Original ArticleDoes nighttime exercise really disturb sleep? Results from the 2013 National Sleep Foundation Sleep in America Poll
Introduction
Experts widely advocate routine exercise for improving sleep quality. As a primary recommendation, exercising regularly is incorporated into standard “sleep hygiene” advice [1]. However, this recommendation is typically presented with the caveat that one should avoid exercising near bedtime. This warning concerning the timing of exercise with respect to bedtime is endorsed by sleep medicine experts [2], [3] and lay media [4], [5].
It is speculated that exercise near bedtime could disrupt sleep by altering circadian phase [6], elevating core body temperature [7], or increasing physiological arousal [8]. However, the few available experimental studies [9], [10], [11] and surveys [12], [13] addressing this issue have generally failed to substantiate such concerns that evening exercise negatively impacts sleep. In fact, arguments could be made that evening might be the optimal time for exercise-related sleep benefits based on findings that decreases in self-reported anxiety and in physiological indices of anxiety such as blood pressure and muscle tension are most evident 1–2 h following exercise [14]. Moreover, people tend to fall asleep when body temperature is rapidly declining [7], which is also most evident following exercise.
The extant literature sheds little light on this subject because methodological and sampling issues limit generalization. Missing and/or incomplete specifications about exercise intensity and narrowly defined sample characteristics diminish broad interpretability. Many experimental studies exploring the exercise timing-sleep relationship only included good sleepers [9], [10], [11] and/or individuals who were accustomed to regular exercise [10], [11].
The proper (or improper) timing of exercise with respect to sleep is an important public health issue. Exercise has well-established benefits for longevity and disease prevention [15], yet most Americans receive much less exercise than needed to realize these benefits [16]. Lack of time is the most commonly cited barrier to regular exercise [17], and individuals may find it difficult to schedule exercise at times other than within a few hours of bedtime. Consequently, discouraging evening exercise may have the unintended consequence of reducing or eliminating exercise altogether for some individuals. Therefore, the purpose of this study was to examine the relationship between sleep, exercise intensity, and exercise timing (morning, afternoon, evening) in a large American sample that participated in the National Sleep Foundation’s 2013 Sleep in America (SIA) poll. Specifically, we examined whether individuals who exercised in the evening reported more disturbed sleep relative to non-exercisers.
Section snippets
Poll content
The poll content was developed by a task force of independent scientists and clinicians. Members were invited based on their expertise in sleep science/medicine and/or exercise science. Poll items were derived from several sources including validated questionnaires (used either in part or in their entirety) and items developed specifically for the poll. A core set of questions used annually in SIA polls were included to examine trends in sleep habits over time. Task force members made final
Demographic, exercise, and sleep variables
Table 1 provides sample demographics by gender for the sample of 1000 respondents. The sample was primarily middle-aged, non-Hispanic White, working, college-educated, married/partnered, and overweight. Men were older and were more likely to work, have 4-year college degree or more, and have a higher BMI than women.
Table 2 provides descriptive physical activity, sleep quality and duration metrics by gender. Men were more likely to report afternoon vigorous and moderate exercise. Women reported
Discussion
Traditional sleep hygiene recommendations suggest that regular exercise facilitates sleep. However, individuals are cautioned to avoid exercise (especially vigorous exercise) near bedtime. Results from this study supported the connection between exercise and better sleep, but failed to confirm the contention that exercising near bedtime is associated with disturbed sleep.
The positive relationship between exercise and sleep is consistent with previous survey findings [12], [13], including a
Conflict of interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2014.01.008.
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