• Boris Clark

'Polarised' VS 'sweet-spot', 'threshold', or 'mixed' training distribution

Several months ago I had an athlete contact me (one I don’t coach), asking if their frequent Zwift racing would ‘negate’ the benefits of a polarised training plan. The first question I asked was why on earth they were restricting themselves to a ‘polarised model’ rather than a ‘whatever training will work best model’ which would make more sense. Wanting to give a bit of explanation to my answer to their questions, but not wanting to waste 30 minutes writing for no reason, I asked if they would be happy for me to give a detailed answer, on the condition I could edit it a bit to turn it into a blog on this topic at a later date, so here we finally are, an explanation of Sweet-spot training vs ‘other training’ and a bit of science behind it for this riders situation (I had some data on him which helped). I must stress the training principles would be different for each individual, but the science behind it remains the same.


Overview of your training, what training distribution model is best?

Basically, it depends what you are wanting to target with your training, and what level you are at.


So for you, obviously you are a high level rider and gains can be difficult to come by, whereas someone who is at a lower level, or has less riding experience can find improvements easier.


Is there an optimal trainign distribution when trainign for Zwift racing? Short answer: No. Training needs to be unique to the individuals physiology.

What this means for you is that to force some sort of adaptation in the body it may take some really focused work on one particular area to work it enough to cause an adaptive response, which is why I say the races won’t ‘negate’ the polarised training, but may not be optimal. So that comes down to how training is periodised which is a whole other discussion.

I think to understand both those training methods it helps to have a basic knowledge of what they do/how they work.


Overview of training models, and how power is composed

In terms of training your ‘threshold’ power, your threshold will be a certain percentage of your VO2max. VO2max is the ceiling of aerobic performance, your threshold is how close you are to that ceiling.


So if you are already close to that ceiling, then polarised training can be really effective.

Many people break this down into 7 zones since that is what several online software programs use, but really it only requires 3 zones based off of 2 physiological break points which occur on an individuals lactate curve as shown below.




You can see there is two labels on the graph. LT1 and LT2.


LT1 is the first point at which blood lactate has a sustained increase. The top end of ‘low intensity training’. This level and below is where your endurance rides and majority of riding time will be spent. The reason for this is that you get pretty much all of the benefit of training a little bit harder than this, but with much less autonomic stress, so you don’t get that fatigued and can therefore complete a lot more training volume at this level. You are also activating primarily type 1 (slow twitch) muscle fibres at this intensity. If you rode harder you would start to favour type 2 (fast twitch) muscle fibres, which is also useful, but not the aim of these rides.


LT2 is the ‘threshold’. This is simply where pyruvate/lactate production = pyruvate/lactate combustion. E.g. why it’s often referred to as the ‘lactate threshold’, this is what we are trying to measure when we use FTP, but in reality FTP will normally be a bit higher, and there is also no ‘time’ component such as 1 hour to LT2, it’s simply a physiological breakpoint. Some people can hold this for 30 min, some for 90min, hence why 1 hour power is not really ‘threshold’.


Polarised training, as you know, simply trains below LT1, and above LT2, while ‘sweet-spot/threshold’ training has you train just below or at LT2.


Basically what training below LT1 does is give you some endurance, increase fat burning capacity etc, but in terms of improving threshold power, long hours spent here help increase aerobic capacity/Vo2max, while training above LT2 also does this, but through a slightly different mechanism/different adaptations.


So combine training below LT1 and above LT2 and you have a potent recipe to ‘raise the ceiling’ / VO2max.


This training works for many people as most people aren’t close to achieving the genetic ceiling of their VO2max. So they raise there VO2max, their top end power goes up, their threshold probably stays at the same percent of VO2max, but since their VO2max goes up so does their threshold.


The ’Sweet-spot’ model

If you are already close to the top of your VO2max however, or if your threshold is a low percent of VO2max, then Sweet-spot training can help increase this. Personally I wouldn’t really prescribe a whole lot of threshold training. Training at the threshold is really stressful, and while it can create good gains, the cost/benefit of it isn’t really optimal.

To explain how sweet-spot works it helps to what causes threshold to be a certain percent of VO2max.


The reason is the anaerobic system.


You use the anaerobic system at all intensities (even just sitting in the chair as I type this some energy is coming from anaerobic metabolism).


Using the anaerobic system isn’t bad per se. But using it produces lactate (which also isn’t bad per se, but is associated with what is!).


As mentioned before, threshold equal the point where lactate production and combustion are equal.


Lactate production depends on the strength of the anaerobic system, while lactate production requires oxygen, so the more oxygen you can use (VO2max), the more lactate you can combust for fuel (it’s a fuel source and an acid buffer not a negative by-product in of itself).


So if you want to hold a higher percent of VO2max at threshold, you need to DECREASE anaerobic capacity, as stupid as this sounds.


Lower lactate production = a higher power at which lactate production and combustion are equal, aka threshold.


The primary muscles which are responsible for producing lactate are those who produce a large amount of energy through anaerobic glycolysis. So this is ‘fast twitch’ muscles.


Sweet-spot is a hard enough intensity that you activate these fast-twitch muscles (primarily 2a and 2x fibres), since there is quite high force (particularly if you use a lower cadence doing it), but not so hard that the muscle has to work too anaerobically (glycolytically).


So as a basic explanation, the muscle fibres produce some lactate, but then they are basically trained to use that lactate for fuel through aerobic mechanisms rather than by just anaerobically producing more lactate.


So you produce less lactate, and therefore threshold increases.


BUT one caveat of this, is a lower anaerobic capacity reduces the ability to do short intense work, particularly approaching and above VO2max, where all extra energy needs to come from anaerobic sources. So a higher threshold, but less ability to do work above this point.

So which you need to focus on depends. . .


You can work this out with power profiling, lactate testing, or if you know your VO2max you can also estimate it.


At high intensity you are using pretty much all carbohydrate. When we burn carbohydrate we get about 5kcal per litre of oxygen used per minute.


With your weight of around 72kg and VO2max of 86 (6.2Litres (huge!))

So we take 6.2*5kcal = 31kcal/min 31kcal*4.18 to convert to kJ = 129.6 129.6*1000 to convert to joules = 129580 A watt is a joule per second, so 129580/60sec=2159 The metabolic rate is 2159watts, but the body is only around 23% efficient at turning this to power at the crank, so 2159*0.23=497w (could measure your exact efficiency with a metabolic cart for more concrete numbers).


So 497w should be somewhere around your max aerobic power with 23% efficiency. So what you could do for say 5min, but you will have a small anaerobic contribution on top of that, so perhaps the low to mid 500w range.


So say 500w is ‘power at VO2max’ for want of a better term. Depending on genetics you can sustain up to perhaps 95% of that at threshold with proper training, but that would make you pretty diesel. A rider like Chris Froome holds around 90% of VO2max power at threshold, so that is pretty optimal for a GC rider.


So for you this would mean you could get your threshold up to around 450w.


So if your threshold is already there, the ideal would be polarised training to try and improve VO2max (probably pretty difficult for you!), or at least to improve efficiency at those high power outputs, increase endurance from the low end work, increase buffering capacity so you can stay above threshold for longer etc.


If your threshold is not close to that, then you would probably benefit substantially from sweet-spot work, to raise your threshold as a percentage of VO2max.


Sprint/short term power

Now obviously threshold is the most important aspect of performance, but not the only one. So what if you want to improve your short term power.


Training really hard, e.g. max 30sec efforts will obviously improve your short term power, but increases anaerobic capacity so can increase lactate production which can lower threshold.

But obviously if your threshold is more than high enough, but you are getting smashed at the finish sprint, or can’t go with attacks, it’s worth improving this. Same goes for those ‘VO2max’ style efforts. Even if you don’t increase VO2max, you can still improve efficiency at these intensities, so more power for the same consumption of oxygen, and you can also tolerate more workload at this level.


As for gym work (the rider had also asked about this). You can probably go really heavy, so like 80+% of one rep max, for 3-5 reps, around 5 sets of each exercise, 4-5min rest between sets, and this will greatly increase absolute force production, lower the oxygen cost of exercise etc, which helps with just about everything, and since you only to like 5 reps, it’s mostly creatine phosphate rather than anaerobic glycolysis, so you shouldn’t really change anaerobic capacity as such, so threshold should remain the same or higher.


That will increase power output on the bike, but to really really turn that into power you would want to then do some training in the 60-80% one rep max range, 6-12 reps, and a bit faster movement. That will really create power development, but may increase anaerobic capacity, which may or may not be a good thing depending on what you need.


As for plyometrics, they can be really effective too. They probably won’t increase max force or power per say, but they can increase what is called the rate of force development, so how fast you can produce that force/how long it takes for the muscle to get to maximum force development. Since they are such a short/brief exercise that shouldn’t change anaerobic capacity much/at all, but has beneficial time/force characteristics.


I literally could write or talk about this all day so if you have any more questions fire away!!