What Does Workload Do To Your Brain?
- Jaime K. Devine, PhD
- 2 hours ago
- 4 min read
Work is tiring. It’s the reason we introduced a Workload Calculator in SAFTE-FAST version 4 (white paper here) and it’s the reason that the International Civil Aviation Organization (ICAO) includes workload in their definition of fatigue. SAFTE-FAST models the workload associated with a predictable job tasks using the Workload Calculator, which can be configured to the user’s specific operational demands. SAFTE-FAST also provides an estimate of all-cause fatigue with our Combined Capacity metric (white paper here). All right, so, we know that increased workload is related to increased fatigue, and we can predict the workload associated with job tasks and how that may interact with fatigue due to sleep loss or circadian misalignment… but why does work make you tired in the first place?
Workload is a term that can either describe time on task, physical labor, or mental effort. When it comes to biomathematical modeling, time on task is the easiest aspect of workload to account for. The longer you are working, the longer it has been since you last slept. The longer you go without sleeping, the more you will want to sleep. The Sleep Reservoir metric already accounts for continuous time awake.
How physical labor impacts fatigue is easy to understand if you’ve ever decided to take a CrossFit class that one time thinking it might be fun. Physical exertion creates fatigue by affecting the biochemical equilibrium within the muscles. Your muscles run on a fuel source (metabolites). Using your muscles to excess means that at some point, the muscles will run out of fuel. Then, you will need to stop. You will feel fatigued and want to rest. Physical fatigue is also related to slower response times on the psychomotor vigilance task (PVT)[1].
Mental labor also makes you feel tired. It isn’t just ephemeral ennui—mental workload is related to observable changes in the brain the same way that physical workload is related to observable changes in your muscles. I have used the metaphor that compares the human brain to a smart phone before. It makes sense to people that the less battery your phone has (Sleep Reservoir) and the more apps you are running simultaneously (Workload) can affect how well your phone works. The brain is a complex computer that requires resources and energy to respond to a query in the same way that AI does (more info on AI energy use here).
Neuroimaging laboratory studies have given us a fairly good idea of what happens to the brain during and after cognitively-demanding tasks. These studies use functional magnetic resonance imaging (fMRI) or electroencephalogram (EEG) to visualize activity in the brain. These studies show that as mental workload increases, brain activity changes [2]. Specifically, there is more slow wave activity (SWA), a type of brain activity usually associated with deep sleep. Brain signals become less synchronized and the amplitude of activity in the brain diminishes.
These changes suggest that the mentally-fatigued brain slows its overall activity, which results in diminished cognitive abilities. The changes in brain activity when someone is mentally fatigued are similar to the changes in brain activity seen when someone is sleep deprived or when they have consumed alcohol [2,3]. This makes sense given that mental fatigue, sleep deprivation, and alcohol intoxication result in similar behavior changes as well (i.e., slower reaction times, diminished executive function, reduced alertness, etc. [4-6].
The human brain is a complex machine that requires proper care. Sleep, hydration, nutrition, regular exercise and mental wellness are some ways that individuals can protect their brains from unnecessary wear and tear. Organizations can help by ensuring that work schedules allow access to sleep, exercise, meals, and time for relaxation. Using features like the Workload Calculator and Combined Capacity metric in SAFTE-FAST can further help organizations create schedules that are not pushing operators to the limits of their cognitive abilities by budgeting time for rest or limits on the amount of workload experienced at a given time.
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