Sleep deprivation shows first in alertness

Four sleepless nights are enough. At that point at the latest, performance collapses. Every night before that has already weakened endurance noticeably.

Progress comes from the ratio of exertion to rest

Performance only develops when exertion and recovery are in a workable ratio with each other. The same applies to physical fitness and to mental wellbeing. Neither side develops on exertion alone.

Rest is therefore not the opposite of training but its condition. Without recovery, exertion stays nothing but exertion.

Enough good sleep repairs the day's exertion. It restores energy and alertness. The repair happens during sleep, not over the course of the next day.

Sleep also carries you through physically hard days. It supports concentration as well, and concentration makes learning something new easier. Hard days come one after another during a training period, and each of them rests on the previous night's sleep.

Alertness weakens first

The largest visible changes from sleep deprivation are in wakefulness and alertness. Those are exactly what is needed in the field the whole time.

Too little sleep lowers performance and slows the development of skills. The return on training shrinks in exactly the part the exercise was undertaken for. Learning something new requires concentration, and concentration is among the first things sleep deprivation takes.

Sleep deprivation also increases the risk of mistakes and dangerous situations. That is a practical reason to hold on to sleep even when the schedule is tight.

In the field the effect is greater

The effect is greater on field exercises. Physical and mental load rises there more readily than in training given at the barracks. The importance of sleep therefore grows at exactly the point where arranging it is hardest.

Sleep deprivation that has continued for a long time puts the body into a state of stress. That state of stress in turn works against recovery from physical exertion.

The situation is difficult precisely because the peak of the load and the obstacle to recovery fall at the same time.

The deficit is covered with short rests

When sleep is unavoidably short, the deficit is covered with short rests and naps whenever that is possible. Moments of rest are taken when they are available. A more suitable moment is not waited for.

Short rest is worth practising during exercises. Then it also works when it is genuinely needed.

Under load the order of priority is simple: look after yourself, eat and sleep whenever it is possible.

Free time belongs to recovery

Choices made in free time also affect recovery. Time is set aside for sleep, for rest and for active recovery such as moving about outdoors. Sleep, rest and light movement are three different things, and time is set aside for each of them separately.

Recovery therefore does not begin only after the exercise. It belongs to the same week as the exertion.

Sources

• Sotilaan käsikirja (Soldier's Handbook, 2024), pp. 210 and 211. A public guide of the Finnish Defence Forces.