How to Train (Part 3)
For those of you who read my blog posts; How to Train (Part 1) and How to Train (Part 2), you’ll be familiar with the four different training models I touched on (Polarized, High Volume, Threshold and High Intensity Interval Training). Additionally, you’ll remember that I covered polarized training (PT) very in-depth in the last post and all of its mechanisms and benefits. However, I was also very outspoken in stating that no any given training model is better than another, and this is what I want to address in this part 3. Often people ask me, “How should I train?” or, “Which model should I use?”. The truth is it’s quite difficult to answer that question and it depends on what you have done in training up until this point, what your goals are, and what you are capable of.
In this post I am going to explore High Volume Training (HVT) and High Intensity Interval Training (HIIT) as two further methods of endurance training. In an effort to be consistent across posts, I will once again define HVT as 100% of training time spent at; less than an RPE of 13/20, Joe Friel’s zones 1 and 2, or light intensity exercise. HIIT, on the other hand, requires spending approximately 50% of all training time in this exercise intensity range, with the other 50% in the; RPE of greater than 17/20, Joe Friel’s zones 5 and up, or very hard intensity exercise. HIIT is characterized by intermittent periods (intervals) of work and rest within any given workout (Whitehurst, 2012). The work intervals are typically in the >17 RPE intensity range, while the rest intervals are at an intensity of <13 RPE. These work intervals typically last anywhere between 30 seconds and 4 minutes with a similar length of rest interval.
These two models are very commonly compared in research studies with several researchers seeking to answer the question of which training model is better for endurance training. In a study by Stoggl and Bjorklund (2017) on the neuromuscular status, anaerobic capacity and acute heart rate recovery of well trained endurance athletes, it was found that HIIT is essential in improving these factors amongst well trained endurance athletes. After a period of 9 weeks, HVT training alone had no effect on these performance or heart rate recovery outcomes. Now this might seem reason enough to discount HVT as a training model, however the fact that these participants were all well trained (VO2 Max of 61.9 +- 8.0 ml/kg/min), is reason enough to understand why the HVT did not elicit improvement in the factors above. These athletes (a mixture of runners, cyclists, skiers, and triathletes) all have extremely high mileage training programs already, and as such, only a high intensity stimulus is likely to induce a training response. Additionally, a PT group also saw less of a training effect compared to their HIIT counterparts (once again most likely because of a much greater proportion of training time spent at high intensity during intervention for the HIIT group than normal). That being said, HIIT training clearly does have a positive effect on the metabolic and neuromuscular components of maximal anaerobic performance in well trained endurance athletes (Stoggl & Bjorklund, 2017). However all this suggests to me is that once you get to a point that you are doing a high volume of training, you need to include high intensity training to see improved training adaptation. Furthermore, HIIT appeared to have a significant effect on heart rate recovery (the rate at which your heart rate decreases immediately after exercise with a quicker decrease meaning enhanced fitness) of well trained athletes compared to HVT, a factor that might be explained by less total training time (per week), and longer rest between sessions.
In a separate study, this time on recreational runners, an HVT and HIIT training group were compared after 8 weeks of training (Vesterinen et al. 2016). The HIIT group had a significant improvement in VO2MAX as well as peak running speed on a treadmill test after 8 weeks of training, but these factors were not improved in the HVT group. Once again however, this apparent improvement in HIIT over HVY is not as simple as it might seem. In the study, the entire group of runners underwent an 8 week HVT program prior to splitting the group into HIIT and HVT groups for a further 8 weeks. In the initial 8 weeks, the entire group reported with an improvement in peak running speed, and as such the subsequent improvement in peak running speed and VO2MAX may once again be explained by the variation in training stimulus (from HVT to HIIT) as opposed to just maintaining the same training model. The take home message is that when doing long term training, it is important to include some high intensity training as opposed to HVT alone (Vesterinen et al. 2016). In the study, heart rate variability (HRV) was assessed as a predictor of endurance performance where a higher HRV is typically seen in more well trained athletes (HRV is the time between successive heart beats). Interestingly, the researchers found that runners with low HRV respond better to HVT, while those with high HRV respond better to HIIT training. Once again, this could be a result of runners with lower HRV typically being less well trained than those with high HRV and consequently those who are well trained responding better to HIIT training in order to see significant adaptation.
At this point you might be asking what makes these different types of training models work – or what is the mechanism behind them? Maximal oxygen uptake has been found to increase significantly in untrained individuals with as little as 2 – 12 weeks of HIIT (Astorino et al. 2017). This could be as a result of an improvement in cardiac output and/or arteriovenous oxygen difference which both have an impact on VO2MAX. Cardiac output is the product of the number of heart beats per minute and stroke volume which is the amount of blood pumped per heart beat, while arteriovenous difference is an indication of how effectively your body can get oxygen to the working muscles. Both these central (cardiac output) and peripheral (arteriovenous difference) systems have found to improve with HIIT training in previous research (Astorino et al. 2017). Both HVT and HIIT training improve arteriovenous difference through an athletes increased oxidative capacity (ability of muscles to use oxygen) and mitochondrial biogenesis (increased mitochondrial density) (Whitehurst, 2012). Lastly, in well-trained triathletes, HIIT was found to improve muscle power and subsequently – running performance (Garcia-Pinillos, 2016). These improvements in muscular power came as a result of improved neuromuscular characteristics such as; enhanced neural drive, improved anaerobic glycolysis and additional fast-twitch muscle fiber recruitment after HIIT (Garcia-Pinillos, 2016).
One of the wonderful benefits of HIIT training is the relatively short amount of time required to achieve a training response. In slightly overweight and healthy, sedentary populations, short duration exercise bouts of three times a week has been found to elicit large improvements not only in VO2MAX, but in work economy, blood pressure and fasting glucose levels (Tjonna et al. 2013). Therefore for people seeking general health benefits, and with tight time schedules, HIIT presents them with a way to improve their general health without a large time investment. This benefit is not limited to slightly overweight or sedentary adults, but older adults too (Whitehurst, 2012).
As suggested at the start of this post, my aim here was to show you why no particular training model is better than another. I have just presented scientific evidence to you that tells you how and why the HIIT model works or is even better than other models – yet in part 2 I did exactly the same for PT. The truth is, many of the research studies I have referred to don’t account for what their participants were doing before the training intervention. As such, merely providing a change in the respective participants’ training is enough to stimulate significant improvements (i.e. if the athlete was doing HVT and then the researcher’s intervention requires them to do HIIT, the change in stimulus is enough to elicit a positive training response). Once again, the crux of the matter returns to when do I use what type of training and why? While HIIT has certain characteristics that are unique to it, such as an improved muscle power output, and the added benefit of being shorter than other training models – it is not the only training model that elicits positive training adaptations to both centrally and peripherally. Additionally, whenever there is a change in training stimulus, generally a positive adaptation is seen. As such, when I meet with someone who has a very poor training history, I typically start them off on an HVT program for 6 – 8 weeks before progressing onto PT, THR, or HIIT training. However, it is clear that for some populations HIIT can be the preferred method of training depending on goals and time restriction.
Astorino, T. A., Edmunds, R. M., Clark, A. (2017). High-intensity interval training increases cardiac output and VO2MAX. Medicine & Science in Sports & Exercise. 265-273.
Garcia-Pinillos, F., Camara-Perez, J. C., Soto-Hermoso, V. M., et al. (2016). A high intensity interval training (HIIT) based running plan improves athletic performance by improving muscle power. Journal of Strength and Conditioning Research. 31(1) 146-153.
Stoggl, T. L., & Bjorklund, G. (2017). High intensity interval training leads to greater improvements in acute heart rate recovery and anaerobic power as high volume low intensity training. Frontiers in Physiology. 8:562.
Tjonna, A. M., Leinan, I. M., Bartnes, A. M., et al. (2013). Low and high volume of intensive endurance training significantly improves maximal oxygen uptake after weeks of training in healthy men. PLOS ONE. 8(5): 1-7.
Vesterinen, V., Hakkinen, K., Laine, T., et al. (2016). Predictors of individual adaptation to high volume or high intensity endurance training in recreational endurance runners. Scandinavian Journal of Medicine & Science in Sports. 26: 885-893.
Whitehurst, M. (2012). High intensity interval training: an alternative for older adults. Physical Activity. 382-386.