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Endurance training 3: Polarised training and the specific value of easy sessions
Last week’s blog (hopefully) provided some rationale for why those grunty high-intensity interval sessions are a crucial component of our endurance training programmes. As promised, in this week’s blog we are moving to the other end of the training spectrum, and advocating for why generous portions of easy training are also valuable to us as endurance athletes, and why we might be aiming for a polarised training intensity distribution.
Training intensity distribution refers to the proportion of training spent in the different training intensity zones, most notably below the aerobic threshold (physiologically easy sessions), between the aerobic and anaerobic thresholds (sometimes called the ‘sweet-spot’), and above the anaerobic threshold (i.e. those high-intensity intervals). The aerobic threshold defines the upper limit of truly physiologically easy training, where things like blood lactate concentration are undisturbed compared to rest and recovery is swift (11). Exercise below the aerobic threshold is sometimes called ‘conversational’ because the exercise does not make chatting difficult. A polarised training intensity distribution refers to a training programme in which the majority of training sessions and overall training time is spent below the aerobic threshold, typically ~75-80 % (6, 12, 15). Accurately identifying the aerobic threshold in a laboratory is therefore something we encourage at Elevate Coaching.
Let easy be easy, so that hard can be hard
The rationale for polarising our training falls into three main categories:
(i) Descriptive studies of elite athletes
(ii) Physiology of training and recovery
(iii) Experimental research
Firstly, there is now a fairly vast amount of observational research showing that many of the world’s best athletes train in this polarised fashion, with ~80% of training time spent in the easy zone below the aerobic threshold (1, 5, 7, 9, 10, 14). People tend to find these observations surprising, which is perhaps itself unsurprising given the widespread attitude that more and harder are better and necessary for top-level performance. This surprise is articulated particularly well by Professor Stephen Seiler, an American exercise physiologist now working at the University of Agdar in Norway, at a recent TEDx event that can be viewed here: https://www.youtube.com/watch?v=MALsI0mJ09I. Seiler is considered by many, including myself, to be the leading mind in the study of training intensity distribution, publishing countless research articles on the topic. In his often recorded lectures, Seiler describes his personal journey from a “no pain, no gain” mind-set to becoming the leading advocate of polarised training and healthy doses of easy work.
Of course, just because elite athletes are doing it, doesn’t mean it is the best or only route to achieve success. What this line of research does show, however, is simply that it is possible to achieve extremely high level performance in endurance sport without dipping into the red zone and training hard in every training session. Having observed this, in science we would next ask for plausible mechanisms for why a given approach or intervention might result in favourable outcomes, and then experimental trials showing the effect exists, before making any firm conclusions.
So, to get at this next level of evidence, it is important to consider why, from a physiological perspective, polarising our training might be the best way to go. I personally think a first concept to consider here goes back to what we discussed last week with high-intensity interval sessions, which, as we know, provide fantastic adaptation through the large homeostatic disturbances they generate. In order to perform these sessions at our best, and therefore be able to generate the biggest possible homeostatic disturbance and stimulus for adaptation, we need to be rested and recovered when we start the session. So, it makes sense that the training we perform prior to these key workouts should not be too stressful, such that we are ready to nail our intervals as best as we can. Low-intensity training sessions performed below the aerobic threshold are an effective means of doing so, given the shorter recovery required and minimal autonomic disturbance (a measure of stress in our nervous system) generated with this intensity of exercise (4, 11). These easy sessions should be truly easy, so that when we come to our key, hard sessions, hard can be properly hard.
Secondly, continually training with high intensity, due to the high levels of stress it evokes physiologically, can lead to suppressed parasympathetic activation and impaired cardiac autonomic balance (7), which may eventually contribute to fatigue and non-functional overreaching (8). I see a lot of weekend warriors who fall into this trap despite only training for 5-10 hours per week. The ‘easy’ sessions many athletes perform throughout the week are actually quite tough, leaving their mark and inducing fatigue going into each of the 2-3 ‘key’ weekly interval-style workouts, during which performance and adaptation are as a result impaired.
Now we’ll move on to the experimental studies. Do they show benefits of polarising training in a direct comparison with other models of training? In short, yes. This is a difficult topic to study with experimental research, given the time commitment when asking participants to come into your laboratory to perform all or most of their training, and the heightened possibility of extraneous factors like injuries and illness impacting results when studying a group of individuals over such a long period. However, the studies that have been conducted in this field do suggest more greater adaptations for endurance athletes training in a polarised fashion rather than with a threshold focus, for laboratory markers of endurance performance as well as in time-trial assessments (6, 13). Indeed, a recent meta-analysis of studies focused on running performance – a process where all available data on a topic is combined – suggested the balance of evidence favoured polarised training. We therefore have a fairly strong argument, based on observational evidence, experimental evidence, and physiological mechanisms, for why polarising our training might be the way to go as endurance athletes.
Why include low-intensity sessions at all?
So, whilst I think it’s fair to say that there is good rationale for polarising our intensity rather than pushing the envelope in every single session, a question that often springs to mind is whether we should bother including the low-intensity work at all, or if we’d be better off with complete rest? Why not put the feet up for even better recovery in advance of those key high-intensity workouts, which as we explained last week are key drivers of adaptation?
Importantly, there is recent suggestion that some of the adaptations we want from our training are actually more specific to training volume rather than intensity, so increasing the overall time we spend training might be useful in this context. These adaptations relate to mitochondrial protein content, which are the proteins in our muscle cells that process oxygen, and are therefore critical for us as endurance athletes. One of the key purposes of training is to increase the number of mitochondrial proteins as well as their functionality (3), and it is possible that training volume is a more critical determinant of mitochondrial protein content, i.e. how much we have, than training intensity (2). This provides support for specific inclusion of low-intensity training within our programmes in order to ensure we are getting all of the adaptations we seek from endurance training, as we can increase our overall training volume without running into the problems of overreaching and overtraining we would see by increasing the number of high-intensity interval training sessions we do each week.
Summary
In summary, in this blog I have tried to demonstrate that, when training for endurance sport, being disciplined about the intensity of each training session is extremely important. Our generous serving of easy sessions should be physiologically easy, so that our small number of key, hard sessions can be physiologically hard! The next blog in this series will be focused on a training monitoring tool we advocate at Elevate Coaching and use to help track the training stress I have referred to throughout this blog series; heart rate variability or HRV.
References
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11. Seiler S, Haugen O, Kuffel E. Autonomic recovery after exercise in trained athletes: Intensity and duration effects. Med Sci Sports Exerc 39: 1366–1373, 2007.
12. Seiler S, Tønnessen E. Intervals, thresholds, and long slow distance: The role of intensity and duration in endurance training. Sportscience 13: 32–53, 2009.
13. Stöggl T, Sperlich B. Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Front Physiol 5: 1–9, 2014.
14. Sylta Ø, Tonnessen E, Seiler S. From heart-rate data to training quantification: A comparison of 3 methods of training-intensity analysis. Int J Sports Physiol Perform 9: 100–107, 2014.
15. Tønnessen E, Sylta Ø, Haugen TA, Hem E, Svendsen IS, Seiler S. The road to gold: Training and peaking characteristics in the year prior to a gold medal endurance performance. PLoS One 9: 15–17, 2014.