Running research

Don't tell Chancellor Brown, but the economy is improving

If you're a runner, are you concerned about how to improve your economy? If so, you can literally breathe easily: new research from Odense University in Denmark shows you a straight-forward way to do it - and reveals a surprising mechanism by which economy improves.

In the Danish investigation, researchers worked with 36 experienced male runners with an average VO2max of 54.8 ml/kg/min, which predicts a 5K race time of about 18:22 (5:56 per mile). Prior to the study, the runners had been training about 2.2 hours per week, usually by running continuously at moderate intensities (Improved Running Economy Following Intensified Training Correlates with Reduced Ventilatory Demands, Medicine and Science in Sports and Exercise, vol. 30(8), pp. 1250-1256, 1998).

The researchers divided the 36 runners into three groups. Three times a week, members of one group carried out tempo runs at about their predicted half-marathon race pace of 6:26 per mile - roughly 14 seconds per mile slower than their potential 10K race speed. For three weeks, these runs were 20 minutes in duration; for the final three weeks of the study, the tempo runs were expanded to 30 minutes. On non-tempo-run days, the subjects simply ran easily for about 30 minutes (there were an average of two easy days per week).

A second group avoided tempo running completely, relying instead on long intervals to improve their fitness. Three times a week, the runners in this group completed four-minute work intervals at a pace of 5:49 per mile, just slightly faster than their predicted 5K race velocity. These four-minute intervals were punctuated with two-minute recoveries. Initially, the long-interval runners completed three work intervals per workout, but they moved up to five intervals per session after three weeks. As was the case with the tempo trainers, the long-interval runners simply ran easily on recovery days.

Finally, members of the third group of runners utilized very short intervals during the three quality workouts they carried out each week. These sessions were composed of 15-second bursts at 4:44 per mile pace, which would correspond closely with the runners' best average velocity for 400-metre competitions. The intense bursts were alternated with 15-second recovery jogs, and the runners completed about 40 reps (ie, 15-second blasts) per workout. Easy running was carried out on non-quality days.

Which training strategy was best?

During the six-week training period, the three groups made no changes at all in stride rate, stride length, or muscle composition. Stride rate remained at 171 steps per minute, stride length stayed stable at 1.36 metres, and muscle composition was a constant 54-per cent slow-twitch. All three groups did improve their overall fitness, however; after six weeks, their blood-lactate levels and heart rates were significantly lower during continuous runs at a pace of about seven minutes per mile, compared to before the study began. Heart rates dipped by about 10 beats per minute, and lactate levels plummeted by 27 per cent.

Although all three groups improved, there were some interesting differences between them. For example, the tempo-run and long-interval groups made greater improvements in VO2max, compared to the short-interval runners. VO2max went up by 6 per cent for the tempo and long-interval runners, compared to just 3.6 per cent for the short-interval competitors. Actual running velocity at VO2max paralleled these changes, averaging a 9- to 10-per cent increase for the tempo and long-interval harriers but moving up by just 4 per cent for the short-interval athletes.

It should be no surprise to you that the short-interval people didn't fare as well, VO2max-wise. The extremely abridged duration and very high intensity of their intervals tended to stress oxygen-independent energy creation (what used to be called anaerobic energy production), rather than the utilization of oxygen to furnish the energy necessary to burst along. Thus, one wouldn't expect the leg muscles of these runners to maximally develop their ability to use oxygen.

In addition, although the short-interval runners ran at a feverish pace (ie, close to their best 400-metre speed) during their 15-second intervals, the total amount of quality running they carried out was considerably lower, compared to the tempo and long-interval athletes. During the final three weeks of the Danish study, the short-interval harriers were completing 40 reps per workout, which added up to just 10 minutes (40 x 15 seconds) of quality running per session (and 30 minutes per week).

In contrast, the long-interval runners were getting in 20 minutes of tough running per workout (5 x 4 minutes) and 60 weekly minutes of hard exertion, while the tempo people were benefiting from 30 minutes per session and 90 minutes per week!
That being the case, it wasn't surprising that the tempo runners enjoyed a huge advantage during a special endurance test devised by the Danish researchers, which consisted of running as long as possible at an intensity of approximately 85% VO2max (for these 36 runners, 85% VO2max meant a pace of about seven minutes per mile). At the end of the six-week period, the tempo people lasted for 69 minutes, a big improvement over their rather meagre 36-minute effort at the beginning of the investigation. Meanwhile, the long-interval-trained athletes held out for just 61 minutes (up from 36 minutes at the beginning of the study), and short-interval runners could manage only 60 minutes (also up from 36).

Is tempo running better than intervals?

Should our lesson be that tempo running is the best form of training for boosting endurance? Some people will interpret the study that way, but remember that 90 minutes of weekly tempo running were required to gain an edge over 60 minutes per week of long-interval training. If the durations of these two types of training had been equalized, the long-interval runners would probably have done just as well - or better - than the tempo subjects.

The tempo runners also enjoyed an unfair advantage in the endurance test. The selected test intensity of 85% VO2max correlated with a running speed which was fairly close to the velocity the tempo runners had used during their 20- to 30-minute tempo runs over the course of the study. The test pace was 7:00 per mile, and the tempo runners had been doing almost all their work at 6:26 to 6:30 pace. Meanwhile, the long- and short-interval runners had worked at much faster speeds of 5:49 and 4:44 per mile, respectively. Thus, the test pace probably felt more familiar and biomechanically comfortable to the tempo runners. And we should mention that the continuous nature of tempo running accustomed the tempo runners to continuous work, while the interval sessions made the runners familiar with starting and stopping (ie, taking lots of breaks). This would of course give the tempo runners a mental edge during a test which called for an hour or more of continuous running.

As an acute reader, you will have noticed already that one last lesson from the endurance testing is that there's not a tight link between VO2max improvement and performance. After all, the tempo and long-interval athletes improved VO2max about equally - and to a much greater extent than the short-interval runners, yet the tempo competitors were much better than the long-interval people during tests of endurance at moderately hard paces, while the long- and short-interval subjects were pretty much in the same boat (even though long-interval runners had increased VO2max more than short-interval competitors).

VO2max is a key physiological variable, but it's not as good as lactate-threshold velocity at predicting performance, and VO2max becomes an especially poor predictor at submaximal intensities of effort (ie, at running paces which represent a moderate percentage of VO2max).

Back to economy

The Danish data were especially interesting with regard to running economy. At that well-worn pace of seven minutes per mile, running economy improved by about 3 per cent from beginning to end of the study - for both the tempo and long-interval runners.

If you're unsure about what running economy actually signifies, this means that both the tempo and long-interval competitors used 3 per cent less oxygen to run at that specific seven-minute per mile pace at the end of the study, compared to the beginning. Of course, that's a good thing, since it means the pace will correspond with a lower percentage of VO2max, burn up less precious leg-muscle glycogen - and feel significantly easier. The short-interval runners didn't do nearly as well, upgrading economy by a lacklustre 1 per cent.

What's the significance of that? Well, we can say that it took 90 weekly minutes of quality running for the tempo runners to make the same improvement in economy achieved by the long-interval runners with just 60 minutes of quality work. And that happened to be the case, even though the tempo runners were much more accustomed to the particular intensity utilized for the economy evaluation.

To sum things up, we should state that the long-interval-trained runners did as well as the tempo people from an economy standpoint, even though the long-interval runners did less quality running and were less familiar with the chosen pace.

A closer look

And a close look at the Danish data reveals that when the pace picked up by just 10 metres per minute, the long-interval runners enhanced economy by the same 3 per cent, while the slower-training tempo runners failed to improve economy at all! Advantage? Faster running! Working at 5K race velocity, as the long-interval runners did, enhanced running economy to a much greater extent at more upscale paces, compared to training at tempo intensities.

At this point, you might be wondering what happened to those poor Danes who used short intervals, bursting along during their workouts at their best 400-metre pace - but for only 15 seconds at a crack. Well, although those fellows fared fairly poorly at the seven-minute pace, economy-wise (as mentioned, they upgraded economy by only 1 per cent at that velocity), they did pretty well at other speeds, including the faster ones. In general, running more quickly during training sessions, as the short- and long-interval runners did, is a solid way to enhance running economy, partly because it spikes leg-muscle strength but also because it has a large positive impact on neuromuscular coordination.

And the Danes detected another mechanism by which economy can improve. In a unique aspect of their research, the scientists were able to show that a portion of the improvement in economy was probably due to ventilatory adaptation, ie, a reduced flow of air into and out of the lungs during running

Breathe easy

So what? Well, when the runners cruised along at 6:40 per mile pace before the study began, their minute volume (VE), which is simply the amount of air breathed in per minute, averaged about 112 litres. After the six weeks of training, VE at the exact same pace was only 99 litres per minute, a 13-per cent drop-off. The athletes were breathing more easily!
And of course that meant that the work load of the respiratory muscles - the diaphragm and the intercostals - was lighter, since they were required to drag in more than three gallons less air per minute of running. Don't forget that the diaphragm and intercostal muscles require their fair share of the oxygen used by the body during running; they need that oxygen to do their work. But since their work load was easier after the six weeks of training, their demand for oxygen was also reduced, which means that they were making their own contribution to the improved economy observed at the end of the study (remember that economy improves whenever oxygen consumption goes down). In fact, the Danes estimated that been 25 and 70 per cent of the improvement in economy was the result of the new parsimony achieved by the muscles of breathing!
There's no reason to delve deeply into the reasons why VE was lower, although you can see for yourself that since less oxygen was needed to work at a particular pace, less air would need to be brought into the body. Another factor was probably that with improved fitness, lactic-acid production was lower and therefore fewer hydrogen ions poured out of the runners' muscles into their bloodstreams, an effect which would calm breathing (the brain reacts to the presence of increased hydrogen ions by stepping up respiratory system activity).

Thinking about all of this, we can't help but note that one of the few advantages of altitude training is an increase in respiratory muscle strength. The limited oxygen concentrations at altitude force the respiratory system to go into overdrive, and even though the amount of work required to move a litre of air into the lungs is less at altitude than it is at sea level (since the air is more dense in the latter case), the total amount of work performed by the respiratory muscles at a particular running pace is greater at altitude because of the hike in breathing rate and depth of inspiration. The overall respiratory-muscle strengthening which ensues can make a runner more economical, especially after a return to sea level.

It's no accident that elite Kenyan runners often concern themselves with the densities of the air which they breathe while training - and prefer to work in cool air, not so much because it is easier to keep body temperature from skyrocketing under more temperate conditions but because the muscles of breathing are forced to work harder to move dense air around. Over time, this increases the strength of the respiratory muscles - and thus running economy. And it also makes hard running feel easier.

That's because much of one's RPE (rating of perceived exertion), which is simply how difficult a pace feels, comes from one's sense of how hard the respiratory muscles are being forced to work and from the depth and frequency of breathing. Thus, improved respiratory strength and efficiency can not only enhance running economy by lowering oxygen consumption: the resulting lower intensity of effort by the muscles of breathing during hard running convinces the brain that it is easier to run at a particular pace than it used to be, even though the leg muscles may be working - and hurting - as much as ever. Any time you feel more comfortable at a rugged pace, it is more likely that you will be able to sustain that pace for an increased period of time. If you want to upgrade your respiratory strength, don't forget that intense training will be more taxing to your muscles of breathing than more moderate exertions, and therefore intense work should be best for raising respiratory power in the long run.

The bottom lines

What lessons should we take home from this densely packed Odense study? Expressed on a benefit-per-minute-of-training basis, working at about 5K race intensity, particularly during relatively long intervals lasting around four minutes, is better for improving two key aspects of your running - VO2max and economy - than are tempo-type runs or very short intervals at unusually high speeds.

However, the Danish investigation also strongly supports the specificity-of-training principle. When tested at tempo-like paces, tempo-trained runners had better endurance than individuals who had trained faster, just as the faster trainers would have performed in superior fashion if the test pace had been set at their own special intensities. Expressing it another way, the individuals who trained in a continuous fashion were better at continuous, submaximal running, compared to the interval-trained people.

The superior VO2max-economy advantages of fast running and the better boost in submaximal endurance capacity associated with tempo-type training help to illustrate why variation of training can be so important. We get certain benefits from specific types of training which we don't acquire quite so well from other forms of work, so we have the best chance of attaining optimal fitness when we touch all the key bases of improvement. While it's true that running intensely, at 3K, 5K, and 10K paces, for example, is better - per minute of training - for your overall fitness than is working more slowly, you can't repeat a magical workout over and over again and hope to perform at your best.

Instead, you must find the right blend of different types of work.

Clipping along at 5K pace will do great things for you, including bringing about the economy bonus associated with a lower VE, but you've got to dip into the less-intense, more sustained type of training, too, to bring your competitive ability into full bloom.

Jim Bledsoe