# Isokinetic Strength in Peritoneal Dialysis Patients: A Reliability Study
## 4 Discussion  
The main finding of this study was that the test-retest reliability of elbow and knee concentric flexion is good or excellent in PD patients. These results were similar to those observed in sit-to-stand-to-sit, six-minute walk, one-leg heel-rise, and handgrip strength tests in people undergoing hemodialysis [20] or in the incremental shuttle walk test, the estimated maximum repetition for quadriceps strength, and VO2 peak by cardiopulmonary exercise testing in non-dialysis chronic kidney disease [21]. However, little was known about the reliability of physical function tests in PD patients and, to our knowledge, this is the first study aimed to evaluate the test-retest reliability of isokinetic measures in this population. The evaluation of physical function is relevant since it is strongly related to quality of life, independence, and the ability to perform activities of daily living. Patients suffering from chronic kidney disease may have a higher risk of having low strength levels and low muscular mass, which is commonly associated with a higher risk of mortality [22]. However, most of the studies aimed to evaluate physical function in patients undergoing dialysis have been conducted with hemodialysis patients [23], while further research is needed in PD patients. According to [PERSON] et al. [24], exercise capacity may be reduced in about 96% of PD patients. This reduction in exercise tolerance could be partially determined by age, sex, and body composition and is strongly associated with health-related quality of life in this population [25]. In this regard, the reduced quality of life and physical function may be similar in patients undergoing hemodialysis or PD [26]. However, [PERSON] et al. [27] observed more favorable mental and physical components in hemodialysis patients compared with PD patients. Although the differences between the two dialysis modalities in terms of physical function and quality of life still remain unclear, patient satisfaction is commonly higher in patients undergoing PD [26; 27]. Therefore, physical function is a relevant measure that should be included in comprehensive health assessments in dialysis patients. The current study provides test-retest reliability parameters that should be used to interpret health-related physical function evaluations in this population. Isokinetic dynamometry is considered the gold standard for dynamic muscle performance testing [28; 29]; thus, clinicians and researchers should be encouraged to use this device to conduct their physical function evaluations. Previous studies have reported the test-retest reliability of isokinetic measures in several populations different from patients undergoing dialysis. In this regard, reliability results obtained in the current study are similar to those obtained in postmenopausal women with osteopenia [30], women with fibromyalgiaalgia [15], patients with knee osteoarthritis [31], or persons with chronic stroke [32]. Furthermore, the current study not only reports the reliability parameters of measures of the lower limb but also assesses the reliability of the elbow flexion and extension strength tests. Therefore, future research may use both the absolute and the relative reliability parameters