Methods of Endurance Training Part 4: Threshold Training

Ok, we’re getting to the end and I’ll have one more part to finish this up on Friday when I finally talk about interval training.  Let me quickly sum up the series so far.  In Methods of Endurance Training Part 1, I talked about some of the basic adaptations that occur with endurance training and discussed one of the primary molecular mechanism that seems to drive adaptations, at least in skeletal muscle.

Last Tuesday I examined perhaps the most common model of building endurance in Methods of Endurance Training Part 2: Miles Builds Champions.  That approach simply consists of doing an enormous volume of fairly low intensity work.  In this vein, a very recent review (I came across it literally yesterday) on modern endurance training practices points out that, in basically all endurance sports, top level athletes have adopted an approach where not only do they do an enormous amount of total annual volume, but the grand majority (easily 70-80% and this holds across sports) is done at relatively low intensity.   You can get the PDF free at SportSci.Org.

Clearly not only does this method work but, as I discussed on Tuesday, it has its own sets of pros and cons (like all types of training).  And the biggest con, at least for the non-professional/full-time athlete is the time involved.  Once past the beginner stages of training, low volumes of low intensity training simply don’t do much.

I’d note again that for athletes who need endurance (but who are not pure endurance athletes), the method can still be valuable simply because the degree of endurance that is needed isn’t as high.  As well, due to the amount of other high-intensity work (technical, weight room, etc.), something has to give and nothing beyond basic endurance training may be possible most of the time.

But when people have limits on how much they can or will train, the Miles Build Champions method just doesn’t get it done.   In that situation, working for shorter periods but at relatively higher intensities tends to have a greater impact simply because the training stress per unit time is higher (similarly, when folks have a lot of time to train, working too hard at each workout tends to be more of a negative than a positive).  I discussed that on Friday in Methods of Endurance Training Part 3: Tempo and Sweet Spot Training.

In that piece, I mentioned that sweet spot training (as conceptualized by exercise physiologist Andrew Coggan) is sort of the point where training stress per unit time peaks along with the duration of sustainability.  That is, it’s an intensity that generates a lot of training stress per unit time but which can be sustained long enough to generate a strong training effect.  Above that intensity and duration is severely limited, below that and you don’t get the same stress per unit time.  It seems to lie for most between tempo training (aka intensive endurance training) and the intensity that would be used for the next method I want to discuss.

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Method 5: Threshold Training

In an earlier article, Predictors of Endurance Training, I talked about some rather pedantic debates over something that has gone by numerous different names over the years including lactate threshold, anaerobic threshold, individual anaerobic threshold, OBLA, ventilatory threshold and a bunch that I’m forgetting that have been suggested over the years.  As I pointed out in that article, most of the debate over what’s happening or what to call it kind of misses the point of the concept.

This threshold, whatever it exactly represents physiologically, can simply be thought of as the highest intensity that can be sustained for an extended period of time, usually and hour is given.  So the speed or power on a bike that you can maintain for an hour, or the running speed you can maintain for an hour is roughly this threshold.  I’d note that most don’t use a full 1 hour time trial to estimate this pace simply because it’s too exhausting.

Rather, most sports have some form of field test (or some other type of test) to determine it.  In the power meter community, a 20 minute isopower time trial is done and 5% subtracted from the average power to estimate the pace that could be held for an hour (note, there are a bunch of other ways to determine this threshold).  Chris Carmichael uses a 3 mile (or 8-9 minute) bike time trial done twice with a 10 minute break with the average HR or power used to set threshold intensity.  Runners can do a time trial or use actual race results.   I think you get the idea.

In many ways, the speed or power at this threshold is one of the absolutely biggest predictors of competitive performance.  While VO2 max can be thought of as a top-end limiter for performance, it’s not terribly predictive in and of itself.  A high VO2 is required for optimal endurance performance but, by itself, is not sufficient.

Rather, what the highest speed/intensity/whatever the metric for the sport you can maintain for extended periods tends to determine performance results.  So finding ways of improving that is a huge part of modern training.

Now, as it turns out, one of the ‘easiest’ ways (in terms of return for the effort put in) to drive up the threshold is to improve the aerobic engine.  I would note that this way of improving threshold tends to take time but the effects are also longer lived (since the adaptations are more structural) than other ‘faster’ methods.

While the exact mechanism is semi-unknown (it’s not lactate but hydrogen ions are probably involved), the threshold is certainly determined by a buildup of waste products (lactate doesn’t appear to be the culprit although hydrogen ions probably are) and, as it turns out, when you develop the aerobic engine,  several things happen:

  1. You can generate more power before starting to generate excessive waste products in the first place.
  2. You can buffer waste products more effectively when they are generated.
  3. You recover more effectively between periods of high intensity work (b/c the aerobic engine is more efficient).

So even for intermittent stuff, having some level of aerobic development can still be valuable.  Not only can you generate more power aerobically delaying the build up of waste products, you can buffer waste products more effectively.  And you recover faster during the in-between bits when you’re resting since aerobic mechanisms can clear the waste products that were built more quickly.

Mitochondria have actually been found to have transporters for hydrogen ions and this helps to explain mechanistically why a big aerobic engine improves ‘anaerobic’ performance, more mitochondria actually improves the body’s ability to deal with the waste products.   There are other adaptations of course.

In that vein, studies of various top level endurance athletes clearly show the following: the amount of time spent in low-intensity training is what’s predictive of performance at various training distances (e.g. for runners, from about the 800m up).  Even if this seems to violate specificity of training it is the case.

Certainly some amount of training at or around race pace (or above) has to be done but volume at low intensity (usually 2 mmol/l lactate or below) is what predicts ultimate performance.  What is clearly NOT predictive of overall performance is the amount of high-intensity work done which is probably a big part of why endurance athletes don’t do much of it.   Keep that in mind the next time you read all of the anti-low intensity endurance training articles out there.

But as I noted earlier in the series, not everybody has time to drive up this threshold with the time honored method of performing endless training at low intensities until your brains fall out.  And that means using different methods.

And certainly one of the most direct methods of driving up this threshold is to train at or at least very close to it.  And that’s what defines threshold training.  Sort of the classic method of training at this intensity is to do 20 minutes straight working either at or at least very near (within a few percentages points of power or heart rate) to it.

This is pretty pure training specificity, you do 20 minutes at threshold and, depending on sport, repeat it anywhere from 1 to 3 times.  Running seems to be happy with one bout of 20 minutes while 2X20 with a 10 minute rest is more common in cycling and rowing; again I can’t speak to most other sports.  Occasionally you will see more repeats done at the highest levels but the above volumes seem fairly standard.

While, as I mentioned, lactate isn’t really deterministic for fatigue, lactate levels during this kind of training will be higher than the other methods.  Years ago an absolute value of 4 mmol/l lactate was used as THE definition of this threshold but this turns out to be incorrect.  There is massive individual variance in terms of the lactate level that will be maintained during threshold training.  Some may be at 4 mmol/l while others might be up at 8mmol/l or whatever value.  If there’s a commonality, it’s that lactate levels will reach that level and then stay stable.  It doesn’t continue going up (as it would at a higher intensity).  In that vein. maximal lactate steady state (MLSS) is another term for this threshold even if the lactate per se is fairly irrelevant.

I should mention something: this type of training hurts like absolute hell.  It’s just grindingly, depressingly difficult, you’re working literally near the highest level you can sustain for the time frame and you just watch the clock tick down ever so slowly.  It’s truly horrible on the bike when you’ve been going for what seems like forever and you look down and you’re only 10 minutes in.  Meaning you have to keep going for an identical amount of time.  And then, after a 10 minute break or so, do it a second time.  At least runners only have to do it once per workout.

I’d note that going the full 20 minutes isn’t mandatory.  Shorter sets with relatively short rest intervals at the same intensity can be equally effective so long as the same total duration of training is performed.  So you might see a cyclist doing 5X8 minutes with a 4′ break, or 4X10 minutes with a 5′ break.  When beginning this type of training, many will suggest starting with multiple shorter repeats and building up to the full 20 minutes over several workouts (e.g. 5X8′, 4X10′, 3X12′, 3X15′, 2X20′ over a series of workouts) as the athlete adapts.

In a related vein, running guru Jack Daniels describes something he calls cruise intervals, shorter bits done at threshold intensity with perhaps a 1′ break in-between. So you do 4X5′ at threshold intensity with a 1′ break.  It makes the workouts a lot less grueling although the same type of training effect can be achieved.  Of course, at some point the athlete has to buckle down and do the full 20 minutes to prepare for the rigors of racing.

An absolutely brutal variation on this is to alternate threshold training with bits above threshold.  This prepares endurance athletes for those situations when they are going hard at threshold but have to speed up to cover a break or surge and then slow back down to threshold without a chance to recover at a lower intensity.  This kind of workout truly sucks.

Others advocate workouts where you sort of wave slightly above and slightly below the threshold for the full duration.  So while the average workload may be effectively at threshold intensity/effort, you have some periods above it and some periods below it.  This tends to reflect the dynamics of certain types of racing better than a pure steady effort.

Physiologically, going back to the AMPk mechanism I discussed in Methods of Endurance Training Part 1, threshold training would be expected to generate a profound training effect through this (and of course, other) mechanism.  You’re getting a rather large disruption of cellular energy status and doing it for extended periods which is why this type of training tends to improve aerobic parameters as much as anything else.

From a buffering perspective, you’re working at an intensity where waste product generation (again, lactate isn’t really the culprit in all of this) is maximal but sustainable.  By exposing the muscle to waste products for extended periods, one adaptation is going to be improved ability to handle those waste products.

As well, since the intensity is higher, you tend to start seeing more Type II fiber recruitment compared to the lower intensity methods which means somewhat more of an aerobic adaptation there (if such is a goal and it may very well not be for more strength/power or team sports athletes who need some endurance but need to avoid aerobic adaptations in the high threshold fibers). Basically, threshold training accomplishes a lot of things in a very short period of time.

Did I mention how much this hurts?

But for time crunched individuals, like tempo training, a 2X20 threshold workout doesn’t take a lot of time.   With a truncated warmup you can just get it done in an hour, more realistically you’re looking at 1.5 hours (less for running since the total duration is less).  And while I have heard of folks doing this three times per week for short periods (on bike, not running), realistically twice per week may be all that’s possible with two other rides at lower intensities (for recovery and to maintain basic endurance).

And that wraps up threshold training.

Read Methods of Endurance Training Part 5: Interval Training Part 1