Monday, December 13, 2010

Periodization

Periodization

Our last article implied that you change the frequency of the different types of workouts throughout the season. This process, the varying your emphasis and training mix for peak performance is called periodization. Periodization hasn't really hit buzzword status for the majority of masters swimmers but it is out there. Even if you haven't heard of it yet, your coach probably has, your coach might even be using it for your training and you didn't even realize it
Most sports use periodization in one form or another even if they don't call it that. In the triathlon world we talk about periodization up and down backwards and forwards. As these things tend to go, the popular image of periodization is a bit different than what it really is. In the popular view of periodization, you start with long and super duper easy in the offseason, do some threshold type work as things get closer and do vo2 max and other intensity stuff at the end. This is *a* form of periodization and for certain sports it works quite well, but it isn't *the* form of periodization for all sports. Most notably for long distance efforts over 3 hours or so, that form of periodization wouldn't make any sense. And why wouldn't it make sense? There are two main ideas that lead us to use a periodized schedule:
  1. Stagnation
  2. Specificity

Stagnation


It's not that hard to understand that if you do the same type of thing all the time, you will stagnate. Your body gets accustomed to the training type and load and it doesn't induce training adaptations any longer. You have to mix it up. The illustration to the right shows an example of how adaptations proceed in time. At first as you get accustomed to a new training load you progress slowly, then there is a time of rapid improvement, seemingly day to day you feel better and better and get faster and faster. But then eventually, the new training load becomes routine and your adaptations either flatline or sometimes even decline. Work by a guy named Verkoshansky indicates that this is roughly 6 to 8 weeks. It varies from person to person and varies by training load type and how much variety you include but in general after doing a certain thing for 6 to 8 weeks you tend to stagnate.
So when planning out a training year or season, we need to consider the stagnation effect. You can’t just bang away at a certain type of training month after month and think it will get the best performance. By changing the training mix, you can spend more time in the rapid adaptation phase shown in the graph. If you started a season and kept the training mix the same you would go through one rapid adaptation phase and that would be it. By substantially changing the training mix, you can go through more than one rapid adaptation phase per season.

Specificity

The principle of specificity is that you get better at what you train for. Or conversely to get better at something your training needs to mimic the requirements of the event as closely as possible. If you want to get better at swimming the 200 breaststroke, you should spend a good bit of time swimming the breaststroke at speeds and distances similar to the event and using the same metabolic processes you will use during that race. For a 200 breaststroker, a two hour run will have limited benefits on his breaststroke performance. For the reason why, think back to the adaptations in article 2, how many of those adaptations needed for 200 performance would be targeted by a two hour run? Not many of them actually. And what about two hours of shoveling snow? Even fewer. Two hours of playing poker? Probably none. In previous articles we have discussed that for most events at a typical masters swim meet, SP2 training is the most specific to what we are doing. So as we get close to the big meet we want to emphasize that type of training above the others. As the big race approaches, you want to be doing the most specific work closer to the big race. This will allow you to train the most important things right before the race. Not only in terms of energy systems and physiology, but you will also be training yourself mentally, training your pacing and even tactical skills. This is to say, since your workouts will resemble the main race, you will tax not only your energy systems as you will in the race but also your mental skills etc.

Why not nail it all year?

But why not just to SP2 work all year? Don’t mess around with anything else, just nail the SP2 work all the time? That goes back to the previous paragraph and stagnation. If you did a heavy SP2 emphasis all year you would stagnate, so you need to change up the training mix during the year. And the reason you do the SP2 emphasis last is that you want to be doing the most specific work right before the big race. In the weeks leading up to the championship meet you want to be refining your racing speed and strategy, you would not want to be putting in huge amounts of long easy yards at that point; you want to be sharpening yourself.

Typical Periodization

So what does a typical periodization schedule look like for a masters swimmer? The chart below shows a periodized schedule you might see for short course season where the final competition is THE main competition. The assumptions are that the main meet is at the very end and that there is no taper or emphasis change for mid-season meets. Another assumption is that the workout group has three or four workouts per week of an hour to 90 minutes. With more frequent workouts you could do more things and cover more bases in a week. The schedule shows the emphasis for a given week. Not to say that you exclude any single type of workout at any given part of the season, but rather for a given week which sets are the most important ones.
Week
1
2
3
4
5
6
7
8
9
10
11
12
Emphasis
EN1
EN1
EN1
EN1
En1
En1
En1
En1
En2
En2
En2
En2
Sp3
Sp3
Sp3
Sp3
Sp3
Sp3
Sp3
Sp3
Week
13
14
15
16
17
18
19
20
21
22
23
24
Emphasis
En2
En2
En2
En2
En2
En2
En3
En3
En3
En1
En1
En2
Sp1
Sp1
Sp1
Sp1
Sp1
Sp1
Sp1
Sp2
Sp2
Sp2
Sp2
Sp3

Endurance

We are assuming that the target event will last from one to three minutes. Of all the endurance set types, EN3 is the most specific type of work. Following the logic laid out above regarding stagnation and specificity, EN3 training would come last among the endurance work. However, for this case endurance work is even less specific than SP2 work. So in weeks 22 and 23, the endurance work gets less intense to make room for more SP2 work. As discussed above, if there were more workouts per week, then there may be more time to do both workout types. But with three workouts per week and 90 minutes per workout it is hard to do both EN3 and SP2 work and have enough rest in the workouts. Three or four workouts per week is pretty common for masters swimmers.

Sprint

At the very beginning of the season, there is no sprint training at all. Only endurance type work to expand the athlete’s work capacity. Soon after though, SP3 work starts. The reasoning behind it is that the SP3 work is relatively low stress and raises the eventual performance capacity. By raising the max speed you can maintain, you increase the room to improve. If you can train yourself to hold a given percentage of your max speed for a 100 swim, then raising the max speed will increase your speed in the 100. There is a fairly long period of SP1 work that leads eventually to four weeks of the very high intensity SP2 type sets right at the end of the season.

Is this the only way to periodize a season?

So is the chart I laid out above the only way to proceed for a masters swimmer? Not at all, the schedule depends on time allowed, the swimmers involved in the program and their strengths and weaknesses and of course it depends on the races being targeted. If we were to go through this exercise for a summer season of open water racing it would look totally different, the endurance work would take the emphasis in the end of the season, not the SP2 work. Also, if we were to value the mid-season meets more heavily, then we would probably shorten the length of the cycle. Once the meets start we might abbreviate the time in between to a sort of mini season. We would not hold an emphasis for the full 8 weeks but rather would shift emphases every two weeks or so while the meets are going on. I Hope that by this point the readers are getting a feeling of why things are usually structured the way they are and can make some sense of what is going on in terms of the season and why the sets are where they are in the season.

Saturday, February 13, 2010

Set Types


Swim Set Types and the Adaptations They Produce

This article is part of a series on why we do the things we do, the series explains set types and periodization through the lens of lactate metabolism. Fatigue is more nuanced than simply being about lactate accumulation and consumption and these articles are getting old. But I have left them in place because while lactate is not itself a cause of fatigue, it is closely related to the causes of fatigue in events from 1 minute to around 30 minutes.

The previous article can be found here, the first article of the series is here

USA Swimming has adopted a set classification system that has seven levels. Recovery (REC), Endurance Level 1 (EN1), Endurance Level 2 (EN2), Endurance Level 3 (EN3), Sprint Level 1 (SP1), Sprint Level 2 (SP2) and Sprint Level 3 (SP3). Other sports and other countries use slightly different classifications but most systems break out along similar lines. Each category aims at a slightly different set of adaptations, as a result the set types have characteristic lengths, rests and intensities.
It is important to realize that different sets are doable in different amounts. As we will see in later articles, the stress induced by SP2 sets is much higher than that induced by EN2 sets. SP2 sets put a big hole in your schedule, recovering from them both during and between workouts is difficult. Conventional wisdom holds for this and other reasons to hold off on the more stressful work until relatively close to the main competition. But more on that later.

Endurance Sets

The bulk of any program in terms of yards, and to a lesser extent in terms of time spent, consists of endurance sets. These types of sets are meant to lead mostly to the aerobic adaptations pointed out earlier. In terms of the bathtub model, you are trying in increase the size of your bathtub drain.

REC

Recovery swims are done at very easy paces and the rest intervals during the set are usually not critical. In an acute situation, a recovery set is used after a hard set or at a meet after a race. In this use the purpose is to help rid your muscles of lactate and other byproducts of effort. It has been shown that active recovery in the form of easy swimming is more effective than passive rest at lactate removal. In the long run recovery sets are used to loosen up or help get rid of stiffness in the days following a hard workout or competition. It is meant to help you recover for the next workout.
Many drill sets can also be thought of as recovery sets. In terms of your physiology this is true, even though the drill will have other useful adaptations outside of your aerobic metabolism. Recovery sets tend to increase fat metabolism at a given speed. Fat metabolism is not addressed in our bathtub model but becomes quite important in races over 40 minutes or so in length. Recovery sets address all the aerobic adaptations but on a minute per minute basis, induce adaptations at a lower rate.

EN1

EN1 type sets are also good at inducing the aerobic adaptations, but due to increased intensity they are more effective at creating these changes than the recovery sets. The intensity of these sets is from around 90 to 95% of critical pace for the stroke you are swimming. This can vary widely with the amount of rest and length of the swim however, longer repeat distances with short rest mean you can swim a little slower and get this adaptation. Longer rest for shorter repeats mean you need to swim a bit faster, closer to your critical pace. The duration of the sets needed to induce adaptations is over 16 minutes and rests are short, generally 20 seconds or less to keep your body from recovering. You want to keep your hr up for an extended time. These sets improve fat metabolism as the recovery sets do but not quite as well. These sets also increase the number of mitochondria in your muscles, as discussed before the mitochondria are the power plants of the cell and are where all the aerobic metabolism takes place. Having more mitochondria means a bigger bathtub drain and pays dividends in every distance of race.

EN2

EN2 type sets are done very near critical pace. A little faster than critical pace for shorter repeats and a little under critical pace for longer repeats. EN2 sets are the most effective way to develop your aerobic metabolism. Minute for minute, the best bang for your buck in aerobic developments, the stress is moderate and they can usually be performed multiple times in a week without causing problems for the athletes. The typical set length for EN2 sets is 16 to 40 minutes. Depending ont the set structure, rests can be from 5 to 40 seconds, or even up to one minute on a very long repeat. In terms of our model, EN2 pace work induces the greatest adaptations in mitochondria, it makes your bathtub drain bigger. It is also the best training pace for raising your MLSS, this is only natural since these sets are done close to MLSS pace. MLSS and critical pace are very close to each other.

EN3

EN3 sets are done at or very close to VO2max. As discussed before this is where your energy metabolism is at full tilt, the firehose is open, the drain is draining and overflow drain is draining as fast as possible. In fact it seems like this should be all we ever do. But like everything there is a downside, the EN3 sets are high stress and can be done in somewhat limited quantities. If we were to continue to do them they would bring on stagnation more quickly than other types of sets.
EN3 sets are also usually 16 minutes long but there is significant amounts of rest in them, up to 1 to 1 ratio of work to rest. Since your hr often gets very close to its max, this type of set affects your heart function. The amount of plasma in your blood goes up, maximum stroke volume is improved, and since you are working near VO2max, your VO2max level is improved.

Sprint Sets

If all you ever did were open water swims an hour or longer, you could pretty much end the discussion here in terms of metabolism and energy production. Go off and develop your aerobic metabolism and be happy and healthy live a good life out there with the sea critters and the jellyfish. Of course, there is more than one way to look at things and sprint sets have uses for marathon type swimmers, it's just that those benefits don't have to do with metabolism. However, the masters swimmers, most of their events are from one to four minutes and involve high lactate levels. A bathtub overflowing just at the last stroke. So to be sharp for raceday sprint work is included. Like sprint racing itself, sprint training also creates high lactate levels.
Work on critical paces has shown that doing a lot of sprint work, the SP1 and SP2 levels can be detrimental to your aerobic fitness. So at the extremes, if all you ever did was sprint work, your aerobic metabolism would get worse and you could actually end up slower in your chosen event for it. The mechanisms once again are not exactly clear, if nothing else, sprint work takes a lot of time in your workout. Thirty minutes spent on an SP1 set would not be unusual, but that is 30 minutes not spent developing your aerobic metabolism. There are other more in depth mechanisms used to explain why, but they are all offshoots of, if you do less aerobic work for one reason or another, your aerobic metabolism won't work as well. And included in that "One reason or another," is a 40 minute set of sprint work.
This is one of the major reasons why coaches tend to switch emphases a bit as the year goes on, too much sprint work early in the season could deteriorate your aerobic metabolism and leave you a step behind come the big race. How much istoo much sprinting? How early is too early to start to emphasize sprint work? That will be discussed in a follow-on article on periodization.

SP1

SP1 sets are also called lactate production sets, these sets are intense and faster than MLSS speed but due to the set structure with shorter intervals and longish rests, the lactate levels don't get too terribly high. On these you should have some lactate type fatigue setting in during the set but not so much that your arms start to burn and really struggle. You should be able to maintain a pretty consistent pace through the set. In terms of our bathtub model, you would say that these sets are meant to increase the size of the firehose and to an extent they also make your bathtub bigger. These ets also induce some aerobic changes, although in magnitude probably less than the recovery sets do. SP1 sets are high stress and can be taken in small doses for a good chunk of the season.
SP1 sets have intervals of 25 yards to possibly out to 200 yards. The speeds are at about 95% of max speed and the total time of an SP1 set would be 20 minutes or more. However rest durations on SP1 sets are equal to or twice the duration of the work interval. So of the 20 minutes half or more of the time would be taken up by rest between swims. These types of sets are usually done earlier in the season than the very hardest work that is the SP2 work.

SP2

SP2 sets or lactate tolerance sets are the hardest sets a swim group will do. They are similar to the distances and speeds of competition events. The idea behind a lactate tolerance set is to get accustomed to the type and amount of pain you might experience in a race. In this way you increase the size of your bathtub. It is thought that your muscles get better at buffering acid and that your brain resets the "STOP!" point on how much you will take and still swim.
SP2 set distances are usually directly relevant to your chosen event. An SP2 sets for a 200 person would consist of 150s to 300s, for a 100 person it would be 75s to 150s. These swims can be done straight through or perhaps broken up with 5 to 15 second rests in the repeat. The rest intervals usually involve active recovery and are 2 to 5 times as long as the swim interval. The effort is 100% for these sets and the lactate levels induced are quite high.

SP3

SP3 sets exist largely outside of the bathtub model. These types of swims are prominent but really don't do THAT much in terms of our bathtub model. The most applicable thing they do is to indirectly increase the size of the firehose. I say indirectly because these types of swims work on your neuromuscular system mostly. They enable you to turn over faster and recruit muscles faster. In a bit of an odd situation, while the SP3 sets are the fastest ones we do, they are not the most stressful. The intervals on SP3 work top out at 25 yards and the rest is complete, a work to rest ratio of 1 to 5 to 1 to 8. Since these sets are lower stress these are actually included both early and late in the season.
Early in the season, before your fitness has really come around you can still work on SP3 without inducing a lot of stress, the work on your turnover and coordination is quite effective and this type of work continues to a degree all through the year. SP3 sets also become a mainstay in the taper, in a taper the general idea is to reduce the training loads so your body gets into the supercompensated state, but you also want to do some fast swimming as well to keep your feel for the water, the SP3 sets can fit the bill late in the taper.
Please see below a summary chart of all the different set types.
Type
Repeat Distance
Rest
Speed
Total Set Time
Exertion (1-10)
Sample Set
REC
Any
Any
Easy
Any
6
400 IM pull / 400 IM kick / 400 IM order
EN1
Any
5 - 30 secs
90 - 95% critical Pace
20 - 120 mins
7-8
800 / 8 x 100 / 600 / 6 x 100 / 400 /
4 x 100 (:20 rest on all)
EN2
25 - 3000 yds
10 - 45 secs
95 - 103% critical pace
30 mins
8-9
15 x 100 on Critical Pace + 0:15
holding Critical Pace
EN3
50 - 2000 yds
30 - 240 secs
>103% critical pace
20 mins
10
3 x 100 max (:05)
4 mins rest between sets
SP1
25 - 200 yds
30 secs - 3 mins
95% max pace
15 - 45 mins
9
5 x 50 at goal pace (:30)
1 minute between sets
SP2
~ Race Distance
2 - 5 mins
~ 100%
15 - 45 mins
11
3 x 100 at goal 200 race pace (2:00)
4:00 active rest between sets
SP3
10 - 25 yds
1 - 5 mins
Max
15 - 45 mins
Ample
Recovery
12 x 25 on 2:00 from a dive

Pitfalls

So now that you have an idea of the general structure of workouts we can look at some ways in which modifying a workout on the part of a swimmer can change what the workout does and may change it significantly from what the coach had intended.

Resting too Little

A common thing that might happen is if the coach puts up an SP1 set. It might be:
12 x 50 (:40) FAST!
Without more input from the coach is is entirely foreseeable that the swimmers may decide it is too much rest and shorten the interval. What is probably happening is that the swimmers don't understand how fast "FAST" is supposed to be in this case. The swimmers swam it "moderately fast" and don't think they are working hard enough. So they swim slower than the coach intended and rest less than the coach intended.
What happens is that the high quality SP1 set turns into an EN1 or EN2 set. The problem with that is that there are not enough yards in this set to get aerobic adaptations from it. So you get a set that is neither here nor there, not fast enough to increase the size of your tub and not long enough to make a bigger drain.

Swimming too Slowly

Swimming too slowly might happen if the coach puts this EN2 set up on the board.
15 x 100 on critical pace + :20
Without further instruction and if the swimmer does not recognize it as an EN2 set, then the set may end up being swum too slowly. Instead of swimming them near his critical pace and getting 15 seconds rest he may find it easier to swim them at 10 seconds slower than critical pace and get 10 seconds rest. In doing so he turns the set from a an EN2 set with very profound effects on his mitochondria, into an EN1 set with much less of an effect and a lower quality.

Swimming too Fast

So the coach puts this on the board:
2 x 800 swim easy (:30)
The swimmer doesn't recognize or doesn't understand set design and so does this at a pace very near to his critical pace. Or how about the swimmer goes out and does the first 400 faster than his critical pace, the 2nd 400 is slower than that and the 2nd 800 repeat is a very difficult slog but he manages to get within 2 seconds of critical pace. He swam that fast because because he "Can't go that slow". Did he do the right thing? Faster is always better, right?
Well what we didn't know about the swimmer is that he is a 51 year old sprinter with excellent times in the 50 and 100 and has struggled his whole life with big yards workouts. So while this set was of decent quality, the BIG main set for the week is in two days on Thursday morning when the coach planned on a 40 minute SP2 set. Come thursday, our swimmer in question is still not quite recovered and just doesn't feel right during the big set for the week.
So those are three problems that can arise when the swimmers don't understand what the underlying purpose of a set is. A problem by the way that YOU my dear reader won't have any longer because you are now versed in a nearly universal language of set construction.

What's Next?

How we change the mix of set types through the year to peak for the big race.

Monday, February 1, 2010

Training Adaptations

Adaptations to Training

If you are having trouble following these terms or the theme, please check out the previous article on lactate metabolism.

Having established the model for lactate metabolism and defined MLSS, aerobic and anaerobic, how do those things affect performance?
Lactate metabolism is the major fatigue mechanism mode for swim races from 100 to 1500 yards. As shown in the chart below, aerobic metabolism is responsible for more of the energy used the longer the race takes. Improvements in the rate of athletes' aerobic metabolism will give corresponding improvements in performance. In races shorter than 30 seconds, contractility and speed are limiting rather than lactate accumulation. In races over ~45 minutes, glycogen depletion can be a limiting factor. For masters swimming, most of the races are right in the range where adaptations to lactate metabolism will have benefits. In terms of the bathtub model, we want adaptations that will keep the tub from overflowing before the end of the race.
Time30s60s2 mins4 mins10 mins
% Aerobic Energy Supply2030506585
% Anaerobic Energy Supply8070503515
The goal is to have the bathtub overflow JUST at the very end of the race; just as you touch the wall. So in contrast to MLSS as discussed previously, swim races are not done at an effort that elicits a steady lactate level. The races are done significantly over MLSS intensity, how much over depends on the length of the race. In most swim races the bathtub is continually being filled until the end of the race, actually for a few seconds after as well.

How do we get faster?

In terms of lactate as the limiting factor in race performance, there are three different avenues to pursue
  1. Increase your lactate tolerance (get a bigger bathtub)
  2. Increase the rate at which lactate can be used by aerobic metabolism (get a bigger drain)
  3. Increase the whole thing from top to bottom, the firehose, tub, drain and even the overflow drain.

Aerobic Adaptations

What exactly happens when we pursue aerobic adaptations; how does the drain get bigger?

Central Adaptations

Central adaptations are changes that happen away from the working muscles, the ones listed here affect the heart.
Increased Plasma Volume
The first change is an increase in blood plasma volume. Plasma is the fluid part of your blood. In general terms, increased plasma volume will make your blood move around better. Better able to deliver oxygen to your working cells, better able to take excess lactate from those working cells and bring it to other parts of your body to be used for energy.
Cardiac Hypertrophy
The second central adaptation is “cardiac hypertrophy,” use it three times in a sentence and that word is yours, work it into conversations often! Cardiac hypertrophy is the term for when your heart gets bigger. Bigger as in the amount of blood it can hold at once. In healthy people, a larger heart is a more efficient heart, you can move more blood with each beat.3 That makes it even easier to get more oxygen rich blood to your working cells.
Improved Ejection Fraction
The third central adaptation is improved ejection fraction. After you stop giggling, you should know that ejection fraction refers to how much of the blood in your heart gets squeezed out with each beat. A higher ejection fraction is better, it will take fewer beats to get the same amount of blood to the working muscles. When you go to your favorite local cardiologist to get a stress test, one of the things he measures is your ejection fraction.

Peripheral Adaptations

Increased Capillary Density
The first peripheral aerobic adaptation is increased muscle capillary density. This change means more tiny blood vessels penetrating the muscle bed. In turn this means a better flow of oxygenated blood to the muscles and a better flow of lactate and CO2 away from the muscles.
Increased Mitochondrial Density
The second peripheral aerobic adaptation is increased mitochondrial density. Mitochondria are the the parts of the cell where energy generation happens. All the aerobic metabolism reactions we have discussed occur in the mitochondria of a cell. More and better mitochondria mean that your aerobic metabolism is more capable of grabbing lactate molecules and using them in aerobic metabolism. In terms of the bathtub model, this is most directly applicable to the idea of making a bigger drain. Or possibly making more drains in the bottom of the tub.
Increased VO2max
VO2max is the maximum amount of oxygen your body can use, in an all hands on deck alert for a longer period of time (6 to 15 minutes). At VO2max your aerobic metabolism is at full tilt and your other organs are are taking up lactate to the maximum extent possible. Not only are the working muscles involved in burning the lactate but also your non-working organs are burning lactate as fuel to maximum extent possible. Your heart is pumping at its max capacity and your lungs are moving oxygen into your blood and CO2 out of your blood at peak rates. This ability, the maximum ability to burn oxygen for energy is very important for races in the four to eight minute range.

Anaerobic Adaptations

Increased Lactate Production
Increased lactate production ability means that speed of glycolysis gets faster after training it. In terms of our model you are getting a bigger firehose and can fill up the tub faster. Depending on the swimmer and the goal races this can be important. In races on the shorter end of the spectrum it is foreseeable that you could finish the race before having the opportunity to fill up your bathtub. So even if it is not used, you do want the ability to create a lot of lactate in a hurry.
Increased Lactate Tolerance
In terms of our model, increased lactate tolerance means a larger bathtub. The ability for your muscles to keep working even though the lactate and acid levels in the muscle cell are high. This encompasses a few different adaptations and as pointed out earlier, the exact mechanisms are not exactly certain. Obvious adaptations would be improved acid buffering capacity and also a reset of the "stop" signal in your nervous system.
Increased Speed
This adaptation exists largely outside of our model. This adaptation is about how fast you can move, irrespective of the lactate metabolism. So assuming lactate fatigue never kicked in, how fast could you go. This is a matter of nervous system function, contractile velocity, and even how fast your body can cycle ATP (the energy currency of your cells). While not clearly covered in the lactate metabolism discussion, I mention it here because one of the types of swim sets USA swimming uses is directed at this adaptation.

What Next?

The next question, What types of sets help make these adaptations will be in the next article.
Notes
3. Diseased hearts also undergo hypertrophy, that's why we say in healthy people cardiac hypertrophy is a good thing.

Friday, January 29, 2010

Lactate Metabolism

Lactate Metabolism and Maximum Lactate Steady State (MLSS) as it Affects Training Structure

Background

Different types of masters swim programs have different ways of doing things. Different types of sets target different sorts of adaptations, understanding the purpose of the sets will help you in following set design and making sure the workout you do is similar to the workout the coach had in mind. In other cases if you need to deviate from the coaches' plan you can do so intelligently.
In terms of physiology, much of what we do can be seen through the lens of lactate metabolism, so before starting the discussion of training sets, a bit about lactate metabolism and maximum lactate steady state.

MLSS


As will be seen later, some types of workouts are meant to create aerobic adaptations, others are aimed at anaerobic adaptations. Before addressing aerobic and anaerobic Adaptations, a little bit to explain the difference.
Aerobic (with oxygen) and Anaerobic (without oxygen) are misnomers to a degree. Your body always uses oxygen for energy, it is simply that the system by which oxygen is used for energy is rate-limited. It can only be delivered so quickly. If your need for energy is outpacing the rate at which you can use oxygen for energy, then intermediate chemicals build up in your system. It’s like there is a logjam and all the logs are stacking up on the upstream side.
In energy metabolism, the first large substep is called glycolysis, it turns a glucose molecule in two lactate molecules1 and creates energy in the process; this first step does not require oxygen. The glycolysis step can happen much faster than the next step in the chain. In normal, everyday situations, the lactate intermediary is then swept up and it goes to two separate subcycles that require oxygen and create MUCH more energy from that lactate molecule. It is these last two steps that are rate-limited.
This is where the logjam happens, if there is a signal to go all out, for example a starting gun, the glycolysis process can create lactate much more quickly than the aerobic metabolism can take it away and use it. I also like to use a bathtub analogy, in figure 1 lactate (water) is being delivered into the tub but is being swept away as quickly as it comes in and there is no net buildup of water in the tub (lactate). In this case the equilibrium is about halfway up the sides of the tub. The bathtub analogy goes even one step further, on your bathtub there is an overflow drain about halfway up the side of the tub. In the case of a muscle cell, something similar exists. In a working muscle cell, when the lactate concentration inside the cell gets too high, some of the lactate is taken out of the cell and enters the bloodstream. Once it enters the bloodstream, the lactate is taken to other organs to be used as fuel for aerobic metabolism in those organs. The lactate is used in other muscles that might not be working as hard, your liver, and actually is used as a fuel for your brain as well.
If instead of using a bathtub spigot to fill the tub, we use a firehose then the situation is a bit different. In this case there is no steady state, the firehose turns on and even though some of the water is being taken away through the drain, the water accumulates. If this situation persists, the bathtub will overflow, even taking into account the overflow drain in the tub halfway up, if the firehose is big enough it will overflow. In the muscle cells, instead of a firehose it is glycolysis that is running wide open and pouring lactate into the cell, even though the aerobic metabolism is dragging away some of the lactate, it is still accumulating in the cell. There is even a little side drain in the cell, some of the lactate will go into the bloodstream and be taken away.
As the lactate builds up too high, then bad things start to happen. Actually several different things and there is actually some debate about exactly how it works. For example, as part of all this when lactate is created, acid is created as well. It has been shown that when your muscles get too acidic, they do not want to fire, some coaches have claimed this is the “tying up” sensation that comes with high intensity exercise. There are others who say that you have acidity sensors and when they fire your brain will stop recruiting muscles; these are only two of many different ideas on exactly what is happening. Even though it is not exactly settled, what matters is that short term fatigue is closely associated with increased lactate levels at exercise, even if the exact mechanism how is not certain.
And what is “Maximum Lactate Steady State (MLSS)?” MLSS is the highest effort level that can be performed without the bathtub overflowing. It is just at the point where the tub is completely full and the water going down the drain and out the side drain is exactly equaled by the water coming in through the firehose. Think about your bathtub and how quickly water flows out of the drain when there is very little water in it, the water drains out pretty slowly. However when the tub is full, the amount of water flowing out per second is higher. If you leave the drain open and turn on the water just a bit, the tub will fill up just a bit until the water draining out equals the water coming in. Turn it on just a bit more and the water will build up higher still to make the water coming in and draining out equal.
You can continue doing this until you reach the point where having the tub filled to brim makes the water flowing in and flowing out equal. In cellular terms, this is the MLSS. This is the usual breakpoint between aerobic and anaerobic exercise. Exercise that is done where you stay under the MLSS effort is usually termed aerobic and exercise performed at an effort higher than MLSS effort is termed anaerobic.
In practical terms MLSS is something close to the pace you can maintain for a 30 minute max effort.

And what about Lactate Threshold?

In the vast majority of cases, when a coach says “Lactate Threshold” he really means MLSS. When a scientist says “Lactate Threshold” he means the effort at which your blood lactate is 1 mmol/L higher than resting level. So for most times you hear “Lactate Threshold” in popular literature or discussions2 think MLSS.

So what?

The next question is “What can be done about it? Can I change the size of my tub? Can I make a bigger drain?” That will be covered in the next article.
1. Actually pyruvate is the intermediate chemical, however it is quickly converted back and forth from lactate to pyruvate depending on if there is oxygen to take the pryuvate away. No oxygen, then it gets converted to lactate until a later time when it can be converted back to pyruvate and taken away by the aerobic metabolism. 

2. Everyone talks about lactate metabolism in normal discussions right?