Lactate Inflection Point (LIP)

Lactate inflection point is often confusing and misunderstood by students.

What is LIP

Lactate inflection point is the point where lactate removal is equal to lactate production. This means at this point there is no excess build up of lactate. It is also important to remember that the amount of lactate is directly linked to the number of hydrogen ions within the muscles which are a cause of fatigue.

LIP occurs when the body is working aerobically.Meaning the predominant energy system is the aerobic energy system when LIP occurs.

Beyond the lactate inflection point the amount of lactate produced increases exponentially(sharply), this is because beyond LIP lactate production is greater than lactate removal as there is insufficient oxygen to remove lactate and the athlete has been relying heavily on anaerobic pathways for energy production.

Therefore the athlete will soon experience fatigue as hydrogen ion build up that accompanies an increase in lactate production will  raise acidity within the muscle causing fatigue.

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(Image obtained from you tube,https://www.youtube.com/watch?v=XvIICKaHbKQ)

Improving lactate inflection point

Lactate inflection point can only be increased via aerobic training. To improve LIP athletes should train just below their own LIP to improve it.

Aerobic training results in chronic aerobic adaptations that are responsible for increasing LIP. For example an increase in mitochondrial number and size results in an increased capacity to oxidise glucose this will cause an increase in LIP.

This is because aerobic adaptations work to improve the body’s ability to make ATP aerobically which reduces the body’s reliance on anaerobic glycolysis which produces lactate. Hence LIP can be delayed as the anaerobic glycolysis system is not used until much higher intensities are reached.

A delayed lactate inflection point is advantageous to aerobic performance as it delays fatigue brought about by high lactate levels so that the athlete can work at higher intensities for longer.

  • LIP in untrained individuals usually occurs at 55-70% of VO2 max.
  • LIP in trained individuals usually occurs at 75-90% of VO2 max.

Difference between Increased lactate inflection point and Increased Muscle buffering capacity

Students should  note that Lactate inflection point is improved as a result of aerobic training and this is different to the increased buffering capacity of the muscle achieved through anaerobic training. Buffering capacity of the muscle refers to the muscles increased ability to cope with higher amounts of metabolic by-products such as lactate and hydrogen ions. Whilst increased LIP refers to the actual delayed production of lactate until higher intensities are reached. So this will enable the individual to work harder for longer aerobically. While increased buffering capacity will enable an athlete to work harder for longer anaerobically until fatigue occurs.