Lactate Thresholds - Determinants

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What are the determinants of the lactate threshold?

The chart below is a model of performance for endurance events

Model of performance in endurance athletic events by Jan Olbrecht

The following are definitions and a brief discussion of each element that feeds into the lactate threshold and thus determines performance:

Aerobic capacity - this is the most important variable determining the lactate threshold in an endurance event but it certainly is not the only one. It is often called VO2 max and it varies considerably over a training season. It is the maximal oxygen transported from the environment to the muscles and used there to create energy for physical activity. It varies depending on the specific activity, since the amount of oxygen that can be transported and utilized for different activities may vary. So an athlete's VO2 max will be different for running versus cycling. It will also vary throughout the training and competitive season. Improving aerobic capacity is the objective of most training for an endurance athlete.

Aerobic power - This is the percentage of aerobic capacity or VO2 max that can be sustained during an event. It is not possible to utilize all of one's aerobic capacity during an event; in reality nearly every athletic event is completed at some fraction of VO2 max. The actual percentage is the aerobic power or the percentage of capacity that can be utilized.

But why cannot an athlete use all his capacity? The anaerobic capacity determines how much of the aerobic capacity can be utilized.

anaerobic capacity - like aerobic capacity it is the ability to generate energy, but through the glycolytic system or the breakdown of glucose. We define it as the maximal or organic potential to produce pyruvate or lactate, which is the output of the anaerobic glycolytic system. This glycolytic system is where lactate originates in the body, and it uses glucose for fuel. The anaerobic system does not produce much energy in an endurance race – most comes from the aerobic system. However, the anaerobic capacity will impede performance if it is either too high OR too low.

The anaerobic system has been ignored by nearly all coaches and exercise physiologists when discussing the training of triathletes. But that is a big mistake. For long endurance events, anaerobic capacity affects performance in two ways besides producing a small amount of energy.

First, anaerobic capacity helps determine aerobic power and thus the lactate threshold, because it interacts with aerobic capacity. Briefly, the anaerobic system limits the body's use of the aerobic system by putting out more lactate and hydrogen ions than the aerobic system can absorb, inhibiting muscle contraction. We refer to this as the gate-keeping effect, which is discussed in detail on the CD-ROM and elsewhere in this triathlon section. If the anaerobic capacity is too high the athlete will be slowed down by the excess acidosis that accompanies lactate production. So for endurance events it is necessary to train the anaerobic capacity down. The lower it is the more the aerobic system can be utilized before acidosis occurs.  But, it can’t be TOO low....

Second, because anaerobic capacity affects performance by determining the total amount of carbohydrates that are available for the aerobic system during competition. Carbohydrates metabolize faster than fats and unless the anaerobic system is generating enough carbohydrate fuel for the aerobic system, the aerobic system will have to use a higher percentage of fats which metabolize slower and force the athlete to slow down. Thus, if the anaerobic capacity is too low, less carbohydrate will be available for aerobic metabolism. In our first point it indicated that a lower anaerobic capacity would be desirable in order to raise aerobic power and the threshold and that is true but if it is too low it will cause the athlete to rely too much on fats and this will slow down the athlete. Supplementing the glucose/glycogen that is used during a race is why an athlete will consume glucose products as the race progresses so that he/she can utilize more of a faster metabolizing carbohydrate fuel instead of fats.

Economy - this is a catch-all for a lot of different things. But essentially the athlete uses energy generated in the muscles to cause contraction of the muscles and this contraction must be directed toward getting the athlete to the finish line as quick as possible. Two athletes can complete a race in the same time but if one of the athletes uses less energy to do so then that athlete is said to have a better economy of motion. There could be several reasons for this:

metabolic efficiency - only about 20% of the energy generated in the muscles is utilized to produce muscle contractions. The rest is converted to heat in the muscle and is dissipated. But some athletes are able to utilize a slightly higher percentage for the contraction of the muscles. This means they are utilizing less overall energy since a higher percentage is being used for contraction. Such athletes are said to be more efficient metabolically. For cycling, cadence may affect metabolic efficiency.

motion mechanics - some athletes have a more economical motion in swimming, cycling or running. Thus, they are able to cover the same distance but with less energy expended than another athlete with inefficient stroke mechanics in swimming or an inefficient running motion/mechanics or an inefficient bike position or motion. Much time is spent in swimming instruction correcting stroke mechanics and body position in order to make the athlete glide through the water with more ease, using less energy. Muscle strength and flexibility are often key.

friction or resistance - some times one can change the interface with the physical environment and go faster with the same energy expenditure by reducing friction. For swimming, the use of a wetsuit or shaving body hair will reduce friction in the water and allow the athlete to go faster. Running shoes can affect one's speed for the same energy expenditure. For cycling, one experiments with position on the bike, clothing, and the bike itself and fittings, all to reduce the friction and resistance encountered during a cycling race. Also the weight of the bike or clothing will have an energy cost. Obviously, body weight and strength affect economy so optimum body weight and muscle development are key objectives of a training program in addition to physiological training.

All these factors come together and produce a physical measure which we call the lactate threshold. And it is this lactate threshold that will determine the performance of the athlete more than any other factor. That is why it is so important and why most endurance training is designed to raise the lactate threshold.

All the modules in the triathlon section are aimed at helping the athlete towards this final goal, raising the lactate threshold.

Other - "Other" is things like psychological factors, hydration, electrolyte replacement, hyperthermia, nutrition, injury etc. Things like wind and current in a distance swimming race, heat and hills in a cycling race or marathon affect things in a major way but this is included under the economy factor, as we are defining economy as everything that affects implementation of aerobic power.

Last update August 7, 2014 All contents © Sports Resource Group, Inc

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