Use Oxygen Effectively

So what exactly is meant by the term VO2max? To be precise it is the maximum volume of oxygen that your muscles consume per minute and is therefore referred to as “aerobic power” since it is a measure of the rate at which oxygen is consumed.

VO2max is the best single indicator of a person’s aerobic fitness. Although a high VO2max alone is not enough to attain elite-level performances, it gains one access into the club. An endurance athlete simply cannot attain a high level of performance without a high VO2max.

It is especially important for the middle-distance events (800m to 3000m) that are run at or close to 100 per cent VO2max. So what determines VO2max?

Cardiac output and blood flow (central factors)
Cardiac output, the amount of blood pumped by the left ventricle of the heart per minute, is dependent on stroke volume and heart rate (HR). Stroke volume (SV), the amount of blood pumped by the left ventricle of the heart per beat, is determined by the return of blood back to the heart through the venous circulation (venous return), the heart’s ability to contract quickly and forcefully, the amount of pressure in the left ventricle (preload) and in the aorta (afterload), and the size of left ventricle. The larger the left ventricle, the more blood it can hold – and the more blood it can hold, the more it can pump.

Oxygen extraction and use by the muscles (peripheral factors)
How much oxygen that can be extracted and used by the muscles is dependent on mitochondrial and capillary volumes. The more capillaries that perfuse the muscle fibres, the shorter the diffusion distance for oxygen from the capillaries to the mitochondria (microscopic “energy factories” that contain the enzymes involved in aerobic metabolism). The number of enzymes is also important, since enzymes, through their effect on chemical reactions, control metabolism.

Oxygen extraction is reflected by the difference in the amount of oxygen going to the muscles through the arterial circulation and the amount coming out through the venous circulation (a-v O2 difference). The a-v O2 difference is determined by the convection of oxygen through the muscle capillaries and its diffusion from the capillaries to the mitochondria. A runner who can shift most of the blood from inactive tissues to the active muscles will have a large a-v O2 difference because the active muscles will extract more oxygen from the blood than the inactive tissues will.

Since the amount of oxygen in the arterial circulation is the same at rest as it is during a race (20ml of oxygen per 100ml of blood), any change in the a-v O2 difference is a result of a decrease in oxygen in the venous circulation, which means the muscles have extracted more oxygen. VO2 is equal to the product of the central and peripheral factors:

VO2 = SV x HR x (a-v O2 difference)
Since SV x HR equals cardiac output (CO), the equation can be written as:
VO2 = CO x (a-v O2 difference)

VO2max occurs when SV, HR (and therefore CO), and the a-v O2 difference are all at their maximum. While unfit people seem to be equally limited by central and peripheral factors (they lack both a high blood flow and abundant metabolic machinery), highly trained runners seem to be more centrally limited. Training appears to result in a shift of the limitation on the sliding scale – the more fit you become, the more you move away from a metabolic limitation to VO2max and the closer you move to an oxygen supply limitation.

Progressive monthly and annual increases in mileage will improve VO2max by increasing the muscles’ metabolic capacity. When you have achieved a high level of mileage (110-120km per week), the intensity of training becomes more important to increase the cardiac factors responsible for maximizing oxygen supply to the muscles.

How is VO2max measured?
The direct measurement of VO2max during a maximum exercise test provides the most accurate assessment of aerobic power. Measuring VO2max requires some sophisticated laboratory equipment, including oxygen and carbon dioxide gas analysers, an expiratory air-flow probe, an air mixing chamber, a dehumidifier, a vacuum pump and a data acquisition system. Some computerised systems contain all of these things in one unit.

VO2max can be measured either in litres of oxygen per minute (L/min) or in millilitres of oxygen per kilogram of bodyweight per minute (ml/kg/min). In order to compare athletes of different sizes, it is usually measured relative to bodyweight. The VO2max of elite male endurance athletes is over 70 ml/kg/min, while that of elite female endurance athletes is over 60 ml/kg/min. Men have a higher VO2max than women because they have a greater cardiac output to send more blood and oxygen to the muscles, more haemoglobin in their blood to transport oxygen, and more muscle mass to consume oxygen.

Humans’ VO2max is equal to that of the pig and the rat, about half that of the horse and the dog and only one-third that of the fox.

As high as the best runners’ VO2max values are, humans actually do not fare well against many other mammals in their ability to consume oxygen at a fast rate. Humans’ VO2max is equal to that of the pig and the rat, about half that of the horse and the dog and only one-third that of the fox. Among all animals, flying insects have the highest rate of oxygen consumption relative to their size. For example, the VO2 max of a hummingbird flapping its wings 80 beats per minute is 40 ml/gram/hour which, in human terms, is equivalent to 666 ml/kg/min! As if this were not impressive enough, the flight muscles of worker bees, flapping their wings 250 beats per minute, consume 6 ml/gram/min, equivalent to 6,000 ml/kg/min!

Improving VO2max
You can improve your VO2max with mileage and speed work. The former focuses on the peripheral variables related to oxygen extraction and use, like mitochondrial and capillary volumes and aerobic enzyme activity. The latter focuses on the central variables related to oxygen delivery, like stroke volume and cardiac output. The more trained you are, the more important the intensity of training becomes to improve VO2max. VO2max has been shown to plateau after three weeks of daily training.

So the training stimulus needs to increase about every three weeks to improve VO2max further. There doesn’t seem to be any further increase in VO2max with more than about 110-120kmper week, unless more intense training is added.

Research shows high-intensity training (95-100 per cent VO2max) is the optimal stimulus for improving VO2max. Long intervals (3-5min) are the most potent because you repeatedly sustain VO2max during the work periods. But short intervals (<1min) can also improve VO2max, as long as they are performed at a high intensity and with short, active recovery periods to keep VO2 elevated throughout the workout.

VO2max pace
Regardless of the duration of the work periods you choose, you should run them at the speed at which VO2max occurs, which is about 3000m race pace for trained runners. However, if you run 3000m in longer than about 10 minutes, your VO2max pace will be between mile and 3000m race pace. If using heart rate as a guide, you should come close to reaching your maximum heart rate by the end of each work period.

So if you want to perform at the highest level you can, train your VO2max. Not only will you set PBs, next time you run in the woods, you may even be able to outrun a dog – or even the honeybee!

» Dr Jason Karp PhD is a recognised speaker, writer, author and exercise physiologist

Tapering For Performance

I attended a high school that was known for its swimmers. They were the best in the country and some of them competed in the Olympics. Before championship meets, you could overhear amusing discussions in the hallways about “shaving down” and “tapering” in an attempt to swim faster. As a member of the cross country and track teams, I was also interested in getting faster, so I couldn’t help but eavesdrop. “What were these odd-sounding things,” I wondered. “Could they work for me, too? Do swimmers have a secret?”

The idea of progressively reducing, or tapering, the training load has been a long tradition among swimmers, the most often-studied athletes in regard to tapering. While it’s not necessary as a runner to shave all of your body hair to run faster, you may benefit from tapering your training. Since most runners are a driven bunch, it seems unnatural to cut your weekly running volume to a fraction of your current training. Competitive runners think they should always do more. But that’s one of the most interesting things about fitness – the adaptations to training occur during the recovery periods from the training, not during the training itself. When you taper your training, you provide your body the opportunity to recover, adapt and overcompensate to the training you’ve done so that you’re prepared to run your best race.

Performance effects of tapering
Most research on runners, swimmers and cyclists has shown that improved performance (from 0.5 to six per cent) is more likely to occur after a period of tapering. Studies on runners have been limited to 800m performance, time to fatigue on a treadmill at 1500m race pace, 5km performance and treadmill half-marathon performance. As with any type of training, these studies have shown a large individual response to tapering. One study using the 800m and another study using a treadmill half-marathon as the performance measure found that while tapering had a positive effect on selected physiological parameters, it did not have an effect on performance.

Physiological effects of tapering
Among the most prominent physiological changes that occur during the taper are in the characteristics of the blood, including increases in red blood cell volume, total blood volume, reticulocytes (immature red blood cells) and improvements in the health of red blood cells. These haematological changes reflect a positive balance between haemolysis (the degradation of red blood cells) and erythropoiesis (the production of red blood cells), leading to a greater oxygen carrying capability and, often, an improved performance.

Tapering also increases muscle glycogen content (giving you more fuel), aerobic enzyme activity (allowing for greater aerobic metabolism), muscular strength and power and it increases or maintains maximum oxygen consumption (VO2max). There is also a decreased level of the enzyme creatine kinase in the blood (an indirect indicator of muscle damage) which reflects an increased recovery.

Taper duration
The goal of tapering is to recover from prior training without compromising your previous training adaptations. In other words, you want to decrease fatigue without losing fitness. Unfortunately, research has not clearly established the time-frame separating the benefits of a successful taper from the negative consequences of insufficient training, leaving most athletes and coaches to take a trial and error approach. This is because studies on tapering in runners have only used one-week tapers and have not examined the taper’s effects on long-distance running performance. Typically, the longer the race, the longer the taper. The exact duration of your taper will vary depending on your prior training load, your level of fatigue and your genetically-predetermined ability to retain your training effects while reducing the training stimulus (how quickly you lose fitness). If you tend to fall out of shape fast, you don’t want a long taper. Positive physiological adaptations and performance gains have been found using tapers lasting six to seven days in university-aged runners, four to 14 days in cyclists and triathletes and 10 days in strength-trained athletes. Masters runners (over age 40) who take longer to recover from hard training may need to taper for longer than one week.

Taper volume and intensity
You can reduce your weekly running volume dramatically during the taper as long as you keep the intensity high. For example, one study found that middle-distance runners significantly improved treadmill time to fatigue at 1500m race pace and increased blood volume, aerobic enzyme activity and muscle glycogen concentration when using a one-week, low volume/high intensity taper (85 per cent reduction in volume and 5x500m at 800m race pace with six to seven minutes recovery, decreasing by one rep each day for five days), but not when using either a moderate-volume/low-intensity taper (10km at 60% VO2max, decreasing by two kilometres each day for five days) or a taper with no running at all. Other studies have also found that a large reduction in volume accompanied by an increase or maintenance in intensity improves training-induced adaptations.

Using a mathematical modeling approach, scientists discovered that training volume should be reduced in a progressive (linear or exponential) manner rather than by a single step reduction. Furthermore, overload training prior to the taper would result in a better performance post-taper than if overload training did not precede the taper. The researchers concluded that the best performance would be achieved with a 39 per cent reduction in training load for 28 days. If overload training does not precede the taper, the best performance would be achieved with a smaller reduction of training for a shorter period (31 per cent reduction for 19 days). Another study using both mathematical and experimental approaches also found that an exponential taper was better than a step-reduction taper and that a fast exponential taper was better than a slow exponential taper. In other words, reducing your training quickly and exponentially is better than reducing it slowly and in a single step.

Practical applications
You can probably expect to improve your racing performance by reducing your weekly mileage exponentially for one to two weeks (two to four weeks for the marathon) and including interval training (if you’ve already been doing so pre-taper) to maintain training intensity. As you get closer to your race, also reduce the volume of intensity by reducing the number of intervals in each session. Research has shown that reductions in training volume up to 60-90 per cent can improve performance, however the research is limited to much shorter races that are not as endurance-dependent as the marathon. Given the length of the marathon, and thus its large dependence on aerobic capacity, I wouldn’t recommend decreasing mileage by as much as 90 per cent.

For the marathon, I typically begin cutting my athletes’ volume and the length of their long runs three weeks before the race (or up to a week later if they haven’t been running high volume). I reduce peak mileage by 30 per cent for the first week, 50 per cent for the second week, and 65 per cent for the week of the marathon (not counting the marathon itself). I keep the intensity high during the first week, including one interval workout at 3km race pace and one moderately-long run (20-24 kilometres) with slightly less than half at lactate threshold pace (about 20-30 seconds per mile faster than marathon race pace for trained runners). Also, I begin to decrease the intensity slightly during the second week, including two short-to-medium distance runs (8-16 kilometres) at marathon race pace. The week of the race, I include one interval workout early in the week at either lactate threshold pace or slightly faster, cutting back on the pre-taper number of reps. The final week also includes a daily reduction in volume over the last few days that mirrors the pattern of the weekly reduction (see Pre-Marathon Taper box). Exactly what you do during your taper will depend on what you did before the taper.

If you want to give your performance a boost, try these tapering strategies before your next race. And if you taper smart enough, maybe you won’t have to shave your body hair!

Dr. Jason Karp PhD lives in San Diego, California and is a recognised speaker, writer, author and exercise physiologist.