Polarized cardiovascular endurance training

In this article, we’ll take a look at the latest scientific evidence on cardiovascular endurance training to help the athlete improve performance while minimizing risks and maximizing health benefits.

Authors: Jay Haydren, M.Sc., Certified Trainer (NSCA), Bruce Cohen, Ph.D., Certified Trainer (NSCA).

A review of traditional endurance training models shows that three methods are most commonly used:

  1. threshold / “running for a while” (5 km or more),
  2. prolonged low-intensity exercise,
  3. high-intensity interval training (HIIT).

Threshold training is characterized by increasing the intensity to a “hard” pace (effort 15-16 on the 20-point Borg scale  or about 75-80% VO2max) and maintaining it throughout the training with a gradual increase in speed weekly linear periodization (five). High-volume workouts are long-lasting and low-intensity (9-10 on a 20-point scale, or about 45-50% of VO2 max). HIIT consists of short and “very heavy” interval loads (18 on a 20-point scale or 90% of BMD) and light, recovery exercises or even without them.

A new model is polarized endurance training (PTT) – a program with nonlinear wave periodization that combines various types of loads. In PTT, between specific high-intensity workouts, one or more light-load sessions are conducted; the intensity is strictly controlled. Workouts are conducted in two intensity zones: “light” long (zone 1) and “very hard” intervals (zone 3). This two-zone model provides optimal recovery from maximum effort workouts. At the same time, “heavy” training (zone 2) in the PTV is reduced to a minimum (2,11,15). An array of scientific data is gradually accumulating comparing PTI for improving sports performance and reducing trauma with the aforementioned traditional models.

Traditional models have their advantages and disadvantages. For example, HIIT (zone 3) rapidly increases the level of fitness in trained athletes , and too much “hard” time running (zone 2) impairs fitness, leading to overtraining. PTT simplifies the training program by reducing training to two intensity zones, helps overcome plateaus, improves recovery, and also minimizes the risk of injury (due to overtraining).

As with strength training, where the intensity is set as a percentage of 1RM, endurance training also measures the level of load to optimize the program and get the best results. In the past, the percentage of VO2 max or heart rate was used to define these training zones. This is not the most accurate way to assess intensity, since different physiological factors, such as thermoregulation or blood pressure, affect the heart rate, and an individual’s maximum aerobic performance is associated with different metabolic thresholds (1,14). More accurate is the linking of training zones to physiological parameters associated with metabolic needs, such as ventilation threshold or blood lactate level (3,15). Of course, blood lactate monitoring is not available to all athletes.

Training within the required zone

The most difficult condition for successfully following the PTV program is to stay within zone 1 for the appropriate workouts, without increasing the intensity to zone 2. This is especially often the case in group races, when the

most prepared athletes train in zone 1, and the lagging participants try to catch up and get into zone 2, exceeding the intensity of the “light” exercise, contributing to recovery.

Let’s look at examples of how to individually assess the load according to several indicators in order to stay in the required zone.

Let’s say a well-trained athlete training in intensity zone 1 has a heart rate monitor of 135 bpm, but physiological indicators indicate that the intensity is high: breathing is difficult, speech is intermittent, profuse sweating, slight muscle pain / burning / discomfort and perceived effort at level 15 on a 20-point scale (“hard”). Apparently, for this individual, the pulse 135 corresponds to the intensity zone 2, so it is worth reducing the speed to reach 125 beats / min. Then the workout will be light and restorative as planned.

Another example: an athlete returns to training after a long break due to injury, and in a session in intensity zone 1, his heart rate reaches 145 bpm. But at the same time, he can freely maintain a conversation, does not sweat too much and does not experience any muscle discomfort, the effort is perceived at a level of 9 on a 20-point scale. This athlete appears to remain in zone 1 and can continue training at the same pace.

In this regard, training in intensity zone 3 is easier. The intensity is extremely high, up to 100% VO2 max and higher (5). Intensive intervals can last from 5 seconds to 5 minutes, with corresponding rest breaks of 1-8 minutes. As with zone 1, it is important to maintain a given intensity, avoiding getting into zone 2. If you fail to give your best in working intervals, this may be due to insufficient duration of rest pauses (<1 minute); according to studies, the optimal duration is about 2 minutes (8,16). In the case of high-intensity loads, group exercises contribute to effective training due to the competitive factor.

Planning your training week

Table 2 shows options for a weekly training program – a regular work week and a holiday (on Monday). High-intensity workouts are more effective after rest days, low-intensity workouts are inserted between interval and strength workouts for the best recovery. To reduce the risk of injury, one should adhere to the principle of progressive overload, not overwork on rest days, use special sports shoes, and avoid excessive training volumes.


This article does not address individual differences (eg fitness level, gender, age) and environmental conditions (temperature, altitude, etc.) that can affect the parameters of training intensity zones. General heart rate recommendations may not be suitable for very well trained athletes or those with no training experience at all.

For individual selection of the training zone limits, it is better to combine all available means of assessing the intensity: heart rate monitor, RPE scale, speech test, etc. It is critical to stay in zone 1 during “light” training, since studies reveal a weakening of adaptive processes when the intensity is exceeded and entering the zone 2.