Glycemic and lactate thresholds during incremental inspiratory muscle exercise: Is there agreement?

To identify and verify the existence of agreement between the lactate threshold (LT) and the glycemic threshold (GT) during an incremental inspiratory muscle exercise test, as well as to investigate the possibility of determining a second LT representing the transition from moderate to intense effort.

An exploratory comparative diagnostic study was conducted with 13 eutrophic male individuals submitted to incremental inspiratory muscle testing (IIMT) with serial collections of venous lactate and capillary glucose. LT1, LT2, GT, and exhaustion point (EP) were determined, with analysis of absolute and relative loads at each point. Agreement between LT1 and GT was assessed using the Bland-Altman test.

LT1 and GT occurred, on average, between 22% and 26% of the inspiratory effort index (Sindex), with no statistically significant difference between them (p > 0.05). Bland-Altman analysis demonstrated reduced bias between measurements, with better agreement observed for relative load. LT2 and EP presented significantly higher values than LT1 and GT (p < 0.01).

The GT and the first and second lactate thresholds (LT1 and LT2) during an incremental inspiratory muscle exercise test can be determined through an IIMT. Furthermore, good agreement exists between the GT and LT1. Therefore, it is possible to infer that the GT can serve as a useful and accurate tool for determining the load in IMT.