However, vO2max, a related physiological variable, is a strong predictor of endurance performance.1 Unlike O2max, which is a rate of oxygen consumption, vO2max is a running velocity. Specifically, it is the minimum running velocity that elicits a runner’s maximal rate of oxygen consumption or O2max. As explained in the next sections, there are many intense running speeds that cause an individual runner to attain O2max; vO2max, although fast, is the slowest of these speeds.
Defining vO2max
To understand vO2max more completely, consider a hypothetical runner named Liz who can run quite easily at a pace of 8 minutes per mile. As she runs at that rate, her exercise intensity is 70 percent of O2max. Expressed another way, the 8-minute pace requires an oxygen-consumption rate of just 70 percent of maximum to provide the necessary rate of energy production to keep her body moving forward at 3.35 meters per second, the tempo needed to run 8-minute miles.
As Liz gradually speeds up, her rate of oxygen consumption also increases in order to provide the higher rates of energy production required for faster running. When she moves up to a 7-minute tempo per mile, she might increase oxygen consumption to 85 percent of O2max, for example, and a 6:30 pace could get her to 92 percent of her O2max. Even faster speeds would move her closer and closer to O2max.
In Liz’s case, she might reach O2max for the first time when she accelerates to a 6-minute tempo per mile. Running at a 6:10 pace would not cause her to hit O2max; that would be slightly too slow. Since 6:00 per mile is the first tempo that elicits O2max, it corresponds with vO2max. In Liz’s case, vO2max would be 1,609 meters divided by 360 seconds (because there are 1,609 meters in a mile and 360 seconds in 6 minutes), or 4.47 meters per second. By convention, vO2max is almost always defined in meters per second.
If Liz warms up on a subsequent day and begins running at a 5:30 per mile pace, she would also reach O2max, probably after just 2 minutes or so of running. Thus, a 5:30 tempo is also associated with the attainment of O2max, but—importantly—it is not the minimum velocity that elicits O2max; that distinction falls to the 6:00 tempo in Liz’s case. The 5:30 tempo cannot be vO2max, even though O2max is reached when Liz runs at this pace.
In fact, there is a range of tempos —in Liz’s case, most likely from 6:00 to about 4:45 per mile (her maximal velocity)—that she could handle for short periods of time and that could cause her to attain O2max. Although this range of speeds can be used in training to reach O2max, only one tempo—in Liz’s case, 6:00 per mile—corresponds with vO2max, the minimum velocity that produces the maximal rate of oxygen consumption. All the other relevant tempos are faster than vO2max.
It is also true that Liz could probably run at faster than a 4:45 pace, perhaps even as quickly as 4:16 per mile (a pace of about 64 seconds per 400 m). However, her ability to sustain this tempo would be quite limited; she might be able to sustain this pace for just 100 meters (16 seconds). This would be too short a time for her heart to attain maximal cardiac output and for her leg muscles to respond with the highest-possible rate of oxygen consumption; thus, she would not reach O2max while running at this higher speed because of its short duration.
Importance of vO2max
For endurance runners, knowing vO2max is highly important. This is because training at vO2max is one of the most potent ways to enhance the physiological variables critical for endurance performance, including vO2max itself, plus running economy and velocity at lactate threshold (see chapter 10).1
Endurance runners, coaches, and exercise physiologists have pondered why O2max is so poor at predicting endurance performance, while vO2max is so good. The answer is simple: O2max contains no information about an athlete’s running economy. A runner might have a high O2max and yet quite miserable running economy, in which case his or her performances would be disappointingly slow despite the high aerobic capacity. In fact, exercise physiologists have noted that a higher aerobic capacity is to some extent a predictor of subpar running economy, or at least that high aerobic capacities and superb running economies do not often go together in the same runner.
Like O2max, vO2max reflects maximal rate of oxygen consumption, but it also incorporates running economy, how well a runner can translate rates of oxygen consumption into various running speeds. A runner with a high vO2max must be doing that translating very well; otherwise, he or she would not be able to reach a high speed (vO2max) when maximal oxygen consumption is attained. Poor running economy would mean that O2max would be attained rather quickly at relatively low speeds (see figure 9.1 for an accompanying plot of oxygen consumption as a function of running speed).
Figure 9.1 Runner A has a higher O2max compared with runner B, but runner B has a superior economy and great vO2max.
Predictive Power of vO2max
To begin to comprehend the lack of predictive power of O2max in contrast to that of vO2max, consider an extremely well-trained runner who happens to have large, clunky feet. Such a runner will tend to have a high O2max because of the demanding training he or she has been undertaking, and the clunky feet will add to O2max, driving it higher compared with a similarly trained runner with small feet. Having to move those large feet down the road at high rates of speed will call for extremely high rates of oxygen production. However, large feet will not make the runner competitive; in fact, they will cause this runner to reach O2max at a rather modest speed since so much oxygen is being used to move the big feet along. Thus, this runner will have a high O2max but relatively poor running economy, and thus a moderate vO2max and moderate performances. As usual, vO2max will be more reflective of performance potential than O2max.
This big-foot scenario is an extreme example of why vO2max predicts performance quite well. It is important to bear in mind that the same situation prevails for runners in general who have modest to poor running economy for reasons other than big feet. Such athletes might have high levels of O2max. If running economy is subpar, however, any particular running speed will elicit an unusually high rate of oxygen consumption, and O2max will be reached at relatively mediocre running speeds. Thus, performance potential will be below what might be expected from the determination of O2max alone.
The power of vO2max to predict performance is illustrated in a study carried out at Lynchburg College in Virginia in which 17 well-trained distance runners (10 males and 7 females) underwent physiological testing and then competed in a 16K race.2 Laboratory tests determined O2max, vO2max, running economy, percentage of maximal oxygen uptake at lactate threshold (%O2max at lactate threshold), running velocity at lactate threshold, and peak treadmill velocity. The Lynchburg researchers found that among all the measured physiological variables, vO2max had the highest correlation (r = −.972) with 16K performance, while %O2max at lactate threshold had the lowest correlation (r = .136). Overall, vO2max was found to be the best predictor of 16K running time, explaining all but just 5.6 percent of the variance. The Virginia scientists concluded that vO2max is the best predictor of endurance-running performance because it integrates maximal aerobic power with running economy.
In a separate study carried out at Fitchburg State College in Massachusetts,3 24 female runners from four different high school teams competing at the Massachusetts 5K State Championship Meet were tested in the laboratory. These tests revealed a high correlation between vO2max and 5K performance (r = .77). In contrast, the correlation between O2max and 5K speed was lower, and running economy at a slow velocity (215 m per minute) was poorly correlated with 5K outcome. Note that economy at race-like speeds is predictive of race competitiveness, while economy at slow velocities is not necessarily linked with racing capacity (another argument against conducting a lot of training at medium to low speeds).
In a classic study carried out at Arizona State University in Tempe, vO2max was found to be a primary determinant of 10K performance in well-trained male distance runners.4 Among these runners, the variation in 10K running time attributable to vO2max exceeded that due to either O2max or running economy.
Imp
act of Training on vO2max and Running Economy
French researchers Veronique Billat and Jean-Pierre Koralsztein have concluded that vO2max predicts running performances very well at distances ranging from 1,500 meters to the marathon. They also noted that vO2max has similar predictive power in cycling, swimming, and kayaking; of course, vO2max would have to be determined for each sport since running vO2max does not carry over to other activities.5 Billat and Koralsztein also discovered that training that emphasizes intervals conducted at vO2max can be extremely productive for distance runners.
In one study, Billat and Koralsztein asked eight experienced runners to take part in 4 weeks of training that included one interval session per week at vO2max.6 The athletes specialized in middle- and long-distance running (1,500 m up to the half marathon), and their average O2max was a fairly lofty 71.2 ml • kg-1 • min-1. This program included six workouts per week, including four easy efforts, one session with work intervals at vO2max, and one session at lactate-threshold speed with longer intervals. Total distance covered per week was about 50 miles (~ 80 km). Over the 4-week period, the runners’ weekly training schedules were formatted in the following way:
Monday: One hour of easy running at an intensity of just 60 percent of O2max.
Tuesday: A 4K warm-up and then vO2max interval training consisting of 5 × 3 minutes at exactly vO2max. During the 3-minute work intervals, the runners covered an average of 1,000 meters (.62 mi; their vO2max tempo was 72 seconds per 400 meters). Recovery intervals were equal in duration (3 minutes), and the cool-down consisted of 2K of easy running. Overall, the workout was a 4K warm-up, 5 × 3 minutes at vO2max, with 3-minute easy jog recoveries, and a 2K cool-down.
Wednesday: 45 minutes of easy running at an intensity of 70 percent of O2max.
Thursday: 60 minutes of easy running at 70 percent of O2max.
Friday: A session designed to enhance lactate threshold composed of a warm-up and then two 20-minute intervals at 85 percent of vO2max; for example, if vO2max happened to be 20 kilometers per hour (5.55 m per second), the speed for these intervals would be .85 × 20 or 17 kilometers per hour (4.72 m per second). A 5-minute, easy jog recovery was imposed between the 20-minute work intervals, and a cool-down followed the second work interval.
Saturday: Rest day with no training at all.
Sunday: 60 minutes of easy running at an intensity of 70 percent of O2max.
After 4 weeks, the results were amazing, to say the least. Although maximal aerobic capacity (O2max) failed to make any upward move at all, vO2max rose by 3 percent from 20.5 kilometers per hour to 21.1 kilometers per hour. In addition, running economy improved by a startling 6 percent. This enhancement of economy was probably behind most of the uptick in vO2max since it lowered the economy line on the graph of oxygen consumption as a function of running speed and thus pushed vO2max out to the right for the French runners (see figure 9.1).
After the 4 weeks of training, lactate threshold remained locked at 84 percent of vO2max. However, since vO2max was 3 percent higher at the end of the training period, running velocity at lactate threshold had also increased by a similar amount. Most of the key variables associated with endurance performance—vO2max, economy, and lactate-threshold speed—had advanced in just 4 weeks.
The 6 percent gain in economy associated with vO2max training was particularly impressive. A handful of training manipulations have been linked with upgraded economy, and the gains in economy have usually been far below the one documented by Billat and Koralsztein’s research. A classic Scandinavian hill-running study (see chapter 25) detected only a 3 percent increase in running economy, even though the hill training was conducted for three times as long (12 weeks versus the 4 weeks needed by the French runners in Billat and Koralsztein’s study). Similarly, improvements in economy associated with strength training have usually been in the 3 percent range, also after fairly long periods of training. It appears that vO2max training can work economy magic in as little as 4 weeks, especially for those runners who have not carried out vO2max work previously.
Advantages of Training at vO2max
Runners, coaches, and exercise physiologists have speculated why training at vO2max simultaneously improves vO2max, running economy, and lactate-threshold speed. It appears that running at vO2max increases leg-muscle strength and power to a considerably greater extent compared with running at slower speeds. Enhanced muscle strength tends to upgrade running economy automatically: Since individual muscle cells are stronger, fewer muscle fibers need to be recruited to run at a specific velocity, and thus the oxygen cost of running is reduced. Or put another way, there are fewer muscle cells grabbing oxygen molecules at high rates and using them to supply the energy needed for running. It is also probable that running at vO2max boosts neuromuscular responsiveness and coordination to a greater degree than does easier pacing. Advances in coordination should also drive down the energy cost of running and thus promote better economy because less energy would be needed to correct suboptimal movements of the lower limbs.
The results obtained by Billat and Koralsztein have some interesting consequences, as is apparent in the chapters in parts IV and V. A traditional belief in endurance running is that a runner works on a single variable at a time during training: For example, the runner might carry out intervals at a 5K pace to increase O2max and conduct reps at faster than 5K tempo in order to enhance economy. It is clear that Billat’s vO2max sessions do not work on a single variable but rather improve several key physiological variables in concert: vO2max, running economy, and lactate-threshold speed were all upgraded through the use of a single running pace.
Expressed another way, it is clearly possible for endurance runners to work on all the key performance variables at once with the use of a high-quality training pace such as vO2max. The traditional formulation of the periodization of training—working on a single variable during an isolated block of training—is out of date since the key variables can move concurrently in response to strong workouts. As outlined in chapters 22 and 23 on building a training program, periodization is thus not the division of the training year into separate blocks of single-variable training but rather is a method of increasing the difficulty and specificity of training over time in a manner that optimizes total running fitness.
The vO2max variable has a sister measurement—time limit at vO2max (tlimvO2max) —that is also important for distance-running performance. Time limit at vO2max is simply the amount of time a runner can sustain his or her vO2max without slowing the pace or stopping. There is fairly wide variation in time limit at vO2max among endurance runners, with 4 minutes being the approximate lower limit and 10 minutes the top end.7 Time limit at vO2max can be a decent predictor of performance in its own right, especially among runners with similar values of vO2max. It is quickly apparent that two runners with similar running velocities at O2max would have quite different results in a 9-minute race (like a 3K), for example, if one of the runners had a tlimvO2max of 4 minutes while the other could maintain vO2max for 10 minutes. The latter runner could sustain vO2max for the entirety of the race while the former would have to back off vO2max after just 4 minutes.
Training to improve time limit at vO2max is discussed in chapter 10, which focuses on improving velocity at lactate threshold. As it turns out, upgrading lactate-threshold velocity is a key way to increase time limit at vO2max. For now, the most important fact to know is that the average time limit at vO2max in endurance runners is 6 minutes.7 This knowledge permits any runner to estimate vO2max properly and then carry out vO2max interval training. This vO2max training (outlined in chapter 26) produces an array of benefits, including sizable improvements in running economy and lactate-threshold velocity plus improvements in vO2max itself.
Conclusion
Research on vVO2max has changed the way coaches and scientists think about setting up and periodizing training plans. It’s important for coaches and runners to realize that vO2max is a key indicator of performance potential;
thus, they should relentlessly pursue ways to optimize vO2max during training. There is no evidence that high-mileage training improves vO2max; rather, high-quality running at vO2max and faster speeds is necessary to keep vO2max moving upward. Conducting intervals at vO2max has positive impacts on vO2max, running economy, and lactate-threshold velocity. Thus, it has remarkable effects on performance enhancements. The challenge, as discussed in chapter 26, is to arrange vO2max workouts properly throughout the overall training program.
Chapter 10
Velocity at Lactate Threshold
Running velocity at lactate threshold is simply the velocity above which lactate begins to accumulate in the blood. At lactate-threshold and lower velocities, blood lactate tends to be stable. Like running economy and vO2max, running velocity at the lactate threshold is a strong physiological predictor of endurance performance.1 In individual runners, running velocity at lactate threshold responds readily to training, and lactate-threshold upgrades lead to major improvements in race times.
Glycolysis and the Krebs Cycle
To grasp why running velocity at lactate threshold has such a tight grip on endurance performances, it is first important to understand a basic metabolic process called glycolysis. Glycolysis is so critical metabolically that its loss would mean that a runner would never be able to run another 5K or marathon. In fact, without glycolysis an athlete would not be able to ride around the block on a bike or even walk to the corner store in a reasonable amount of time. Glycolysis is actually a series of 10 different chemical reactions that break down glucose, the simple six-carbon sugar that is the body’s most-important source of carbohydrate fuel, into something called pyruvic acid (see figure 10.1). This glycolytic conversion of glucose to pyruvic acid can quickly provide some of the energy a runner’s muscles need for running.
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