Assessment of Cardiorespiratory Fitness in Individuals With Type 2 Diabetes Mellitus: Protocol for a Systematic Review and Meta-Analysis.

BACKGROUND: Reduced cardiorespiratory fitness (CRF) is a well-recognized but underaddressed complication of type 2 diabetes mellitus (T2DM), contributing substantially to cardiovascular morbidity, mortality, and reduced quality of life. Evidence related to pulmonary function, functional exercise capacity, and autonomic dysfunction in T2DM remains fragmented and methodologically heterogeneous. OBJECTIVE: This protocol describes a systematic review and meta-analysis that aims to synthesize evidence on CRF in adults with T2DM, evaluate associated clinical and demographic determinants, and examine relationships with glycemic control and diabetes-related outcomes. METHODS: The protocol is registered with PROSPERO (CRD420251009300) and follows PRISMA-P (Preferred Reporting Items for Systematic Review and Meta-Analyses Protocols) guidelines. A comprehensive search of PubMed, Cochrane Library, Web of Science, ClinicalTrials.gov, World Health Organization's International Clinical Trials Registry Platform, and gray literature will be conducted for studies published between 2013 and 2024. Randomized controlled trials, cohort studies, and cross-sectional and case-control studies involving adults with T2DM will be included. Primary outcomes include pulmonary function test parameters, 6-minute walk test distance, and heart rate variability indexes. Two reviewers will independently screen studies, extract data, and assess risk of bias using the Revised Cochrane Risk-of-Bias Tool for Randomized Trials (RoB 2), Newcastle-Ottawa Scale, and the JBI critical appraisal tools, as appropriate. Meta-analyses will be performed using random-effects models when sufficient homogeneity exists. The GRADE (Grading of Recommendations Assessment, Development and Evaluation) framework will be used to assess certainty of evidence. RESULTS: The study was approved by the Doctoral Research Committee on December 19, 2024, and the Standing Scrutiny Committee and Institutional Ethical Committee on October 1, 2025. Data collection began after approval in December 2024, and the meta-analysis was completed in April 2026. The results of the meta-analysis will be published in August 2026. CONCLUSIONS: The findings will support evidence-based clinical assessment and guide future research on integrative cardiopulmonary and autonomic evaluation in T2DM. TRIAL REGISTRATION: PROSPERO CRD420251009300; https://www.crd.york.ac.uk/PROSPERO/view/CRD420251009300. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/91185.