Ventilatory Threshold

I am often asked if the 80/20 rule of intensity balance applies to athletes who train at very low volumes. It’s a fair question. We know that low-intensity exercise doesn’t do a lot of good in small amounts, whereas high-intensity exercise does. It is plausible therefore that, below a certain volume threshold, doing less than 80 percent of one’s training at low intensity will yield better results than sticking to the 80/20 rule.

A new study by Luca Festa of the University of Verona and colleagues addresses this question—sort of. The subjects were recreational runners with at least four years of experience. For eight weeks, half of them followed a “polarized” training program in which 77 percent of training was done at low intensity, 3 percent at moderate intensity, and 20 percent at high intensity, while the other half maintained a 40/50/10 intensity split (“focused endurance training”). Volume was adjusted to ensure that the total training load (intensity and volume combined) was equal for the two groups. This required runners in the polarized group to run slightly more than runners in the focused endurance group, though volume was quite low in both groups, averaging out to 3.73 hours per week and 3.1 hours per week, respectively.

Physiological and performance measures were taken on all of the subjects before and immediately after the eight-week training intervention. The table below summarizes the results.

Polarized Focused Endurance
Fat Mass -12.7% -8.6%
VO2max +1.2% +0.9%
Velocity at VO2max +3.2% +4.0%
Running Economy +5.3% +7.0%
Average Velocity in 2K time trial +3.5% +3.0%

As you can see, they’re kind of a mixed bag. The polarized group saw bigger improvements in body composition, VO2max, and (what is arguably the only result that matters) time-trial performance, while the focused endurance group experienced bigger gains in running economy and velocity at VO2max. None of these differences was judged to be statistically significantly, however, so Festa’s team concluded that “Focused Endurance Training obtains similar improvements [as] Polarized Endurance Training[,] saving 17% of training time in recreational runners.”

There you have it: 80/20 training is a waste of time. You get equal results in less time by doing half of your training at moderate intensity, which is precisely the opposite of what 80/20 advocates like me tell athletes not to do.

But wait—there’s another interpretation. Remember the commonly asked question I mentioned at the top of this article? We started out with the premise that it is likely that, below a certain threshold of training volume, an 80/20 intensity balance might not yield optimal fitness benefits. The results of Festa’s study suggest that this threshold is very low indeed, if indeed it exists at all. Members of the polarized group and the focused endurance group ran just 32 minutes and 27 minutes per day, respectively, during the eight-week study period, and improved by roughly equal amounts. So it’s safe to say that you would have to run less than 25 minutes a day, on average, for a more intense training approach to possibly produce better results than the 80/20 method, emphasis on “possibly.”

It’s also worth drawing attention to the fact that the only performance test included in Festa’s study was a 2 km time trial. That’s pretty short. Why 2 km? Because Festa and his colleagues wanted to set up the focused endurance group for success, that’s why! Clearly, a short performance test was going to give the group doing shorter runs the best chance of equaling the improvement of the other group. Even then, though, the polarized group improved slightly more. And although the difference was statistically significant, meaning it could have happened by chance, I’d be willing to bet that if this same experiment were rerun 100 times, the polarized group would improve more with a frequency that exceeded chance, hinting at the beginning of a trend that would only grow as the distance of performance tests increased.

Furthermore, although Festa’s study itself was quite short, its brevity was appropriate in the sense that it doesn’t take long for a training program of such low volume to yield the full measure of its potential benefits. In other words, had the experiment lasted longer, it’s unlikely that either group would have improved much more. But suppose you were to actually follow one of the two programs involved in this study, getting whatever benefit you could squeeze out of it in 8-10 weeks, and then decided that you wanted to improve more going forward.

Here’s what would happen: If you were on the focused endurance plan and you proceeded by gradually increasing the volume of training you did at the same 40/50/10 intensity ratio, you would gain fitness at a gradually decreasing rate for a little while before reaching a point of negative returns at a still fairly modest volume level. That’s because any training done above the first ventilatory threshold—whether moderately intense or highly intense—is significantly more stressful to the body than training done below the VT1, and on this program you’re doing 60 percent of your total running above that threshold. Festa’s team collected data on perceived effort from their subjects but did not report it, and again, I’d be willing to bet that members of the focused endurance group perceived their training to be harder than members of the polarized group perceived their training to be, even though mathematically their training loads were equal.

But if instead you went through the same process on the 80/20 program, you would continue to improve for a very long time, albeit at a diminishing rate, not reaching the point of negative returns until you’re doing a ton of running. And that’s because training below the first ventilatory threshold is so gentle on the body that even the average athlete can handle (and benefit from) massive amounts of it. I would only add that, whereas in this study almost all of the 20 percent of training done above the VT1 was done at high intensity, a runner training at ever-increasing volumes would be wise to gradually shift minutes from the high-intensity bucket to the moderate-intensity bucket as volume grew.

Festa and his colleagues admit that it is a well-established fact that an 80/20 intensity balance provides the best possible results for athletes who train a lot, writing, “several studies have shown that it allows them to achieve greater improvements in performance,” and that “this distribution is necessary for athletes who perform a large volume of training, to prevent overtraining or steady state of performance.” What this new study shows is that the 80/20 approach is also at least as effective as a more intense training approach at a very low training volume of around 30 minutes a day. In other words, the title of this article is a joke.

The lactate threshold gets so much attention in endurance sports that, despite its esoteric name, most athletes who have passed beyond the newbie stage are familiar with it. The term “lactate threshold” refers, of course, to the exercise intensity at which lactate, an intermediate product of aerobic metabolism, begins to accumulate in the bloodstream because the muscles are producing it faster than they can use it.

Simple enough. But when you drill down into the concept of the lactate threshold, things get messy. The first wrinkle is that there are numerous ways of defining the lactate threshold. Among them: the exercise intensity at which the blood lactate concentration reaches 4 mmol/L, the exercise intensity at which the blood lactate concentration begins to increase exponentially, and the exercise intensity at which the rate of blood lactate concentration’s rate of increase is greatest. No single definition of lactate threshold is inherently more valid than the others, and when they are applied to the results of a single lactate threshold test, they set the LT at slightly different levels.

A second wrinkle is that, even when you settle on a particular definition of lactate threshold, the specific testing protocol used to determine an individual athlete’s LT will affect the results. For example, an LT test with 4-minutes stages is likely to yield a slightly different result than an LT test with 2-minute stages.

A third wrinkle is that, because the lactate threshold is a metabolic event, it is affected by a variety of factors other than an individual athlete’s current fitness level, such as diet. If you do an LT test after a day of low-carbohydrate eating, you’ll get a different result than you will from an LT test done the day after high-carbohydrate eating.

Then there’s the question of the LT’s practical relevance. Contrary to pervasive beliefs in the endurance sports community, there is no sudden leap in the rate of fatigue when the lactate threshold exceeded. Athletes can sustain speeds/power outputs slightly above LT almost as long as they can sustain speed/power outputs slightly below LT. Nor is training precisely at LT uniquely beneficial. Training slightly above or slightly below this level produces pretty much the same results.

The ventilatory threshold is a different story. It is defined is the exercise intensity at which the breathing rate begins to increase at a faster rate than it does at lower intensities. The reason this happens is that the brain is required to begin to recruit large numbers of fast-twitch muscle fibers in order to meet the desired level of work output. This makes exercising even slightly above the VT is significantly more stressful to the nervous system than exercising even slightly below it. Consequently, training above the VT generates more fatigue and takes longer to recover from.

Research has consistently shown that endurance athletes at all levels gain the most fitness when they do about 80 percent of their training below the ventilatory threshold. Although supra-VT training is important and beneficial, athletes just can’t handle very much of it, whereas sub-VT training is so much gentler on the nervous system that athletes can handle a whole lot of it and must do a whole lot of it to realize its full benefits. The single most important thing you can do to keep your training on track is to know where your personal ventilatory threshold lies and is this knowledge to stay below it about 80 percent of the time.

Now, you might be wondering: If the ventilatory threshold is so much more reliable and important than the lactate threshold, why are our 80/20 training intensity zones based on lactate threshold? The short answer is “tradition.” The LT and the VT are measured in completely different ways. Direct measurement of the LT requires taking of small blood samples throughout an exercise test, whereas direct measurement of the VT is done through a method known as spiroergometry, which entails collecting and analyzing exhaled gases during exercise. It so happens that the LT was first identified in 1930 and the VT almost three decades later, in 1959. Having gotten a big head start, LT testing has remained the preferred method of quantifying moderate exercise intensity, despite its limitations. Hence, all of the commonly used field tests for establishing individual training intensity zones, including those that the 80/20 scale relies on, are designed to determine LT, not VT.

Because there is a mathematically consistent relationship between the two thresholds, however, LT tests can be used to determine VT as well, and this is precisely what the 80/20 zone scheme is set up to do. A new study conducted by Spanish researchers and published in Frontiers in Physiology found that, in a group of 22 trained male runners, the ventilatory threshold consistently fell slightly below the lactate threshold (actually the maximal lactate steady state, in this case) in terms speed, heart rate, and perceived effort, as shown in the table below (Note that MAS = Maximum Aerobic Speed, VT1 = Ventilatory Threshold, MLSS = Maximal Lactate Steady State, HRmax= Maximum Heart Rate, and VT2= Second Ventilatory Threshold, which is the exercise intensity at which hyperventilation occurs).

On the 80/20 intensity scale, the lactate threshold corresponds to the top end of Zone 3, which puts the ventilatory threshold in Zone X, which, in turn, ensures that when you train in Zones 1 and Zone 2—as you will do about 80 percent of the time when you follow one of our 80/20 training plans—you are at low intensity.

Having said all of this, I will also say I am hopeful that one day soon we will be able to develop a complementary alternative intensity scale that is anchored directly to ventilatory threshold testing. Currently I am trying out a wearable device that is capable of measuring the VT through accelerometer technology, specifically by measuring the rate and degree of lung expansion and contraction. Bending to tradition, though, the makers of this device are currently using the device’s VT estimates to determine LT. I’d like to talk them into providing users with their VT value instead, or additionally. Stay tuned.

Easy runs get no love. Whenever a video is made of elite runners in training, it’s always some type of workout that’s filmed (a track session, hill repetitions, a long run at marathon pace), never an easy run. This is the case despite the fact that easy runs are the foundation of any good training program and collectively contribute more to race-day performance than any other type of run.

The tendency in our sport to take easy runs for granted has practical consequences. These runs are considered so basic that no one can possibly screw them up, and yet no run type is screwed up more often or with greater consequences. I’m referring to the moderate-intensity rut, of course—the almost universal tendency of runners to do their easy runs too fast, slightly above the ventilatory threshold (VT), making each session more stressful than it should be and creating a chronic burden of fatigue that inhibits fitness development and compromises performance in runs that are intended to be harder.

But I’m sick of talking about the moderate-intensity rut. Today I’d like to talk instead about another important element of easy run execution, which is allowing your easy run pace to vary wildly from day to day and even within individual easy runs based on how you’re feeling. Contradictory though it may seem, only by pacing yourself inconsistently in your easy runs will they consistently serve their intended purpose, which is to ensure that your overall training workload is close to, but within, the limit of your body’s present tolerance for training stress.

Erratically paced easy runs are essentially a method of ensuring that a good training plan is correctly applied. Before you start to train for any important race you should, of course, devise (or choose) a training plan. Your overarching goal in developing this plan is, as I just suggested, to prescribe a workload that is near to, but less than, the limit of your body’s tolerance for training stress. To achieve this goal, you need to decide on an appropriate volume of training, design key workouts that are hard but not too hard, and determine the right target paces for these key workouts.

If you are experienced and knowledgeable enough, it’s not too difficult to come up with a training plan that fits. But no matter how experienced and knowledgeable you are, you cannot design a plan that prescribes the perfect workload every day for its entire length. This would require an almost godlike degree of foresight. The power of planning is limited by the impossibility of knowing exactly how your body will respond to the training you plan. Therefore your plan must have built-in flexibility, allowing for a certain amount of responsiveness in its execution.

It’s best not to change things unnecessarily, though. You had specific reasons for deciding how much running you would do and what your key workouts would be and how fast you would run in those sessions. These elements of your training are not the first ones that you should alter in response a discrepancy between expectation and reality, such as not feeling good in several consecutive runs. A much better way to tweak your training on the fly is to adjust your easy run paces to ensure that your workload is at every point high enough but not excessive. This approach makes a lot of sense because whereas no single easy run is terribly important, collectively easy runs account for the bulk of your total training stress, so they present a lot of opportunity to fine-tune your workload.

The way to do this is to try to maintain a consistent comfort level throughout all of your easy runs regardless of pace. Ideally, you will feel very comfortable from the beginning to the end of every easy run you do. On days when you are carrying fatigue from recent hard training or you’re just feeling flat for no particular reason, staying comfortable may require you to run one or even two minutes per mile slower than your ventilatory threshold pace. And on days when you’re feeling good, your legs may want to carry you right at VT pace, and there’s no reason not to do so in this situation. And if you’re like me and you often feel bad and good at different points within a single easy run, you should allow your pace to fluctuate.

How you feel during your easy runs is not arbitrary. It’s information about how your body is doing and what sort of training stimulus is appropriate. By allowing comfort to set your pace, you will not miss out on opportunities to run faster and get a bigger training stimulus when your body’s up to it but at the same time you will avoid overtaxing your body when it requires a gentler training stimulus. And the long-term effect will be that your overall training workload is in the Goldilocks Zone—high enough but not too high.

The pros practice erratic easy run pacing. For example, during an easy run I did with the Northern Arizona Elite team a few weeks before the Chicago Marathon, Aaron Braun observed that as his key workouts were getting faster and faster, his easy runs were getting slower and slower. (I think we were jogging at just under 8:00/mile at the time, or more than 2.5 minutes per mile slower than Aaron’s VT pace.) Of course, Aaron wasn’t slowing down in his easy runs because he was physically incapable of going faster. He was slowing down because he chose to, and he chose to because like most pros he habitually paces his easy runs by feel, aiming to maintain a consistent comfort level throughout all of them.

Now you try it!

$ubscribe and $ave!

  • Access to over 600 plans
  • Library of 5,000+ workouts
  • TrainingPeaks Premium
  • An 80/20 Endurance Book


30 day money back guarentee

For as little as $2.32 USD per week, 80/20 Endurance Subscribers receive:

  • 30-day Money Back Guarantee