The effects of sleep extension on the athletic performance of collegiate basketball players
Study objectives: To investigate the effects of sleep extension over multiple weeks on specific measures of athletic performance as well as reaction time, mood, and daytime sleepiness.
Setting: Stanford Sleep Disorders Clinic and Research Laboratory and Maples Pavilion, Stanford University, Stanford, CA.
Participants: Eleven healthy students on the Stanford University men’s varsity basketball team (mean age 19.4 ± 1.4 years).
Interventions: Subjects maintained their habitual sleep-wake schedule for a 2-4 week baseline followed by a 5-7 week sleep extension period. Subjects obtained as much nocturnal sleep as possible during sleep extension with a minimum goal of 10 h in bed each night. Measures of athletic performance specific to basketball were recorded after every practice including a timed sprint and shooting accuracy. Reaction time, levels of daytime sleepiness, and mood were monitored via the Psychomotor Vigilance Task (PVT), Epworth Sleepiness Scale (ESS), and Profile of Mood States (POMS), respectively.
Results: Total objective nightly sleep time increased during sleep extension compared to baseline by 110.9 ± 79.7 min (P < 0.001). Subjects demonstrated a faster timed sprint following sleep extension (16.2 ± 0.61 sec at baseline vs. 15.5 ± 0.54 sec at end of sleep extension, P < 0.001). Shooting accuracy improved, with free throw percentage increasing by 9% and 3-point field goal percentage increasing by 9.2% (P < 0.001). Mean PVT reaction time and Epworth Sleepiness Scale scores decreased following sleep extension (P < 0.01). POMS scores improved with increased vigor and decreased fatigue subscales (P < 0.001). Subjects also reported improved overall ratings of physical and mental well-being during practices and games.
Conclusions: Improvements in specific measures of basketball performance after sleep extension indicate that optimal sleep is likely beneficial in reaching peak athletic performance.
Keywords: Sleep extension; athletes; athletic performance; basketball; collegiate; extra sleep; fatigue; mood; reaction time; sports.
Sleep deprivation has traditionally been the major approach to illuminating the role of sleep in human functioning. This research has documented the detrimental consequences of sleep restriction and the sleep debt that subsequently accumulates on cognitive function, mood, daytime sleepiness, and traditional performance indices such as reaction time and learning and memory tasks.1–3 Several studies have also demonstrated the negative impact of sleep restriction on physical performance including weight-lifting, cardiorespiratory functioning, and psychomotor tasks that require accuracy and consistent performance.4–6 In general, our understanding of sleep via a sleep deprivation model has been fairly well documented and characterized.
Very few investigations have studied the converse: the impact of extended sleep over multiple nights to weeks; of the few that have, the study designs and results are inconsistent. Many of the limited number of previous sleep extension studies support the idea that obtaining additional sleep is beneficial to human functioning. For example, sleep extended to 10 h/night for 4 days resulted in decreased daytime sleepiness as assessed by the Multiple Sleep Latency Test (MSLT).7 In undergraduate students, extending sleep resulted in faster reaction time, improved mood, and improvements in MSLT scores.8 The results from these 2 studies are supported by young adults who experienced improvements in both MSLT and mood testing after extended sleep independent of preexisting sleep debt.9 Additionally, obtaining sleep through napping after sleep loss has been shown to improve reaction time, sprinting times, and performance on vigilance tasks.10–12 However, on the other hand, other previous studies have shown that 2 nights of extended sleep resulted in decrements in vigilance performance tasks13 and 4 days of sleep extended to 10 h in bed did not result in significant changes in cognitive performance tests.14 These variable results underscore that the effects of sleep extension have yet to be thoroughly investigated.
While sleep extension studies have begun to examine the relationship between obtaining extra sleep and cognitive functioning, minimal research has investigated the effects of sleep extension over relatively longer periods of time and on physical performance. Furthermore, little if any research has addressed how sleep extension specifically affects athletic performance, rather than just traditional indices of physical performance measured in the laboratory. To our knowledge, there are no studies to date that document sleep extension and the athletic performance of actively competing athletes.
The aim of the current study was to extend the nocturnal sleep duration of collegiate basketball players for a number of weeks and to examine the effects on specific indices of athletic performance as well as the traditional measures of reaction time, daytime sleepiness, and mood. With a better understanding of the relationship between total sleep time and athletic performance, athletes may be able to optimize training and competition outcomes by identifying strategies to maximize the benefits of sleep.
Subject Selection Process
This study was conducted over 2 National Collegiate Athletic Association (NCAA) seasons (2005–2008) at Stanford University, where there are 35 varsity sports, 19 for women, 15 for men, and 1 coed, with approximately 800 total student athletes. During any given quarter of the academic calendar, approximately 11 sports are in-season although various sports’ schedules span multiple quarters. Subjects were selected from a pool of undergraduate athletes that were currently participating in a varsity sport at Stanford University. The full roster of men’s and women’s sports whose main competitive season occurs during the collegiate winter quarter from January to March, when this study was initiated, received a general solicitation email. A sport was examined if ≥ 5 athletes responded in the 2005 season. Inadequate numbers, such as only 1–2 athletes per sport, would not be sufficient to draw generalized conclusions from because each sport investigates specific athletic performance measures not comparable across sports.
Next, a detailed screening questionnaire was administered to athletes who responded to the solicitation email inquiring about their current and past medical health as well as sleeping habits. Subjects were included if they were healthy, did not report current difficulties with their sleep, and were “in season” for their sport, regularly practicing, and competing in games or competitions. Subjects were excluded if they had existing injuries that prevented them from regular practice or games. Subjects were also excluded if they had a history of a sleep or psychiatric disorder, took medications with sleep related side effects, or had illicit drug use or other health concerns. Finally, athletes were excluded if they no longer had interest in participating, or were unwilling to or did not feel that they could comply with the study’s protocol after the details were explained to them. The Stanford Panel on Human Subject Research approved the study and written informed consent was obtained from all subjects.
Subjects maintained their habitual sleep-wake patterns for a 2–4 week baseline period during the NCAA basketball season and stayed within the limits of 6–9 h of subjective sleep time each night. Subjects then extended their nocturnal sleep duration for 5–7 weeks during which they obtained as much extra sleep as possible with a minimum goal of 10 h in bed per night. The baseline and sleep extension periods occasionally varied in length across subjects because of the academic schedule. Some subjects were allowed to enroll slightly later due to changes in their academic courses and schedule at the beginning of the quarter, which coincided with the study’s initiation. During sleep extension, subjects were assigned final exams on different days which prevented some subjects from continuing the sleep extension protocol. These slight variations in subjects’ schedules resulted in the differences in baseline and sleep extension periods.
A regular sleep-wake schedule was strongly encouraged as well as daytime naps. Sleep duration, athletic performance, reaction time, daytime sleepiness, and mood measures were recorded throughout the baseline period and sleep extension. Subjects were required to sleep alone in their regular bedroom, except when traveling, during which subjects shared a hotel room with another teammate but slept in separate beds. Subjects were also required to refrain from alcohol and caffeine consumption throughout the study. The study was terminated when subjects could no longer obtain additional sleep each night or the academic quarter which they were enrolled in the study ended, preventing them from continued participation.
Subjects frequently traveled to compete at other universities throughout the study which occurred during the regular NCAA basketball season. Travel duration typically was 3–5 days, occurring once to twice a month. Subjects traveled by bus and plane often within Pacific Standard Time zone, and occasionally crossed into Mountain and Central Standard Time zones. Most trips included travel to play games at 2 universities in different cities within the same state. The team’s travel schedule included fluctuating times for flights, bus rides, practices, games, and team meetings. Consequently, subjects had less control over their sleep-wake times when traveling and thus frequently had atypical sleep-wake schedules for these 3–5 day periods. When subjects were not able to obtain 10 h of nocturnal sleep due to travel, they were encouraged to nap during the day.
Sleep-Wake Activity, Daytime Sleepiness, and Mood Measurements
To monitor daily sleep-wake activity, actigraphy was utilized in addition to subject reported daily sleep logs and journals. Actigraphy is an accepted method used to quantify sleep-wake activity based on subject movement.15 Actigraphy devices were worn on the wrist corresponding to the subject’s dominant hand 24 h/day except during practices and games (AW-64, Philips Respironics, Andover, MA). The raw actigraphy data (1-min epoch length) was reviewed to remove periods of device malfunction. The nocturnal sleep and napping periods were manually determined from subject recorded sleep journals. Nocturnal sleep was defined as the period between subject reported bedtime and awakening time. Manually setting the nocturnal sleep periods to account for time zone changes during travel was also performed. Actigraphy sleep data was scored by a validated proprietary algorithm within the commercial software (Actiware software, Philips Respironics, Andover, MA). Subjects reported sleep-wake activity in sleep journals including time in bed, awakening time, minutes awake during the night, and hours napping during the day.
To assess the level of daytime sleepiness and monitor changes in mood states, the Epworth Sleepiness Scale (ESS)16 was administered during the baseline and at the end of sleep extension, while the Profile of Mood States (POMS)17 was recorded weekly. The ESS measures sleep propensity on a 0–3 scale in 8 standardized daily situations. Possible scores range from 0 to 24, with higher scores reflecting greater sleepiness. The POMS questionnaire is a psychological assessment commonly used to monitor and compare distinct mood states. Subjects report on 65 identifiable mood states over the previous 7 days, which are categorized into 6 mood subscales: tension, depression, anger, vigor, fatigue, and confusion. The POMS questionnaire was hand-scored.
Athletic Performance Measures and Testing
Indices of athletic performance specific to basketball were measured after every practice to assess changes in performance. Practices were typically in the afternoon and athletic measures were correspondingly recorded typically between 12:00–15:00. The indices measured, including a timed sprint and shooting accuracy, were chosen because of their routine use during most practices and strong reflection of individual performance in basketball games. The first athletic performance measure was a timed 282 feet sprint (baseline to half-court and back to baseline, then to full-court and back to baseline) and was timed after each practice by the same person. The second and third performance indices were free throw and 3-point shooting accuracy. Specifically, shooting accuracy was assessed by a subject’s successful attempts of 10 free throws (15 feet) and 15 three-point field goals (5 in the right corner of the court, then 5 directly facing the basket, and finally 5 in the left corner of the court). It is important to note that the official men’s NCAA 3-point field goal line was extended from 19 feet 9 inches (6 subjects) to 20 feet 9 inches (5 subjects) from the basket starting in the 2008–2009 NCAA season. In addition, subjects’ subjective mental and physical well-being were assessed after every practice and game by soliciting how they felt during the practice or game on a 10-point rating scale.
Psychomotor Vigilance Task
Subjects performed the Psychomotor Vigilance Task (PVT, Walter Reed Army Institute of Research, Silver Spring, MD) on a personal digital assistant (PDA) (Palm Pilot, Palm USA, Sunnyvale, CA) twice daily throughout the study. The PVT is a standard measure of reaction time and is commonly used to monitor changes in performance.18,19 Each 10-min trial consisted of stimuli occurring at intervals ranging from 2 to 12 sec. Subjects responded to the stimuli by pressing a button on the PDA using their dominant thumb. Due to differences in each subject’s daily schedule (including academic classes, practices, and team meetings), subjects aimed to complete the 2 PVT trials during the same 1-h periods each day (e.g., 10:00–11:00 and 18:00–19:00 daily) to minimize the effects of circadian rhythms. On days that subjects were traveling, PVT trials continued to be conducted during the same 1-h time intervals based on the time zone in which subjects were located. Subjects also completed an additional PVT trial during their weekly meeting with study investigators. The PVT primary outcome of interest was mean reaction time; secondary outcomes were minimum, maximum, and median reaction times, and number of lapses > 500 millisec.
Subjective and objective sleep times were examined during the baseline and sleep extension periods. Total sleep time included nocturnal sleep as well as daytime naps. The initial 2–4 week period established baseline measures of sleep-wake activity, athletic performance, reaction time, daytime sleepiness, and mood. Sleep times during sleep extension were compared to the mean sleep time for each subject to determine the change in sleep time.
Fixed-effects linear regression models examined the association between the day of the study and outcome measures including total sleep time, athletic performance measures, mean PVT reaction time, ESS, and POMS global and subscale scores. These models were necessary to compare outcome measures during baseline and sleep extension due to the repeated measures testing of individual subjects. All baseline data (considered as day 0) for outcome measures were incorporated into the regression analysis. Descriptive statistics for baseline and sleep extension periods are reported for all outcomes, with P-values determined using the regression models. P-values < 0.05 were considered statistically significant. There was no adjustment for multiple comparisons.
Men’s basketball was the only sport that satisfied the subject selection criterion of ≥ 5 athletes responding to the solicitation email during the 2005 season, and therefore was the sport examined in the present study. In total, 13 men’s basketball players responded with interest, and ultimately 11 healthy undergraduate students (aged 18–22 y) on the Stanford men’s varsity basketball team (mean age 19.4 ± 1.4 y) were enrolled in the study. Two were excluded because they were unwilling to or did not feel that they could comply with the protocol. Table 1 lists subjects’ demographics and demonstrates no statistically significant difference between basketball players who enrolled in the study and those who did not participate, with the exception of weight. Body mass index, which accounts for both height and weight, was not significantly different between the 2 groups.
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