THE GAS EXCHANGE THRESHOLD-LACTATE THRESHOLD RELATIONSHIP ACROSS CYCLING FITNESS LEVELS

A.J. Seipel, S.M. Partridge, J.T. Penry Oregon State University, Corvallis, OR Endurance athletes set the intensities of training sessions using blood lactate data from a maximal graded exercise test (GXT). Specifically, these intensities are set as a percentage of heart rate (HR) at lactate threshold (LT). Often, however, gas exchange threshold (GET) data is used to replace LT values as they are less invasive and less expensive. A correction equation exists to predict LT using GET, but a consistent relationship between the two has not been established. PURPOSE: This study examined (1) the relationship between GET (V-slope) and LT (Dmax, LTDmax; 1.5 mmol blood lactate, LT1.5), and (2) the uniformity of this relationship across a range of fitness levels. METHODS: A GXT was administered to thirty-one subjects (mean age 24.3 ± 6.0 years) of various fitness levels. During this test, blood lactate and gas exchange data were collected. The HR associated with LT was determined using the Dmax and 1.5mmol increase methods, while GET was determined with the V-slope method. Repeated measures ANOVA examined differences in intrasubject GET-LT data, while Bland-Altman plots assessed the agreement between LT and GET HR. The GET-LT difference was plotted across fitness levels using two scatter plots, with GET expressed as a percentage of VO2max (GET%max) serving as the independent variable in each case. RESULTS: There was no significant difference between HR at GET and HR at LT using either LT methodology (GET = 167.84 ± 13.93, LTDmax = 167.32 ± 11.28, LT1.5 = 165.87 ± 10.30; P \u3e 0.05). Bland-Altman plots showed the relationship between GET and LT (LTDmax and LT1.5) tended to become more positive in those individuals with higher HR threshold values. Scatter plots of the HR difference vs. GET%max showed GET was lower than LT in those individuals with low GET%max values, whereas GET was higher than LT in those individuals with the highest GET%max values. CONCLUSION: While GET appears equivalent to LTDmax or LT1.5, the relationship between GET and LT is better described by accounting for inter-individual differences in GET%max. With this study showing an increased difference between threshold HR measures in more highly trained individuals, it is possible that gas exchange variables are more sensitive to changes in endurance training status than blood lactate variables. As such, future research should investigate the mechanisms underlying this relationship