Knowing When Enough Is Enough
There is an upper limit of weekly training distance beyond which increases in volume do not enhance O2max or performance. The Swiss research on 16K (10 mi) runners suggested that performance time does not improve as training mileage expands above about 80 to 100 kilometers (50-62 mi) per week.6 In a study carried out at Ball State University, Dave Costill monitored two runners who gradually increased weekly mileage after a layoff period.15 In these two individuals, O2max continued to increase until a weekly volume of 75 miles (121 km) was attained. Above that level, there were no further improvements in aerobic capacity, even when volume soared to 225 miles (362 km) per week! The upper volume limit of 50 to 75 miles (81-121 km) per week probably applies to other variables. For example, a survey conducted by Swedish researchers Bertil Sjodin and Jan Svedenhag found that improvements in the fractional usage of O2max at marathon pace were capped at a specific number of kilometers completed per week.16
Research carried out with swimmers strongly supports the idea that the benefits of training volume are kept to a relatively modest volume level. In another of Costill’s studies, swimmers who trained for 1.5 hours per day performed just as well as swimming competitors who worked out for 3 hours daily.17 The athletes who trained for 3 hours per day did not do as well during various tests of swimming fitness as those who trained for 1.5-hours a day.
No scientific study has ever linked advances in running-training volume beyond 91 kilometers (57 mi) per week with increases in running performance or performance-related physiological variables, yet elite and serious runners routinely climb the so-called volume ladder beyond this mileage point instead of focusing on tweaking the intensity of their training and developing an outstanding running-specific strength program. Intensity of training can often be the most potent producer of running fitness, trumping both volume and frequency. The importance of training intensity is discussed in chapter 20.
Conclusion
Runners often ask, “How many times should I train per week?” hoping there is a magic number of weekly workouts that will have the greatest impact on fitness. Science reveals that there is no optimal number of weekly workouts and that volume usually has a stronger impact on running fitness than does frequency. Volume has its limits, however: The gain in fitness decreases as volume expands, approaching zero as training volume rises beyond about 40 miles (64 km) per week for many runners, and perhaps beyond 50 to 70 miles (81-113 km) per week for more experienced and highly competitive athletes.
Chapter 20
Intensity
The training of endurance runners characteristically emphasizes the completion of long-duration, low- to moderate-intensity efforts, especially during the base or preparation phase of training, but research reveals that such running has a rather weak effect on performance-related variables and running performance compared with higher-intensity exertions.
Intensity can be defined as a percent of maximal heart rate or an actual running speed, but it is usually defined as a percentage of O2max. When an athlete is said to be running at an intensity of 90 percent of O2max, it simply means that the runner’s speed is producing an oxygen consumption rate that is 90 percent of maximum.
Studying the Effects of Intensity
One of the first published scientific investigations examining the effects of intensity on fitness asked three groups of subjects to train three times a week at intensities of either 65, 75, or 85 percent of maximal heart rate.1 All three groups expended the same number of calories per session, which meant that the lower-intensity groups had to exercise longer per workout. Workout duration was 14.5 minutes for the 85 percent group, 22.5 minutes for the 75 percent group, and 35 minutes for the 65 percent group. Over a 10-week training period, the 85 and 75 percent groups raised O2max by about 20 percent, while the 65 percent group failed to improve O2max at all! This study was one of the first to reveal that intensity is a considerably stronger force than workout duration (i.e., total time spent training) from the standpoint of improving fitness. Note that the 75 percent group trained 50 percent longer than the 85 percent group and yet failed to gain a fitness advantage over the 85 percent group. The 65 percent group trained more than twice as long and didn’t improve O2max at all.
In a subsequent study, university students trained five times per week for 2 weeks at a heart rate of either 140 or 172 beats per minute.2 At the end of two weeks, O2max increased by 16 percent for the high-intensity group but failed to move upward at all for the lower-intensity group.
Since then, many studies have revealed that training at relatively higher intensities produces superior physiological adaptations compared with training at lower levels of effort. In one study, 40 runners were randomly assigned to one of four training groups:
Long, slow distance training at 70 percent of O2max
Lactate-threshold training at 85 percent of maximum heart rate (probably corresponding to about 76 percent of O2max)
High-intensity 15/15 interval running (i.e., 15 seconds of running at 90 to 95 percent of maximal heart rate alternating with 15 seconds of recovery at 70 percent of maximal heart rate)
High-quality 4 × 4 interval training (i.e., four work intervals, each consisting of 4 minutes of running at 90 to 95 percent of maximal heart rate with 3 minutes of recovery at 70 percent of maximal heart rate after each work interval)
All four plans resulted in similar total oxygen consumption during training so that total work performed would be roughly equivalent between groups; the workouts were conducted three times a week for 8 weeks.3
At the end of the 8-week period, O2max had increased by 5.5 percent in the 15/15 group and by 7.2 percent in the 4 × 4 group but had failed to improve at all in the long, slow distance group and the lactate-threshold group. Stroke volume, or the amount of blood pumped by the heart per beat, increased by approximately 10 percent in both interval groups (i.e., 15/15 and 4 × 4) after 8 weeks but failed to budge in the slow-distance and lactate-threshold groups. This study is one of many that reveal that higher training intensities produce greater training responses compared with lower intensities of effort.
Greater Intensity Equals Greater Improvement
In research conducted by three-time Olympic gold medal winner Peter Snell and his colleagues at the University of Texas Southwestern Human Performance Center, well-trained runners with average O2max values of 61.7 ml • kg-1 • min-1 participated in a 16-week study that initially involved running 50 miles (81 km) a week for 6 weeks.4 For the next 10 weeks, half of the runners substituted tempo training twice a week for their usual daily runs; these tempo sessions involved 29 minutes of continuous running at intensities of about 70 to 80 percent of O2max. The other half substituted two interval sessions per week for their usual workouts. Each interval session involved about 3 miles (5 km) of work intervals, with the intensity of each interval at 90 to 100 percent of O2max, or about 10K to 3K race pace.
After the 16 weeks, the runners who followed the interval plan improved their 800-meter times by 11.2 seconds and their 10K times by a full 2.1 minutes. In contrast, the group that used tempo training boosted 800-meter performances by just 6.6 seconds and 10K efforts by 1.1 minute. O2max increased by 12 percent for the higher-intensity interval group but by only 4 percent for the group using tempo training. Overall, the higher-intensity interval training produced greater improvements in performance and aerobic capacity than did a greater volume of lower-intensity work.
Upgrading training intensity is the most potent producer of higher fitness.
Anthony Stanley/Action Plus/Icon SMI
Since intense training is such a potent producer of running fitness, it follows that the careful and progressive replacement of moderate-intensity running with higher-speed effort in an overall training program should produce upswings in fitness and performance. In one study, experienced 5K runners replaced about 32 percent of their usual moderate-intensity aerobic running with explosive efforts involving high-speed sprints, boun
ds, and hopping drills; they subsequently upgraded their 5K performance by about 3 percent.5 In the process, these 5K runners also enhanced running economy, a key indicator of endurance-running capability.
In a separate investigation, experienced, competitive 10K runners added 3 days a week of high-intensity interval training at 90 to 95 percent of O2max, or 10K to 5K race pace, to their programs. As a result, they upgraded 10K performances, bolstered endurance during high-speed running, and decreased plasma lactate concentrations at intensities of 85 and 90 percent of O2max, which indicates an underlying improvement in lactate-threshold speed.6
In a study that examined the merits of high-volume versus high-intensity training, a group of experienced runners replaced 82 kilometers (51 mi) per week of moderate-intensity running with high-intensity running and cycling.7 Running volume was reduced to about 30 weekly miles (48 km) of hard effort, and three tough cycling sessions were inserted into the program each week. The cycling workouts were 5 × 5: five 5-minute work intervals at an intensity that produced O2max with 5-minute recoveries. Despite the significant decrease in running volume, the emphasis on intense running and cycling training led to significantly faster 10K race times: Average 10K clocking improved by 81 seconds.
Searching for the Training Threshold
Many runners believe that there is an exercise intensity that must be exceeded during a workout in order for the session to produce physiological adaptations. The theoretical training intensity above which adaptation occurs and below which no response in fitness is observed has sometimes been called the training threshold. Identification of this threshold is of more than esoteric interest since many runners would like to know whether there is a danger of dipping too low on the intensity scale during their relatively easy workouts.
Unfortunately, scientific research has had a difficult time locating a training threshold with any degree of precision or unanimity. Various studies have suggested that the threshold might occur at about 50 percent of O2max;8 75 percent of maximal heart rate, which would correspond with approximately 62 percent of O2max;1 slightly above 60 percent of the difference between maximal heart rate and resting heart rate;9 or simply at a heart rate of about 140 to 150 beats per minute.2, 10 This range of results is substantial enough to call the training threshold concept into question. In addition, a heart rate of 140 to 150 would correspond with the highest-possible level of exertion for a runner with a maximal heart rate of 145 or so and yet would represent easy effort for a runner with a maximal heart rate of 220.
Casting more than a little suspicion on the threshold concept, one study found that adaptation to training occurred at the extremely light intensity of 36 percent of O2max, or about 55 percent of maximal heart rate.11 Other studies have noted that adaptation can occur when training intensity is maintained at just 45 percent of O2max.12, 13 Adaptation has also been documented when exercise intensity is set at a relatively low heart rate of 110 to 120 beats per minute.14 It would seem that just moving around—jogging at a very slow pace—would produce physiological change in relatively untrained runners.
Nonetheless, it appears that a threshold exists for some runners, particularly those with a significant training background. In one study, moderately trained individuals who ordinarily trained 45 minutes per day, three times a week, embarked on a program involving exercise durations as great as 5.5 hours per day (!) carried out six times per week over an 8-week period.15 The average exercise intensity was an extremely moderate 45 percent of O2max, or about 63 percent of maximal heart rate. Since no training effect (i.e., adaptation) was observed at all after the 8 weeks, it can be assumed that these athletes were below some sort of training threshold—or else that they were not recovering enough for the adaptations to become apparent.
Such studies have an inherent weakness in the sense that all of the training was conducted at a specific intensity, after which the involved athletes were checked for adaptation. In the real world, runners train at a variety of intensities over the course of a week or month. A more-interesting question would focus on whether lighter days of training really provide enough stimulus for adaptation to complement the higher-quality work conducted during the same period. For example, if a runner is covering 40 miles (64 km) total per week during training, with 10 quality miles (16 km) above lactate-threshold speed, is it necessary for the other 30 miles (48 km) to be completed above a certain intensity in order for increased fitness to accrue? No study has provided an answer to this basic question.
The solution to the training threshold paradox may also be that the actual training response depends to a large extent on the underlying fitness of the individual. Specifically, very fit runners require a high intensity of training to move performance capacity upward, while less fit individuals may benefit from running that is much more moderate in intensity.16, 17 Beginning runners can benefit a lot from running at an intensity of 70 percent of O2max, for example, but it is unlikely that such an intensity would produce major physiological movements in an experienced runner. Unfortunately, many elite runners fail to take this training truism into account and adjust their training to include higher and higher volumes of moderate-intensity work instead of shifting toward gradually increasing amounts of high-intensity effort.
Determining the Ideal Intensity
Runners have a wide range of intensities from which to choose for their high-quality workouts. Can a specific intensity be identified as the most potent producer of running fitness? Is there one training intensity that produces the greatest combined improvements in the key predictors of endurance-running performance—vO2max, running economy, lactate-threshold speed, and maximal running velocity—as well as in performance itself?
These are tough questions to answer. One could survey the published scientific work in this area and attempt to draw conclusions, but it would be very difficult to compare different research investigations. Studies use runners with different backgrounds and ability levels and subject the runners involved to training regimens that vary in frequency, workout duration, volume, and intensity. Nonetheless, a consensus is gradually emerging that the most productive intensities may be in the range of 95 to 100 percent of O2max.18
This suggests that vO2max, the minimal running speed that elicits O2max, may be an extremely beneficial training intensity. In research carried out by French physiologist Veronique Billat, 8 experienced runners with high aerobic capacities of 71.2 ml • kg-1 • min-1 carried out one vO2max workout each week over a 4-week period in addition to their usual training. The actual vO2max session was 5 × 1,000 meters (.6 mi) at vO2max, with 3-minute jog recoveries. After just the 4 weeks, vO2max improved by 3 percent, running economy was enhanced by an extremely impressive 6 percent, and lactate-threshold speed rose by 4 percent!19 In addition, one of the greatest gains in maximal aerobic capacity ever documented in a study carried out with experienced, competitive runners resulted from using vO2max as the key training intensity.20
Such findings do bring coaches and runners back to the threshold questions: If quality training is conducted at 95 to 100 percent of O2max or at 90 to 100 percent of O2max, which would be from a 10K pace up to vO2max, what is the minimal intensity for complementary, easy workouts? How fast must one run on light days to nudge key performance variables in the right direction?
The answer is that on easy days, a runner is simply playing the volume game, using miles or kilometers rather than intensity to advance fitness. Thus, it probably does not matter how fast the runner is moving—just covering the miles will produce the desired positive effect, with most of the gains in running capacity coming from the quality efforts on other days of training. Note, though, that the volume game can be overplayed. If a runner is already covering 50 to 70 miles (81-113 km) per week or more, additional easy miles are unlikely to have any effect on fitness at all.
Conclusion
Runners, running coaches, and especially proponents of high-volume training models often suggest that a relatively high volume
of moderate-intensity training can produce an adaptive response similar to the one associated with a lower volume of high-intensity work. In relatively inexperienced and untrained runners, this can sometimes be true.21 However, it is unlikely to be the case in experienced and elite runners, who require a steady diet of high intensities to make the indicators of physiological variables move upward.4, 5, 7, 16, 17
A reasonable idea is to keep track of intense volume (i.e., number of miles or kilometers run at 10K pace or faster) as a percentage of the total volume, or the number of miles or kilometers completed per week. If this percentage is consistently below about 25 percent, a runner should certainly begin replacing less intense miles with more intense exertions until the 25 percent figure is attained. After 25 percent is reached successfully, without injury or overtraining, the relative amount of intense training can cautiously and progressively be increased over a training year.
Chapter 21
Recovery
Recovery involves the restoration of neuromuscular, cardiovascular, and endocrine function following a training session. Recovery also includes adaptation, a process by which various physiological systems transform themselves and improve their ability to function during exercise. For runners, the recovery period spans the time between running workouts; it includes immediate recovery (i.e., what a runner does during the critical hour after a running session ends) and between-session recovery (i.e., what a runner does between running workouts, including nonrunning activities carried out on off days).
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