Test-retest Reliability Of The Gas Exchange Threshold And Respiratory Compensation Point And Associated Heart Rates

To improve cardiorespiratory fitness, exercise prescription is often based on heart rate (HR) or oxygen consumption rate (VO2max). The gas exchange threshold (GET) and respiratory compensation point (RCP) from a graded exercise test (GXT) have been used to examine the onset of physiological fatigue and predict endurance exercise performance. Therefore, it is important to consider the HR associated with the GET and RCP. PURPOSE: To examine the reliability of the GET and RCP (expressed as a VO2) as well as the HR associated with these thresholds. METHODS: Nine females (mean ± SD, age = 22 ± 2 years, height = 167.2 ± 5.5 cm, body mass = 58.26 ± 7.35 kg, VO2max = 39.69 ± 7.92 mL·kg-1·min-1) performed two GXTs to determine the GET and RCP. Each GXT started at 50 W, increasing 30 W every 2 min until volitional exhaustion or when subjects could no longer maintain a cadence of 70 rev·min-1. Using visual inspection, the GET and RCP were determined as the point of departure from the linearity of the VCO2 versus VO2 and VE versus VCO2 relationships, respectively. The HRs associated with the VO2 value corresponding to the GET (HRGET) and RCP (HRRCP) were determined using linear regression. Analyses consisted of paired samples t-tests (p ≤ 0.05) to examine the test 1 and test 2 mean GET, RCP, HRGET, and HRRCP values, intra-class correlation coefficients (ICC2,1), standard errors of the measurement (SEM), minimal differences (MD), and coefficients of variation (CoV). RESULTS: There were no significant differences between test 1 and test 2 (p = 0.20, p = 0.07, p = 0.08, p = 0.06) for HRGET, HRRCP, GET, or RCP, respectively. The HRGET (ICC = 0.391, SEM = 6.8 b·min-1, MD = 18.8 b·min-1, CoV = 3.9%) demonstrated “poor” reliability. The HRRCP (ICC = 0.834, SEM = 3.4 b·min-1, MD = 9.5 b·min-1, CoV = 2.2%), GET (ICC = 0.848, SEM = 1.649 mL·kg-1·min-1, MD = 5.536 mL·kg-1·min-1, CoV = 6.9%), and RCP (ICC = 0.959, SEM = 1.259 mL·kg-1·min-1, MD = 3.491 mL·kg-1·min-1, CoV = 3.6%) demonstrated “excellent” reliability. CONCLUSIONS: The present study indicated no systematic error and excellent reliability for the HRRCP, GET, and RCP. Although there was no systematic error, caution may be warranted when using the HRGET to prescribe or monitor exercise training due to its poor test-retest reliability.