Results of meta-analysis should be interpreted with caution

We read with interest a recent article by Cai et al. in Annals of Palliative Medicine, which analyzed the effects of aerobic exercise combined with resistance training on urea dialysis clearance rate, physical functioning, mental health status, and social functioning in maintenance hemodialysis (MHD) patients from a perspective of systematic review and meta-analysis (1). We do not doubt the results that exercise is “good medicine” for MHD patients. However, several methodological issues of the authors lead us to question the legitimacy of their results and conclusions.

First, the search strategy listed by the authors was flawed. It is well known that both the Cochrane Library and PubMed databases provide standardized subject terms, i.e., medical subject headings (MeSH). In the case of “exercise”, for example, the MeSH terms “resistance training (https://www.ncbi.nlm.nih.gov/mesh/?term=resistance+training)”, “exercise (https://www.ncbi.nlm.nih.gov/mesh/68015444)”, and “exercise therapy (https://www.ncbi.nlm.nih.gov/mesh/68005081)” are provided. Appropriate subject terms and broad free text words should be selected to retrieve as many relevant records as possible. In particular, the authors were missing the search term “resistance training”, which may have led to some missing studies.

Second, we note that the authors’ purpose was to evaluate the application value of aerobic exercise combined with resistance training in MHD patients. However, not all the included studies used this exercise type as an intervention. For example, Abreu et al. (2) and Dong et al. (3) implemented resistance training only in the exercise group, so why were these studies included in this meta-analysis?

Third, the data extracted by the authors were incorrect. The problem appears in Fig. 4 of the original article, where the data for Xu et al. (4) (a study published in Chinese) in the forest plot were baseline data, not the post-intervention means and standard deviations. It is actually 72.75±8.83 (n=40) vs. 67.80±7.07 (n=41). After correcting for the authors’ included data and excluding the Abreu et al. (2) study, the results of the fixed-effects model, including the four studies, showed a mean difference of 3.43 (95% CI: 0.83 to 6.03, I²=0.0%), higher than the authors’ erroneous conclusion.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was a standard submission to the journal. The article did not undergo external peer review.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://apm.amegroups.com/article/view/10.21037/apm-22-613/coif). The authors have no conflicts of interest to declare.

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References

1. Cai X, Zeng D, Deng J. A systematic review and meta-analysis of the efficacy of aerobic exercise combined with resistance training on maintenance hemodialysis patients. Ann Palliat Med 2022;11:1360-8. [Crossref] [PubMed]
2. Abreu CC, Cardozo LFMF, Stockler-Pinto MB, et al. Does resistance exercise performed during dialysis modulate Nrf2 and NF-κB in patients with chronic kidney disease? Life Sci 2017;188:192-7. [Crossref] [PubMed]
3. Dong ZJ, Zhang HL, Yin LX. Effects of intradialytic resistance exercise on systemic inflammation in maintenance hemodialysis patients with sarcopenia: a randomized controlled trial. Int Urol Nephrol 2019;51:1415-24. [Crossref] [PubMed]
4. Xu T. Effect of Aerobic and Resistance Training on Physical Function and Quality of Life among Patients on Hemodialysis. Zhengzhou University 2016.