I'm sure you have conducted an interview or interrogation for a couple hours and afterwards you walked out of the room physically and mentally drained! It's not like you were lifting weights or running on a treadmill, so why does an intense interview or interrogation take such a physical and psychological toll on you, and what can you do about it?
We talk to people all day and don't get drained like that. Think about it; at a house party or bar you may spend the same amount of time talking with someone about their vacation, their job or their family and walk away fine, even invigorated at times! Although you were talking for the same amount of time, the cognitive demand placed upon an interviewer during an investigative interview or criminal interrogation is tremendous! What's interesting from a biological perspective is that on a regular basis our brain consumes roughly 25% of our blood glucose, our energy source, and the more stress and mental energy we face the more fuel our brain uses. This is why you get physically and mentally drained during an investigative interview or criminal interrogation!
Take this into consideration next time you are preparing for an interview or interrogation and fuel up your body so your mind stays sharp! Snacking on some brain-healthy foods such as dark chocolate, nuts, blueberries, or avocado, in addition to a little caffeine boost with some coffee or tea, may help feed your brain power. Avoid doughnuts and sugary foods as the boost may be temporary but then then you will likely crash and lose focus easily.
Also, make sure you fuel up your mind and continue to get ongoing training and practice your skills so they become second nature. Doing so will make it one less thing for you to consciously worry about during an interview freeing up more of your cognitive abilities. If your training and skill level is high and you function with "unconscious competence", you won't be consciously worrying about tactics and techniques during your interview and you will be able to more effectively focus on the task at hand...question effectively, listen with forensic intensity and to get the truth!