Melissa leads a global team launching a new product. With colleagues spread across time zones, calls start early and often run late into the evening. More than 60% of her day is spent in meetings, while the remaining time is fragmented: she starts a report, gets an MSTeams message, checks her dashboard, replies on WhatsApp and 20 minutes later can no longer remember what she originally sat down to do. Increasingly, she struggles to switch off and sleep well.
When we equipped Melissa with a heart rate variability (HRV) measurement device, the data were troubling. For most of the day, her body remained in a state of high sympathetic activation, indicating she was stressed. This was puzzling: the product launch was on track, and her team was functioning. But the density of activity, the length of the day and the constant need to respond and keep things moving had created what felt like the HRV signature of frantic.
The 47-second workday
Gloria Mark at UC Irvine has tracked screen attention for two decades. In 2004, knowledge workers spent an average of 2.5 minutes on a single screen before switching. Today, the average is 47 seconds. Half of all screen sessions are shorter than the time it takes to read this paragraph.
The recovery cost is even steeper: it takes around 25 minutes to fully re-engage with a task after an interruption. A worker who switches every 47 seconds never reaches the depth where meaningful cognitive work occurs. They are perpetually reorienting.
What the body is doing while the mind is switching
When we measure executives and teams across a full working day using HRV, a clear pattern emerges. Most “work stress” comes not from the task itself, but from the physiological cost of constant switching – the inner tension of staying endlessly “on it.” Each ping, tab change and context shift triggers a small sympathetic stress response – a micro-burst of cortisol and noradrenaline. Repeated hundreds of times a day, these keep the nervous system in a prolonged state of elevated arousal that never fully resolves.
In our screening data across more than 1,800 professionals, we also found individuals with very different patterns. Some meetings required high activation, but much of the day remained low-intensity — and during two to three hours of focused email blocks or concentrated report drafting, HRV data even showed parasympathetic recovery. Unlike Melissa’s 10 hours of near-continuous activation, they had two hours of high activation, four hours of low and three hours of recovery.
Fragmented attention is a symptom and a cause of high stress. Laboratory studies of task-switching consistently show suppressed vagally mediated HRV and a measurable drop in nonlinear HRV dynamics within the first 15 minutes. The body reads constant interruption as a continuous low-grade threat. Subjectively, this is the “draining day” — even when nothing meaningful was achieved.
An economy with a focus problem
This is no longer just an individual well-being issue. In a Bank of England Bank Underground post, Dan Nixon suggested that the productivity weakness across advanced economies may partly reflect a collective “crisis of attention.” The argument is twofold: the direct cognitive cost of interruptions – including 25-minute recovery times and IQ drops linked to constant notifications – and the habit-forming nature of constant notifications. People who are repeatedly interrupted become more likely to interrupt themselves, even when no notification arrives. The mind learns to fragment.
Global smartphone shipments rose roughly tenfold over the same decade, while productivity flatlined. That is not proof of causation. But it is a hypothesis we have largely failed to test seriously, and the physiological data are increasingly consistent with it.
AI will push us further in this direction — unless we choose otherwise
Early evidence suggests AI may intensify this pattern before it eases. Deloitte’s 2025 Workforce Intelligence research found mental fatigue and cognitive strain now predict burnout more strongly than workload volume. Microsoft’s 2025 research on heavy AI users found cognitive effort is shifting from generating output to evaluating it — a mode that, paradoxically, can be even more draining. A typical AI-augmented task often involves constant switching between tools, with each handoff carrying a physiological cost.
The phrase “AI brain fry” is now appearing in the literature for precisely this reason. AI does not remove decisions; it multiplies them. Used well, it can be a focus tool. As it is currently deployed in most enterprises, it multiplies interruptions.
Treating attention as infrastructure
The implication for leaders is uncomfortable but clear: attention is no longer a personal habit, but organizational infrastructure. The same employers who would never tolerate a building without quiet rooms still tolerate workflows that make uninterrupted thinking impossible. Three shifts make a measurable difference: protecting focus time at the team level, reducing default notifications and training attention like any other performance capability.
Melissa does not lack discipline. She is operating in an environment that makes focused thought biologically difficult, and constant switching feels necessary. Reverse those defaults and her nervous system — and her thinking — will change within weeks. Leave them in place, and we should not be surprised that the most expensive cognitive workforce in history is producing less, feeling worse and increasingly unable to say why.
Opinions expressed by SmartBrief contributors are their own.
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