As a clinical psychologist and sleep researcher at the Feinberg
School of Medicine at Northwestern University, Kelly Glazer
Baron frequently heard complaints from aggrieved patients about
exercise. They would work out, they told her, sometimes to the point of
exhaustion, but they would not sleep better that night.
Dr. Baron was surprised and perplexed. A fan of exercise for treating
sleep problems, but also a scientist, she decided to examine more
closely the day-to-day relationship between sweat and sleep.
What she and her colleagues found, according to a study published last week in The Journal of Clinical Sleep Medicine,
is that the influence of daily exercise on sleep habits is more
convoluted than many of us might expect and that, in the short term,
sleep might have more of an impact on exercise than exercise has on
sleep.
To reach that conclusion, Dr. Baron and her colleagues turned to data from a study of exercise and sleep originally published in 2010.
For that experiment, researchers had gathered a small group of women
(and one man) who had received diagnoses of insomnia. The volunteers
were mostly in their 60s, and all were sedentary.
Then the researchers randomly assigned their volunteers either to
remain inactive or to begin a moderate endurance exercise program,
consisting of three or four 30-minute exercise sessions a week,
generally on a stationary bicycle or treadmill, that were performed in
the afternoon. This exercise program continued for 16 weeks.
At the end of that time, the volunteers in the exercise group were
sleeping much more soundly than they had been at the start of the study.
They slept, on average, about 45 minutes to an hour longer on most
nights, waking up less often and reporting more vigor and less
sleepiness.
But Dr. Baron wondered if the novice exercisers had experienced
immediate improvements in their sleep patterns. And on a day-to-day
basis, had working out on any given day produced better sleep that
night?
Boring deep into the data contained in the exercising group’s sleep
diaries and other information for the new study, Dr. Baron discovered
that the answer to both questions was a fairly resounding no. After the
first two months of their exercise program, the exercising volunteers
(all of them women) were sleeping no better than at the start of the
study. Only after four months of the program had their insomnia
improved.
They also rarely reported sleeping better on those nights when they
had had an exercise session. And perhaps most telling, they almost
always exercised for a shorter amount of time on the days after a poor
night’s sleep.
In other words, sleeping badly tended to shorten the next day’s
workout, while a full-length exercise session did not, in most cases,
produce more and better sleep that night.
At first glance, these results might seem “a bit discouraging,” Dr.
Baron said. They also would seem to be at odds with the earlier
conclusion that four months of exercise improved insomniacs’ sleep
patterns, as well as a wealth of other recent science that has typically
found that regular exercise lengthens and deepens sleep.
But, Dr. Baron pointed out, most of these other studies employed
volunteers without existing sleep problems. For them, exercise and sleep
seem to have a relatively uncomplicated relationship. You work out,
fatigue your body and mind, and sleep more soundly that night.
But people with insomnia and other sleep disturbances tend to be
“neurologically different,” Dr. Baron said. “They have what we
characterize as a hyper-arousal of the stress system,” she said. A
single bout of exercise on any given day “is probably not enough to
overcome that arousal,” she explained. It could potentially even
exacerbate it, since exercise is itself a physical stressor.
Eventually, however, if the exercise program is maintained, Dr. Baron
said, the workouts seem to start muting a person’s stress response. Her
or his underlying physiological arousal is dialed down enough for sleep
to arrive more readily, as it did in the 2010 experiment.
Of course, both of these studies were small, involving fewer than a
dozen exercising volunteers, all of them middle-aged or older women. “We
think the findings would apply equally to men,” Dr. Baron said. But
that idea has yet to be proved.
Likewise, it is impossible to yet know the sleep-related impacts of
workouts of different types (like weight training), intensities or
timing, including morning or late-evening sessions.
Still, the preliminary message of these findings is heartening. If
you habitually experience insomnia and don’t currently exercise, Dr.
Baron said, start. Don’t, however, expect that you will enjoy or even
complete workouts the day after a broken night’s sleep, or that you will
sleep better hours after you’ve exercised.
The process is more gradual and less immediately gratifying than the
sleep-deprived might wish. But the benefits do develop. “It took four
months” in the original study, Dr. Baron said, but at that point the
exercising volunteers “were sleeping at least 45 minutes more a night.”
“That’s huge, as good as or better” than most current treatment options
for sleep disturbances, including drugs, she said.
The New York Times.
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