Circadian Phase-Shifting Effects of Bright Light, Exercise, and Bright Light + Exercise.

Limited research has compared the circadian phase-shifting effects of bright light and exercise and additive effects of these stimuli. The aim of this study was to compare the phase-delaying effects of late night bright light, late night exercise, and late evening bright light followed by early morning exercise. In a within-subjects, counterbalanced design, 6 young adults completed each of three 2.5-day protocols. Participants followed a 3-h ultra-short sleep-wake cycle, involving wakefulness in dim light for 2h, followed by attempted sleep in darkness for 1 h, repeated throughout each protocol. On night 2 of each protocol, participants received either (1) bright light alone (5,000 lux) from 2210-2340 h, (2) treadmill exercise alone from 2210-2340 h, or (3) bright light (2210-2340 h) followed by exercise from 0410-0540 h. Urine was collected every 90 min. Shifts in the 6-sulphatoxymelatonin (aMT6s) cosine acrophase from baseline to post-treatment were compared between treatments. Analyses revealed a significant additive phase-delaying effect of bright light + exercise (80.8 ± 11.6 [SD] min) compared with exercise alone (47.3 ± 21.6 min), and a similar phase delay following bright light alone (56.6 ± 15.2 min) and exercise alone administered for the same duration and at the same time of night. Thus, the data suggest that late night bright light followed by early morning exercise can have an additive circadian phase-shifting effect.

Circadian rhythms of psychomotor vigilance, mood, and sleepiness in the ultra-short sleep/wake protocol.

Despite its advantages as a chronobiological technique, the ultra-short sleep/wake protocol remains underutilized in circadian rhythm research. The purpose of this study was to examine circadian rhythms of psychomotor vigilance (PVT), mood, and sleepiness in a sample (n=25) of healthy young adults while they adhered to a 3 h ultra-short sleep/wake protocol. The protocol involved 1 h sleep intervals in darkness followed by 2 h wake intervals in dim light, repeated for 50-55 h. A 5 min PVT test was conducted every 9 h with the standard metrics of mean reaction time (RT; RT(mean)), median RT (RT(med)), fastest 10% of responses (RT(10fast)), and reciprocal of the 10% slowest responses (1/RT(10slow)). Subjective measures of mood and sleepiness were assessed every 3 h. A cosine fit of intra-aural temperature, assessed three times per wake period, established the time of the body temperature minimum (T(min)). Mood, sleepiness, and PVT performances were expressed relative to individual means and compared across eight times of day and twelve 2 h intervals relative to T(min). Significant time-of-day and circadian patterns were demonstrated for each of the PVT metrics, as well as for mood and sleepiness. Most mood subscales exhibited significant deterioration in day 2 of the protocol without alteration of circadian pattern. However, neither sleepiness nor performance was worse on the second day of observation compared to the first day. These data provide further support for the use of the ultra-short sleep/wake protocol for measurement of circadian rhythms.

Self-reported long sleep in older adults is closely related to objective time in bed.

Although self-reported long sleep is associated with increased morbidity and mortality, little is known about the objective sleep patterns and daytime functioning of long sleepers, particularly those aged ≥50 years. Our primary aim was to compare the objective and subjective sleep patterns of a sample (n = 35) of middle- to older-aged adults who reported sleeping ≥8.5 h per night. A secondary aim was to characterize the mood and functioning of the sample. Over a 2-week period, sleep was recorded via actigraphy and a daily diary. Sleepiness was assessed daily. At the conclusion of the 2-week period, daytime sleepiness, mood, and quality of life were assessed. Measures of sleep and functioning were compared with available representative data. In the sample, actigraphic total sleep time (TST; 7.35 ± 0.97 h) was approximately 60 min greater than age-related representative values but substantially less than diary-assessed TST (8.59 ± 0.74 h) and survey-assessed TST (8.92 ± 0.78 h). Survey and diary-based subjective TST assessments agreed more closely with actigraphic time in bed (TIB; 9.11 ± 0.72 h) than TST, and correlations between subjective TST and actigraphic TIB were similar to those between subjective and actigraphic TST. Measures of mood, sleepiness, and daytime functioning were similar to population-representative values. These results suggest that, among middle- to older-aged adults, self-reported long sleep is primarily indicative of long TIB, but it also represents long objective sleep duration, particularly in comparison to age-matched data. Findings of little functional impairment corroborated previous descriptions of older long sleepers.

Tolerance of chronic 90-minute time-in-bed restriction in older long sleepers.

STUDY OBJECTIVES: To examine the influence of chronic time-in-bed (TIB) restriction on selected health-related outcome variables in older long sleepers. DESIGN: Randomized, controlled trial. SETTING: Home-based. PARTICIPANTS: Forty-two older adults (aged 50-70 y) who reported sleeping at least 8.5 hours. Following extensive screening, participants were assessed for 10 weeks. INTERVENTION: During a two-week baseline, participants followed their usual sleep-wake habits. Participants were then randomized to one of two eight-week treatments: (1) TIB restriction, in which participants were asked to follow a fixed sleep schedule with a TIB of 90 minutes less than recorded during baseline or (2) a control treatment, which involved following a fixed sleep schedule (consistent with average baseline) but no TIB restriction. MEASUREMENTS AND RESULTS: Continuous wrist actigraphic sleep estimation indicated that TIB restriction elicited significant reductions in TIB and total sleep time compared with the control treatment and significant (albeit modest) improvements in sleep efficiency and sleep latency. However, compared with the control treatment, TIB restriction elicited no significant change in depression, sleepiness, health-related quality of life, or neurobehavioral performance. Moreover, follow-up assessments for one year indicated that, after completing the experiment, the participants assigned to TIB restriction continued to restrict their TIB (at their own initiative) by an average of approximately one hour. CONCLUSIONS: The results suggest good tolerance of chronic moderate TIB restriction, without detrimental effects, among older long sleepers.

Circadian variation in swim performance.

Previous findings of time-of-day differences in athletic performance could be confounded by diurnal fluctuations in environmental and behavioral "masking" factors (e.g., sleep, ambient temperature, and energy intake). The purpose of this study was to examine whether there is a circadian rhythm in swim performance that is independent of these masking factors. Experienced swimmers (n = 25) were assessed for 50-55 consecutive hours in the laboratory. The swimmers followed a 3-h "ultra-short" sleep-wake cycle, involving 1 h of sleep in darkness and 2 h of wakefulness in dim light, that was repeated throughout the observation. The protocol distributes behavioral and environmental masking factors equally across the 24-h period. Each swimmer was scheduled to perform six maximal-effort 200-m swim trials that were distributed equally across eight times of day (n = 147 trials). Each trial was separated by 9 h. A cosine fit of intra-aural temperature data established the time of the lowest body temperature (Tmin). Swim performances were z-transformed and compared across the eight times of day and across twelve 2-h intervals relative to Tmin. Analysis of covariance, controlling for trial number, revealed a significant (P < 0.001) pattern in swim performance relative to environmental and circadian times of day. Performance peaked 5-7 h before Tmin (approximately 2300) and was worst from 1 h before to 1 h after Tmin (approximately 0500). Mean swim performance was 169.5 s; circadian variation from peak to worst performance was 5.8 s. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioral masking effects.