A comparative analysis of mathematical methods for detecting lactate thresholds using muscle oxygenation data during a graded cycling test.

Threshold determination for improving training and sports performance is important for researchers and trainers, who currently use different methods for determining lactate, ventilatory or muscle oxygenation (SmO2) thresholds. Our study aimed to compare the identification of the intensity at the first and second thresholds using lactate and SmO2 data by different mathematical methods in different muscles during a graded cycling test. Twenty-six cyclists (15 males and 11 females; 23 ±6 years, 1.71 ±0.09 m, 64.3 8.8 Kg and 12 3 training hours per week) performed a graded test on the cycle ergometer. Power output and saturation of muscle oxygen in four muscles (vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior) were measured, along with systemic lactate concentration. Our results showed that any method was reliable for determining the first muscle oxygenation threshold (MOT1) when comparing the lactate threshold in any muscle. However, the best method for determining the second muscle oxygenation threshold (MOT2) was the Exp-Dmax (p < 0.01; ICC=0.79-0.91) in all muscles. In particular, the vastus lateralis muscle showed the highest intraclass correlation coefficient (ICC=0.91, CI95%[0.81, 0.96]). However, results varied per sex across all muscles analyzed. In conclusion, although the first muscle oxygenation threshold could not be determined using mathematical methods in all the muscles analyzed, the Exp-Dmax method presented excellent results in detecting the second systemic threshold in the vastus lateralis.