Breaks are certainly an inevitable occurence, in the course of day spent studying, but there is good chance that you've never considered these few periods of your life a tool which can be leveraged in favour of your productivity.
I've have fallen as frequently into the practice of running as I have out of, and have come to realise that each attempt was only successful when the act of running required me to think of intentionally what I was doing, or rather not doing outside of the short 30 min activity. When I first entertained the idea of running, I would leave the house in suitably sporty attire at just /try/ to run for 20 mins straight. I would eventually tire out 5 mins in, walk for 15 mins back home - obviously exhausted and not motivated to begin again.
When one of runner friends heard that I'd tried and failed in passing, he was visibly excited to induct me into the sport and, much to my chagrin, visibly amused at these first attempts. He then advised that I run for 1 minute and walk for 1.5, and repeat this pattern for 30 minutes, no more than 3 times a week and then each week incrementally reduce the time spent walking or increase the time spent running. This was revolutionary stuff to unseasoned runner, and thinking on precisely why it works, is hugely transferable to the art of studying.
The most important part of that program was not running till exhaustion. You might ask if I knew I could run for at least 5 minutes straight, why would I run for just 1. Well good sir, if I had run for 5 mins straight, it would take me 15 mins to recover enough to run 5 mins again, and after this 5 minute interval, it would take me 30 mins to recover enough to run another. Recovery time would keep increasing as my legs and mind grew wearied and after 1 hour of being "on a run", I would only been "running" for 15 mins. Terribly inefficent! However by recovering before I was completely exhausted, and I could run for 24 mins per hour.
That a jump from 25% to 40% time spent training, and the difference would be even larger the longer the sessions progressed. I admit however that at short intervals: say 25 mins, both methods would yield 10 mins of running, but nevertheless the analogy holds!- as we tend to study for 3 or hours at a time rather than 30 mins. Furthermore we are less tired at the end of run even though we spent more time running, as recovering completely from exhaustion takes much longer than from slight fatigue. What this translates to in the language of productivity is that we have the potential to learn more and feel less tired while doing so.
1. Take breaks before exhaustion - you can study for longer and feel less tired doing so.
PS - Practically this may mean taking breaks more frequently, but this is a trap. The pomodoro methods consists of working for 25 mins and resting for 5, which seems to follow the principle above, but it does not work for most types of work. In fact, it seems to work best for mindless, passive "work", which learning should not be if it seeks to be time-efficient.
What I truly advocate is taking a break as soon as you sense the first soft touches of fatigue. Please fight the urge to push on - if you know you will have to return to this within the at most the next hour.
2. In pushing on, you are working towards the undesired outcome.
Crucially this means, depending on the work being asked of you, you may feel this occurs 30 mins, or 90.
Being aware of your mental state allows you take breaks before exhaustion, while taking breaks frequently, excessively incurs the start-up and wind-down cost of taking breaks, which will be in the discussed next post.