Lactate threshold

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Lactate inflection point (LIP) is the exercise intensity at which the blood concentration of lactate and/or lactic acid begins to increase rapidly. [1] It is often expressed as 85% of maximum heart rate or 75% of maximum oxygen intake. [2] When exercising at or below the lactate threshold, any lactate produced by the muscles is removed by the body without it building up. [3]

Contents

The onset of blood lactate accumulation (OBLA) is often confused with the lactate threshold. With an exercise intensity higher than the threshold the lactate production exceeds the rate at which it can be broken down. The blood lactate concentration will show an increase equal to 4.0 mM; it then accumulates in the muscle and then moves to the bloodstream. [2]

Regular endurance exercise leads to adaptations in skeletal muscle which raises the threshold at which lactate levels will rise. This is mediated via activation of the protein receptor PGC-1α, which alters the isoenzyme composition of the lactate dehydrogenase (LDH) complex and decreases the activity of lactate dehydrogenase A (LDHA), while increasing the activity of lactate dehydrogenase B (LDHB). [4]

Training types

The lactate threshold is a useful measure for deciding exercise intensity for training and racing in endurance sports (e.g., long distance running, cycling, rowing, long distance swimming and cross country skiing), but varies between individuals and can be increased with training. [2]

Interval training

Interval training alternates work and rest periods allowing the body to temporarily exceed the lactate threshold at a high intensity, and then recover (reduce blood-lactate). [2] This type of training uses the ATP-PC and the lactic acid system while exercising, which provides the most energy when there are short bursts of high intensity exercise followed by a recovery period. [5] Interval training can take the form of many different types of exercise and should closely replicate the movements found in the sport being trained for. [2] Interval training can be adjusted to the individual, however it is important to consider the intensity of each interval, duration or distance of each interval, length of rest/recovery, number of repetitions, frequency of training and recovery type. [2]

Fartlek training

Fartlek and interval training are similar, the main difference being the structure of the exercise. Fartlek is a Swedish word, meaning speed play. [2] This type of training is a combination of continuous (generally aerobic) and interval training (generally anaerobic), involving consistent changes of pace/intensity throughout the session. [2]

Aerobic and anaerobic training

Aerobic training will not increase lactic acid tolerance, however, it will increase the lactate threshold. [2] Anaerobic training will increase tolerance of the effects of lactic acid over time, allowing the muscles’ ability to work in the presence of increased lactic acid. Training at or slightly above the lactate threshold improves the lactic acid tolerance. [3]

Measuring lactate threshold

Muscles are producing lactate even at rest, with resting blood lactate levels in the 1–2 mmol/L range. [6] Although the lactate threshold is defined as the point when lactic acid starts to accumulate, some testers approximate this by crossing the lactate threshold and using the point at which lactate reaches a concentration of 4 mmol/L of lactate. [3] Accurately measuring the lactate blood concentration involves taking blood samples (normally a pinprick to the finger, earlobe or thumb) during a ramp test where the exercise intensity is progressively increased. [7]

Accuracy of blood samples

Blood samples are a popular way of measuring the lactate blood concentration, however there are many factors that may affect the sample. Every individual has a different health status, thus the results from the blood lactate response can vary from factors prior to exercise such as the glycogen status of the participant and ambient temperature. [8] “Furthermore, the lactate concentration measured may vary depending on the sampling site sweat contamination, and the accuracy of the lactate analyser.” [8] There are many factors that may give this test a false reading; it is important that an individual takes these into consideration, to receive an accurate test. [7]

Lactate measurement of aerobic and anaerobic thresholds

The aerobic threshold (AeT or AerT) is sometimes defined equivalently to the lactate threshold (LT); as the exercise intensity at which blood lactate concentrations rise above resting levels. [8] In contrast, at the anaerobic threshold (AnT) the exercise is at an intensity beyond which blood lactate concentration is linearly related to exercise intensity, but increases with both exercise intensity and duration. [3] The blood lactate concentration at the anaerobic threshold is called the "maximum steady-state lactate concentration" (MLSS). [8]

AeT is the exercise intensity at which anaerobic energy pathways start to operate, considered to be around 65-85% of an individual's maximum heart rate. [2] Some have suggested this is where blood lactate reaches a concentration of 2 mmol/litre (at rest it is around 1). [3] The anaerobic energy system increases the ability to produce blood lactate during maximal exercise, resulting from an increased amount of glycogen stores[ clarification needed ] and glycolytic enzymes. [2]

In zone-based polarized training methodologies, LT1 is commonly used to designate the linear inflection point, often observed around blood lactate levels of 2.0 mmol/L, while LT2 is commonly used to designate the non-linear inflection point, often observed around blood lactate levels of 4.0 mmol/L.

See also

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References

  1. ↑ Goodwin, Matthew L.; Harris, James E.; Hernández, Andrés; Gladden, L. Bruce (Jul 2007). "BlLactate Measurements and Analysis during Exercise: A Guide for Clinicians". J Diabetes Sci Technol. 1 (4): 558–569. doi:10.1177/193229680700100414. PMC   2769631 . PMID   19885119.
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  4. ↑ Serge Summermatter; Gesa Santos; Joaquín Pérez-Schindler; Christoph Handschin (21 May 2013). "Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A". Proceedings of the National Academy of Sciences. 110 (21): 8738–43. Bibcode:2013PNAS..110.8738S. doi: 10.1073/pnas.1212976110 . PMC   3666691 . PMID   23650363.
  5. ↑ Hood, M. S; Little, J. P; Tarnopolsky, M. A; Myslik, F; Gibala, M. J (2011). "Low volume interval training improve muscle oxidative capacity in sedentary adults". Medicine and Science in Sports and Exercise. 43 (10): 1849–1856. doi: 10.1249/MSS.0b013e3182199834 . PMID   21448086.
  6. ↑ "Lactate Profile". University of California Davis.
  7. 1 2 Moran, Paul; Prichard, Jonathan G.; Ansley, Les; Howatson, Glyn (Feb 2012). "The influence of blood lactate sample site on exercise prescription". J Strength Cond Res. 26 (2): 563–567. doi: 10.1519/JSC.0b013e318225f395 . PMID   22240552. S2CID   207503948.
  8. 1 2 3 4 Mann T, Lamberts RP, Lambert MI (Jul 2013). "Methods of prescribing relative exercise intensity: physiological and practical considerations". Sports Med. 43 (7): 613–625. doi:10.1007/s40279-013-0045-x. PMID   23620244. S2CID   3291348.
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