Posted: December 3, 2004

Science of Sport: The Truth About Oxygen And Running

By Owen Anderson, Ph. D. - Copyright © 2002-2004

Many athletes currently believe that altitude training has a positive impact on fitness and competitive ability. Such faith in altitude has been reinforced by the incredible successes of the Kenyan distance runners, most of whom train at altitude when they are in Kenya.

The practice of altitude training is also logically appealing. After all, residing at altitude increases red-blood-cell concentrations. Lofty densities of red cells can supply oxygen to muscles at higher rates, compared with parsimonious red-cell levels. Consequently, VO2max should improve, and athletes should be able to perform longer and faster without being limited by fatigue after an extended period of altitude training. In effect, altitude residency is a legal form of "blood doping."

Not everyone is convinced that altitude is a good thing, however. Altitude naysayers point out that altitude giveth - and also taketh away. The problem, they say, is that while altitude is chipping in a few more red corpuscles, it is also chipping away at overall fitness, because of the lower quality of training which is carried out at higher elevations. This viewpoint is also a reasonable one: Scientific research has shown that when athletes journey to altitude, the quality of their workouts usually declines significantly, unless they are 100-meter sprinters who carry out nothing more than short-duration, highly intense training.

Many of these naysayers contend that what most athletes should be looking for is more oxygen - not less. Their contention is that although high oxygen concentrations do not boost red-blood-cell production, they can hike the quality of training sessions to such a degree that a high-altitude trainee will inevitably become much fitter than a poor sap who works out in regular air or in the thin atmosphere prevailing at altitude. Some of these oxygen proponents also suggest that a few blasts of inhaled, 100-% oxygen before a competition or high-quality workout can enhance performance considerably.

Are these oxygen-lovers right? To find out, let's first examine the question of whether pre-exertion oxygen might be helpful to athletes. To understand the research carried out in this area, let's think for just a moment about oxygen and the blood. Bear in mind that the rationale for the use of supplemental oxygen before exercise is that such inhaled oxygen can be "stored" in the blood via attachment to a protein contained in red blood cells called hemoglobin. The extra oxygen could then used by muscles during the beginning stages of exercise to create usable energy at higher-than-usual rates.

However, under normal circumstances (when an individual is simply breathing in regular air while at rest) the hemoglobin in human arterial blood is already about 97-% saturated with oxygen. This 97-% saturation produces a total blood-oxygen concentration of approximately 200 milliliters of oxygen per liter of blood. Thus, if an athlete were to breathe in 100-% pure oxygen, the amount of oxygen bound to hemoglobin could rise by only 3% (from 97 to 100%), or just six milliliters (.03 X 200 = 6) (1).

That makes it sound as though breathing in pure oxygen would be somewhat trivial, but it turns out that the amount of oxygen dissolved in solution in the blood (not just bound to hemoglobin) is proportional to oxygen's arterial partial pressure. When this pressure increases from approximately 100 mm Hg (when breathing in sea-level air with 21-% oxygen) to about 700 mm Hg (when breathing in pure oxygen), the oxygen dissolved in the blood increases from three milliliters per liter to 21 milliliters per liter. In other words, a human with a typical blood volume of five liters can store almost 100 extra milliliters of oxygen prior to exercise by breathing in the pure stuff. That's nothing to sneeze at - or to sneeze out.

So - does research really show that those 100 milliliters of O2 can make a difference to athletes? Remarkably enough, investigations in this area have often focused on short-duration, high-intensity, primarily "anaerobic" exertions. This should seem strange to you. After all, anaerobic (literally, "without oxygen") efforts are precisely the ones which depend to the smallest extent on the utilization of oxygen. It seems to make little sense to add oxygen to a situation in which the poor gas normally plays such a small role.

If that was your thought, good thinking! However, remember that in longer-duration, "aerobic" events those 100 milliliters of oxygen would be a drop in the bucket and would be very unlikely to determine overall success. For example, an elite athlete running a 10-kilometer race in 28-minutes flat could easily be consuming oxygen at a rate of more than 5000 milliliters per minute, which would sum to over 140,000 milliliters for the whole race. The 100 milliliters would add up to no more than seven-hundredths of one percent of the needed oxygen! However, it is important to be cautious when interpreting this research. For one thing, the evidence seemed to suggest that the oxygen would have to be inhaled for an adequate amount of time - and also no more than two minutes before the start of an athletic event (3). If the time interval between the last breath of pure oxygen and the start of competition or high-quality training is longer than two minutes, the effect of breathing in oxygen would be negligible; the surplus O2 would simply be lost via the lungs to the external environment. Of course, this represents a real problem: 800-meter runners can not take oxygen tanks to the starting lines of their races, for example, nor can sprint swimmers position O2 tanks near their starting blocks. Breath-holding is not a viable way to skirt this problem; in fact, it might actually harm athletic capacity.

In addition, in the studies in which oxygen boosted performance the athletes involved knew that they were breathing in pure oxygen, and thus a powerful placebo effect may have vitalized their performances. No "double-blind" research has ever linked pure-oxygen breathing and heightened performance in a convincing way.

Occasionally, one hears of sports drinks which have been "enlivened" with pure oxygen, but such products are unlikely to increase performance - or even nudge blood-oxygen concentrations up a notch. Once the sports-drink bottle is uncorked (or the cap is screwed off), the excess oxygen immediately begins a mad rush to the atmosphere around the bottle. Similarly, any supplemental O2 which actually reaches the gullet will try to bubble its way up the esophagus, and the amount of extra oxygen which reaches the bloodstream and courses its way to a real muscle cell will assuredly be small.

Now that we have disheartened you thoroughly about the possibility of taking 30 seconds off your next 5K by fitting an oxygen mask to your face in the starting area, let's pose another interesting question: How about using pure oxygen after exercise is over? After all, some coaches and athletes have suggested that post-exercise oxygen should boost the recovery process after strenuous training, making it easier for athletes to carry out subsequent high-quality efforts (later in the day, for example, or on the following day). Once again, this appears to be a very reasonable hypothesis. In theory, the increased rate of oxygen flow to tired muscles should increase energy availability and kick-start important recovery processes, including the repair of cell structures damaged by exercise and the re-synthesis of that ubiquitous and all-import high-energy compound - glycogen.

Alas, the news is again not good. Some studies have indeed detected quicker recovery with post-exercise oxygen intake, but again the subjects in these investigations knew exactly what they were breathing and might have taken in a psychological boost along with their nice gas. Overall, it appears that breathing in oxygen after exercise is over has no positive impact on heart rate, ventilation rate, post-exercise oxygen uptake, or any known physiological variable associated with recovery (3).

When examined closely, such findings really should not be surprising. After all, the post-exercise recovery period is a time frame which is marked by sub-maximal heart rates and sub-maximal rates of oxygen consumption. In other words, recovery does not require oxygen delivery to be extremely high, as it is during intense exercise. Piling on the oxygen during recovery is like adding another half-cup of water to your goldfish's aquarium; the poor little fellow already has enough aqueous medium, and a little more will not be helpful in any way.

This anti-O2 line of thinking has been supported by studies which show that oxygen breathing has no positive effect on performance when sub-maximal exercise is followed by maximal exercise, with supplemental oxygen intake sandwiched in between the two types of exertion (4). However, there is one time when breathing in extra amounts of oxygen can be very helpful, and it is during exercise.

Before we talk about oxygen supplementation during exercise, however, let's review what we have learned so far. As we noted, pulling in extra O2 could theoretically be helpful just before a competitive effort, except that athletes would have to hold their breaths for a rather extended period - from the time they took their last draught of oxygen until their events actually began (oxygen tanks are not permitted on the track before an 800-meter race for example, or at the edge of the pool prior to a 200-meter swim). Such breath-holding is impractical and in some cases impossible, and indeed no well-controlled scientific study has ever linked pre-exercise imbibitions of oxygen with significant upswings in performance. When you see an athlete with an oxygen mask over his/her face just before entering a competition, you can rest assured that the practice will have as predictable an effect on performance as cartomancy.

While it might seem logical that post-exercise oxygen would boost the recovery process (by spurring metabolism and potentially hiking the synthesis of valuable chemical compounds within muscle cells), there is also no evidence that après-ski (or after-anything) O2 could be particularly salubrious to muscles and connective tissues. In fact, the post-exercise period is ordinarily marked by submaximal heart rates and modest rates of oxygen delivery to tissues which have been involved in the workout. In other words, there is not a high demand for oxygen during recovery; if there were such a demand, the heart would willingly kick more blood and oxygen in the muscles' direction. Actual oxygen supplementation would not be required.

Nonetheless, a plethora of scientific research suggests that athletes can exercise longer and more intensely when they breathe in extra oxygen during their exertions. Of course, the rationale for the utilization of oxygen during exercise is based on the idea that during intense exercise the rate of supply of oxygen to working muscles does not satisfy the demand for oxygen created by the muscles. Hypothetically, an athlete could - by breathing in supplemental oxygen - more fully saturate his/her blood with O2 and thus supply the desired oxygen without actually increasing blood flow or heart rate (during intense exercise, both of those variables - blood flow and heart rate - might already be "maxed out" anyway).

If you are an oxygen-supplementation skeptic, you might at this point be asking that short but often-critical question: "So?" As you are undoubtedly aware, even if taking in additional oxygen during exercise did boost performance, it is hard to imagine soccer players running around the pitch with oxygen tanks strapped to their backs, and it is equally difficult to envision swimmers moving back and forth in the pool while well-tethered with oxygen tubes.

Those are of course good points, but the basic idea would be to use oxygen during training, not during competition. An athlete might train in an environmentally controlled room with an oxygen-enriched atmosphere, for example, or even pedal away on a cycle ergometer, engage in full-tilt effort on a rowing machine, or run at high speed on a treadmill while wearing a tight-fitting mask connected to an oxygen-supplying device. The additional oxygen could enhance the quality of the workout being performed, which of course is a good thing: Competitive fitness is after all an attribute which is built up slowly but steadily over time as a result of the completion of high-quality training sessions. The higher the quality of the training, the greater the chance that the highest-possible level of fitness will be attained.

There is one oxygen-related problem which still must be surmounted, however: Although the basic "meet-the-muscles'-demands" rationale for using oxygen during training seems as straightforward as a set of Cartesian coordinates, the principle has not always held up well under scientific scrutiny. In fact, one well-conducted investigation found that although the breathing of hyperoxic gas mixtures did indeed increase the oxygen content of arterial blood, this oxygen-concentration upgrade in the blood was perfectly balanced by a decrease in blood flow to the working muscles - so that actual oxygen delivery to the muscles was exactly the same in hyperoxic and normoxic conditions (1). Through physiological feedback mechanisms, the muscles seemed to be saying, "Thanks! The blood you are sending me is richer now, so I don't need quite so much of it. Let some other part of the body use some of the red stuff I've been consuming up until now."

Nonetheless, VO2max (maximal rate of oxygen consumption) does increase by 2 to 5% when athletes exercise in a hyperoxic environment, compared with a normoxic one, and performances improve by up to 40% when athletes breathe pure, 100-% oxygen, in contrast with normal, 21-%-oxygen air (2). How can this be - if actual oxygen delivery to muscles is not different in the two situations?

There are various possibilities, but it is clear that an increased availability of oxygen decreases pulmonary ventilation (the movement of air in and out of the lungs) and thus reduces the muscular work required for breathing (3), an effect which could lead to a significant improvement in athletic performance. In one study, nine well-trained individuals ran to exhaustion on a treadmill on five different occasions while breathing in one of a range of five different gas mixtures - 20%, 40%, 60%, 80%, and 100% oxygen. In all five cases, the running speed selected for the treadmill exertion was exactly 10-% faster than the velocity required to elicit VO2max (4). For many good runners, this would be comparable to a topmost, 1500-meter running tempo.

The five bouts of exercise were scheduled one week apart to minimize the effects of test-related fatigue on subsequent tests, and the athletes were given no cues regarding the gas mixtures they were breathing in - or even their actual running times. The results showed clearly that as percent oxygen increased beyond 60-% O2, running time at 110-% vVO2max also increased; 80-% oxygen was better than 60%, and 100-% O2 was preferable to 80%, from the standpoint of fatigue resistance at a running speed of 110-% vVO2max. Notably, ventilation decreased at the higher-end oxygen mixtures, and the decrease was a function of decreased breathing frequency, not the amount of air exchanged per breath.

In a unique follow-up study (3), 10 athletes ran to exhaustion on a treadmill while breathing in one of four gas mixtures:

	(1) 20-% oxygen and 80-% nitrogen (very similar to "normal" air),
	(2) 20-% oxygen and 80-% helium,
	(3) 80-% oxygen and 20-% nitrogen, and
	(4) 80-% oxygen and 20-% helium.

In this investigation, performance times increased significantly under hyperoxic conditions (#s 3 & 4), but they also improved appreciably whenever helium was "in the mix" (#s 2 & 4). In other words, performance improved whenever oxygen was better supplied, but it also was attenuated when oxygen was simply normal and helium "pinch-hit" for nitrogen. How should we interpret these findings?

As it turned out, the mass of air moved in and out of the lungs was less whenever helium - rather than nitrogen - was combined with oxygen, as in cases 2 & 4 (remember that helium is considerably lighter than nitrogen), and thus the work performed by the respiratory muscles was considerably less. In addition, the work carried out by the muscles was lower whenever oxygen levels were elevated (cases 3 & 4), as though the respiratory muscles realized they did not have to make such a fervent effort to pull oxygen in from the atmosphere. The broad conclusion can be that performance rises whenever the load on the respiratory muscles is reduced.

There are two possible reasons for this: (1) Perceived effort - the level of difficulty an athlete consciously assigns to a specific type of intensity of exercise - depends on a variety of physiological cues, including the degree of stress experienced by the respiratory system during the conduct of the exercise. If this degree of respiratory stress is lightened, then the intensity of exercise is felt to be lower and easier, and an athlete will usually have confidence that he/she can perform at the given intensity for a longer period of time. (2) A reduced respiratory-system workload translates into a lower whole-body demand for oxygen during exercise (don't forget that the respiratory muscles require oxygen during exercise, too, just as the arm and/or leg muscles do). Since the oxygen cost of exercise is reduced, an athlete will be operating at a lower fraction of VO2max, and thus the duration of exercise can be increased (there is a direct inverse, relationship between exercise sustainability and %VO2max; the higher the % VO2max, the shorter the time period over which exercise can be sustained).

There is also one other key reason why oxygen supplementation can work. Interestingly enough, some athletes who are able to sustain exercise at very high intensities experience "desaturation" of their hemoglobin (i. e., the amount of oxygen bound to hemoglobin declines) when they work very strenuously under normoxic conditions (remember that hemoglobin is the red-blood-cell compound which actually "carries" oxygen through the blood). In theory, these accomplished athletes might benefit from breathing in high-oxygen gas mixtures as they trained at very high intensities, since under such conditions it would be less likely that their hemoglobin would become desaturated with O2, and thus oxygen could be supplied at higher rates to working muscles.

To investigate this possibility, researchers at the University of Florida divided 20 healthy male athletes into two groups. 13 of the athletes were placed in a "trained" group which had an average VO2max of 56.5 ml/(kg-min), and the other seven were positioned in a "highly trained" group with a mean, lofty VO2max of 70.1 ml/(kg-min). Members of this latter group were known to experience hemoglobin desaturation during exercise, which was defined as a condition in which the percentage of oxygen bound to hemoglobin fell to 92% or below (the "normal" or resting value is considered to be about 97%).

Athletes in both groups performed two incremental cycle ergometer tests at sea level to determine VO2max (5); one exam was completed under normoxic conditions (at 21-% oxygen), while the other was undertaken in a slightly hyperoxic situation (26-% oxygen). As it turned out, the percentage of oxygen bound to hemoglobin during maximal exercise was significantly higher for both groups under hyperoxic conditions. However, the highly trained group was able to elevate VO2max from 70.1 to 74.7 under hyperoxic conditions, while the trained-group's members were unable to push up VO2max. Thus, it seems clear that pulmonary gas exchange can contribute significantly to the limitation in maximal aerobic capacity in highly trained athletes; after all, once the Florida researchers improved pulmonary gas exchange (by adding oxygen to the mix), VO2max increased rather dramatically.

The benefits of oxygen supplementation for workout quality became apparent in research carried out at the University of New Mexico several years ago (6). Initially, the cyclists involved in the study trained in a very basic way: They spent about two-fifths of each training session working at a modest intensity of 50 percent of their maximal work load (max work load was simply the highest work rate - in Watts - which the athletes could sustain for at least 30 seconds). Heart rates probably reached 50 to 60% of maximal during these light efforts.

During the remainder of each workout, however, the athletes trained at a fairly difficult intensity of 85% of maximal work load, which produced heart rates of around 90 to 95% of maximal. The cyclists continued training in this manner for several weeks until their performances reached a plateau, beyond which no further improvements in endurance were attained. Depending on the athlete, it took from seven to 35 weeks (!) to reach this plateau.

After reaching their leveling-off points in performance capacity, the athletes tried to step up their workout quality by alternating three-minute work intervals at 95% of maximal work load (instead of the previous 85%) with two-minute recovery intervals at 50% of maximum. However, the 95-% intensity proved to be so tough that it was impossible for the cyclists to complete a full 40-minute workout. In fact, the best they could do was to cycle for a total of about 10 minutes - or just two work intervals and two recoveries!

To make it possible for the cyclists to complete a full workout at the seemingly unattainable 95-% intensity, the New-Mexico scientists allowed the athletes to breathe an air mixture containing 70-% oxygen as they exercised (remember that the oxygen concentration of "normal" air is 21 percent, unless you happen to live in London, New York, or Los Angeles, where oxygenated air is slightly more elusive). With the added oxygen, the cyclists were suddenly fully able to complete the higher-intensity, 40-minute workouts (containing eight work intervals and eight recoveries), and they carried out a rather remarkable total of four of the workouts per week over a six-week period!

Note that this is exactly the kind of situation in which you would expect oxygen supplementation to be beneficial. The athletes were experienced, and they were working at close-to-maximal levels during their workouts. Thus, their hemoglobin was likely to be desaturated, a situation which the supplemental oxygen could at least partially correct. The improved oxygen supply allowed exercise to continue longer at the chosen, red-hot intensity. A key factor may have been that the added oxygen decreased respiratory-muscle work and thus made the flaming efforts feel more tolerable.

You will be glad to hear that the six weeks of hyperoxic work also improved the athletes' performances considerably (after all, what good are hard workouts unless they actually lead to better physical outcomes?). The athletes' endurance levels while pedaling at 85% of max work load (90 to 95% of max heart rate) increased by 32% (!) after six weeks, and heart rate during high-intensity cycling declined by around five beats per minute. Importantly, the athletes achieved their gains without having to spend more time training; they worked out with the same frequency and duration which they had utilized prior to the six-week, hyperoxic-training period. The only change was the raising of interval intensity from 85 to 95% of maximal, an increase made possible only with the use of supplemental oxygen.

The New-Mexico scientists speculated that - among other things - the hyperoxic training may have boosted the blood volumes of the athletes. A spike in blood volume is one of the key adaptations to endurance training, and intensity - not the number of workouts per week or the total duration of workouts - is the most potent elevator of blood plasma. That's because high-intensity workouts stimulate special tubules within the kidneys to hold onto more plasma, thus thwarting the kidneys' perverse desire to literally urinate away fitness. The resultant, increased quantity of blood permits more red fluid to reach athletes' muscles during exercise. More blood means that the muscles get more oxygen, and more oxygen translates into greater energy production and higher performances.

So what are your bottom-line "oxygen lessons?" Obviously, you shouldn't trouble yourself to go to altitude to train in hopes of improving your performances. High-altitude locations are nice places to live, because of the great views and clean air and also because the decreased oxygen pressures associated with altitude can really jazz up your blood-hemoglobin levels. Unfortunately, however, the impoverished oxygen pressures associated with altitude decrease the quality of training sessions and thus hamper sea-level fitness. To put it another way, it is very difficult to develop the ability to move faster when you are always moving more slowly during your training.

No - instead of jumping into a low-oxygen environment, you should jump at any chance you have to train under high-oxygen conditions. If there is a university or other research laboratory near you which provides increased-oxygen training, such workouts can be completed at faster speeds than you are usually capable of handling, and the faster speeds can be sustained for unusually long periods of time. This kind of training will make you fitter, even in normoxic environments. In short, high-oxygen exercise can really gas up your training sessions - and thus your ultimate performances.

As the University of Florida research suggests, such training will be particularly valuable to experienced athletes, the ones who can really crank up training intensity and "hang around" at high intensities for long enough to desaturate their hemoglobin. Currently, most such athletes think "altitude" when it comes to fundamental alterations in training, but going up in elevation (and thus down in intensity) is exactly the wrong move to make. ©

References

(1) Exercise Physiology. (2001). New York: McGraw-Hill.
(2) Ergogenic Aids in Sports. (1983). Champaign, IL: Human Kinetics.
(3) Ergogenic Aids and Muscular Performance. (1972). New York: Academic Press.
(4) Medicine and Science in Sports and Exercise, Vol. 24, pp. 720-725, 1992
(5) Journal of Applied Physiology, Vol. 42, pp. 385-390, 1977
(6) Powers, S. & Howley, E. (2001). Exercise Physiology: Theory and Application to Fitness and Performance. Boston: McGraw Hill.
(7) Medicine and Science in Sports and Exercise, Vol. 12(5), pp. 380-384, 1980
(8) Medicine and Science in Sports and Exercise, Vol. 7(1), pp. 48-52, 1975
(9) Journal of Applied Physiology, Vol. 66, pp. 2491-2495, 1989
(10) Running Research News, Vol. 10(2), pp. 14-16, 1994

By Owen Anderson, Ph. D.

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