Polarized Training and Injury Prevention
Training methods for a triathlon or longer running events have traditionally been a bit of an enigma for many athletes and coaches. There have been so many methods touted (Lydiard, Daniels, Run Less/Run Faster, Crossfit’s Endurance etc) how is the average runner supposed to know what to do?
In this post, I will talk about the method I typically endorse – the “Polarized Training” method – a training method that leans heavily on low heart rate/Zone 1 training, with some high intensity workouts/Zone 3 training but very little Zone 2/race pace training. This flies in the face of the “specificity of training” notion, but I base this recommendation on all the research outlined in this blog post.
If you’re short on time, let me give you this brief outline: Injuries in distance running are extremely common and I blame training errors for most of them. The “no pain, no gain” attitude is all to common and is unfortunately promoted by many coaches. Despite the lack of “specificity of training”, polarized training is the method that I typically endorse. I base this on many hours of researching papers and looking at what world-class endurance athletes are apparently doing and studies that compare polarized training to other methods of training.
I am assuming that there will be a varying amount of knowledge in the people who read this article, so I have divided it up into sections. In Section #1, I will get angry email replies from coaches. Section #2 briefly outlines some of the basic terms of exercise physiology needed to understand the rest of the article. In Section #3, I talk about why there should be an emphasis on Zone 1 training. Section #4 explains what polarized training is and Section #5 outlines some studies showing that for endurance athletes, polarized training generally seems to be a superior way of training. You can click on the links below to be taken to each section.
Section 1: My Thoughts on Coaching
Let me start by saying that I’m not a running coach. What I am about to say is not to throw all coaches under the bus…just some coaches.
Despite having taken multiple courses in exercise physiology in undergrad and chiro school as well as doing some brief work in a lab testing athletes in VO2max, lactate threshold etc., I don’t feel capable of coaching athletes because I don’t feel knowledgeable enough…plus I don’t have the patience for most athletes! That being said, I think it’s important that most runners/triathletes DO ask their running/triathlon coaches what educational background they have. A working knowledge of how to use the TrainingPeaks website doesn’t qualify.
I have seen way too many coaches have the “no pain, no gain” philosophy. Their runners do tempo run after tempo run and suffer the consequences in injuries, overreaching and burn-out I see this happening in well intentioned community level tri/running coaches, high school coaches, but particularly in collegiate coaches. Don’t even get me started on the running coaches who claim to do running gait analysis – that actually keeps me up at night!
So, since I’m not a coach, you may be wondering why I want to talk about endurance training. The answer is simple – the majority of running injuries are due to training errors – too much (volume), too soon (frequency), too fast (pace).
If you have terrible running mechanics, your body’s tissues should be able to adapt; given enough time. Loading the body’s tendons, ligaments, muscles and bones in the “zone of optimal stress” will allow them to become stronger, more resilient and resistant to injury. The “zone of optimal stress” is kind of a Goldilocks idea: Not enough stress applied to the tissues means the tissues won’t be exposed to enough stress to stimulate an adaptation response. Too much stress means the amount of stress exceeds the physical capabilities of the tissues and they will fail (injury). Just the right amount of stress means that the load is enough to stimulate adaptation, but not enough to cause failure.
Finding the zone of optimal stress for each athlete as an individual, is the art of being a running coach.
I find that many of my patients have undergone some amount of training errors. For example, more than 50% of their weekly mileage is on one long run, they exhibit a couch to marathon in 1 year type of mentality etc., but the overwhelming amount of training errors are that they just try and run too fast, too often. They do way too many tempo runs and way too many training sessions at or near race pace. This is where we get into the convergence of the coaching and the clinician: if the coach and the clinician have different goals and are giving different advice, the athlete is stuck between two competing interests.
That being said, I often run into endurance athletes and coaches who are resistant to the idea of training below their aerobic threshold. They can’t understand how not running at race pace will help them in a race (the lack of specificity of training). I have written about this in the past but this post is an update where I want to present more up to date studies.
Section 2: A Brief Primer on Exercise Physiology Terms:
Before we get into the nuts and bolts of polarized training, let me do an extremely brief primer on some exercise physiology terms.
Aerobic exercise: Low intensity exercise where oxygen is used by the body in the steps needed to generate energy
Anaerobic exercise: Higher intensity exercise that is intense enough to produce lactate as a bi-product of energy production. Uses two sources for energy production: 1) Creatine Phosphate and ATP and 2) Anaerobic gycolosis which uses glucose
Ventilatory threshold 1 (VT1): While exercising, your breathing is relaxed enough that you can speak in full sentences. Any increase in exercise intensity will cause a spike in your breathing rate.
Ventilatory threshold 2 (VT2): While exercising, your breathing allows you to speak, but not in full sentences. Any increase in exercise intensity will increase the lactate concentration in your blood to rise beyond a point where sustainable exercise is possible.
So now that we know the basics of threshold training, we can start talking about zone training. Depending on where you are from, or who is talking, there are either 3 or 5 zones and they have to do with the VT1 and VT2. These charts should explain:
5 zone model on left, 3 zone model on right
In the 3 zone model, it is generally accepted that any exercise in Zone 1 is below VT1 and any exercise in zone 3 is above VT2:
These zones are basically related to blood lactate levels, which is a bi-product of energy production. In Zone 1, blood lactate is very low. In Zone 2, lactate production is high, but an equilibrium can be achieved through increased respiration rate. In Zone 3, lactate production exceeds the body’s ability to clear it and fatigue is imminent.
The inevitable question now, is, “How do I know what my running pace should be to train in zone 1, 2 or 3?” This is a legitimate question and we can get very complicated in its answer. There are many services available to runners where VO2max testing is available. The drawback here is there is a significant fee associated with it, and the runner’s VO2 max will hopefully change as you train, so the runner will be required to revisit the facility periodically in order to be re-tested. Another method has been proposed by Phil Maffetone which is a relatively simple method to estimate your VT1 and can be found here. In his method, the runner simply subtracts his age from 180 and then adds or subtracts based on some factors such as running history and previous injuries, illness etc.
I recommend an even simpler, but more effective method (in my opinion) and one that can be performed every time you run. This method is simply to pay attention to your breathing. We know that when a runner’s pace exceeds VT1, there is a spike in his breathing. In addition, there is a distinct difference in breathing after the runner exceeds VT2. If the runner simply pays attention to his/her breathing, they should be able to distinguish when they have passed each threshold. Breathing and pace do not have a linear relationship and one can see from the graph below. The breathing rate curve takes distinct changes in it’s slope as the runner passes VT1 and VT2:
There is benefit to “going by feel” with this method since our physiology changes every day. If we have our VO2 max tested, or go by our % of max heart rate or the Maffetone method, we are going by a number on a heart rate monitor, but the VT1 and VT2 relative to our heart rate can change daily, depending on our physiology for that day. Most runners know they have good days and bad days, so we should monitor our breathing/pacing daily to determine our zones on any given day.
Section #3: The Case for Zone 1 Training.
While the main thrust of this article is on polarized training, I feel it necessary to talk about the importance of Zone 1 training since polarized training requires athletes to spend 75-85% of their training time in Zone 1. It is Zone 1 training that most amateur endurance athletes are resistant to when I bring it up in my clinic; “How can you expect me to run fast in a race if most of my training is at a slower pace?“. I get called a nutter, or worse.
There are three main arguments for Zone 1 training for endurance athletes; reducing injury, increasing performance and reducing over-training.
a) Reducing Injury: This should be intuitive, but some aspects of increased pace are different. A good review of the literature by Nielson et al (here) found that PFPS, ITBS, patellar tendinopathy and other injuries may not be related to pace, but injuries such as achilles, plantar fasciopathy and calf strains are related to pace. In addition, hamstring injuries appear to be more prevalent with increased pace. In a separate study, Nielson (here) found that the vertical ground reaction force at initial contact to increase by 100% during an increase in speed from 2 m/s to 6 m/s, while the increase in the anterior-posterior force during the propulsive phase at a similar increase in speed was 250%.
Again, it would seem intuitive that injury rates increase as pace increases, given the higher muscle loads, ground reaction forces and propulsive forces.
b) Increasing Performance: Craig Neal PhD, posted his thesis online which is extremely in-depth, but worth the read if you are a coach. In his thesis, he analyzed many papers on the training distribution of elite-standard athletes and he stated that most training time spent in zone 1 was >80% of the total training time. In contrast, studies on sub-elite runners show less time spent in zone one (71%). One study showed negative correlation between time spent in zone 1 and performance time during a 10 km cross country race (i.e. more time training in Zone 1 was resulted in faster race times).
“Thus, data to date suggest that more time spent training in zone 1 is beneficial for physiological adaptation and subsequent exercise performance. Studies with elite-standard athletes (Ingham et al., 2008) and sub-elite athletes (Esteve-Lanao et al., 2007) that have examined training-intensity distribution agree that a greater percentage of training time spent in zone 1 is beneficial to performance and/or physiological adaptation. These studies found that with no difference in training load, a group focusing on training in zone one (≥80%) had a greater improvement in performance(Esteve-Lanao et al., 2007) and gained greater physiological adaptation (Ingham et al., 2008) than a group who spent less training time in that zone (~70%)”
c) Reducing over-training/over-reaching: Over-training/over-reaching can be measured by a number of variables including Heart Rate Variability, immunological parameters, metabolic markers in the blood (on a personal note, my TSH jumped to 46 following an Ironman race when I was out of shape), hormone levels, reduced performance etc. Billat et al here) found that blood markers for over-training/over-reaching are increased if high intensity training is performed >3X/week in runners. Furthermore, Seiler et al (here) found that VT1 is the cutoff point for disturbances in the autonomic nervous system (an imbalance in the nervous system is what is disturbed in over-training/over-reaching). For a thorough discussion of over-training vs overreaching and the physiologic consequences, I highly recommend Halson and Jeukendrup’s paper, “Does Over-training Exist?” (full text here)
Section #4: What is Polarized Training?
Now that we’ve established a basic understanding of Zones and VT1, VT2, we can move on to how to properly utilize that knowledge for endurance training.
There are two popular training methods when it comes to zone based training: Threshold Training and Polarized Training. Threshold training does the majority of training at or near race pace (Zone 2). Conversely, polarized training states the vast majority of training should be done in Zone 1 (approx 75-85%) and some in Zone 3 (15-20%), but very little in Zone 2 (<10%). Essentially, the polarized method gets it’s name due to polarizing the training away from the middle zone 2 and into either Zone 1 or Zone 3 (much more in Zone 1)
The threshold model has been studied many times and shown to have significant improvements in untrained subjects (here, here and here). Similarly, the polarized training method has been studied numerous times, as I will outline in Section 3 below. It is my opinion, based on studies comparing the two, that the polarized method is much better than threshold training. The philosophy of polarized training comes from Stephen Seiler PhD and the late Charlie Francis (a Canadian sprint coach ahead of his time). Essentially, Zone 2 training is considered a “black hole” since it is poor at achieving the benefits that Zone 1 and Zone 3 training are capable of:
Why not do all training at low intensity? As outlined in the chart above, both high and low intensity training have their benefits and to focus on one would be folly. It is evident that most elite athletes do around 75-85% of their training in Zone 1, however doing all training in Zone 1 would not promote other changes in the neuromuscular system and cardiovascular system such as increased Vo2 max, lactate threshold and economy. As such, it has been shown that adding a small amount of high intensity training over a 4-8 week period can improve performance significantly in well trained endurance athletes (here, here and here)
Why not do more training at higher intensity? Adding more intensity does not seem to advance performance, but can induce over-training/overreaching (here) . The question is – how much high intensity is too much? That certainly is an individual question, but it is without question that overreaching can be easily induced with increasing intensity. As I wrote above, Billat et al., found that high intensity training 3X/week is enough to cause over-reaching/over-training. A thorough review of the literature has been done by Halson and Jeukendrup in their paper, “Does Over-training Exist?” (full text here)
Section #5: The Evidence Behind Polarized Training
This section will look at the evidence and will be subdivided into 2 categories: i) how do the top athletes train (i.e. observational studies) and ii) Studies comparing threshold and polarized training (i.e. intervention studies)
i) How do the world-class endurance athletes train?
Let’s first look at the training logs of world-class athletes to see how they actually train. Most people are surprised by how little race pace training elite endurance athletes actually do. This lack of specificity training seems counter intuitive to most, but take a look at these studies looking at training logs:
a) Billat et al (full text here): This 2001 study looked at the training logs of elite marathoners (2:06-2:11 marathon times). This is the distribution of their training intensities:
b) Karp (full text here): This study looked at training logs for 93 U.S. qualifiers (37 men, 56 women) for the 2004 Olympic Marathon Trials. The vast majority of training distance was slower than marathon pace. The author states, “The tendency to perform most training at a low intensity is a common finding of studies on elite endurance athletes…men averaged only 9.7% and women 12.8% of their yearly training at marathon pace”
c) Seiler (full text here): This study looked at 12 elite, national team level cross country skiers and followed then for 318 training sessions. They found the training intensity distribution as follows:
d) Orie et al, 2014 examined the training logs and interviewed coaches and athletes from 38 years of speed skating. These were national level skaters that went to many Olympics and collected 8 gold, 5 silver and 4 bronze Olympic medals. They saw a major shift in training toward a polarized method and concluded: “Our data indicate that for successful middle- and long-distance speed skaters there was a shift toward polarized training over the last 38 years. Surprisingly, there was no increase in net training hours and hours of on-ice skating over these years, while performance increased considerably.”
e) Fiskerstrand et al (full text here): This paper looked at 27 Norwegian rowers from 1970-2001. Together, these athletes won 11 gold, 15 silver, and 8 bronze medals with a distribution seen at the senior European (three medals), World (23 medals), or Olympic (eight medals) levels. Over the 30 year time span, the best athletes got better. Compared with the winning athletes in the 1970’s the athletes in the 1990’s increased their VO2 max by 12% on average.
After looking at their training logs, the researchers found 3 main changes in training: 1) an ~20% increase in training volume, 2) a significant shift to emphasize training at an intensity below VT1 (<2mmol lactate) and 3) a significant increase in altitude training. With these three variables at play, it is difficult to single out increases in Zone 1 training as the main factor for success. However, I think we can de-emphasize altitude training due to many recent studies showing that the promise of altitude training may not be what we once thought it was (here and here). Alex Hutchinson made an interesting post about that here.
Regardless of the reason why these improvements in Vo2 max were seen, the fact remains that there has been a historical shift toward increased volume of training below VT1. As the authors of this last study concluded, “Large increases in basic endurance training at intensities clearly below the first lactate turn point have been utilized.”
ii) Studies Comparing Threshold and Polarized Training
When looking at the way elite endurance athletes train, one has to wonder whether or not they train 75-85% of the time in Zone 1 because it’s the best way to train, or because that’s “just the way it’s done”. These next studies actually compared polarized training to other forms of training to see what happens when training intensity distribution is altered:
a) Esteve-Lanao et al., 2007 took 12 sub-elite runners (10km PR’s of 30 -35 mins) and split them into 2 groups for a 5 month period. Group 1 was to run with in Zones 1,2 & 3 for 81%,12% and 8% respectively, while Group 2 was to run in Zones 1,2 &3 for 67%,25% and 8%. Their weekly running volume was equal between groups.
Following the 5 month training in these zones, Group 1 (the polarized group) improved significantly more than Group 2.
b) Neal et al., 2013 published a study specifically on polarized training. They had 12 cyclists take 4 weeks off to slightly detrain, then they did either a polarized training block (80% zone 1, 0% zone 2, 20% zone 3) for 6 weeks or a threshold training block (57% zone 1, 43% zone 2, 0% zone 3) for 6 weeks. Following this, they did another 4 week detraining period and then switched training methods (the athletes that initially did polarized, switched to threshold and the athletes that initially did threshold, went to polarized). Despite the lower training load (intensity X duration) during the polarized training block, the athletes ended up having better improvements in performance (peak power output and high-intensity exercise capacity) following the polarized training block than the threshold block.
This study is a really well designed and convincing study. I find it intriguing that the polarized group did NO training in Zone 2. Alex Hutchinson spoke about this study in this article and posted this chart of the results:
c) Yu et al 2012, had 5 men and 4 women from the Chinese National speed skating team undergo a threshold training (40% Zone 1, 56% Zone 2 and 4% zone 3) in 2004-5 and then switch to a polarized training model (82% Zone 1, 5% Zone 2 and 13% zone 3) in 2005-6. They found that under the polarized training model, all skater’s performance improved and their lactate after competition decreased significantly. The interesting aspect of this study is that it was done on sprint skaters, not endurance. There are certainly many holes in the design of this study, so it’s wise to be a bit skeptical of these results.
Conclusion: Polarized training appears to be a common training method for most world-class endurance athletes and is backed up by interventional studies comparing it to other forms of training. It is worth noting that this method will not work for all people, but it is a good place to start.
Footnote: A great deal of this update is also reviewed in a presentation by Dr. Stephen Seiler PhD in this video on polarized training. I highly recommend you watch the video. He is a great researcher.