Abstract
Background and Aims
Individuals living with CKD are characterised by adverse changes in physical function. Knowledge of the factors that mediate impairments in physical functioning is crucial for developing effective interventions that preserve mobility and future independence. Mechanical muscle power describes the rate of performing work and is the product of muscular force and velocity of contraction. Muscle power has been shown to have stronger associations with functional limitations and mortality than sarcopenia in older adults. In CKD, the role of mechanical muscle power is poorly understood and is overlooked as a target in many rehabilitation programmes, often at the expense of muscle mass or strength. The aims of this study were to 1) explore the prevalence of low absolute mechanical power, low relative mechanical power, and low specific mechanical power in CKD; and 2) investigate the association of mechanical power with the ability to complete activities of daily living and physical performance.
Method
Mechanical muscle power (relative, allometric, specific) was calculated using the sit-to-stand-5 (STS5) test as per previously validated equations. Legs lean mass was derived from regional analyses conducted using bioelectrical impedance analysis (BIA). Physical performance was assessed using two objective tests: usual gait speed and the ‘time-up-and-go’ (TUAG) test. Self-reported activities of daily living (ADLs) were assessed via the Duke Activity Status Index (DASI). Balance and postural stability (postural sway and velocity) was assessed using a FysioMeter. Sex-specific tertiles were used to determine low, medium and high levels of relative STS power and its main components.
Results
102 participants with non-dialysis CKD were included (mean age: 62.0 (±14.1) years, n=49 males (48%), mean eGFR: 38.0 (±21.5) ml.min.1.73m2). The mean estimated 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 35/102 (34%) patients. Relative power was a significant independent predictor of self-reported ADLs (via the DASI) (B=.413, P=.004), and performance on the TUAG (B=-.719, P<.001) and gait speed (B=.404, P=.003) tests. Skeletal muscle mass was not associated with the DASI or any of the objective function tests
Conclusion
Patients presenting with low muscle power would benefit from participation in appropriate interventions designed to improve the physiological components accounting for low relative muscle power. Assessment of power can be used to tailor renal rehabilitation programmes as shown in Figure 1. Incorporation of power-based training, a novel type of strength training, designed by manipulating traditional strength training variables and primarily movement velocity and training intensity may present the best strategy for improving physical function in CKD.
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