Association between different Non-Invasively Derived Thresholds with Lactate Threshold during graded incremental...

We compared lactate threshold (T_Lac) with non-invasive markers of an aerobic-anaerobic transition; namely, ventilatory (VT) and tissue saturation index (TSI_T) thresholds. While identification of a breakpoint in blood lactate concentration ([BLa]) is common for determination of an aerobic-anaerobic transition, non-invasive measures, VT and NIRS, have also received attention as a means of determining this critical exercise intensity. We hypothesised that one or other of these non-invasive measures would have a strong association with T_Lac. Thirty-one (n=31) competitive male athletes (mean ± SD, age 29±9 yr, height 1.81±0.1 m, body mass 77.7±10.0 kg) performed graded incremental cycling to volitional exhaustion. Heart rate, TSI and gas exchange data were measured throughout and [BLa] was determined at fixed intervals. Threshold detection involved a segmented linear regression analysis minimising the squared sum of the residuals to determine T_Lac, TSI_T and VT. Workload and HR at T_Lac, VT and TSI_T were analysed using repeated measures ANOVA and correlation assessed using Pearson's and interclass correlation coefficients. Thresholds at TSI_T and T_Lac were not significantly different (255±35 vs. 249±30 W, P>0.05), suggesting that limitations in O₂ delivery could be closely linked to an aerobic-anaerobic transition. However, poor correlation (r=0.55, ICC=0.54 and 95%LoA of +67 and -54 W) suggested other factors may exert an influence. Mean VT occurred at a significantly higher workload than T_Lac (271 ±35 vs 249±30 W, P<0.001). Consequently, VT proved less useful, giving an indication of when an aerobic-anaerobic transition had already occurred. In conclusion, non-invasive markers of the aerobic transition are not concurrent with T_Lac.