Before beginning the discussion of anaerobic threshold, there are a couple common misconceptions I would like to address-

1) When anaerobic metabolic pathways are active, no oxygen is present.

TRUTH: The body is never relying on anaerobic metabolism alone. Aerobic and anaerobic pathways are active concurrently; the balance merely shifts from one pathway to another when exercise intensity changes. Therefore, just because anaerobic pathways are preferentially activated does not mean cells do not have any oxygen available.

2) Lactic acid is what builds up in the bloodstream during intense exercise.

TRUTH: Upon production, lactic acid is immediately dissociated into lactate plus a hydrogen ion. Lactate build-up occurs in the bloodstream and may be measured in order to determine the lactate threshold.

At low to moderate exercise intensities, the body relies primarily on aerobic metabolism. When exercise intensity increases, the body shifts to utilization of anaerobic metabolism (however, aerobic metabolism is still occurring, just at lower levels) (1). The increased reliance on anaerobic pathways results in the build-up of lactate in the bloodstream. Also, during high intensity exercise, there is a sudden increase in carbon dioxide excretion. Lactate threshold is determined by the point in exercise where lactate clearance cannot keep up with lactate production, and thus lactate begins to accumulate in the bloodstream. Anaerobic threshold is determined by the exercise intensity where lactate increases above resting levels, and ventilation and excretion of carbon dioxide increase disproportionately to uptake of oxygen. In most cases, lactate threshold and anaerobic threshold occur at the same point in exercise. Because lactate threshold requires sampling of blood, anaerobic threshold is often used as a non-invasive way to estimate lactate threshold (2).

During anaerobic threshold testing, the volume of air expired, as well as the percentage of oxygen and carbon dioxide in the expired air, is measured. The ratio of the volume of air expired (V_E) to the volume of carbon dioxide in the expired air (VCO₂), and the ratio of V_E to oxygen uptake (VO₂) are used to determine the anaerobic threshold. Anaerobic threshold occurs at the point where V_E/VO₂ increases without an increase in V_E/VCO₂ (2).

In terms of athletic capacity, just how important is anaerobic threshold? In the past, VO₂max was utilized as the primary indicator of exercise capacity. We’ve all heard of athletes, such as Lance Armstrong, who have a VO₂max that is off the charts. However, not all elite athletes have such high VO₂max values. Recently, evidence has pointed to the importance of lactate/anaerobic threshold in predicting endurance capacity (2, 3). So don’t get discouraged if your VO₂max is not as high as you would hope, there is more to the story!

References:

(1) Owles WH. Alterations in the lactic acid content of the blood as a result of light exercise and associated changes in the CO2 combining power of the blood and in the alveolar CO2 pressure. Journal of Physiology. 69:214-237, 1930.

(2) Wilmore JH and Costill DL. Physiology of Sport and Exercise: 3^rd Edition. Champaign, IL: Human Kinetics. 2005.

(3) Karlsson J, and Jacons I. Onset of blood lactate accumulation during muscular exercise. I. Theoretical considerations. Int J Sports Med. 3: 190-201, 1982.

Hi everyone and welcome to the MB Endurance Sports blog!

VO2max. Most people have heard of it, but many do not understand what VO2max really is, aside from knowing that higher is better. Physiologically, oxygen is necessary for many processes within the human body. During exercise, oxygen must be transported to the working muscles to support the increase in muscle metabolism due to contraction. As the intensity of exercise increases, so does the transport of oxygen to the muscle, as well as the uptake of this oxygen by the muscle. At a certain point, the transport and uptake of oxygen cannot increase any further, a point known as VO2max.

You may have seen VO2max values expressed as L/min, or ml/kg/min. The first, L/min, is an absolute value, referring to the oxygen consumed per minute, regardless of body size. The second, ml/kg/min, relative VO2max, is more informative as it takes into account a person’s body mass. Using relative values, it is possible to directly compare individuals of different body sizes. However, gender differences in VO2max limit the ability to directly compare values of males and females. In untrained individuals, VO2max for females is around 20-25% lower than males (1). The gender gap is reduced to 10% in highly trained athletes (1).

In addition to gender differences, variation in VO2max exists from person to person due to genetics and training status. While training may increase VO2max, a strong genetic component predetermines 25-50% of an individuals maximal oxygen uptake capacity (2). Not all people will respond the same to exercise. In fact, there are some people, termed “non-responders,” who will not increase VO2max even with training (3). However, don’t be discouraged, there are other factors beside VO2max that play a large role in athletic performance!

Further, VO2max values vary between athletes in different sports. The highest values for VO2max have been recorded in Nordic skiers, with values up to 94 ml/kg/min in males, and 75 ml/kg/min for females. Runners aren’t too far behind, with well-trained males ranging from 60-85 ml/kg/min, and females 50-75 ml/kg/min. Swimmers and cyclists exhibit similar VO2max values, in the range of 50-70 ml/kg/min for males and 40-60 ml/kg/min for females. It is important to note that the values listed are from relatively young athletes, approximately 18-30 years old, as VO2max declines with age. In the non-athletic population in the same age range, VO2max averages 43-52 ml/kg/min for males and 33-42 ml/kg/min for females (1).

VO2max plays a big role in endurance capacity, but let’s not forget the importance of anaerobic threshold, which will be discussed in my next post!


(1) Wilmore JH and Costill DL. (2005) Physiology of Sport and Exercise: 3rd Edition. Champaign, IL: Human Kinetics.
(2) Bouchard C, Dionne FT, Simoneau JA, Boulay MR. Genetics of aerobic and anaerobic performances. Exerc Sport Sci Rev. 1992; 20:27-58.
(3) Green HJ, Jones S, Ball-Burnett M, Farrance B, Ranney D. Adaptations in muscle metabolism to prolonged voluntary exercise and training. J Appl Physiol. 1995 Jan; 78(1):138-45.