The Dichotomy of Endurance Training (Part 3)
By Scott K. Ferguson, Ph.D.
The limit of human performance has been tested throughout history. How fast can a human cover a given distance has been a question that millions of viewers tune in to find out when it comes time for our summer and winter Olympic games. In 1925 the great physiologist A.V. Hill plotted the time to complete a variety of race distances vs. average speed using data from current world-records at the time. In doing so, he discovered the curvy-linear relationship that we now call the critical speed, which is the highest sustainable speed for humans performing the event. This relationship still holds true. For example, if I plot the average speed vs. the time to complete a race for current world-record holders of a variety of track events, we still get the same curvy-linear response, where the leveling out of the curve (the asymptote) is the highest sustainable speed for the human species. The critical speed of the best of our species.
What does this mean? Simple; the best competitors cover their race distance in the shortest amount of time possible for our species. Not much of an epiphany, but let's dig deeper and ask the question, should we train at the same speeds at which we perform during a race or event? Intuition tells us, yes, and indeed many people train at their highest sustainable speed thinking its the best approach since they will be running at that intensity on race day, it also makes us feel like we are training because it's difficult! But is training at or near our critical speed what the pro's do?
The short answer is it depends. For shorter events lasting less two hours or less, the answer is no, at least not all the time. Most elite endurance athletes do not spend the majority of their time training at their race pace or critical speed (or power if you're talking cycling). In part 1 of this series, we dispelled the myth that lactate is bad and makes your muscles sore after training. In part 2 we defined three distinct training zones and discussed what separates them from one another. In this final installment of our series on endurance training thresholds and theory, we will discuss the polarized training approach utilized by the majority of elite endurance athletes and discuss how you can use this method to guide your training.
How do the pros train?
A prominent study that helped characterize the training habits of endurance athletes was published by Seiler and Kjerland in 2006. Their article entitled "Quantifying training intensity distribution in elite endurance athletes: is there evidence for an ‘‘optimal distribution?" did an excellent job of describing the difference between the threshold training model, which emphasizes time spent training at or near the critical speed or maximum lactate steady state (see part 2 of this series if these terms are unfamiliar) and the polarized model, which emphasizes time spent below the lactate threshold (denoted as LT1 in the figure) with some additional doses of high-intensity work (90-100% VO2 max). Let's break these two models down.
Threshold Training Model: This is the type of training model that many casual and new athletes adhere to without even knowing it. Most of the time is spent training at an intensity or speed very close to the maximal sustainable speed for the individual (shown as VT2, LT2 and MLSS in the figure to the right). These sessions are challenging, but fun and allow the athlete to push themselves on a regular basis. A great example of where this training principle is used is in high school cross country athletes, where organized practice sessions are often restricted to periods when the students are “in session” leaving very little time to prepare for the season's races. The benefits of a threshold training plan include a rapid increase in performance, as untrained or even undertrained athletes can see significant increases in VO2 max as well as performance for a given race event. However, these initial gains in performance come at a cost as plateaus and stagnations typically develop by mid-late season due to the unsustainable amount of training pressure placed on the athlete’s body and mind.
Polarized Training Model: Athletes utilizing this training model spend the majority of their time executing low-intensity training that is below the lactate threshold ( shown as VT1 and LT1 above). For a casual athlete who is unfamiliar with this training approach, these sessions can seem easy as they don’t (and shouldn’t) leave the athlete gasping for air or exhausted at the end of the session, nor do they push for personal records on a routine basis. The key here is time in the saddle, as the lower intensity affords the athlete an ability to perform longer training sessions that induce beneficial skeletal muscle adaptations for endurance exercise performance, while not fatiguing the athlete to a point that compromises their ability to recover from training. The process of building endurance performance through lower intensity training sessions is also known as base-building and is a key facet of a periodized training plan for many professional endurance athletes. This is the approach we take when training our clients and has proven to be the most successful for long term growth of the athlete while also minimizing the risks for burnout or overtraining.
There are many practitioners of high-intensity interval training schemes that promise similar adaptive changes in a shorter amount of training time. Crossfit is one example of these training methodologies and has done an excellent job of encouraging physical activity and improving the functional strength of a variety of casual and high-end athletes. While I’ll save the high intensity vs. traditional base-building debate for another post, I will mention that while Crossfit and other high-intensity training schemes may work wonders for improving fitness in the general population, these types of programs are not optimized for endurance athletes looking to spend many hours, days, and weeks covering distance over steep terrain. Simply put, they are not designed to focus on endurance, and this is why elite endurance athletes still spend hours upon hours in the saddle working on their aerobic base at lower intensities.
As mentioned earlier, the observational study by Seiler and Kjerland not only described threshold vs. polarized training methodology, it also sampled the training strategies of some junior elite level cross-country skiers to determine which approach these athletes adhered to. So, what did they find?
Out of the 384 training sessions performed by the 12 cross-country skiers in this study, 75% of the sessions were performed below the lactate threshold (i.e., zone 1), with another 15-20% of sessions performed above the critical speed (i.e., zone 3). Only ~5-10% of sessions were performed at an intensity between the lactate and critical speed thresholds (i.e., in zone 2), which is where these athletes are likely to operate during a race. This “75-5-20” training distribution is the same type seen in a variety of high-level endurance performers including rowers, gold medal track cyclists, and international class marathon runners and encapsulates what appears to be the optimal intensity distribution for those serious about their endurance performance (see studies cited at the end of this article for further reading).
Thus, as with many things in life, we have a dichotomy when it comes to endurance training. While we may perform an event at a given speed, that does not necessarily mean we should spend the majority of our time training at that speed or intensity. For mountaineers, climbers, and backcountry hunters, the speed you operate at during your event will likely be far below your critical speed, but you need to operate at this relatively lower intensity for very long periods of time. Thus, it should not come as a surprise that you need to devote many sessions to low-intensity longer duration type of work. For these, you should feel tired from the duration, not the intensity, and your heart rate should remain on the low side throughout the session. For trail runners, depending on the race distance, you might operate the majority of your race at and occasionally slightly above your critical speed. However, a polarized training methodology will still likely take you further in your long-term quest for performance by limiting injury and burnout as well as performance plateaus.
What have we learned:
1. We learned that Professor A.V. Hill was the first to identify the curvy-linear response known as the critical speed (can’t forget that history fun-fact).
2. We learned the differences between the threshold and polarized training approaches and (very briefly) discussed some of the pros and cons of high-intensity training schemes like Crossfit for the endurance athlete.
3. We identified that many endurance athletes utilize a polarized training approach in which ~75% of their training sessions are dedicated to training at intensities under the lactate threshold.
4. We learned that every training session should have a purpose, whether its to build endurance or speed. If endurance is the goal, you shouldn't finish every session laying on the ground gasping for air. Although that's not to say that sometimes a high-intensity session shouldn't be mixed in with your lower intensity work. Just do so so sparingly; A little goes a long way here.
5. Finally, base-building sessions should leave you tired from the duration, not the intensity of the exercise. Keep your heart rate under control throughout the session. This might mean you need to walk the hills during a long-run. Know that this is OK, and part of the plan!
1. BILLAT VL, DEMARLE A, SLAWINSKI J, PAIVA M, and KORALSZTEIN J-P. Physical and training characteristics of top-class marathon runners. Medicine & Science in Sports & Exercise 33: 2089-2097, 2001.
2. SCHUMACHER YO, and MUELLER P. The 4000-m team pursuit cycling world record: theoretical and practical aspects. Medicine & Science in Sports & Exercise 34: 1029-1036, 2002.
3. Steinacker JM, LORMES W, LEHMANN M, and ALTENBURG D. Training of rowers before world championships. Medicine & Science in Sports & Exercise 30: 1158-1163, 1998.