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

We compared lactate threshold (TLac) with non-invasive markers of an aerobic-anaerobic transition; namely, ventilatory (VT) and tissue saturation index (TSIT) 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 TLac. 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 TLac, TSIT and VT. Workload and HR at TLac, VT and TSIT were analysed using repeated measures ANOVA and correlation assessed using Pearson's and interclass correlation coefficients. Thresholds at TSIT and TLac 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 TLac (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 TLac.