Limiar glicêmico durante teste muscular inspiratório incremental em indivíduos saudáveis e com doença pulmonar obstrutiva crônica

Abstract

Introduction: The glycemic threshold (GT) during the incremental inspiratory muscle test (IIMT) has been proposed by our research group as a tool for inspiratory muscle functional assessment and individualized inspiratory muscle training (IMT) prescription. However, its agreement with the first lactate threshold (LT1) and its applicability in individuals with chronic obstructive pulmonary disease (COPD) have not yet been investigated. Objectives: To evaluate the agreement between GT and LT1 during the IIMT in healthy individuals and to investigate the determination of GT in individuals with COPD, as well as its associations with clinical and functional variables. Methods: Two studies were conducted using the IIMT. In the first study, healthy individuals performed the IIMT with simultaneous determination of GT, LT1, and the second lactate threshold (LT2). In the second study, individuals with COPD performed the IIMT for GT determination and analysis of its association with rating of perceived exertion, dyspnea, functional capacity, and cardiovascular autonomic balance. The incremental protocol started at 10% of the S-Index, with progressive workload increments until the point of exhaustion (PE). Results: In the first study, GT showed good agreement with LT1. LT1 and GT occurred at 22±8.3% and 26±13.2% of the S-Index, respectively, whereas LT2 and PE were identified at 44±10.1% and 60±14.1% of the S-Index. Bland–Altman analysis demonstrated low bias between methods for relative workload (−3.84±10.44% of the S-Index) and no proportional bias (p=0.06; R²=0.25). In the second study, GT was identified at 25±11.6% of the S-Index and showed a strong correlation with rating of perceived exertion during the IIMT (r=0.84; p<0.01). In addition, PE and ΔGT–PE were correlated with cardiovascular autonomic balance (LF/HF: r=−0.83 and r=−0.71; p<0.01), whereas ΔGT–PE was also correlated with dyspnea assessed by the modified Medical Research Council (mMRC) scale (r=−0.68; p=0.01) and Borg dyspnea at the end of the six-minute walk test (r=−0.83; p<0.01). Conclusion: GT is an identifiable physiological marker during the IIMT, showing agreement with LT1 in healthy individuals and association with important clinical and functional variables in individuals with COPD. These findings support its potential as a tool for inspiratory muscle functional assessment and individualized IMT prescription.