“He is best that is trained in the severest school”
-Thucydides
New Zealand is a small country and yet their SAS regiment has to maintain the capabilities and lethality of their larger commonwealth SAS peers in Australia and Britain, to the point of seamless integration on joint operations. For this reason, I have been greatly inspired by the NZSAS, specifically their selection and training, for its high demands for constant performance. Though the NZSAS is closely modelled operationally off the British counterpart, their selections are different. Joe Hotai, who went through both the NZ (10 days + 9 Months) and Australian (3 weeks + 16 Months) SAS selections, NZSAS was much harder. All the information I am about to share is generalized for the sake of brevity, but there is more detail on msigwarrior.com or YouTube.
The use of sleep and food deprivation in NZSAS training is not only great for compounding/magnifying mental and physical fatigue, but it can be used as a training tool. At least weekly I will fast through the day and train and workout through the night. In fact that is how most of this article was written. Every hour I am doing a 5-10 minute workout, high paced precision weapons training under a timer, or running my dogs for 2 miles under a timer. After I pull an all-nighter, I will break my 24 hour fast and continue on the following day like normal (breaking a fast always drains you like after having a huge meal), hitting my workouts hard despite being sore, concentrating on my weapons/medical training despite having difficulty focusing, and absorbing new information despite having difficulty concentrating. After the day is done, I do active recovery and prep for the next day. By the time I lay my head down at night, my body will have cut a lot of fat and my brain will be quick to go into REM. This type of training renews your sleep/rest cycle and burns alot of fat. Not to mention that you can adapt to sleep deprivation and perform better and better as you experience it more. You can legitimately train to operate under sleep deprivation as you can train your body to run continuously for hours in a marathon.