“Individuals with CKD are characterized by adverse changes in physical function, which is associated with increased mortality and morbidity,” explains Thomas J. Wilkinson, PhD. “Knowledge of the factors that mediate impairments in physical functioning is crucial for developing effective interventions that preserve mobility and independence. Mechanical muscle power may be superior to other measures such as maximum muscle mass and strength in its association with muscle function and clinical outcomes. However, the assessment and utilization of mechanical power is poorly addressed in the clinical setting and is often overlooked in the aims and outcomes of rehabilitation programs.”

For a study published in Nephrology, Dr. Wilkinson and colleagues examined the link between mechanical muscle power and the ability to engage in activities of daily living (ADL), as well as physical functioning. “The aim of our study was to explore the prevalence of low power in CKD, to investigate the association of power with the ability to complete ADL and physical performance, and to determine the contribution of power over low muscle mass to the above factors,” Dr. Wilkinson notes.

Adult patients with CKD were recruited from nephrology outpatient clinics between 2013-2020. The researchers used the sit-to-stand-5 (STS5) test to examine mechanical muscle power and bioelectrical impedance analysis to determine lean leg mass. The study team evaluated physical performance with gait speed and timed-up-and-go (TUAG) tests, balance and postural stability (postural sway and velocity) with a FysioMeter, and self-reported ADL with the Duke Activity Status Index.

Muscle Power More Important Than Mass and Strength

“We found that the mean relative power was 3.1 (±1.5) W/kg in females and 3.3 (±1.3) W/kg in males; this is low,” Dr. Wilkinson says. “Low relative power was found in 34% of patients, and the prevalence of low power is similar to that reported in older persons, around 15 years older than those in our cohort.”

The researchers also found that relative power served as an independent predictor of ADL and physical performance. “Interestingly, the amount of skeletal muscle mass had no effect of function,” Dr. Wilkinson says. “Therefore, patients presenting with low muscle power would likely benefit from participation in appropriate interventions designed to improve the physiological components accounting for low relative muscle power.”

The findings demonstrate that “power is more important than muscle mass and strength,” Dr. Wilkinson continues. “As such, we recommend that power training should be used in patients with CKD. There is growing evidence to suggest that power training is safe, and more effective and potentially superior to traditional ‘slow velocity’ resistance training for muscle power and functional performance improvements in older adults.”

Patients with CKD and low relative muscle power should be identified after conducting the STS5 test, Dr. Wilkinson says. “In those with low relative muscle power, it should be determined whether it is related to low allometric power, high BMI, or both. If low power is not detected, then more general activity programs can be employed, encompassing both general aerobic and strength training components (Figure).”

Incorporate Resistance Training for Patients with CKD

The researchers described two primary implications of their results, the first of which shows that power should be evaluated among patients with CKD. “Second, using our model, participants could be stratified to a difference resistance-based training goal,” Dr. Wilkinson notes. “Based on research in older adults, incorporation of high-intensity explosive resistance training presents the best strategy for simultaneous improvements in whole-body peak power, strength, and local muscular endurance. This includes incorporating traditional (slow) high-intensity (60%-80% of one rep maximum) resistance training together with light-to-moderate explosive resistance training (30%/40%–60% of one rep maximum) during 1–3 sets per exercise, with 6-10 repetitions per set.”

Future research should examine the impact of power-focused training on functional outcomes, according to Dr. Wilkinson. “In this study, we propose a model on how and why power is important,” he says. “It is also unknown how reductions in body fat (body mass) would impact muscle power, especially in a population of patients with CKD.”