Educational paper literature review 2

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Journal of Adolescent Health 51 (2012) 615–622

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Original article

Daily Morning Running for 3 Weeks Improved Sleep and Psychological Functioning in Healthy Adolescents Compared With Controls

Nadeem Kalak, M.Sc.a, Markus Gerber, Ph.D.b, Roumen Kirov, M.D., Ph.D.c, Thorsten Mikoteit, M.D.a, Juliana Yordanova, M.D., Ph.D.c, Uwe Pühse, Ph.D.b, Edith Holsboer-Trachsler, M.D.a, and Serge Brand, Ph.D.a,* a Center for Affective, Stress and Sleep Disorders, Psychiatric Hospital of the University of Basel, Basel, Switzerland b Institute of Exercise and Health Sciences, University of Basel, Basel, Switzerland c Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria

Article history: Received September 20, 2011; Accepted February 28, 2012 Keywords: Intervention study; Objective and subjective sleep improvements; Psychological functioning; Exercising; Adolescents

A B S T R A C T

Purpose: To compare sleep electroencephalographic patterns and psychological functioning of ealthy adolescents running regularly in the mornings with those of control subjects. Although everal studies have shown that regular moderate-to-vigorous exercise is related to favorable sleep nd psychological functioning in adolescents, research on the effectiveness of short interventions is ore limited. ethods: Fifty-one adolescents (mean age � 18.30 years; 27 female [53%]) took part in the study;

they were randomly assigned either to a running or to a control group. The running group went running every morning for 30 minutes at moderate intensity during weekdays for 3 consecutive weeks. Sleep electroencephalographic patterns and psychological functioning were assessed in both groups before and after the 3-week period. All participants also kept a sleep log for 3 weeks. Results: Objective sleep improved (slow-wave sleep increased; sleep onset latency decreased) in he running group compared with the control group. Subjective sleep quality, mood, and concen- ration during the day improved, whereas sleepiness during the day decreased. onclusions: Thirty minutes of running in the morning during weekdays for 3 consecutive weeks mpacted positively on sleep and psychological functioning in healthy adolescents compared with ontrol subjects. Running is inexpensive and easy to implement during school schedules, and as oth objective and subjective improvements were observed within 3 weeks, regular physical xercise should be promoted.

IMPLICATIONS AND CONTRIBUTION

Moderate running in the morning for 3 consecutive weeks impacted positively on objective and subjective sleep and psychological functioning among healthy adolescents. Regular exer- cise, such as running should be promoted as both rem- edy and preventative mea- sure for poor sleep and poor psychological functioning.

� 2012 Society for Adolescent Health and Medicine. All rights reserved.

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Adolescence is a critical period for both neural and psycho- ogical [1] development, in which sleep plays an important func- ional role [2,3]. Owing to a variety of different factors, such as hysical maturation (e.g., dramatic increase in secretion of rowth hormones), psychological factors (e.g., identity forma-

* Address correspondence to: Serge Brand, Ph.D., Center for Affective, Stress and Sleep Disorders, Psychiatric Hospital of the University of Basel, Wilhelm Klein-Strasse 27, 4012 Basel, Switzerland.

w E-mail address: [email protected] (S. Brand).

N.K. and M.G. contributed equally to this work.

1054-139X/$ - see front matter � 2012 Society for Adolescent Health and Medicine. A http://dx.doi.org/10.1016/j.jadohealth.2012.02.020

ion), social factors (relative dependence from parents and eers), and extracurricular factors (e.g., sports and leisure activ- ties, academic achievements), total sleep time (TST) decreases 2–5], although adolescents seem to still require 9 or more hours f sleep per night [4,5]. Daytime sleepiness is common among dolescents, and acute [6] and chronic [7] sleep disturbances ave been related to poor physical and psychological function- ng. In a cross-sectional survey [8], �60% of respondents were ategorized as poor-quality sleepers, and shorter sleep duration, oor sleep quality, and sleepiness were independently associated

ith poor school achievement in children and adolescents [9].

ll rights reserved.

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N. Kalak et al. / Journal of Adolescent Health 51 (2012) 615–622616

Exercise appears to be a simple and inexpensive method for ddressing sleep loss and daytime sleepiness. Although there is mpirical evidence for young and elderly adults [10], relevant esearch on adolescents is scarce, and studies have predomi- antly involved cross-sectional designs [11,12]. In previous stud- es, we have been able to show a relation between exercising and mproved subjective and objective sleep in adolescent elite ath- etes [13,14] and in moderately exercising adolescents [15], com- pared with control subjects. A limitation was that findings were derived from cross-sectional group-comparison designs, whereas intervention studies do allow stronger conclusions regarding the direct effects of exercising. In this respect, Dworak et al [16] were able to show that acute bouts of exercise increased objectively recorded sleep.

Additionally, there is evidence that regular exercise is associ- ated with improved psychological functioning in adolescents [14,15,17,18]; exercising buffered the effects of family conflict on depressed mood [19], and sports participation has been shown to be a protective factor against depression and suicidal ideation, mediated by its impact on increased self-esteem and social sup- port [20]. Additionally, there is also evidence that the implemen- tation of regular exercise as a therapeutic intervention leads to positive psychological outcomes: regular exercising improved self-esteem in children and adolescents [21], and walking regu- larly for 30–45 minutes during weekdays for 12 consecutive weeks led to complete psychiatric remission in half of patients suffering from therapy-resistant major depressive disorders, as compared with control subjects [22].

Thus, there is reason to anticipate that exercise interventions an improve sleep and psychological functioning. Therefore, the ollowing two hypotheses were formulated. First, we expected positive impact of a moderate-to-vigorous exercise (here, oderate-to-vigorous exercise was defined as planned and con-

inuous running without interruption at a speed such that con- ersation is not possible) training program on sleep [13,16] as

compared with a control condition. Second, following previous research [13–18], we anticipated an improvement in psycholog- ical functioning (such as stress perception, curiosity, somatosen- sory amplification, mood, concentration, and sleepiness) in exer- cising adolescents as compared with control subjects.

Methods

Sample

Participants were recruited from a high school in the canton of Basel-Landschaft, a district of the German-speaking north- western part of Switzerland. Figure 1 shows the study flowchart and dropout rates. Of the 60 adolescents originally approached, 51 (85%) completed the study (see Figure 1; age: mean [M] � 18.30 years; standard deviation [SD] � .89; range: 17.5–19.5 years): 27 were female (age: M � 18.11 years, SD � .80) and 24 were male (age: M � 18.13 years, SD � 1.00). Participants were randomly assigned to either the running or the control group (see later in the text). Neither gender distribution (�2(1) � .30,

� .87) nor age (analysis of variance [ANOVA]: group: F(1, 47) � 01, p � .97; gender: F(1, 47) � .02, p � .97) differed significantly etween the two groups. Body mass index differed significantly etweenmaleandfemaleparticipants(male:M � 23.29,SD � 2.27; emale: M � 20.74, SD � 1.54; gender: F(1, 47) � 18.62, p � .000) ut not between the two groups (group: F(1, 47) � .44, p � .51).

s in previous studies [14,15], mean weekly vigorous exercise

as assessed through the following question: “For how many ours do you do vigorous exercise? Vigorous exercise means: ou are playing sports at such a level as to have a markedly ncreased heart rate and to sweat.” Answers indicated the num- er of hours over which intense exercise was undertaken for ach of the 7 consecutive days. These values were then summa- ized to generate a total weekly exercise index (hrs/wk). At the eginning of the study, mean vigorous exercise did not statisti- ally differ between the two groups (running group [RG]: M � .19 hours (SD � 1.56); control group [CG]: M � 2.24 hours (SD �

1.78); t(49) � .53, p � .60, d � .15). All students were informed about the purpose of the study

and about the voluntary basis of participation. Participants were assured of the confidentiality of their responses and gave written informed consent. Of the 51 participants, 10 were younger than 18 years. For these participants, parents’ written informed consent was requested. For participation, they received a voucher of 30.00 Swiss francs for a sports shop. The study was approved by the local ethics committee of Basel (Switzerland; trial number: 72/10).

Procedure

Figure 1 depicts the study structure, assessments, randomiza- tion, and total sample sizes. First, a psychiatric interview [23] ensured that only participants without psychiatric disorders (e.g., affective disorders, eating disorders, substance abuse disor- ders, sleep disorders, or others) were enrolled in the study. Ad- ditionally, brief questions related to physical health state en- sured that only participants without medical illnesses, allergies, and cardiovascular, pulmonary, or orthopedic diseases took part in the study. Thereafter, participants were asked to refrain from any intake of psychoactive or sleep-altering substances (alcohol, cannabis, nicotine, mood- or energy-enhancing drinks) for 2 weeks before commencement of and during the study itself.

Participants kept a sleep log (see later in the text) for 3 weeks (21 consecutive days), covering 3 � 5 weekdays and 3� 2 week- end days. To compare possible effects of regular running, at the beginning and at the end of the study, participants completed a series of questionnaires related to psychological functioning and sleep (see later in the text). Additionally, at the beginning and at the end of the study, objective sleep assessment was executed (which will be described further).

The study was conducted during a school term from mid- August to the end of September 2010, that is, during the summer season with high light exposure from early morning.

Participants were randomly assigned to one of the two study conditions, namely, the RG or the CG. For 3 consecutive weeks, during the 5 school days per week, participants assigned to the RG or the CG met every morning at 7 AM at school. Afterward, the RG went runningforbetween30and37minutes.Allparticipantsin the RG had 3 � 5 running sessions. Running was cross-country; after two laps on the school’s running track, running continued in the forest close to school. Participants were allowed to maintain their own pace though while running without interruption in groups of at least four people. Running differed from jogging in that running speed was such that talking was more difficult. All participants had to pass a checkpoint and a turning point, and the track did not allow shortcuts. After participants completed the session, they got ready for school, and a breakfast was provided before school commenced.

In contrast to the RG participants, those in the CG remained

on the school’s running track, remained seated, followed

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N. Kalak et al. / Journal of Adolescent Health 51 (2012) 615–622 617

school activities, and completed homework. They could speak and interact with each other, but they were not allowed to use electronic devices such as mobile phones or electronic note- books. Participants in the CG had 3 � 5 sessions of resting activity. They ceased their activities when the last of the runners returned. Next, after all participants in the RG had prepared for school, a breakfast was provided for both groups. By arranging the same study conditions (with the exception of running itself) for both the RG and the CG, potential confound- ers, such as morning schedule, exposure to daylight and arti- ficial light, social interaction, and eating at school, were rigor- ously controlled for. Moreover, meeting at 7 AM at school did

Assessed

Analysed (n= 27) Excluded from analysis (n= 0)

Lost to follow-up (n= 0)

Allocated to intervention (n= 28) Received allocated intervention (n= 28) Did not receive allocated intervention

(accident) (n= 1)

An

Ran

Sleep-EEG-recordings

Questionnaires; beginning of log

Sleep-EEG-recordings

Questionnaires; end of log

Figure 1. Flow diagram for recruitment and analysis of participants.

not interfere with participants’ habitual sleep/wake pattern. p

Assessing psychological functioning

Daily log. Participants filled out the sleep and mood log in the evening and in the morning. For evenings, participants answered questions on an 8-point visual analog scale about sleepiness during the day (1 � very sleepy; 8 � not at all sleepy), concen-

tration during the day (1 � very bad concentration; 8 � very high concentration), and mood at bedtime (1 � very bad mood; 8 � very good mood). For mornings, the questionnaire asked about sleep quality (1 � very bad sleep quality; 8 � very good sleep uality) and mood on awaking, using the same analog scale Cronbach � � .89). Nights were defined as weekday nights if the

ligibility (n= 60)

Excluded (n= 4) Declined to participate (n= 4)

Lost to follow-up (n= 0)

Allocated to intervention (n=28) Received allocated intervention (n= 28) Did not receive allocated intervention

(illness) (n= 4)

Analysed (n= 24) Excluded from analysis (n= 0)

p

ed (n= 56)

Sleep-EEG-recordings

Questionnaires; beginning of log

Sleep-EEG-recordings

Questionnaires; end of log

for e

aly

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articipant went to school the next day; weekend nights were

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N. Kalak et al. / Journal of Adolescent Health 51 (2012) 615–622618

Friday and Saturday nights. To compute data, weekdays of a single week and weekend days of a single weekend were aggre- gated, resulting in three composite variables for weekdays (weeks 1, 2, and 3) and three composite variables for weekends (weekends 1, 2, and 3).

Similar to a previous study [15], we tested whether perceived stress, coping strategies, somatosensory perception, and curios- ity and exploratory behavior (see later in the text) might change in a positive direction over time.

Perceived stress. The Perceived Stress Scale [24] consists of 10 items and was used to determine perceived overall stress occur- ring over the previous month. Answers were given on a 5-point rating scale ranging from 1 (never) to 5 (very often), with higher scores reflecting greater perceived stress (Cronbach � � .89).

Coping with stress. The questionnaire consists of 18 items and assesses positive and negative coping strategies [25]. Positive coping strategies are those that reduce tension in both the short- and the long-term, including minimizing the situation, control- ling the situation, and self-instruction. Negative coping strate- gies are those that reduce tension in the short-term but increase stress in the long-term, including social withdrawal, rumination, and resignation. Answers were given on a 5-point rating scale ranging from 1 (very unlikely) to 5 (very likely). The higher the score, the more pronounced is the coping strategy (Cronbach � � .82). Two composite mean scores were computed reflecting pos- itive and negative coping strategies.

Somatosensory amplification. Somatosensory amplification re- fers to a tendency to experience somatic and visceral sensations as unusually intense, noxious, and disturbing. Assessment was through the Somatosensory Amplification Scale [26]. The ques- tionnaire consists of 10 items relating to body hypervigilance and the predisposition to focus on certain weak and infrequent body sensations. Answers were given on a 5-point rating scale ranging from 1 (not at all true) to 5 (completely true). Higher scores reflect an increased tendency to somatosensory amplifi- cation (Cronbach � � .88).

Curiosity and exploratory behavior. Kashdan et al’s [27] Curiosity and Exploration Inventory was used to assess this dimension. Curiosity is conceptualized as a positive emotional–motivational system associated with the recognition, pursuit, and self-regulation of novelty and challenge. The inventory consists of seven items, and answers were given on a 7-point rating scale with the anchor points 1 (not at all true) to 7 (completely true). Higher scores indicate greater curiosity/exploration (Cronbach � � .79).

Sleep evaluation

Objective sleep electroencephalographic recordings. Sleep was ob- jectively assessed at the beginning and at the end of the study. At the beginning of the study, before starting the intervention, the sleep electroencephalographic (EEG) device was applied twice. With the first application, participants slept with the sleep EEG device to avoid possible unfavorable “first night effects.” No registration was performed. The following night, sleep registra- tion was performed.

On the day of the recording night, participants had to attend regular schedules, but without evening exercise so as to avoid

possible effects of acute bouts of exercise on sleep [16]. Partici-

ants were requested to go to bed at the usual time, which was etween 9 and 10.30 PM and to get up between 6 and 6.30 AM. fter the intervention was completed 3 weeks later, objective leep assessment was repeated. Sleep EEG recordings were per- ormed at home using a three-channel EEG device (Fp2-A1, C3- 2, C4-A1; electrooculogram; electromyogram; SOMNOwatch; omnomedics, Randersacker, Germany). Sleep polygraphs were isually analyzed by two experienced raters according to the tandard procedures [28] (inter-rater reliability: � � .91). Raters were completely blinded to participants’ group assignments. The SOMNOwatch device provides assessment of TST, sleep period time, sleep onset latency (SOL), sleep efficiency, stages 1–4 (min- utes and %), light sleep (stages 1 � 2), slow-wave sleep (stages 3

4), rapid eye movement (REM) sleep, REM sleep latency, and umber and times of awaking after sleep onset.

ubjective assessment of sleep. Participants also completed at the eginning and at the end of the study the Insomnia Severity ndex [29], a screening tool for insomnia. The seven items, an- wered on 5-point rating scales (1 � not at all, 5 � very much), efer to difficulty in falling asleep, difficulties maintaining sleep, ncreased daytime sleepiness, and worrying about sleep. The igher the overall score, the more the respondent is assumed to uffer from insomnia (Cronbach � � .86).

Statistical analyses

To calculate changes on the daily log dimensions (e.g., mood, concentration) across the 3 weeks, a series of ANOVAs for re- peated measures with the factors time (six conditions: weekdays weeks 1–3; weekend days weeks 1–3) and group (RG vs. CG) was performed. For before to after comparison of objective sleep variables, ANOVAs for repeated measures were performed with the factors time (pre vs. post) and group (RG vs. CG) as indepen- dent variables. In case of deviations from sphericity, statistical tests were performed using Greenhouse–Geisser-corrected de- grees of freedom, and the original degrees of freedom are re- ported with the relevant Greenhouse–Geisser epsilon value (�). Test results with an � level �.05 are reported as significant. Effect sizes for ANOVAs (partial eta squared [�2]) were calculated fol- lowing Cohen [30], with .059 � �2� .01 indicating negligible ractical importance, .139 � �2� .06 indicating moderate prac-

tical importance, and �2 � .14 indicating crucial practical impor- tance effect sizes.

Results

Daily log

Tables 1 and 2 provide the descriptive and inferential statis- tical overview of the data from the daily log, separately by groups (RG vs. CG) and time (weeks 1–3, weekdays and weekend days).

Sleep quality significantly increased over time and was signif- icantly higher in the RG compared with the CG; the group � time interaction was also significant, reflecting a significantly greater increase in sleep quality over time in the RG than in the CG (Figure 2).

Mood in the morning significantly improved over time and was significantly higher in the RG than the CG; the group � time inter- action was also significant; mood in the morning increased signifi-

cantly over time in the RG compared with the CG.

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N. Kalak et al. / Journal of Adolescent Health 51 (2012) 615–622 619

Concentration during the day did not differ between groups and did not change over time. However, the group � time inter- action was significant; concentration increased significantly over time in the RG, but not in the CG.

Sleepiness during the day did not differ between groups but decreased significantly over time. The group � time interaction was significant; sleepiness decreased significantly over time in the RG compared with the CG.

Mood in the evening did not differ between groups. Over time, irrespective of group, mood in the evening improved. The group � time interaction was not significant.

Psychological functioning

Table 3 provides the descriptive and inferential statistical overview of objective sleep measurements, separately by groups (RG vs. CG) and time (before vs. after assessment).

Perceived stress, positive and negative coping strategies, and curiosity and exploratory behavior did not differ significantly be- tween groups or over time. Moreover, no statistically significant group � time interactions were observed.

Somatosensory amplification scores decreased significantly over time. Moreover, the group � time interaction was statisti- cally significant, with decreased scores over time in the RG com- pared with the CG.

Table 1 Daily log: Overview of descriptive values, separately for weeks (week 1, week 2,

Variables Group Study weeks

Week 1

Weekdays M (SD)

Wee M (S

Sleep qualitya RG 4.44 (1.05) 5.50 CG 4.54 (.98) 5.13

Mood: Morninga RG 4.28 (.76) 4.44 CG 4.36 (.61) 4.54

Concentration during the daya RG 4.56 (1.40) 4.83 CG 5.33 (1.58) 5.52

Sleepiness during the daya RG 3.84 (.67) 3.77 CG 3.98 (.69) 3.69

Mood: Eveninga RG 3.80 (.86) 4.32 CG 4.12 (1.45) 5.05

� mean; SD � standard deviation; RG � running group; CG � control group. a Higher means reflect a more positive position on the dimension; for example 3 (RG � 6.35; CG � 5.15). Likewise, sleepiness during the day decreased from

Table 2 Daily log: Overview of inferential statistics separately fo and weekend days)

Daily log variables Greenhouse–Geisser epsilon value (ε)

Sleep quality .611 Mood: Morning .560 Concentration during the day .687 Sleepiness during the day .692 Mood: Evening .492

Degrees of freedom: Always � (5, 245). * p � .05.

** p � .01. *** p � .001.

Sleep

Subjective sleep. Insomnia scores decreased significantly over time. Moreover, the group � time interaction was statistically significant, with decreased scores over time in the RG compared with the CG.

Objective sleep recordings

Table 4 provides the descriptive and inferential statistical overview of objective sleep measurements, separately for groups (RG vs. CG) and time (before vs. after assessment).

No statistically significant mean differences between groups, over time (from before to after assessments), or combining group and time (group � time interactions) were observed for TST, awakenings after sleep onset (number, time), stage 2 (minutes), stage 3 (minutes), light sleep (minutes; %), or REM sleep (%).

SOL significantly decreased in the RG compared with the CG over time.

Sleep efficiency was significantly higher in the RG compared with the CG. No statistically significant mean differences were observed over time or for the group � time interaction.

Over time, stage 1 (minutes; %) significantly decreased, whereas stage 3 (%) and REM sleep (minutes) significantly increased, with no mean differences for group or for group � time interactions.

3), for week days (weekdays, weekend days), and for groups (RG, CG)

Week 2 Week 3

Weekdays M (SD)

Weekend M (SD)

Weekdays M (SD)

Weekend M (SD)

5.24 (.84) 6.13 (.78) 5.71 (.75) 6.35 (.72) 4.73 (.78) 4.92 (1.15) 4.80 (1.28) 5.15 (1.08) 4.64 (.75) 5.11 (.68) 5.21 (.85) 5.53 (.97) 4.36 (.44) 4.53 (.90) 4.34 (.48) 4.91 (.85) 5.29 (1.18) 4.93 (.95) 5.74 (1.09) 5.60 (.88) 4.74 (.89) 5.45 (1.25) 4.71 (.85) 5.19 (.78) 3.93 (.75) 4.35 (.69) 4.77 (.70) 5.74 (.94) 3.90 (.89) 4.13 (.86) 4.01 (.67) 4.17 (1.49) 3.93 (.81) 4.71 (.71) 5.11 (1.50) 5.02 (.76) 4.04 (1.16) 4.86 (.72) 5.10 (1.84) 4.94 (.73)

quality increased in the weekdays from week 1 (RG � 4.44; CG � 4.54) to week k 1 (RG � 3.84; CG � 3.98) to week 3 (RG � 5.74; CG � 4.17).

p (RG vs. CG), and time (3 weeks; blocs of weekdays

roup Time Group � time interaction

�2 F �2 F �2

4.02* .223 17.28* .261 5.98** .11 4.42*** .083 16.08* .247 6.32** .114 .00 .000 3.02 .058 17.13* .259

2.68 .052 38.01* .437 2.82*** .054 1.05 .021 15.50* .240 1.36 .027

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(.95) (.90) (1.05) (.98) (1.06) (1.00) (.78) (.96) (.87) (1.00)

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N. Kalak et al. / Journal of Adolescent Health 51 (2012) 615–622620

Stage 2 (%) was significantly higher in the control compared ith the RG, with no significant time or group � time interac- ions.

Stage 4 (minutes, %) was significantly higher in the RG com- ared with the CG; the significant group � time interaction howed that stage 4 (minutes, %) increased in the RG compared ith the CG from before to after assessment. Likewise, deep sleep minutes; %) was significantly higher in the RG compared with he CG; moreover, the significant group � time interaction howed that deep sleep (minutes) increased in the RG compared ith the CG from before to after assessment. REM sleep latency (minutes) was significantly prolonged in

he RG compared with the CG; moreover, the significant group � ime interaction showed that REM sleep latency (minutes) was onger in the RG compared with the CG from before to after ssessment.

iscussion

The key finding of the present study is that, compared with a ontrol condition, an intervention involving running for 30 min- tes in the morning daily during weekdays for 3 consecutive eeks improved sleep (objectively and subjectively) and psy-

0

1

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4

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7

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W1; WD W1;WE W2; WD W2;WE W3; WD W3;WE

Sl ee p q u al it y

Weeks

RG

CG

Figure 2. Subjective sleep quality improved over time in both the running group and the control group; however, improvement was more pronounced in the running group (for statistics see Tables 1 and 2). W1 � week 1; W2 � week 2; W3 � week 3; WD � weekdays; WE � weekend days; RG � running group; CG � control group. For further statistical information, see Tables 1 and 2. Points are means, and bars are standard deviations.

Table 3 Descriptive and statistical overview of psychological functioning, separately by g

Psychological functioning RG CG

Before assessment n � 27 M (SD)

After assessment n � 27 M (SD)

Befor asses n � 2 M (SD

Perceived stress scale 2.94 (.68) 2.95 (.68) 2.81 Coping strategies Positive coping 3.29 (.64) 3.14 (.78) 3.32 Negative coping 2.93 (1.08) 2.65 (.68) 2.71

Somatosensory amplification 14.74 (3.35) 12.14 (4.83) 15.25 Curiosity and exploratory behavior 5.28 (.58) 5.26 (.49) 5.46 Insomnia severity 13.89 (3.83) 11.22 (3.30) 13.17

Degrees of freedom: Always � (1, 49). * p � .05.

** p � .01. *** p � .001.

hological functioning. The results add to the existing literature n showing that even a short-term intervention of regular run- ing in the morning does have a favorable impact on the sleep nd psychological functioning of healthy adolescents. Two hypotheses were formulated and each of these is now

onsidered in turn. With the first hypothesis, we expected a favorable impact of

oderate-to-vigorous exercise on adolescents’ sleep [13–16], nd findings fully confirmed this; compared with control sub- ects, participants in the RG reported improved sleep quality, and bjectively assessed sleep improved, in that deep sleep in- reased, SOL decreased, and REM sleep latency became longer ver time. Thus, the present findings echo those of the numerous tudies that have confirmed an association between exercise and leep [13–16,31]. Importantly, the present results add to the iterature in demonstrating the impact of moderate exercise, amely, running for 30 minutes in the morning for only 3 weeks. With the second hypotheses, we anticipated a favorable influ-

nce of regular exercise on psychological functioning, but this as only partly confirmed. Whereas no changes were observed

n perceived stress and coping or in curiosity and exploratory ehavior, running was related to decreased pain perception. The ack of any association between exercising and stress is in arked contrast with the many studies demonstrating a positive

nfluence of exercise on stress management [32–34]. The follow- ng are possible explanations for this difference: (a) The time nterval of 3 weeks was too short to induce the relevant changes; b) trait (as compared with state) characteristics, such as curios- ty, perception of stress, and coping strategies, are relatively table over time and therefore more difficult to modify; (c) per- eption of stress and coping did change but in ways too subtle to e captured by the questionnaires used; (d) participants were articularly healthy and this would result in ceiling effects. By contrast, the experience and appraisal of bodily sensations

nd its cognitive–emotional elaboration (i.e., the somatosensory mplification or pain) is much more adaptable and sensitive to ituation-specific conditions [35]. Our results suggest that pain hreshold increased as a function of exercise, and this pattern of esults is in accord with previous findings [15,35].

Despite the clarity of the findings, several issues warrant gainst overgeneralization. First, as in all studies with exercising, onfounders, such as exposure to daylight and social contacts, ay bias results. However, we note that social contacts, expo-

(RG vs. CG) and assessment time (before vs. after assessment)

Statistics

After assessment n � 24 M (SD)

Group Time Group � time interaction

F �2 F �2 F �2

2.63 (.63) 1.71 .034 2.25 .044 2.97 .057

3.41 (1.22) .45 .009 .12 .002 1.48 .029 2.63 (.67) .40 .008 2.26 .044 .67 .014

) 15.58 (7.96) 1.55 .031 5.78* .106 9.69** .165 5.28 (.73) .37 .008 2.66 .051 1.75 .034

) 13.88 (3.45) 1.14 .023 8.94** .154 26.57*** .352

roup

e sment 4 )

(.61)

(.68) (.59) (6.72 (.69) (3.03

T D

N. Kalak et al. / Journal of Adolescent Health 51 (2012) 615–622 621

sure to daylight, and eating at school were equal for both condi- tions; therefore, these possible confounders could be ruled out. Second, it is unclear to what extent the intervention was success- ful because it took place in the mornings as compared with interventions during the day or in the evening, and research on this is limited and results are inconclusive [36,37]. Specifically, there is no research with respect to adolescents. Third, results may potentially be biased because they are based on data from particularly healthy and motivated adolescents willing to com- plete questionnaires and to undergo sleep EEG registration. Thus, participants might not be representative for adolescents as a whole [6,7]. In this view, we also note that participants in the present sample were far from sleeping for the recommended 9 hours per night (see Table 4). Fourth, we did not assess individual fitness, nor did we assess running objectively. However, it was our firm intent to arrange a study design close to a practicable and easy-to-implement intervention. Finally, the relevant di- mensions may be linked by means of as-yet unidentified further variables, such as the secretion of adenosine, cortisol, or melato- nin or issues related to motivation and volition. Based on these limitations, future research should (a) compare exercise inter- ventions at different times of day, (b) assess the impact of exer- cise intervention based on objectively assessed physiological parameters, or (c) assess neurobiological variables, such as cor- tisol, melatonin, or BDNF (brain derived neurotrophic factor).

Conclusion

Moderate running in the morning for 3 consecutive weeks impacted positively on objective and subjective sleep and psy- chological functioning among healthy adolescents. Moderate,

able 4 escriptive and statistical overview of sleep EEG variables, separately by group (

RG CG

Before assessment n � 27 M (SD)

After assessment n � 27 M (SD)

Before assessm n � 24 M (SD)

TST (minutes) 409.32 (24.46) 434.89 (45.10) 400.17 Sleep onset latency (minutes) 10.17 (5.33) 7.42 (4.73) 9.38 Sleep efficiency 93.38 (4.41) 94.03 (2.22) 91.83 Awakenings after SO (number) 7.52 (7.64) 6.41 (3.25) 5.50 Awakenings after SO (minutes) 22.76 (21.78) 22.18 (18.07) 29.86 Stage 1 (minutes) 13.06 (8.40) 7.57 (3.75) 13.13 Stage 1 (%) 3.23 (2.32) 1.56 (1.14) 3.18 Stage 2 (minutes) 186.28 (15.28) 192.96 (28.95) 190.75 Stage 2 (%) 45.63 (4.48) 43.58 (6.68) 47.41 Stage 3 (minutes) 28.07 (9.18) 29.65 (12.42) 26.08 Stage 3 (%) 6.83 (1.99) 8.62 (3.89) 6.68 Stage 4 (minutes) 99.20 (21.40) 105.69 (15.05) 87.38 Stage 4 (%) 24.24 (5.33) 27.17 (7.38) 22.26 Light sleep (minutes) 199.33 (21.05) 200.17 (29.36) 203.04 Light sleep (%) 48.89 (6.33) 45.13 (7.32) 48.26 Deep sleep (minutes) 127.22 (24.23) 135.33 (18.04) 114.29 Deep sleep (%) 31.05 (5.81) 35.78 (10.39) 29.48 REM-S (minutes) 82.78 (18.11) 84.63 (27.65) 82.83 REM-S (%) 20.08 (3.37) 19.09 (5.76) 22.27 REM latency (minutes) 83.88 (18.39) 98.53 (36.90) 80.20

Degrees of freedom: Always � (1, 49). TST � total sleep time; SO � sleep onset; REM-S � rapid eye movement sleep; M * p � .05. ** p � .01. *** p � .001.

but regular, exercise such as running should be promoted as both [

a remedy and a preventative measure for poor sleep and poor psychological functioning.

Acknowledgments

The authors thank Marielle Koenig and Vladimir Djurdjevic for sleep EEG scoring. Moreover, they are grateful to Ladina Schlatter for data collection and data entry. Finally, they thank Nick Emler (Surrey, UK) for proofreading the manuscript.

The entire study was conducted without external funding, and the authors have declared that no competing interests exist.

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Statistics

After assessment n � 24 M (SD)

Group Time Group � time interaction

F �2 F �2 F �2

) 406.00 (56.00) 2.71 .052 3.95 .075 1.56 .031 10.43 (4.41) 4.31* .081 3.59 .082 6.12** .120 92.51 (3.65) 4.78* .089 .66 .013 .00 .000 6.67 (2.75) .70 .014 .01 .000 1.75 .034

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