“The precision of entrainment is vital if the organism is to be at peak performance.”
- Russell Foster and Leon Kreitzman
Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing
“Does anybody really know what time it is?
Does anybody really care?”
If you’re like most trainers, you like to offer your clients and athletes a holistic experience, one that offers benefits to mind, body and spirit. Chances are you spend a lot of time on diet and exercise and maybe add some stress education as well. That’s a good start, but if you really want to make things comprehensive, you’ve got to add in one additional element: light.
Light is usually underrated as a factor in human health, but we are now beginning to understand just how crucial it is in guiding our physiology and performance. Modern discoveries in chronobiology are revealing the power of light in health, disease, psychology and happiness. As it turns out, light acts as a master force, tuning and synchronizing every process in the human body.
The story begins deep in human prehistory, on the semi-wooded grasslands of East Africa. Over the course of thousands of generations, our bodies were bathed in regular cycles of natural light and darkness. Humans are equatorial animals, evolved to live in an environment where daylight and darkness are almost precisely 12 hours each, all year round. Our entire hunting and gathering lifestyle was built around the position of the sun. Every action and movement was linked to light conditions (only a fool goes hunting at night or during the heat of mid-day). Ultimately, our health became inextricably linked to cycles of illumination.
But today, we find ourselves having to contend with a new kind of world, a world that I like to call “an alien environment.” This modern world is alien in many ways of course. It’s obvious, for example, that we live in an alien nutritional environment (non-natural food products), an alien acoustic environment (chronic noise), an alien social environment (non-tribal living) and an alien kinetic environment (sedentary living). What may be less obvious is that we also live in an alien circadian environment, a world in which our physiology is scrambled by chaotic, non-natural light. This simple fact is now proving to be a far greater challenge to the human body than anyone realized. In the years to come, trainers, therapists and body professionals of all sorts are going to be waking up to the importance of circadian health.
The Master Rhythm
When it comes to understanding the fundamentals of the human body, the key point to keep in mind is that all animal physiology is fundamentally rhythmic and that one master rhythm holds sway over every other, which is known as the circadian, day-night rhythm. All animals, including humans, are intimately connected to this cyclic pattern. All organisms on earth are driven by circadian cycles.
The story of chronobiology has recently been told in Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing by Russell Foster and Leon Kreitzman. Foster and Kreitzman tell a fascinating story of scientific discovery, and the basic fact comes down to a simple bit of neuroanatomy. That is, the human brain comes equipped with a circadian pulse generator called the suprachaismatic nucleus (SCN). This bit of tissue consists of a mere 20,000 neurons that keeps a circadian beat, roughly timed to 24 hours.
This is plenty astonishing in its own right, but even more fascinating is the fact that this endogenous pulse generator is only a blunt timing instrument that approximates the earth’s circadian rhythm. To manage physiology effectively, it needs to be fine tuned (entrained) by actual environmental conditions, specifically by exposure to direct, natural sunlight.
The crux of the problem is that our modern world provides weak, ineffective cues to day-night cycles. Unnatural light sources scramble our physiological rhythms and wreak all sorts of downstream havoc with our health and fitness. From the modern body’s point of view, it is almost as if dawn and dusk are constantly shifting in random patterns. It is no wonder that we’re confused. We are literally cue-less.
The problem is most pronounced in those of us who try to live on the wrong side of the clock such as shift workers, airline pilots and college students. But even for those who practice roughly diurnal lifestyles, things can still go astray. We stay up late into the night and/or get up before dawn. We watch television and live in front of computers. And even when we are awake during the day, we expose ourselves to artificial lights that are simply too weak to entrain our biological clocks. According to one researcher, people working indoors view objects and surfaces illuminated at between 50 and 500 lux. These light levels are considerably dimmer than those experienced by those who work outdoors, such as construction and agricultural workers who view objects and surfaces illuminated by the sun and daylight at about 5,000 to 100,000 lux.
Clearly, the light coming off a computer screen is no substitute for the sun. It’s no surprise that our rhythms tend to drift. Ultimately, the result is physiological mischief. There is no telling how many physical afflictions stem, directly or indirectly, from poorly synchronized physiology.
Timing is Everything
The implications of chronobiology for health and fitness are immense. For example, consider our encounters with food, dietary supplements or drugs. We now know that such substances have different effects when administered at different times of the day. For example, Foster and Kreitzman tell of a study that tested cancer patients' responses to chemotherapy. The trial divided patients into two groups. Each received the same drugs at the same dosages but at different times of day. There was a dramatic difference in outcome. One group developed far fewer side effects including less hair loss, less nerve damage, less kidney damage, less bleeding and fewer transfusions. According to the lead researcher, “Every toxicity was markedly diminished several-fold, simply depending on what time of day the drugs were given.”
If we stop to think about this, it makes perfect sense. If physiology is constantly in flux, there are bound to be variations in response to substances that the body encounters. What’s toxic in the morning might actually be therapeutic in the afternoon and vice versa. A glass of wine at 6:00pm may give you a warm, healthy glow, but have it at 11:00pm, and it’ll disrupt your sleep.
Heraclitus was right of course: you can’t step into the same river twice. The river of physiology is always changing. As body professionals, we are taught that homeostasis is the body’s prime directive, but that is only half the story. The body drives towards a stable homeostatic state, but it also seeks oscillation and synchronization with the environment. Thus, my physiology is different at sunrise than it is at noon. And of course, it will be different tomorrow than it was today. I am constantly rearranging my tissue in waves of anabolic and catabolic activity.
As for substances, so too for exercise and movement. It’s safe to assume that a hard, sweaty workout will have dramatically different effects at different times of the day. And it’s probably the case that, given enough knowledge, we will ultimately be able to customize the timing of our training sessions to achieve particular outcomes. If a client has diabetes, high blood pressure or depression, there is probably a best time of day to train that person.
For the moment, we can build on a few key findings. For example, we know that tissue repair peaks between midnight and 4:00am. (“Go to bed!”) We know that concentration, logical reasoning and alertness are at their lowest between 4:00am and 6:00am. (“Take your time waking up.”) We know that heart efficiency, muscle strength and flexibility are all highest between 4:00pm and 8:00pm. (“Try for your personal best in the late afternoon.”) With experience, we will ultimately be able to tune our clients' activity to match up with these circadian realities.
Time to Take Light Seriously
Chronobiology is a hot field that holds incredible promise for refining our approaches to the human body. Unfortunately, not enough people are taking it seriously. Aside from sporadic interest in jet lag, shift work and seasonal affective disorder, very few professionals are integrating the discoveries of chronobiology into their practices. Very few physicians tell their patients when to take medications for example, and scarcely any trainers are scheduling their sessions to match up with circadian realities. And in the world of big fitness, modern health clubs show blatant disregard for light, dark or time of day. With constant levels of illumination in 24 hour facilities, every hour is the same as every other hour.
As trainers, we find the principles of chronobiology to be both exhilarating and perplexing. We’re excited by the promise of bringing our clients' bodies into better harmony with circadian cycles and, in the process, improving their physiological function, performance and maybe even their happiness. But the body is a moving target, and this makes our job incredibly difficult. Not only do we have to provide high quality movement experience and motivation to people, we have to do it at the right time of day. It’s no longer enough to simply schedule people into open time slots. Now we have to take the circadian environment into account as well. This is no simple matter.
Over the course of the next several decades, we will ultimately have the knowledge to craft training programs that are chronologically appropriate for every client. But in the meantime, there are some simple steps that we can take to entrain their physiological rhythms. First and most important, do whatever you can to get your clients out into the morning light. Think of outdoor light as an essential nutrient. If you can find a way to get your people outside, do it. And if you can’t get your people out, nag them to do it on their own.
At least once a year, try to get your clients into some sort of outdoor adventure that’s highly circadian. For example, backpacking tends to be a truly "in your face" circadian experience. When the sun goes down, it gets cold and you snuggle into your bag. And as soon as it starts to get light, you’re up again. Live this cycle for a few days, and you’ll be re-synchronized and ready to head back to the alien environment, refreshed and invigorated.
- Foster, Russel and Kreitzman, Leon. Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing. Profile Books, 2004
- Hrushesky, W.J. Circadian Timing of Cancer Chemotherapy. Science, 228, 73-75, 1985
- Stevens & Rea, Light in the Built Environment: Potential Role of Circadian Disruption in Endocrine Disruption and Breast Cancer. Cancer Causes Control, 12, 279-87. 2001