The Effects of Longer Stage Durations During an Incremental Graded Exercise Test on the Finnish Lactate Threshold Concept

Abstract: Background: The end-product of glycolysis is lactate, which is subsequently oxidised to produce more energy. With increasing intensity, the rate of lactate production exceeds the capacity to eliminate lactate, leading to an exponential accumulation of blood lactate. Clinicians use incremental graded exercise tests to induce this blood lactate curve. Two distinct thresholds can then be determined from the curve, of which the second threshold is highly correlated with competitive endurance performance. The exact threshold intensities depend on the threshold concept used as well as on variations in the test protocol. Aim: To evaluate how the Finnish lactate threshold concept is affected by using stage durations of 5 minutes instead of the recommended 3, and to determine how this affects the maximal oxygen uptake. Methods: Seven well-trained adults were recruited to perform two separate incremental graded exercise tests with 3- and 5-minute stages, respectively. Lactate thresholds were determined directly by blood lactate measurements and according to the instructions of the Finnish Society of Sport Sciences. Breath-by-breath gas exchange was measured throughout the tests.  Results: No significant differences occurred at the first lactate threshold. At the second lactate threshold, heart rate, oxygen uptake and blood lactate remained unchanged, while speed dropped (-0.81 ±0.81 km/h; p=0.037) when comparing the 5-minute protocol with the 3-minute protocol. Both protocols resulted in similar peak oxygen uptakes, while speed at peak oxygen uptake decreased (-1.07 ±0.89 km/h; p=0.015) for the 5-minute protocol. Conclusion: This study showed that the chosen stage duration does not affect the blood lactate at the first or second lactate threshold, while a longer stage duration does affect the work intensity corresponding to the second lactate threshold of the Finnish lactate threshold concept. As the work intensity at LT2 is often used to prescribe endurance training and to predict competitive endurance performance, these findings can be of interest to the endurance testing community. It enables an extended understanding when designing test protocols and when analysing the results of a lactate threshold test. This might in turn contribute to more accurate exercise intensity prescriptions and thereby faster development among endurance athletes. Further research with more subjects as well as research into the validity of the Finnish lactate threshold concept is recommended.