Recognizing the importance of physical activity on sarcopenia in chronic kidney disease.

To the editor,

We read with interest the article by Dubey et al [1] which discussed the prevalence and determinants of sarcopenia in 188 Indian pre-dialysis chronic kidney disease (CKD) patients. Sarcopenia is an important clinical problem, which has likely been compounded further by COVID-19 restrictions [2]. Although we do commend the authors for their original investigation in an under-represented population, we have several observations on their interpretations.

Firstly, it is stated that sarcopenia was defined using the 2014 Asian Working Group for Sarcopenia (AWGS) criteria [3]. However, in fact, the present study only looked at the presence of low muscle mass. Both the 2014 and updated 2019 [4] AWGS criteria consider a sarcopenia diagnosis of sarcopenia to occur only in the presence of either low physical function (ie, low handgrip strength and/or slowness). The presence of low muscle mass solely should not confer a diagnosis of proper sarcopenia status. This is an important distinction as it is widely recognized that physical function has stronger prognostic value than muscle mass in predicting adverse outcomes [5], and in both the AWGS and European criteria, there is renewed focus on function as a key characteristic of the sarcopenia phenotype. By focusing only on muscle quantity, the ‘true’ prevalence of sarcopenia is unknown and we are at risk of excluding the important role of muscle function, arguably more crucial to a patient's ability to complete activities of daily living. There is an ever-growing problem in sarcopenia research where continuous revisions of the definition, parallel establishment of several international working groups, modification of cut-offs, and use of different criteria are causing confusion and misinterpretation among research and clinical professionals. Consistency is fundamental if we are to drive the sarcopenia field forward, particularly in establishing sarcopenia in routine clinical practice.

Secondly, the authors primarily focus on nutritional factors in their discussion and state that dietary counseling should be emphasized. However, while it states that ‘physical activity needs to be encouraged’, we believe the role of physical activity in mitigating the development and effects of sarcopenia has been understated. Work from the UK in ∼1/2 million participants, including > 8700 individuals with CKD, found that the largest risk factor for (probable) sarcopenia was physical inactivity. It is well-recognized that individuals with CKD are inactive [6] and given the well-documented effects of resistance exercise on muscle synthesis and function, it is unsurprising physical inactivity contributes to sarcopenia development. Importantly, exercise behaviour is modifiable and the use of resistance exercise should be considered as the ‘primary’ treatment of sarcopenia; in CKD there are a plethora of data showing exercise can ‘reverse’ the main components of sarcopenia [[7], [8], [9]]. While the current evidence on exercise for sarcopenia is encouraging, real-life applications in clinical settings are limited [10]. It is likely that a multidisciplinary patient-centered approach with regular follow-up is needed; yet, for this to happen, long-term randomized control and implementation trials utilizing consistent terminology are required.

Conflicts of interest

The authors declare no competing interests.