What does thinking look like? If I’m running a marathon or swimming, I can see which parts of my body I’m using and the ensuing pain tells me I’m overdoing it. But thinking isn’t like that: I can’t see it happening so over-exertion doesn’t trigger alarms. This means it’s easy to ignore a simple fact: thinking is a physical act.

The organ we use for thinking is our brain and just like all other organs, it has its limitations. Research into human productivity began in 1888 with Ernst Abbe at the Zeiss lens laboratory. He demonstrated that we can work well for about 40 hours a week, after which productivity drops. Why? Because we get tired and make mistakes – and then need extra hours to clear up the mess.

We get tired and make mistakes – and then need extra hours to clear up the mess.

No subsequent research has ever seriously changed this finding. We can work longer days in crunch mode, but only for short periods of time. A forty year study of civil servants found that those who’d worked a 55 hour week routinely performed more poorly when tested for vocabulary, reasoning, creativity, problem-solving and reaction times: all the things they were needed for. And their risk of depression and early dementia had doubled.

You can’t see this damage but you can feel it. And you can prevent it. On recognizing that throwing unlimited time at problems won’t solve them (but might make them worse) most people become more thoughtful about where they spend their time. Some companies have become highly creative about this. Recognising that there are essentially two kinds of work – ‘real work’ which involves quiet concentration and ‘everything else’ which includes meetings, phone calls, email and the all-important office football pool – has encouraged some organisations to schedule different work for different times.

A Canadian company forbade meetings or interruptions before 10am; this meant anyone with a big thinking project might get in early, confident of several hours’ thinking time. A food business forbade anything but ‘real work’ after 4pm. These simple rules had two benefits: the real work got done – but the rest of the time people were more relaxed, knowing the thinking time they needed was protected. Managers initially resented the loss of their power to interrupt – but not when they saw the productivity gains.

The brain you take to bed is not the brain you wake up with.

Sleep matters too – and not just because losing one night's sleep is cognitively equivalent to being over the alcohol limit. The brain you take to bed is not the brain you wake up with. When we are asleep, our minds consolidate, organize and review recent memories and experiences – and that restructuring produces insights. Mendeleyev, the father of the periodic table, is said to have gleaned its underlying principle in a dream; Larry Page says the idea for Google came the same way. These aren’t flukes; they’re evidence of the work your brain will do for you – if you give it the time it needs.

Allowing your waking mind to wander can sometimes have the same effect. When we focus too hard on work, we become inflexible and unreceptive to new ideas and patterns. But when we look away from work, we access other parts of our brain that help us see patterns and retrieve relevant information.

Playing Mozart or doing brain gym exercises won’t make any difference, but physical activity will; walking in particular increases creative output by around 60 percent. Walking outdoors appears to produce the greatest number of new ideas while also renewing previously exhausted cognitive capacity. It’s counter-intuitive but when you’re stuck on a problem at work, often the most productive thing you can do is stop and take a walk.

I love my work enough to want to do it well – and that means the equipment needs to be well maintained.

I wish I’d known this sooner. I routinely used to throw time at problems and took pride in my apparently infinite capacity for work. Now I think that time is my most precious asset because I can’t make more of it. So I cherish it, want to use it well and spend it on the things that matter. I try to use travel time as mind-wandering time, I don’t work weekends and if I have an 18 hour day today, I’ll schedule recovery time tomorrow. I love my work enough to want to do it well – and that means the equipment needs to be well maintained. I also bought a dog so I’d walk more. I just haven’t yet convinced the tax authorities that he is a business expense. They should read the research….