Training until the mind (and sometimes other body parts) are numb with boredom or pain offers both benefits and detriments in one's training.
Mind-numbing training (MNT) consists of challenging, repetitive, or boring tasks, or a combination thereof, that take place continually over a long duration.
Examples of mind-numbing sessions include:
A few hard, short repeats on [airbike/rower/SkiErg] do not qualify, as they generally aren't boring or long enough to elicit the desired effects.
For those serious about training, pain tolerance should be a staple in the regimen, whether developed in specific, standalone sessions (applicable to the discipline the majority of training is geared for or not—both work) or as a part of a standard training session. I don't know if a consensus has been reached on if pain tolerance can be trained, i.e, holding a certain RPE or RPE range over a longer period of time. I vote it is. There are many ways to deal with pain, allowing the athlete to continue the effort longer than they would had those tools not been at their disposal. As to finding those ways, it's a subjective experience only the athlete can find out. What works for one may not work for the other.
Pain tolerance deals with the mental aspect just as much as, if not more than, the physical side of things. Muscles burn, the mind begs the muscles to stop working; lungs gasp for air, the mind tries to rationalize the decision to quit; the feet are blistered and raw, the mind asks why, what's the point of this torture? The mind and body are interconnected, making it rare for only one to be trained at a particular time. In general, however, the body is the first to ask for relief, quickly followed by the mind after the signals of discomfort come knocking.
MNT contradicts this generalization, instead often bringing the mind to its threshold for wanting to quit before the body has a chance to send an S.O.S. After 40 minutes of climbing the same hill 10 times, the mind is gone: it's the same trees, the same potholes, the same number of sidewalk slabs that have been there the last 9 times. The legs and lungs feel fine, it's only been 40 minutes. Another 10 hills go by as the legs begin to complain and the mind is talking louder, trying to explain why it's okay to stop, give up, quit. The irrational mind refuses its more reasonable sibling's efforts, continuing to will the legs forward unto more pain.
It is in moments like these—where both physical and mental anguish are being experienced—that MNT becomes valuable. The athlete learns to deal with the voices in their head and burning in their body in moments like these, finding out what works for them and what doesn't, taking notes for future occurrences, as similar situations are bound to happen on the training journey.
Similar to pain tolerance, discipline can be trained and improved upon. Committing to and finishing a hard session requires discipline: the athlete is following the rules they set for themself. Doing this for weeks in a row results in what I refer to as "discipline momentum", the idea that practicing discipline reproduces it into a stronger form. Discipline momentum is not exclusive to one aspect of life, e.g., discipline in exercise can carryover to producing discipline in academics. This is a similar idea to McRaven's suggestion to make beds in the morning:
If you want to change the world, start off by making your bed. If you make your bed every morning, you will have accomplished the first task of the day. It will give you a small sense of pride, and it will encourage you to do another task, and another, and another. By the end of the day, that one task completed will have turned into many tasks completed.
Continuing to train until the mind is numb requires immense discipline both intra- and inter-session: it's challenging to both continue another hour or two past numbness and do it again the next week. But the provided value is well worth it. Discipline improvements will be seen in the rest of training and any other pursuits in life.
Complete thoughts on boredom can be found here, but the final paragraphs provide some main discussion points:
Boredom implies monotony, which implies consistency, which produces results (along with other required factors, of course). Consistency is quite often the key to progress in most realms. Training? Check, strength and conditioning progress will be lost if there's no training being performed. (I'm leaving programming out of this paragraph, as the principles are not necessarily learned in the same way a foreign language's vocabulary is.) Language learning? Check, rules and vocabulary begin to be forgotten. Investing? Check, not putting money in regularly leads to low gains or purchasing investments at higher values. Weight loss? Check, a 500 calorie deficit one day doesn't make up for a 600 calorie surplus the next—the caloric deficit needs to be maintained on a consistent basis, as an entire week's worth of effort can be destroyed in one meal.
The misconception that in order for something to be effective it must be exciting—or at least not boring—is endemic in society. Companies are aggressive in claiming how their product is not boring, which makes obvious sense from a business standpoint, but not from a progress standpoint. Next time either boredom or excitement is felt, consider the role it's playing and the benefit it's providing. From there adjustments can be made.
Boredom educates. Boredom moderates. Boredom progresses.
Motivation can decrease rapidly with MNT, below the threshold of required to maintain discipline. Who looks forward to being bored to death early on a Saturday morning, regardless of the benefits it provides? The dread of another MNT session is overwhelming, enough that discipline can't compensate for it and the session—and in some cases, momentum of training–are cancelled.
Training regulations must be put in effect to avoid this issue. First, like any athlete, the goals of pursuing MNT must be well-defined and purposeful. Ill-defined goals ultimately lead to quitting: no reason for MNT leads to rationalization, resulting in quitting. What does the athlete hope to get out of MNT? Is there another, easier way that is close to or even more effective? Second, a frequency limit must be put on MNT sessions, for the body and especially the mind, as both are heavily taxed during such efforts. This limit is subjective, but no more than once per week is a good baseline. I've found that motivation falls post-MNT, only to gradually rise again over the coming days. The limit should be low enough that both mind and body are recovering from the sessions while still allowing the sessions to be performed and successfully completed. The "successfully completed" part is important. Success builds confidence and improves outlook on the next session; failure does the opposite. Third, the session cannot be too difficult to the point of quitting and never returning back to it. There is progression to MNT: 20 hills one week, 25 the next, 35 the next, and so on. Jumping straight into a "see god" session with minimal preparation is a recipe for disaster.
This prompts the question: how is lack of motivation reconciled with discipline? As said before, there is some lower motivation threshold that is required for discipline to be active—if motivation is below that, nothing can be done until it's brought up. This varies by time, by person, and by activity. Time in that some days/weeks/months/years it may be different; person in that everyone has different thresholds; activity in that cycling's threshold may be lower than running. However, in personal experience, I've found that while the threshold doesn't move much during the session, simply starting the session can cause my motivation to jump from just above the threshold to well above.
Commit to at least two MNT sessions over the next month. Climb a hill for a few hours, pick a movement and number and do a SMMF, something. Learn how the mind tries to escape and find ways to trick it to last longer and go farther. Learn to understand and—gasp!—enjoy the suffering that comes from this type of training. Learn to be uncomfortable for long periods of time because it's going to happen at some point and as Schwarzkopf so wisely said:
The more you sweat in peace, the less you bleed in war.