The short answer, it all depends on your fitness level.
Historically, lactic acid has been blamed for fatigue, delayed-onset muscle soreness, and cramps. This is not the case at all. In fact, once lactate or lactic acid are metabolized, they are actually a preferred fuel source for quick, intense activities and exercise.
Exercise and Lactate Production from Glucose
When we exercise, glycogen, stored glucose within the muscle, is the primary fuel
source. During intense exercise when oxygen is limited, lactate increases more
rapidly than it can be utilized during the breaking down of glycogen (called
glycolysis).
Here is how it happens:
Glucose from the blood stream enters a cell and gets broken down via several enzymatic steps into pyruvate. One enzyme, lactate dehydrogenase (LDH), can
convert pyruvate into lactate in one easy step with or without oxygen. In biochemistry and physiology, this is an example of a very efficient way to make energy compared to other ways of making energy. The concentration of oxygen will determine how easily the lactate molecule will be produced into energy. In the presence of oxygen, a lot of lactate can be converted into energy. Without oxygen, lactate may still be converted into energy, but it is more dependable on several other factors which will be discussed in a moment. Because of how energy efficient lactate formation occurs, there is a lot of potential for lactate to be a preferred energy source.
The speed of lactate formation and removal is dependent upon a number of factors including:
• the type of muscle fiber that is exercising (more lactate is produced in fast-twitch muscles during intense exercise than slow-twitch muscles)
• the concentration of monocarboxylate transporters. These are molecules that transport energy-related molecules, such as pyruvate or lactate, into a cell.
• the amount and type of LDH (mentioned above)
• the overall ability for tissues to create energy from other energy systems, such as the oxidative system.
In addition, lactate and pyruvate formed in muscle during exercise can be used to manufacture glucose by a process called gluconeogenesis. This “extra” glucose supplements any existing blood glucose and muscle glycogen.
Lactate and Fatigue
Muscle fatigue is not due to “lactic acid build-up" in a muscle like motor oil in a car. During the formation of lactate (or lactic acid), there is an increase of positively charged hydrogen ions from the breakdown of the energy-producing molecule called adenosine triphosphate (ATP). These hydrogen ions increase the acidity of the blood, and they interfere with the muscle contraction process and the efficiency of the enzymes involved in ATP production.
Lactate and the Athlete
Athletes want to delay the feelings of fatigue in order to maximize their
performance. When the rate of lactate accumulation exceeds the rate of removal,
fatigue is initiated. The intensity of exercise has to be decreased if the
activity is to continue. This threshold is called the blood lactate threshold
or Onset of Blood Lactate Accumulation (OBLA).
Many tissues, particularly skeletal muscles, continuously produce and use lactate. Blood levels of lactate reflect the balance between lactate production and use. An increase in lactate concentration does not necessarily mean that the lactate production rate was increased. Lactate may increase because of a decreased rate of removal from blood or tissues.
Elite endurance and intermediate-anaerobic athletes are able toperform at such a high intensity level because:
• Their OBLA occurs at a higher percentage of their aerobic capacity.
• They can remove lactate more rapidly or convert it more efficiently to glucose.
Proper training programs can speed lactic acid removal from muscles while exercising. This can be achieved by combining high intensity, interval and over-distance training.
Unfortunately, in order to increase the OBLA, there must be an increase in lactic acid load during training – this hurts in the working muscles and it is exhausting! Training with a lot of lactic acid in the body stimulates an efficient use of lactic acid as a fuel.
High-intensity interval training will cause cardiovascular adaptations thatincrease oxygen delivery to your muscles and tissues. Also, better circulation helps speed the transport of lactate to tissues that can remove it from the blood. However, individuals who are not used to experiencing intense exercise that create a high concentration of lactate in muscles will require longer amounts of recovery time. As their fitness level improves, the recovery time can be decreased.
Because resistance training utilizes carbohydrates primarily as energy,high-intensity resistance training that produces high levels of lactate, such as certain CrossFit programs, are an effective way to improve OBLA which will improve overall fitness.
Long-distance or endurance training causes muscular adaptations that speedthe rate of lactate removal. Adaptations of endurance training increase the blood supply and the mitochondrial capacity of a trained muscle. Mitochondria are structures within the cells that process fuels, consume oxygen, and produce large amounts of ATP. A larger muscle mitochondrial capacity increases the use of fatty acids as fuel, which decreases lactate formation and speeds its removal.
Thus, many long-distance training programs incorporate different trainingmodalities throughout their overall training program in order to allow the body to develop a better ability to slow lactic acid production from carbohydrates and to enhance tissues ability to use lactic acid as fuel.
Summary
Lactate is an important fuel for the body during rest and exercise. It is one of our most important energy sources.
In order for you to improve your fitness level in the shortest amount of time, it is best to train at a high intensity. This is uncomfortable because it will involve training at a low-oxygen availability. However, over time, this will improve your body’s ability to use lactate as an energy source under strenuous exercising conditions, thereby increasing your fitness level and longevity. Therefore, get the most out of your time to exercise with the most benefits by training intensely!