Running Science

by Owen Anderson

  Altitude Training Lacks Scientific Support

  Exercise scientists have been hard pressed to demonstrate the specific benefits associated with altitude training. In fact, one of the earliest investigations of the practice revealed that altitude training could be quite detrimental to performance. In this research, well-trained collegiate runners completed 9 weeks of altitude training and residency at an elevation of about 4,000 meters (~ 13,000 ft) and returned to sea level in a detrained state.6 During postaltitude time trials at sea level at distances of 880 yards (805 m), 1 mile, and 2 miles, the athletes ran 3 to 8 percent slower compared with their performances before altitude training. Follow-up studies at more moderate elevations have usually struggled to link altitude training with specific performance advantages.7

  The esteem with which altitude training is nonetheless regarded depends entirely on an outdated model of the determinants of endurance-running success. In this obsolete schema, running performance hinges primarily on the functioning of the heart and leg muscles, with the nervous system just along for the ride. The heart is supposed to be a big oxygen pump, and the muscles are understood to be acceptors of massive amounts of the oxygen sent their way by the mass of cardiac tissue. When this so-called aerobic system is optimized, endurance running potential is also maximized.8 Unfortunately this ignores the important role played by the nervous system.

  In a study carried out in France,9 nine international swimmers who ordinarily trained at sea level conducted 13 days of training at an elevation of 1,850 meters (~ 6,000 ft). This relatively short period of altitude training had no effect at all on O2max or 2,000-meter (6,562 ft) swimming performance.

  In another study, elite distance runners trained for 4 weeks at a high-altitude training camp (1,500-2,000 m, or 4,921-6,562 ft); a group of runners of similar ability trained at sea level.10 When the altitude-trained athletes returned to sea level, they exhibited no improvements at all in lactate-threshold speed and running economy; in fact, high-speed performance declined by 2 percent. This downturn in high-velocity running capacity is exactly what one would predict because training at altitude slows down speed. At altitude, the nervous system spends less time controlling speeds of sea-level vO2max because it is more difficult to attain and sustain such velocities at altitude; therefore, high-speed running capability can be harmed.

  Summing up, it is fair to say that scientific research does not support the idea that carrying out a period of training at altitude will improve endurance performance at sea level.11

  Live High, Train Low

  Over the past 10 years, a scientific consensus has gradually developed that suggests it is optimal for endurance athletes to live at altitude but train at sea level. Living at higher altitudes is supposed to improve blood characteristics (e.g., higher red blood cell concentration and therefore augmented O2max) and nonhematological factors, while sea-level training is believed to upgrade overall training quality (e.g., attaining higher speeds during workouts, sustaining those speeds for longer periods).

  This combination of living at altitude and training at sea level appears to be a potent producer of fitness, and research supports this strategy of living high and training low. In studies carried out by James Stray-Gundersen and B.D. Levine of the Cooper Clinic in Dallas, Texas, runners who live for about 4 weeks at an altitude of approximately 2,500 meters (8,203 ft) and carry out their intense training sessions at close to sea level are able to upgrade O2max by around 5 percent and improve their running performances in events lasting from 7 to 20 minutes by an average of about 1.5 percent.12

  By following this approach, some runners actually augment their performances by up to 6 percent after 4 weeks of live high, train low, while others do not improve at all, accounting for the overall 1.5 percent average gain. Although it might seem odd that some athletes do not respond to higher-altitude living, research has revealed that there is considerable variation among people in altitude responsiveness and adaptation; the sources of this variation are poorly understood.12 The improvements—when present—ordinarily last for about 3 weeks after returning to sea level. For a runner with a normal standard of 18:36 for the 5K, a 1.5 percent improvement would trim approximately 17 seconds from his or her finishing time.

  Like Stray-Gundersen and Levine, other researchers have shown that improvements in performance after a regime of living high and training low can be extremely variable, with some runners improving greatly and others showing no improvement.13 Factors unrelated to altitude including unfamiliar living situations, changes in daily schedule, disturbances in sleep patterns, and motivation issues may play significant roles that tend to override the specific impact of living at altitude.

  For marathon running capability, logical thinking suggests that altitude training would probably not be useful. The proposed, most positive effect of altitude training is the enhancement of aerobic capacity, an outcome that should improve performance in high-speed endurance events in which runners top out or reach O2max. In such events, oxygen usage is limiting performance because O2max is a maximum; no further oxygen is available to spur faster running. Therefore, it would be better to have a higher O2max. Elite marathoners run the event at just 85 to 88 percent of O2max, however, indicating that oxygen supply to the muscles is not a limiting factor in the event and thus O2max expansion is not critical.

  Simulated Altitude

  While living at 2,000 to 2,500 meters (6,562-8,203 ft) and training simultaneously at sea level will enhance performance for most runners, from a practical standpoint it is out of reach for most endurance athletes, elite and nonelite. As a result, considerable interest has developed in sleeping high: sleeping in an enclosure, usually a tent-like structure, within which the air has oxygen pressure similar to what prevails at altitude. This approach can be costly. A sturdy hypoxic tent with low-oxygen generator can sell for about US$5,000. Paula Radcliffe, who holds the world marathon record, is said to employ such a system, and the World Anti-Doping Agency (WADA) has considered artificially induced hypoxic conditions to be so performance productive that it has considered outlawing them and placing so-called hypoxic tents and similar structures on its list of prohibited substances and methods.

  Scientific research supports the idea that sleeping or living at simulated altitude can enhance endurance performance.14 The minimal amount of simulated altitude sleeping or living for increasing red blood cell production may be 11 to 12 hours per day, and the amount of total time required at simulated altitude to induce performance benefits may be 320 to 400 hours.14 There is a suggestion in the scientific literature that simulated altitudes of 2,200 to 2,500 meters (6,562-8,203 ft) may be best for upgrading hematological factors, while about 3,000 meters (9,843 ft) may be optimal for producing nonhematological changes (e.g., alterations in running economy, muscle buffering capacity, and ventilatory function).

  Despite the lack of scientific support for the usefulness of altitude training, many elite runners and their coaches continue to spend significant periods of time each year engaged in the practice. This is particularly true for elite marathon runners and their coaches who seem to believe that altitude training is essential for optimal marathon preparation. This strong attraction toward altitude training is the natural consequence of a belief in the outdated paradigm that running success depends entirely on the heart, muscles, and aerobic capacity.

  Conclusion

  When an endurance runner embarks on a period of high-altitude training, O2max may improve as a result of living at higher altitudes, but the effect on performance will be uncertain. A key problem is that altitude training harms average training speed. Altitude residency is good for running capacity, and a strategy of living high and training low can improve performance. Exposure to simulated altitude can also upgrade endurance capacity.

  Part V

  Training Variables and Systems in Running

  Chapter 19

  Frequency and Volume

  Volume and frequency are two basic training variabl
es fundamental to all programs. “How much should I run?” (volume) and “How often should I run?” (frequency) are two questions runners face every week of training. Volume is simply the number of miles or kilometers completed in a specified period (usually a week), and frequency refers to the number of running workouts conducted per week. As runners explore different permutations of volume and frequency, they are constantly attempting to find the sweet area of training between too much and too little; many runners try to push their bodies and expand their limits by advancing volume and frequency without pushing so hard that injury occurs. Decisions about volume and frequency are often made without much scientific backing, even though science has much to say about the issues.

  Training Frequency

  Scientific studies suggest that training frequency—the number of workouts conducted per week—can have a positive impact on O2max and performance. Research indicates that the improvement in O2max that occurs during a training program is directly proportional to the frequency of training.1 In one study in which male subjects ran for 30 to 45 minutes per workout over a 20-week period, upgrades in O2max were significantly greater for individuals who trained four times per week than for runners who worked out just two or three times weekly.2

  For beginning runners, frequency usually has a profound impact on aerobic-capacity improvement. Research indicates that a training frequency of five to six times per week can increase O2max by up to 43 percent for initially unfit runners with a low O2max. With a frequency of two to four times per week, O2max increases average just 20 to 25 percent.3 It usually takes 6 to 9 weeks for such changes in O2max to appear.

  Noncontrolled cross-sectional studies also support the idea that training frequency is related to performance. In an analysis carried out with 50 male runners whose marathon times ranged from 2:19 to 4:58, the total number of workout days during the 9 weeks prior to the race was inversely related to marathon performance: the higher the number of workouts, the lower, or faster, the marathon finishing time.4 In this study, a workout was defined as any kind of run: fast, medium paced, or slow. In a separate survey of 35 female runners whose average marathon time was 3:47, the total number of workouts completed over a 12-week period was negatively correlated with marathon performance: again, the greater the number of workouts, the faster the overall time for the race.5 A Swiss study conducted with 4,000 joggers showed that a higher training frequency was linked with better performance times in a 16K (~10 mi) race, the Berne Grand Prix.6 Individuals who trained five to six times per week completed the 16K significantly more quickly compared with runners who completed three workouts weekly.

  However, it is necessary to use care when interpreting such analyses. Good runners tend to train more frequently than slower runners and also tend to achieve superior performance times. Thus, it is sometimes the quality of the runner and not training frequency that is the fundamental underlying basis for the connection between frequency and both performance and O2max.

  Training Volume

  An additional problem is that training frequency is confounded with another important variable: training volume, the number of miles or kilometers run per week or the number of minutes of running training completed each week. Increases in training frequency tend to be linked with upswings in volume unless workouts are shortened as frequency rises, and thus it is possible that volume—not frequency—of running training is the primary cause of increases in O2max and performance improvements. Research into the true effects of frequency on fitness would have to hold volume constant while varying frequency. This research could answer questions such as these: Are six 5-mile (8 km) workouts per week actually better than three 10-mile (16 km) sessions for O2max improvement or competitive success? Do advances in frequency hold some fitness magic of their own?

  Fortunately, several studies have been completed in which volume was held constant while training frequency varied. In one study, 18 middle-aged men ran for 30 minutes per day over an 8-week period, while 18 other male subjects completed three 10-minute periods of running each day with at least 4 hours separating the 10-minute workouts. Running intensity was the same in the groups (65 to 75 percent of maximal heart rate), and thus training volume was equivalent. After 8 weeks, overall endurance and the decrease in heart rate associated with submaximal running were the same in the two groups of runners, but O2max increased to a significantly greater extent in those who ran for 30 minutes per workout.7 This implies that training frequency may actually be inversely related to the gain in aerobic capacity when volume is held constant; in addition, there might be something important about longer-duration workouts for achieving gains in O2max, at least when running intensity is moderate. The mechanism underlying this relationship between workout volume and O2max is uncertain although it is known that longer workouts deplete leg-muscle glycogen to a greater extent than do shorter sessions; glycogen depletion in muscles stimulates the production of aerobic enzymes and structures that can lead to an increase of O2max.

  In a similar study carried out with middle-aged women, 12 subjects took three 10-minute walks per day, five times per week, over a 10-week period, while 12 other females completed one 30-minute walking workout 5 days each week during the same period.8 The intensity of the walking was 70 to 80 percent of maximal heart rate in both groups, and thus training volume was equal. Both training plans produced gains in O2max and enhancements of blood lactate profiles, but there were no significant differences between the groups. This research seems to refute the previous study that showed that one longer workout was better than three shorter ones, but it does support the idea that training responses are relatively independent of training frequency as long as intensity and volume are held constant.

  The Swiss study mentioned earlier, in which higher training frequency was linked with superior 16K (10 mi) performance time, actually supports the idea that training frequency is not a major player in fitness improvement when training volume is similar.6 In a subanalysis, 414 of the Swiss joggers who used the same training volume (20-25 km or 12-16 mi per week) were further divided into groups that had trained either two, three, or four times per week to achieve this volume. Although training frequency and thus workout duration were dramatically different in these three groups, finishing time in the 16K did not vary significantly between the runners.

  In some research, training volume has been found to have a fairly strong effect on performance-related physiological variables and competitive race times. In general, runners who increase their training volume from a low level of about 5 to 10 miles (8-16 km) per week to 35 to 40 miles (56-64 km) per week can expect upgrades in O2max of about 15 to 20 percent or more.9 Studies carried out with marathon runners have revealed that the total volume of training during the year preceding a marathon and also during the two months prior to the race are significantly correlated with marathon finishing time.10 Another study conducted with 18 male Swedish marathoners found that marathon running performance was directly related to lactate-threshold speed and the ability to run at a velocity close to that speed during the race. In turn, these two variables were significantly related to training volume.11

  Ability

  Research does not always show that more volume means higher performance. When S.Y.J. Grant and colleagues at the University of Glasgow in Scotland analyzed the training and performance of 88 male and female runners who competed in the Glasgow Marathon, they found there was only a limited relationship between weekly training volume and marathon finishing time.12 In this study, the best predictor of marathon running pace was the average speed used during competitors’ 6- to 10-mile (10-16 km) training runs. Grant and colleagues concluded that the intensity of marathon training was the key factor that determined marathon success.

  The applicability of such studies, including the ones that link higher volume with better performance and those that find little connection between volume and finishing time, is weakened, however, by the consideration mentioned previously: Excellent runners tend
to adopt greater training volumes and also perform at a higher level in races than average competitors. It may be the quality of the runner and not the volume of training that truly underlies the contrasting connections between volume and performance.

  Some better-controlled studies that monitored runners as they increased their mileage suggest that volume can be important. In one such study, experienced marathon runners who boosted their training volume by about 20 percent, from 76 to 91 kilometers (47-56 mi) per week, managed to improve marathon time significantly from 3:20:42 to 3:10:48.13

  However, a study carried out at the University of Northern Iowa with first-time marathoners found that a significant uptick in mileage had no effect on marathon performance.14 High-mileage runners in the study increased their weekly training volume from 23 to nearly 50 miles (37-81 km) over the course of an 18-week training period, while low-mileage marathoners increased their volume from 18 to almost 40 weekly miles (29-64 km) during the same period. Despite the 25 percent volume advantage, high-mileage marathoners did not finish the race faster than their lower-mileage counterparts. Average finishing time was 4:17 for both higher- and lower-mileage males and 4:51 for the corresponding two groups of females. Surprisingly, improvements in O2max, running economy, lactate-threshold speed, and body composition were also equivalent between the groups, defying the notion that increases in mileage are especially important for fitness enhancement in relatively inexperienced runners who start from low-mileage bases. It is likely that changes in volume have a strong impact on performance at low mileage levels and a much weaker influence as volume increases. For many runners, 40 miles (64 km) per week may represent a volume cutoff point beyond which improvements are difficult to measure.