Excerpted from Running Periodization by Jason Karp
How much training should you do in each intensity zone? That’s a tough question to answer and depends on many factors. Several research studies have tried to approach an answer to this question by documenting what elite distance runners typically do. Those descriptive studies have found that, using measurements of blood lactate levels, heart rate, and perceived exertion, elite distance runners run about 75 to 80 percent of their volume in zone 1 below acidosis threshold (low intensity) and about 20 to 25 percent at and above acidosis (lactate) threshold (high intensity).[1]-,[2],[3],[4],[5],[6]
Given the unique intensity of the acidosis threshold, some research has narrowed in on the 20 percent at and above threshold, and has found that the three-zone training intensity distribution is about 75-80/5-10/15 percent for below, at, and above acidosis threshold.[7],[8] This is a robust finding among the handful of descriptive studies on this subject, including my study on the U.S. Olympic Marathon Trials qualifiers, which revealed the training intensity distribution to be 85/10/5 percent for the male runners and 81/12/7 percent for the female runners.[9] Thus, it seems that elite endurance athletes have settled on a training pattern that involves a large volume of work at low intensities (zone 1; less than 80 percent VO2max) combined with a small amount of work at intensities higher than threshold (zone 3; greater than 90 percent VO2max), with not much time spent in the middle at threshold (zone 2; 85 to 90 percent VO2max).
While most research has quantified the intensity distribution based on time or distance in each zone, some research has quantified it based on the primary work portion of the session (instead of counting the low-intensity warm-up and cool-down before and after interval workouts and the jogging recovery intervals between reps, which would inflate the amount of low-intensity work). That research has shown that different methods of training intensity quantification impact the distribution quantification. For example, in elite endurance athletes, a 90/10 low/high intensity distribution based on the amount of time spent in each zone typically corresponds to an 80/20 distribution based on the type of workout, which equates to two to three workouts per week at acidosis threshold (zone 2) or at higher intensities (zones 3, 4, 5) for athletes training 10 to 14 times per week.[10]
When calculating the intensity distribution as a percentage of distance or time run per week, the percentage of low-intensity training is always going to be much greater than the percentage of high-intensity training. You can run a lot more volume of easy than of hard. That’s because of the inverse relationship between volume and intensity. The higher the intensity, the less work (time or distance) you can do. For example, if you do an interval workout at VO2max pace today (zone 3), say 5 x 800 meters, the whole period of high intensity is two and a half miles. Then, tomorrow, you run easy for 8 miles at 70 percent max heart rate (zone 1). That gives you a 76/24 percent low/high intensity distribution. But that’s not really reflective of your training, which, in this two-day case, would be 50 percent low/50 percent high. If you run six days per week and do two hard interval workouts and four easy runs, that’s a 67/33 percent intensity distribution. Thus, 80/20, which is based on elite athletes who train 10 to 14 times, or 10 to 25 hours, per week, really is an artefact of the inverse volume-intensity relationship rather than a true reflection of how runners train. Truth is, elite runners do quite a bit of high-intensity training, but they do such a high volume of low-intensity training that it makes the high-intensity training look small in comparison. When someone trains a lot, the majority of training is consequently skewed toward low intensity. If it were possible to do as much high-intensity work as low-intensity work and athletes are choosing to do more low-intensity work, then it could be said that an 80/20 percent intensity distribution may be the optimal way to train, at least among elite athletes. Because of the inverse relationship between volume and intensity, it’s simply not possible to do as much high-intensity training as low-intensity training.
Regardless of the exact intensity percentages, distance runners do spend a lot more time running slow than running fast. But what about nonelite runners? What’s an optimal training intensity distribution for them? Scientists in Spain wanted to find out. In a study at the European University of Madrid, researchers randomly divided 30 recreational runners, matched for age, weight, body mass index, and VO2max, into two groups of 15: one group followed a training program that emphasized the amount of training in zone 1 (easy running) for 10 weeks (Zone 1 group), while the other group followed a training program that emphasized the amount of training in zone 2 (threshold) for ten weeks (Zone 2 group).[11] Both groups did an equal amount of training in zone 3. The training plan of the Zone 1 group was designed to achieve a 75/5/20 percent intensity distribution in zones 1, 2, and 3 (based on heart rate), while the training plan of the Zone 2 group was designed to achieve a 45/35/20 percent intensity distribution. The actual result of the training equaled 73/13/14 (Zone 1 group) and 47/37/16 (Zone 2 group), just slightly off from what the researchers had designed. Prior to the specific training intervention, both groups did the same training for eight weeks, which consisted of intensity distributions of 100/0/0 percent in weeks 1 to 3, 88/5/7 percent in week 4, 54/27/19 percent in week 7, and a recovery week of 78/14/8 percent in week 8. Running distance averaged 31 miles per week in 5 to 6 runs per week for both groups over the course of the study, with an average peak of 44 miles per week. All runners raced the same 10K at the end of the 8-week preparation training and another 10K at the end of the 10-week intervention. After the 8-week preparation period, during which both groups did the exact same training, the 10K race result was the same between groups (39:18 vs. 39:24). After the 10-week intervention period, the Zone 1 group improved 10K time by 1 minute and 59 seconds, from 39:18 to 37:19, while the Zone 2 group improved by 1 minute and 24 seconds, from 39:24 to 38:00. This 1.5 percent greater improvement in 10K time for the Zone 1 group compared to the Zone 2 group, while meaningful to runners, was not a statistical difference. Since there was a large variation in the actual intensity distributions because the study participants didn’t carry out the training exactly as prescribed, the researchers compared the 10K times among the individuals in both groups whose training was predominantly in zone 1 and predominantly in zone 2. Six individuals from the Zone 1 group with an intensity distribution of 78/11/11 percent improved their 10K time by an average of 7.0 percent, while six individuals from the Zone 2 group with an intensity distribution of 32/53/15 percent improved their 10K time by an average of only 1.6 percent. In this light, it appears that the greater zone 1 training is superior to the greater zone 2 training, although the researchers concluded that the overall findings did not support one approach over the other.
Another study at the European University of Madrid compared the effects of two training programs distinguished by the amount of training in zone 1 (low intensity) and zone 2 (acidosis threshold intensity), with the same amount of zone 3 (high intensity).[12] Twelve competitive runners with a 10K PR between 30:30 and 35:00 were divided into two training groups for five months: one group followed a training plan designed to achieve a percentage distribution in zones 1, 2, and 3 of 80/10/10, while the other group followed a training plan designed to achieve a percentage distribution of 65/25/10. Using heart rate to determine the amount of time spent in each zone, the actual result of the training was very close to that prescribed: 80/12/8 (Zone 1 group) and 67/25/8 (Zone 2 group). When the time spent in each zone was adjusted for the time spent during warm-ups, recovery intervals between reps, and cool-downs before, during, and after interval workouts, respectively, the intensity distributions equaled 74/11/15 percent for Zone 1 group. (No similar information was given for Zone 2 group.) Prior to the training intervention, the runners performed the same initial three-week training program, with intensity distributions of 100/0/0 percent in week 1, 87/9/4 percent in week 2, and 93/3/4 percent in week 3. Running distance averaged 50 to 56 miles per week for both groups over the course of the study, with a peak of 75 miles per week. Before and after the training period, study participants ran a 10.4-kilometer cross-country time-trial race. After five months of training, both groups improved their race times, however, Zone 1 group, which did more low-intensity training, improved significantly more than did Zone 2 group, which did more acidosis threshold training (2 minutes and 37 seconds vs. 2 minutes and 1 second, respectively). While the 36-second improvement difference between groups for a 10.4-kilometer cross-country race is not a huge difference, the interesting finding of this study is that devoting more time at moderately high intensities (zone 2) did not cause runners to get any faster compared to simply devoting more time to running easy (zone 1).
In another study, this one at the University of Salzburg in Austria, scientists randomly assigned 48 runners, cyclists, triathletes, and cross-country skiers to one of four training programs for nine weeks: low intensity, threshold, high intensity, and polarized (a combination of low and high intensity) to compare the effects of the different training programs on physiological markers of endurance performance.[13]
Low intensity, threshold, and polarized training all included three blocks of three weeks each, with the third week of each block used for recovery. High intensity training included two blocks of 16 days with one adaptation week prior to and one recovery week after each block. Specifically, this is what each group did:
- Low intensity: 83/16/1 percent intensity distribution for zones 1, 2, and 3. Three 90-minute workouts, two 150- to 240-minute workouts (all zone 1), and one threshold workout (zone 2) per week.
- Threshold: 46/54/0 percent intensity distribution for zones 1, 2, and 3. Three threshold workouts (zone 2), one 75-minute fartlek (zone 1 to zone 3), and two 90-minute, low-intensity workouts (zone 1) per week.
- High intensity: 43/0/57 percent intensity distribution for zones 1, 2, and 3. The adaptation week included two interval workouts (zone 3) and four low-intensity workouts (zone 1). The 16-day interval block included 12 interval workouts: four blocks of three days of interval workouts and one day of recovery. All interval workouts were 4 x 4 minutes at 90 to 95 percent max heart rate (zone 3) with 3 minutes active recovery between reps.
- Polarized (low-high intensity): 68/6/26 percent intensity distribution for zones 1, 2, and 3. Two interval workouts (zone 3), two 150- to 240-minute low-intensity workouts (zone 1) that included 6 to 8 maximal 5-second sprints separated by at least 20 minutes, and two 90-minute, low-intensity workouts (zone 1).
After nine weeks of training, the polarized training group increased VO2max more than did the other groups, by 11.7 percent, compared to 4.8 percent after high intensity, 2.6 percent after low intensity, and a decrease of 4.1 percent after threshold. Polarized also increased peak speed (treadmill) or power (bike) by an average of 5.1 percent, compared to 4.4 percent after high intensity, 1.8 percent after threshold, and a decrease of 1.5 percent after low intensity. Other variables also seemed to favor polarized training, including time to exhaustion during a laboratory test that incrementally increased speed (treadmill) or power (bike), which increased by an average of 17.4 percent after polarized, 8.8 percent after high intensity, 6.2 percent after threshold, and 8.0 percent after low intensity, and the speed/power at lactate threshold, which increased by an average of 8.1 percent after polarized, 5.6 percent after high intensity, 1.4 percent after threshold, and 1.2 percent after low intensity. Running and cycling economy did not improve following any of the training programs.
In yet another study at the Institute for Sport Sciences at Julius-Maximilian University in Würzburg, Germany, 45 male and female recreational runners were randomly divided into three groups that trained differently for three weeks: one group trained with 94/6/0 percent intensity distribution for zones 1, 2, and 3, respectively (low intensity), another group trained with 39/21/40 percent intensity distribution (high intensity), and the third group trained with a mix of the other two, a 70/13/17 percent intensity distribution (low-high intensity).[14]
Prior to the three-week intervention, all participants ran at the same intensity distribution (71/22/7 percent) for a four-week preparation period and, after the three-week intervention, all participants had a one-week taper at the same intensity distribution (92/8/0 percent). Physiological variables (VO2max, speed at lactate threshold, and running economy) and a track 5K time trial were tested four times: before and immediately after the initial four-week preparation period, immediately after the three-week training intervention, and immediately after the one-week taper. All three groups improved 5K time. Although the intervention period was only three weeks in this study, low intensity came out on top, with 71 percent of runners in that group improving 5K time by nine percent or more, compared to 23 percent in the high intensity group and 27 percent in the low-high intensity group. Overall, 13 of 16 runners in the low intensity group experienced a positive response to the training, whereas only 6 out of 13 in the high intensity group and 8 out of 16 in the low-high intensity group had positive responses. High intensity and low-high intensity training had the greatest effect on VO2max, while there was little to no effect of any of the training programs on speed at lactate threshold and running economy. Based on the individual responses to the different types of training, the scientists found that the risk of not responding to training is greater with high intensity and low-high intensity compared with low intensity. This may be the most interesting finding of the study, because it supports that, at least for recreational runners, low-intensity training has a better chance of working.
However, the exact training intensity distribution doesn’t always matter. That was the contrasting finding of scientists in the Department of Physical Education and Sports at the University of Alicante in Spain, when they compared half-Ironman race results among 18 recreational triathletes who trained under the direction of the same coach for 20 weeks, but with different intensity distributions for 13 of those weeks.[15] Some triathletes trained with a greater emphasis on zone 2, with intensity distribution 78/19/3 percent in zones 1, 2 and 3, respectively, and others trained with a greater emphasis on zone 3, with an intensity distribution 85/4/11 percent. Prior to the 13-week differing training period, all athletes trained the same for 7 weeks, with an 88/10/2 percent intensity distribution. At the end of the 20 weeks, turns out that the type of training didn’t make a difference, with no correlation between training intensity distribution and race performance. Indeed, only two seconds differentiated both groups in the race that took more than five hours. The only difference between groups was in running, with the greater zone 2 training group improving its speed at acidosis threshold, which resulted in better performances in the running segment and overall in the half-Ironman triathlon. Triathletes who spent more time in zone 3 at higher intensities had worse times in the running segment and in the triathlon. It’s possible that the reason this study contrasts the others is because of the distance of the performance test. For longer races, like half-marathons and marathons (including those as part of half- and full-Ironman triathlons), acidosis threshold (zone 2) training is important. The longer the race, the more predictive the speed at acidosis threshold is to racing performance.
From these and other experimental studies, one thing we know for sure is that runners, whether they are elite or recreational, should skew the training more toward zone 1, with some training in zone 3.[16] For longer races, zone 2 is also important, especially as you get closer to the race. Most research on intensity distribution has used a two-zone or three-zone model, collapsing zones 4 and 5 into zone 3. However, since zone 3 represents any intensity above the acidosis threshold, dividing the training into three zones leaves a lot unanswered about what kind of high-intensity training to do, since there is a large range of possible intensities in zone 3 (e.g., VO2max, anaerobic capacity, and anaerobic power). As mentioned earlier, for distance runners to maximize endurance-related adaptations, it seems that 100 percent VO2max (zone 3 in the five-zone model) is the optimal high intensity.
A review of 16 research studies on training intensity distribution among middle- and long-distance runners published in 2018 found that the most popular and effective training intensity distributions are (1) pyramidal training, which includes a heavy emphasis on zone 1 training, a somewhat lesser amount of zone 2 training, and even less zone 3 training, and (2) polarized training, which includes a heavy emphasis on zone 1 training, a lesser amount of zone 3 training, and very little zone 2 training.[17] A third, but less common, pattern is threshold training, which includes a greater emphasis on zone 2 training and, despite the descriptive and experimental research to the contrary, is used by many of the best distance runners in the world. All the experimental studies on training interventions are of relatively short duration (3 to 20 weeks), leaving a lot unknown about the structure and organization of successful long-term training. Of the few experimental studies that have compared polarized training to threshold training, it seems that polarized training is better than threshold training (although study designs and methods make strong conclusions difficult), despite its lesser race specificity and the historically strong evidence of the importance of the acidosis threshold to distance running performance.[18] How much training in zone 2 (threshold) is optimal is a little bit tricky to figure out, and likely depends on the targeted racing distance and, perhaps more critically, on what type of distance runner you are (speed-type vs. endurance-type). In my coaching experience, endurance-type runners do better with more zone 2 (threshold) training as well as a lot of zone 1 training, while speed-type runners do better with more zones 3, 4, and 5 (high-intensity) training, with little emphasis on zone 2 (threshold) training. Thus, pyramidal training may be better for endurance-type runners, while polarized training may be better for speed-type runners.
One of the reasons for skewing training to low intensity may be optimization. Low-intensity training may be the most optimal intensity at which to adapt because it comes with the least stressful work. You could get equal or even greater adaptation with higher-intensity work, but that comes at the price of a lot of fatigue and physiological stress, with large hormonal disturbances and downregulation (reduced activity) of the sympathetic nervous system. When the amount of training in zone 3 is increased, for example, to a larger percentage of total training time, runners find it too demanding after just two to three weeks and show signs of overtraining.[19]
Before you start doing 75 percent of your training at a low intensity, 5 percent at threshold, and 15 percent faster than threshold, it’s a mistake to simply copy what elite athletes do. Although elite athletes are very successful with that (or similar) training intensity distribution, that doesn’t mean everyone should train that way, or that those athletes wouldn’t be even better if they trained a different way. For one thing, few studies have experimented with different training methods to test which method is more effective than another method, and no studies have been done using the same group of people (or on identical twins, with half of each pair training a different way). Other than the studies described above, the published research in this area is largely descriptive, rather than experimental, in nature, documenting what elite endurance athletes do. Although elite athletes and coaches, through years of trial and error, have settled on a method that works best for them, that doesn’t mean another method wouldn’t or couldn’t work better. It also doesn’t mean that their results are because of their method of training, as it’s possible their results may be in spite of it. Although this book is about training rather than about genetics, it must be acknowledged that genetics (talent) supersedes everything else and even influences an individual’s ability to improve with training.[20]-,[21],[22],[23],[24],[25],[26],[27],[28],[29]
Secondly, elite athletes do not have the same time constraints as everyone else. The athletes whose training has been documented in the scientific literature have an unlimited amount of time to train, as well as to recover, while everyone else has work or school and other responsibilities of life to keep them busy. Having unlimited amount of time to train influences the training volume. Most people don’t have time to run upwards of 100 miles per week. Running that much will undoubtedly cause a low intensity to make up a large percentage of the training.
Thirdly, the superior physiology of elite athletes enables them to get a lot of value from a low intensity. For example, spending 75 percent of their training time at a very low intensity may be enough of a stimulus for elite runners to adapt, but may not be enough of a stimulus for you. Here’s why: for elite athletes with a high VO2max, a low intensity still generates a large volume of oxygen that is quickly delivered to the muscles (called “oxidative flux”). Thus, an elite runner training at 60 percent of his or her VO2max of 80 or 70 milliliters of oxygen per kilogram body weight per minute, respectively (about 75 percent max heart rate) would have about the same muscle oxidative flux as a recreational runner running at or near his or her VO2max (0.60 x 80 = 48 ml/kg/min; 0.60 x 70 = 42 ml/kg/min). In other words, an elite runner can achieve a similar muscle oxidative flux (which may be translated into a similar signal for adaptation) at a much lower intensity than can a recreational runner. Also, research has shown that when training is performed below a certain intensity, the hormonal responses that trigger adaptation occur only when the duration is long enough.[30],[31] The duration (volume) of any specific intensity is crucial to induce training effects. Thus, elite runners’ high volumes and durations of low-intensity training (often twice per day) may be enough of a stimulus to which to adapt, while nonelite runners may need a higher intensity. In other words, if you do most of your training at a low intensity, you need to do a lot of volume to optimally adapt.
Taken together, the research and the training methods of successful endurance athletes suggests that distance runners shouldn’t do too much high-intensity training, and coaches shouldn’t extol the benefits of intensity over volume. While the effects of high-volume/low-intensity training on physiology and performance take a while, the effects of low-volume/high-intensity training are relatively rapid. However, high-intensity training is also accompanied by a rapid plateau. A systematic increase in training volume from year to year is the preferred way to ensure long-term development.
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