The new dimension in HIIT
Safe Energy Production™
We have been continuously monitoring Olympic and World champions in various sports for over a decade, focusing on high-intensity training. Our aim is to create a device for professional, semi-professional, and amateur athletes that helps them during HIIT. During training sessions, mnsX continuously monitors the aerobic and anaerobic energy generation systems, providing real-time feedback to help optimize the training protocol, ensure the safe execution of HIIT workouts, and improve the desired ability without reducing other abilities.

One of our Tokyo Olympic champions has been using mnsX every day since 2016. Thanks to him and our other dedicated athletes, we have amassed over 100,000 training experiences. We built all our knowledge and experiences into mnsX, so from now on, it can help professional, semi-professional, and amateur athletes in their HIIT sessions.
In this section, we're going to introduce SEP, what it is, and how to use it. We suggest you first watch the animation video (below) and then read this section. The animation video is about mnsX in a nutshell. It will help you understand the rest of the information easier.
What is SEP?
During training, our body has an energy consumption that depends on the intensity of the exercise. Our aerobic and anaerobic energy systems are trying to fulfill this consumption, and both systems produce energy simultaneously. The question is: The exerted influence on each other is supportive or suppressive?
If the intensity is low, the aerobic system can produce enough energy, and the anaerobic system works on a low level (t0-t1). In this case, the aerobic is the dominant energy system. If the intensity goes above the AT level, the anaerobic will help the aerobic, but the aerobic remains dominant (t1-t2). If the intensity increases, the anaerobic support will increase too. When the aerobic system reaches its maximum energy production capability (t2), the anaerobic system becomes dominant and starts suppressing the aerobic.
As the intensity increases, the anaerobic system's energy production and dominance increase as well, and it suppresses the aerobic system to a greater extent (t2-t3). At t2, that is the momentary SEP value.
Aerobic and Anaerobic energy systems
SEP, the Safe Energy Production, shows the momentary maximal energy generation that the aerobic system is capable of with aerobic domination.
What does that exactly mean, and how do you use it? Let's see!
How to use SEP?
The mnsX continuously monitors the aerobic and anaerobic energy systems and calculates SEP during the training session. However, it is important to note that SEP is NOT the momentary energy generation. It is the maximal energy that the aerobic system can generate with aerobic dominance at that moment. SEP value is relative, and its range is 0-100%. It is also important to note that the effort that belongs to 100% is changing from training to training.
(For more information, please check the monitoring page.)
The main goal of mnsX is to ensure safety at high-intensity training. Serial HIIT sessions do not reduce the aerobic energy generation capability, the endurance, that has been built up over a long period of time. Additionally, mnsX provides users with real-time feedback, indicating whether they are in the appropriate power zone to improve their desired ability or if their effort is higher or lower than it should be.
I will use Figure 1. to illustrate how to use, read, and understand SEP. This HIIT is designed to improve anaerobic capacity. The red line represents SEP, while the blue line represents anaerobic support. The anaerobic system supports aerobic energy generation if the effort is above AT. The anaerobic support can be either supportive or suppressive.
SEP figure 1
Figure 1. (Click to open)
Is the energy generation safe or not?
Energy generation is aerobic dominant and safe: as a result of increasing intensity, SEP increases, even if slowly.
Energy generation is anaerobic dominant and unsafe: as a result of increasing intensity, SEP decreases rapidly, much like an avalanche.
Safe and Unsafe energy generation
Safe and Unsafe energy generation
Anaerobic overload
During warmup, SEP slowly increases (t1-t5). When the intensity is below CP20'/FTP20', SEP slowly follows the intensity change. If the warmup is decent and the effort is continuous at CP20'/FTP20', SEP can reach 100% (t6-t7).
SEP's behaviour below CP20'/FTP20'
SEP's behaviour below CP20'/FTP20'
However, if the intensity is above CP20'/FTP20', SEP can rapidly change. When the anaerobic support becomes suppressive, the aerobic system is overloaded. SEP instantly starts decreasing (t10-t11, t13-t14, t16-t17).
Anaerobic overload is necessary for adaptation when you want to improve some of your abilities. However, without total control, the regular suppression of the aerobic system can cause a reduction in endurance. Aerobic system regeneration is crucial between HIIT intervals. The aerobic system is regenerated when SEP's value reaches at least the same level as it was at the start of the previous high-intensity interval. The dynamic of aerobic system regeneration fundamentally depends on your aerobic capacity and your momentary fatigue (good: t11-t12, bad: t14-t15).
SEP's behaviour above CP20'/FTP20'
SEP's behaviour above CP20'/FTP20'
SEP in “normal mode”, when intensity is below CP20'/FTP20', reacts slowly to changes in intensity. However, when intensity exceeds CP20'/FTP20', it takes seconds for SEP to react, and within a few seconds, SEP decreases significantly (t10-t11, t13-14).
After the high intensity is reduced, it takes a few seconds for the aerobic system to start regenerating. It usually takes a few minutes for the aerobic system to regenerate completely (t11-t12, t14-t15). (For more information about endurance reduction, please check the monitoring page.)
Real-time feedback
After a high-intensity section during a long race or training, or after a high-intensity interval during HIIT workout, proper regeneration is crucial before starting the next high-intensity effort. Regeneration is considered proper if SEP regenerates back to at least the same level as the start of the previous high-intensity interval. Ability improvement (adaption) occurs during the regeneration phase in HIIT. If regeneration is improper, it can lead to a reduction in ability rather than improvement.

During training, mnsX sends data to your Garmin device, which displays information similar to that shown in Figure 1. Additionally, Garmin uses sound alerts when anaerobic support becomes suppressive, indicating anaerobic overload. You can monitor in real-time when the anaerobic overload occurs and observe the regeneration process between each interval. Thanks to real-time feedback during training, you can adjust the training protocol at any time to ensure proper regeneration between intervals and avoid a decrease in ability.
The total energy generation capability (in case the 'race' duration is more than 30 seconds) is the sum of aerobic and anaerobic capacity. When aiming to improve anaerobic capacity, it's important to maintain endurance (aerobic capacity).
In Figure 1, you can observe a HIIT workout designed to improve anaerobic capacity but with an inadequate training protocol (similar issues can arise when overstraining the improvement of VO2 max). The athlete has to perform sprints from a race-cruising speed.
SEP figure 1
Figure 1. (Click to open)
During the first sprint, the significant anaerobic dominance suppresses the aerobic system, causing SEP to decrease rapidly (t10-t11), which is a normal response. The R1 regeneration phase (t11-t12) and subsequent race-cruising speed phase (t12-t13) help in the aerobic system's recovery, allowing SEP (t13) to regenerate to the same level (t10) as the previous sprint started.
The sprints' intensities appear to be too high, as SEP decreases even more significantly during the second sprint (t13-t14). After the second sprint, aerobic regeneration notably slows down due to fatigue. In the R2 phase, the rise of SEP diminishes (t14-t15). By the end of the race-cruising speed phase (t16), SEP fails to fully recover to its previous value (t13) because of fatigue and higher sprint intensities.
The athlete has two options to address the aerobic regeneration issue: either lower the sprint intensity to perform more sprints (preferred for anaerobic capacity improvement) or increase the duration of the regeneration phase (which treats the problem but isn't a complete solution).
SEP regeneration process
SEP regeneration process
The example training protocol remains unchanged, and sprinting at the same intensity exacerbates the situation, causing a further decline in SEP (t19-t20). The athlete “dies” and can't continue the training protocol.
It's crucial to note that if this situation occurs, the athlete shouldn't stop training in a 'dead' condition. Instead, athlete should focus on regenerating his/her aerobic energy system. Otherwise, not only endurance but also the ability to regenerate between two training sessions will be reduced.
The athlete attempts to raise SEP to the starting level (t10) by regenerating with mini-intervals (t21-t22). However, because of the unchanged training protocol, the ahtlete is forced to stop training after the fourth sprint.
SEP regeneration with mini-intervalls
SEP regeneration with mini-intervalls
Once more, this is an example of an inadequate HIIT protocol. The athlete had mnsX but didn't adjust the training protocol… By using mnsX and monitoring SEP, you've got the power to adjust the training protocol anytime during training, maximize the training efficiency, and improve the desired ability while not reducing others.
Next: Monitoring
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