targeted treatment programs. METHODS: Transverse images of the RF were obtained by B-mode 2-dimensional ultrasound imaging. Sarcopenic levels of muscle mass were defined by established criteria (1, appendicular skeletal muscle mass [ASM]; 2, ASM/height2 ; and 3, ASM/body mass index) based on the ASM and total muscle mass measured by a bioelectrical impedance analysis. The discriminative power of RF-CSA was assessed by receiver operating characteristic curves, and optimal cutoffs were determined by the maximum Youden index (J). RESULTS: One hundred thirteen patients with CKD (mean age [SD], 62.0 [14.1] years; 48% male; estimated glomerular filtration rate, 38.0 [21.5] mL/min/1.73m2 ) were included. The RF-CSA was a moderate predictor of ASM (R2 = 0.426; P < .001) and total muscle mass (R2 = 0.438; P < .001). With a maximum J of 0.47, in male patients, an RF-CSA cutoff of less than 8.9 cm2 was deemed an appropriate cutoff for detecting sarcopenic muscle mass. In female patients, an RF-CSA cutoff of less than 5.7 cm2 was calculated on the basis of ASM/height2 (J = 0.71). CONCLUSIONS: Ultrasound may provide a low-cost and simple means to diagnose sarcopenia in patients with CKD. This would allow for early management and timely intervention to help mitigate the effects in this group.

The validity of the 'General Practice Physical Activity Questionnaire' against accelerometery in patients with chronic kidney disease.

BACKGROUND: The majority of patients with chronic kidney disease (CKD) are physically inactive. Simple yet accurate assessment of physical activity is important in identifying those in need of intervention. The 'General Practice Physical Activity Questionnaire' (GPPAQ) is a well-used clinical and research tool, but has not been validated. METHODS: Forty individuals with CKD (age 62.5 (SD: 11.1) years, estimated glomerular filtration rate (eGFR) 33.2 (SD:19.1) ml/min/1.73 m2) completed the GPPAQ and objective physical activity was measured using a GENEActiv accelerometer for 7 days. Physical activity status was grouped as 'Active' (i.e. meeting current physical activity UK guidelines) or 'Inactive.' Sensitivity and specificity were calculated. Accuracy was defined as the probability the GPPAQ could correctly classify a patient as either 'Active' or 'Inactive' (based on accelerometery). RESULTS: Using accelerometery, 18% of participants met the current UK guidelines, whereas 27% were classed as 'Active' according to GPPAQ. Sensitivity of the GPPAQ was 54.6% and specificity was 96.6%. The 'accuracy' of the GPPAQ was 85.0%. The accuracy of the GPPAQ was greater in males and those not in employment/retired, although these differences were not statistically significant. CONCLUSIONS: The GPPAQ may be a useful tool to identify CKD patients who would benefit most from a physical activity intervention. In particular, the GPPAQ can accurately identify those not sufficiently active.