Well, then, what do you need to do to acquire that kind of stamina?
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I have but one answer, and a very simple one: you have to become physically fit. You need to become robust and physically strong. And make your body your ally.
This is all my own personal opinion, of course, based on my own experience. There might not be any universal application. But I’m speaking here as one individual to begin with, so my opinions are, no matter what, individual and experiential. I’m sure there are differing opinions, but you need to hear those from other people. I’m only giving my own personal opinions here. It’s up to you to decide if there’s anything universally applicable about them.
Most people think that since the work of a novelist just involves sitting at a desk and writing, it has nothing to do with physical stamina. They seem to think that as long as you have enough strength in your fingers to tap away at a computer keyboard （or write on paper with a pen） that’s all you need. There’s still a deep-rooted sense that writers are, in the first place, unhealthy, antisocial, and unconventional, so maintaining good health or physical fitness is beside the point. And to some extent I can understand that objection. Such a stereotypical image of writers is not easily overcome.
However, if you try writing yourself, you’ll no doubt understand that sitting at a desk in front of a computer screen （or even at an empty orange crate with manuscript paper on top, there’s no difference） every day for five or six hours, focused solely on creating a story, requires an extraordinary amount of physical strength. When you’re young this might not be so hard. In your twenties and thirties you’re brimming with vitality and your body doesn’t complain when it’s overworked. Focus and concentration, too, are relatively easy to summon up when needed, and can be maintained at a high level. It’s truly wonderful to be young. （Not that if I were told to relive my youth I’m sure I’d want to.） But generally speaking, once you reach middle age, unfortunately, physical strength declines, dynamic strength deteriorates, and you lose stamina. Your muscles atrophy, and you put on unneeded pounds. As far as our bodies go, the bitter truth is that it’s easy to lose muscles and easy to put on weight. And to make up for that decline, sustained, self-directed effort is needed to maintain one’s physical strength.
And as physical strength declines （I’m speaking in general terms here）， there is a subtle decline in mental fitness, too. Mental agility and emotional flexibility are lost. Once when I was interviewed by a young writer I declared that “once a writer puts on fat, it’s all over.” This was a bit hyperbolic, and of course there are exceptions, but I do believe that for the most part it’s true. Whether it is actual physical fat or metaphoric fat. Most writers are able to compensate for this through improved writing technique or a more mature consciousness, but there is a limit to these as well.
Recent research shows that aerobic exercise leads to a rapid increase in the number of neurons produced in the hippocampus in the brain. Aerobic exercise is sustained exercise such as swimming or jogging. However, if left as is, in twenty-eight hours these newly formed neurons will disappear without having served any purpose. It’s a real waste. But give these newly formed neurons some intellectual stimulation and they are activated—they connect with the network in the brain and become an organic part of the signal-transfer community. In other words, the network within the brain becomes broader and denser. The ability to learn and remember is elevated. And this makes it easier for our minds to respond to changed circumstances and for us to display exceptional creativity. We can think in more complex ways and can come up with bolder, original ideas. In other words, the everyday combination of physical exercise and the intellectual process provides an ideal influence on the type of creative work the writer is engaged in.
I began running once I became a full-time writer （I started when I was writing A Wild Sheep Chase）， and for thirty years running for an hour a day, or sometimes swimming, has been a regular part of my daily schedule. Perhaps I have an inherently strong constitution, but during this time I’ve never been seriously ill and never hurt my legs or back （though I did sustain a torn muscle once when playing squash）， and I have continued to run every day with hardly ever taking a break. Once a year I run a full marathon, and I’ve participated in triathlons as well.
People tell me I must have a strong will, running like that every day, but the way I see it, it’s much more physically trying for ordinary company employees who ride in crowded commuter trains every day. Compared to riding for an hour in a rush-hour train, running for an hour outside whenever you feel like it is nothing. It’s not that I have a particularly strong will. I enjoy running and am just continuing something that suits my personality. No matter how strong your will might be, you’re not going to do something for thirty years if it doesn’t suit you.