Lactate threshold is a common phrase in the running community but has been a topic of some debate over the years. Traditionally, lactate threshold was recognised as the point on the lactate curve (generated during an incrementally increasing exercise test) where blood lactate concentrations rise above baseline. The thought was that this increase is lactate (or more commonly, "lactic acid") was due to a lack of oxygen delivery to the working muscles. Further build-up of lactate then coincided with fatigue and, subsequent, exhaustion. This led to the assumption that "lactic acid" build-up is what causes exhaustion during maximal exercise. This theory has since been disproven with lactate being somewhat redeemed.
Lactate is a product of a process called glycolysis which is the oxidation of glucose (sugar) in the mitochondria of cells. Glycolysis is vital for energy production but also produces acid (H+ or hydrogen ions) as a byproduct. One of the functions of lactate is to shuttle the hydrogen ions out of the mitochondria into the blood, where it can be transported elsewhere. This function is vital for balancing pH in the muscles where the working enzymes are sensitive to changes in acidity. Apart from the pH balancing function of lactate, it is also gets used as a fuel source in other resting/working muscles or by the liver to make more glucose. So what happens during exercise?
During exercise, the working muscles require more energy to produce the necessary power output. As intensity increases, so too do the energy demands. Increased energy demands increase the rate of glycolysis. This then means an increase in H+ ions and subsequently lactate to balance the increased acidity. This leads to a rise in blood lactate levels above resting (lactate threshold or LT1). After LT1, there is a steady increase in blood lactate as intensity increases. Here the body's ability to clear lactate is able to keep up with the increased production due to high rates of glycolysis. As intensity further increases, there is a point where the body can't clear lactate fast enough to cope with the increased production and there is a rapid increase in blood lactate. This point is known as LT2 or maximal lactate steady-state (MLSS). Beyond this point, more energy will be supplied through anaerobic metabolism - which will likely result in exhaustion.
The lactate curve can be used to identify intensity domains that are separated by two thresholds: lactate threshold and MLSS. Lactate threshold, therefore reflects the shift from moderate to heavy intensity whereas MLSS reflects the shift from heavy to severe intensity (along with critical power and FTP).
Graph taken from Faude et al. 2009 (4).
Methods of improving lactate threshold in runners has been widely studied, with the literature showing high intensity type training to be effective (1–3). A study conducted in 2011 compared two different methods of HITT training and its effect on maximal oxygen uptake, lactate threshold and running performance in a group of moderately trained runners. The training protocols compared a high-volume (70 km) lower intensity (65–82% of HRmax) training group; and a high-intensity (82–92% of HRmax) low-volume (50 km) training group. Although the study found both types of training to be successful, the greatest benefits were seen in the low volume high intensity group (3). Similarly, another study showed that training at a person’s lactate threshold has a greater effect on improving performance markers such as lactate threshold and VO2max than when training at lower intensities (2). Interesting, a study conducted in 2020 showed that although altitude training has a positive effect on aerobic performance markers, it had no effect on lactate threshold or anaerobic performance (1).
References:
- Bahenský P, Bunc V, Tlustý P, Grosicki GJ. Effect of an eleven-day altitude training program on aerobic and anaerobic performance in adolescent runners. Medicina (Lithuania). 2020 Apr 1;56(4).
- Enoksen E, Shalfawi SAI, Tønnessen E. THE EFFECT OF HIGH-VS. LOW-INTENSITY TRAINING ON AEROBIC CAPACITY IN WELL-TRAINED MALE MIDDLE-DISTANCE RUNNERS [Internet]. Available from: www.nsca-jscr.org
- Esfarjani F, Laursen PB. Manipulating high-intensity interval training: Effects on over(V, ̇) O2 max, the lactate threshold and 3000 m running performance in moderately trained males. J Sci Med Sport. 2007 Feb;10(1):27–35.
- Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Med. 2009;39(6):469–90.
WAYS TO IMPROVE IT:
running performance, .VO(2max), V.VO(2max), T(max) and v(LT) can be significantly enhanced using different HIT programmes - 10.1016/j.jsams.2006.05.014
Short duration altitude appears to yield meaningful improvements in aerobic but not anaerobic power in trained adolescent endurance runners - 10.3390/medicina56040184
The findings show that male middle-distance runners tested in this study improved in vVO2max and vLT more when they train around LT, than training with low intensity for a short period of 10 weeks - 10.1519/JSC.0b013e3181cc2291
