energy – sportsgeek

V02MAX

Here is the long promised posting on V02max.

V02Max and Work Intensity

Scientists frequently use V02max measurements to equate the intensity of exercise within and between groups of subjects. They speak in terms of work being performed, for example, at a speed that elicits oxygen consumption that is 70% of a person’s V02max. By doing so they can quantify the level of effort relative to each person’s individual maximum oxygen consumption and provide a more accurate representation of the work intensity. This method is great for scientists but not so good for coaches as coaches will often not know the V02max of their athletes. Coaches prefer to refer to efforts subjectively as a percentage of maximum. To help equate the two, information from studies in which work intensity has been reported as a percentage of V02max can be translated to percent efforts as follows:

efforts of 50% to 60% of V02max are probably equivalent to subjective feelings that the effort is 30% to 40% of maximum
efforts of 70% to 90% of V02max are probably equivalent to subjective feelings that the effort is 60% to 80% of maximum
efforts of 100% of V02max are probably equivalent to subjective feelings that the effort is 80% to 90% of maximum
efforts of 90% to 100% of maximum are probably equivalent to values that are between 110% and 130% of V02max

The distance of swimming repeats has a considerable effect on these crude estimates. During short repeats the athlete may sense a lower percentage of maximum effort than the actual percentage of V02max at which he or she is swimming because the duration of the swimming will not cause intense fatigue. Subjective feelings of percent effort will correspond more closely to the percentage of V02max indicated earlier when the repeats are longer.

Heart rates, if counted correctly and interpreted properly, can provide a more accurate method than subjective percentages of maximum effort for estimating the percentage of V02max during work.

V02Max and Performance

Although a person can improve V02max by training, research shows that heredity sets limits on the amount of improvement. Generally, athletes can improve their absolute maximum oxygen consumption by 15 to 20%.

For many years, the capacity to consume oxygen maximally was considered the most valid measure of an athlete’s ability to perform in endurance events. It was believed that a large V02max would provide an athlete with a distinct advantage in endurance events and, for that reason, endurance training emphasized improving this measure. However, persons who are able to consume large quantities of oxygen during races do not always defeat those with smaller maximum consumption rates. Other factors are involved.

Percentage Utilization of V02max

More predictive of performance in endurance events is fractional percentage of maximum oxygen consumption (%v V02max). It refers to the highest rate of work that a person can perform for a long period, say 20 to 40 minutes, without becoming fatigued. It is determined by measuring an athlete’s oxygen consumption during a maximum effort swim of 20 to 40 minutes and then determining what fraction of the athlete’s maximum oxygen consumption rate it represents. For example, let us assume an athlete has the ability to consume oxygen at a maximum rate of 70ml/kg/min. If the highest rate of oxygen consumption that the person can maintain for a long time with becoming fatigued is 60ml/kg/min, then the person is able to work at 85% of V02max.

As with V02max, heredity seems to play a role in determining the highest percentage of maximum that athletes can reach (about 20% trainable). A more common term used to identify the highest fractional utilization of V02max that can be maintained for a long period is anaerobic threshold. The anaerobic threshold does not indicate the rate of work at which anaerobic metabolism begins. It represents a manageable level of anaerobic metabolism that a person can sustain for a long period without experiencing severe fatigue.

Advantages of Increasing %VO2Max

Most athletes can only maintain speeds that require them to consume oxygen maximally for 1 to 3 minutes of continuous effort before they are forced to slow their pace because of fatigue. In long races and long training sets, athletes must select speeds that require less than a maximum rate of oxygen consumption so that they do not accumulate too much lactic acid in their muscles too early. For example, most runners can complete a marathon at an average pace that requires them to use 75% to 80% of their maximal oxygen consumption capacity. You should be able to understand now why the ability to use a larger fraction of V02max in these races would be a decided advantage. Athletes who can train themselves to use 85% to 90% of V02max without becoming fatigued should be able to run their long races at a faster average pace.

The ability to compete at a higher percentage of V02max should also be advantageous in shorter events. In middle distance and distance swimming races, the pace at which athletes must compete always exceeds the pace that would produce maximum oxygen consumption. Let us assume that two athletes with identical maximum oxygen consumption ability are swimming a race that requires each of them to work at a rate equivalent to 130% of V02max. Let’s assume also that one athlete is able to work at 85%of V02max without becoming fatigued whereas the other can work at only 80% of V02max without becoming fatigued. It should be easy to see that the athlete who can swim closer to 100% of V02max will be producing less lactic acid at race pace and should therefore be able to maintain that pace longer.

Athletes with a smaller V02max can sometimes excel over competitors who have larger values through their ability to compete at a higher percentage of maximum. For example, Alberto Salazar, former world record holder in the marathon, had a V02max of 70ml/kg/min, which was lower than that of many of his competitors. But he was able to run the marathon at a pace that used 86% of his maximum, a much higher percentage utilization of V02max.

Respiratory System

Respiratory System

The 2 primary purposes of respiration are to provide our bodies with oxygen and to remove carbon dioxide. This process makes life possible (along with a few other things). We could not live more than a few minutes without oxygen. A lesser-known but almost equally important function of respiration is to regulate the acid-base balance of the blood (this becomes important later when we learn the role acidosis plays in fatiguing).

The respiratory system consists of the lungs and a set of branching tubes that transport air and oxygen from outside the body to the bloodstream. During inhalation we take air from the outside into the mouth and nose, down the pharynx or throat, and into each lung by means of two large tubes called the bronchi. Within the lungs air travels through an ever smaller system of branching tubes called bronchioles until these finally end as small sacs called alveoli. Capillaries surround the alveoli.

The inhalation phase of respiration allows us to take in oxygen as a component of the air that comes into our bodies. Some of that oxygen remains in our bodies when we exhale the air. With the air we expel during the exhalation phase, we also expel carbon dioxide and some water vapor that our bodies produced.

We take in air through the nose and mouth. It travels down the pharynx through the bronchi, the bronchioles, and lastly to the alveoli, where it inflates these small elastic sacs. From there, some of the oxygen in that air diffuses from the alveoli into the bloodstream by way of the pulmonary capillaries. At the same time, carbon dioxide produced in the muscles diffuses in the opposite direction, that is, out of the capillaries and into the alveoli. The carbon dioxide is then transported through the bronchioles and finally exhaled into the air from the nose and mouth.

The term for the amount of air exchanged per breath is the tidal volume. The amount of air exchanged per minute is termed the minute volume. Average tidal volume is between 500 and 700 ml of air per breath, and we breath 12 to 15 times per minute. The average minute volume is thus 6 to 10 L of air.

Oxygen Consumption and Athletic Performance

Oxygen consumption refers to the amount of oxygen used during exercise. That amount is equal to the amount of oxygen taken in during exercise minus the amount exhaled, usually expressed as litres per minute.

The amount of oxygen used by the muscles each minute will be directly related to the intensity of the exercise until a maximum rate is reached. That maximum rate will be between 2 and 3L per minute for average nonathletic females and males, respectively. The rate can be as high as 4 to 6 L per minute for female and male endurance athletes. The term for the maximum amount of oxygen that a person can take in during 1 min of exercise is maximal oxygen consumption, more commonly referred to as VO2max. Values for VO2max are a direct expression of a person’s ability to supply energy for muscular contraction through aerobic metabolism.

Maximal Oxygen Consumption

We calculate maximal oxygen consumption, VO2max, by measuring oxygen consumption during repeated intervals of exercise at progressively faster speeds until the athlete reaches a plateau where a further increase of speed does not cause an increase in oxygen consumption. When that happens, the athlete has reached his or her maximum ability to consume oxygen.

One aspect of VO2max difficult for many people to understand is that athletes will reach it when they are exercising slower than their maximum speed. Athletes can continue to increase their speed even after they have reached their maximum ability to consume oxygen because of their capacity for anaerobic metabolism. Anaerobic capacity makes it possible for them to continue supplying energy to their muscles even though not enough oxygen is available to metabolize the chemical sources of that energy. They will only be able to this for a short time however because the chemicals that were not completely metabolized, principally lactic acid and more specifically the hydrogen ions in that compound, will accumulate in the muscles and change their pH from neutral to acidic, which will slow the speed and force of muscular contraction and in the process slow the swimming (running/cycling etc) speed.

During submaximal exercise, oxygen consumption will increase from its resting rate of around 0.25 L per min to some level that will sustain the contractile energy needed by the muscles. It will usually take between 1 and 3 minutes to reach this level of increased oxygen consumption. An oxygen deficit occurs during this period of adjustment. The oxygen deficit represents the oxygen that was needed but not available during the first few minutes of exercise. The athlete can repay the deficit during the remainder of the exercise if the intensity of work is low. To repay the deficit, the body can make available for a short time more oxygen than it needs to provide energy for work. The amount of oxygen consumed during the exercise period plus the oxygen deficit is termed the oxygen requirement for the task at hand.

If the demand for oxygen exceeds the amount that the athlete can repay during exercise, it will continue to build. The athlete will repay it after exercise by maintaining a high level of oxygen consumption for a short period. This period of additional oxygen consumption after exercise has become known as the oxygen debt. Although this term is in common use by members of the sporting community, it has become obsolete in the scientific community because sophisticated evaluation techniques have shown that the increased consumption of oxygen after exercise does not correspond directly to the oxygen deficit that occurred in the first few minutes of exercise.

New thoughts on oxygen debt

We now understand that the extra oxygen consumed after exercise does not entirely represent the repayment of a debt incurred during the exercise (we tend to take in more extra oxygen than what we owe). For this reason, scientists have suggested other terms for the additional oxygen consumed during recovery. One of these terms is excess post-exercise oxygen consumption (EPOC).

Typically, recovery oxygen uptake has fast and slow components. About half of the total amount of excess oxygen consumed during recovery will take place within 30 sec to 3 min after completion of the exercise, depending on the length and intensity of the exercise. This portion is termed the fast component for obvious reasons. The slow portion of recovery oxygen uptake refers to the slightly elevated breathing rate that can continue for several minutes or even several hours after exercise. One explanation is that the additional oxygen is probably used to metabolize the lactic acid produced during exercise. Another is that an increase of body temperature keeps the respiration rate elevated.

A Little Bit On Fast Twitch and Slow Twitch Fibres

Much of the info that will end up in this ‘Simple Science’ section will come from a magnificent book I have (all 2.5kg!!! of it) called Swimming Fastest by Ernest Maglischo. But don’t let the word ‘swimming’ put you off if you aren’t a swimmer. For most of this you can take out the word swimming and just plop in running, rowing, cycling, tennis, bob-sled, tiddly winks, whatever you are into. Only the middle section of the book is on physiology and energy systems, so don’t worry, if you print out the posts you won’t end up lying in bed for your nighttime reading with 2.5kg of pages scattered about. Besides which, although I make no apology for lifting info straight out of the book, in the interests of keeping everything nice and simple it has all been and will be radically condensed, hopefully without changing the meaning.

Ok, so this first bit is on fast twitch and slow twitch fibres:

Slow twitch (ST) fibres (red) contract 10 to 15 times per second (still sounds quite fast to me). Fast twitch (FT) fibres (white) contract 30 to 50 times per second. FT fibres also shorten more rapidly, and can shorten up to 6 fibre lengths per second. ST fibres have more endurance and they have more capacity for aerobic work, but their capacity for anaerobic metabolism is limited. ST fibres have more myoblobin, which is the substance that transports oxygen across the muscle cell. ST fibres also contain more mitochondria, the protein structures within muscle cells where aerobic metabolism occurs and ST fibres also have a greater concentration of the aerobic enzymes that catalyze the release of energy during aerobic metabolism. On the other hand FT fibres have a lower capacity for aerobic metabolism as they have less myoglobin, fewer mitochondria and a lower concentration of enzymes. FT fibres produce more lactic acid than ST fibres at equivalent workloads and so fatigue more quickly. They also use glycogen more quickly.

Now I thought this bit on endurance training was interesting and a bit unfair. Endurance training will increase the aerobic capacity of slow twitch and fast twitch fibres. Trained fast twitch fibres never reach the level of aerobic capacity of trained slow twitch fibres. An athlete can increase the aerobic capacity of fast twitch fibres, however, to a level that surpasses that of untrained slow twitch fibres. Conversely, strength and sprint training will increase the size and contractile speed of fast twitch and slow twitch fibres as well as their potential for rapid energy release. Fast twitch fibres however, possess a greater potential than slow twitch fibres for such increases. Although an athlete can increase contractile speed and force in slow twitch fibres that have been sprint trained, they never reach the level of even untrained fast twitch fibres. Sounds like sprinters get the best deal. I wish I was a sprinter!

There are 3 subgroups of FT fibres. Fta, FTb and FTc. We’re going to forget FTc as they, and what they do, are controversial and make up only about 3% of our fibres anyway. Fta fibres contract faster and with greater force than ST fibres and make up about 33% of our fibres. FTb fibres contract with about twice the force of Fta fibres and make up about 14% of our fibres. Roughly 50% of fibres are ST.

It’s not true that we only use ST fibres when we go slow and FT fibres when we go fast. ST are the first to contract. When the resistance increases, both the ST and FT fibres will contract to overcome it whether the movement is slow or fast.

It seems that although you can’t change an ST fibre into a FT fibre you can change the proportion of FTb’s and Fta’s. Most notably, FTb’s becoming Fta’s by an increase in the amount of myoglobin etc.

So that was ok wasn’t it? About 10 pages of the mighty tome condensed into one manageble post. The next section/s are some really easy back-to-basic stuff on the circulatory and respiratory systems.