Lactate Threshold and VO2 Max

Both lactate threshold and VO2 Max are both important concepts of mitochondrial adaptation. Let’s look at both.

Lactate Threshold

Lactate threshold (LT) is the point at which lactate production and release into blood by the muscles exceeds lactate clearance from the bloodstream. Resting blood lactate levels are about 1 milli mol per liter.

Other terminologies used to describe LT include Onset of Blood Lactate Accumulation (OBLA), Lactate Inflection Point (LIP), Maximum Lactate Steady State, etc.

The onset of blood lactate accumulation (OBLA) starts between 2 and 4 milli mols per liter of lactate in the blood.

A person’s lactate threshold indicates the extent of his/ her VO2 max or aerobic potential that is being utilized. With equal VO2 max, an athlete with a higher lactate threshold is likely to perform better in a continuous endurance event. Lactate is a byproduct of anerobic energy production. Anerobic metabolism is initiated to support short bursts of intense activity such as lifting weights or sprinting. Such activities that last less than 2 minutes are supported purely by anerobic energy production processes. If the activity lasts longer, there will be a mix of aerobic and anerobic energy production involved.

In the body, there are 2 types of muscle fibers – fast twitching and slow twitching. Fast twitching fibers are employed during activities that occur in short bursts. This is when anerobic energy production is triggered leading to lactic acid production.

Anerobic energy production kicks in after the upper limit of energy production from the aerobic pathway has been reached which corresponds to VO2 max. Lactate threshold is expressed as a percentage of VO2 max. So, if an athlete has a VO2 max of 70ml/ Kg/ min, and reaches the lactate threshold when VO2 is 35ml/ Kg/ min, then this athlete is said to have a lactate threshold of 50% VO2 max.

Lactate threshold can be increased through training. Even if the VO2 max stays the same, an increase in lactate threshold will improve performance. Increases in lactate threshold have been found to be because of increases in lactate clearance from the blood than decreases in lactate production.

In order to utilize a high lactate threshold, the athlete has to have sufficient glycogen stored in the body. If not, the body will start producing energy from fat which is suboptimal.

Lactate threshold may be determined using a graded exercise test conducted in a lab setting. A normal person usually has a lactate threshold of about 60% of VO2 max. With regular training in athletes, this goes up to about 80% of VO2 max. Elite athletes have lactate thresholds as high as 85% – 90% of VO2 max.

VO2 Max

VO2 max is an indicator of an athlete’s endurance. It is denoted in milliliters of oxygen per kilogram of body weight per minute. It is a measure of the maximum amount of oxygen that can be utilized by the body in a minute. Scientifically, VO2 max marks the upper limit of energy production using the body’s aerobic energy system. Elite athletes, because of their endurance training, tend to have a high VO2 max. VO2 max is more a measure of a person’s aerobic potential and cardiovascular fitness than a predictor of success.

The amount of oxygen utilized during activity increases linearly with the intensity of the activity until it reaches the VO2 max level at which it plateaus off. The higher the level of utilization of oxygen, the higher the energy produced by the athlete also. VO2 max is usually measured in sports performance labs using strict protocols. The volume and concentration of oxygen in inhaled and exhaled air are measured at different levels of exercise intensity to derive this. There are easier ways to estimate the approximate VO2 max such as the Bruce Treadmill Test, but the results will not be very accurate.

The highest VO2 max is usually recorded around the age of 20. By the age of 65, it usually falls by about 35%. With an increase in altitude, because of the lesser oxygen availability, VO2 max falls by about 5% for each additional 5000 ft climb. For a person with a sedentary lifestyle, a VO2 max of about 35ml/ Kg/ min should be expected. For elite athletes, this will be in the range of 70ml/ Kg/ min. The highest recorded VO2 max is 90ml/ Kg/ min, in a cross country skier. Lance Armstrong, the ace bicyclist, has a VO2 max of 85ml/ Kg/ min.

VO2 max can be increased through physical training. However, 25 – 50% of the variability in VO2 max between individuals has been linked to heredity.

There are two drivers of VO2 max that are often discussed and these are 1) the amount of oxygen that is transported to the muscle cells and 2) the ability of muscle cells to use this oxygen to generate energy. The first of these is directly related to the ability of the heart to pump blood since oxygen is carried to cells by hemoglobin in the blood. The ability of the heart to pump blood is, in turn, the function of the stroke volume (the volume of blood pumped by the heart during each beat) and the heart rate (the number of times the heart beats in a minute). Both these fall with age beyond the age of 40 or so. The stroke volume decreases when the heart muscle loses its compliance. Even with normal heart muscle, the volume of blood reaching the cells during each beat falls when the blood vessels narrow due to the deposition of cholesterol plaques with age (atherosclerosis). Similarly, the maximum heart rate possible also falls with age beyond 40 yrs as is clear from the oft used formula, Maximum Heart Rate (MHR) = 220 – Age. When age goes up, the MHR comes down. The second driver of VO2 max, the ability of muscle cells to utilize oxygen to generate energy, is dependent on the level of oxidative enzymes available in the mitochondria of muscle cells. Mitochondria are the power generators of the cells. The influence of oxidative enzymes in the mitochondria on VO2 max has not been studied extensively as of now.