Abstract
Purpose
Mental toughness (MT) is understood as the display of confidence, commitment, challenge, and control. Mental toughness is associated with resilience against stress. However, research has not yet focused on the relation between MT and objective sleep. The aim of the present study was therefore to explore the extent to which greater MT is associated with objectively assessed sleep among adolescents.
Methods
A total of 92 adolescents (35% females; mean age, 18.92 years) completed the Mental Toughness Questionnaire. Participants were split into groups of high and low mental toughness. Objective sleep was recorded via sleep electroencephalograms and subjective sleep was assessed via a questionnaire.
Results
Compared with participants with low MT, participants with high MT had higher sleep efficiency, a lower number of awakenings after sleep onset, less light sleep, and more deep sleep. They also reported lower daytime sleepiness.
Conclusions
Adolescents reporting higher MT also had objectively better sleep, as recorded via sleep electroencephalograms. A bidirectional association between MT and sleep seems likely; therefore, among adolescence, improving sleep should increase MT, and improving MT should increase sleep.
Keywords
Adolescence is defined as the period of gradual transition between childhood and adulthood, with conceptually distinct physical changes marking puberty and maturation [
1
, 2
]. Along with dramatic changes in physiology and neural networks [3
, 4
], adolescents have to face new challenges and assume responsibility for issues such as their academic and vocational careers; peer and intimate relationships; increased physical, emotional and financial independence from parents and siblings; use of psychoactive substances; extra-curricular employment; and leisure-time activities such as sports participation and music [[1]
]. Dealing with these issues is potentially stressful; accordingly it is assumed that adolescents with better coping skills will deal more successfully with these challenges [[5]
].A psychological construct related to favorable stress management is mental toughness (MT). Mental toughness is a relatively new area of academic research [
[6]
] and a cognitive strength variable known to be associated with good performance both in elite sport [[7]
] and, more recently, in non-elite sport [8
, 9
, 10
, 11
]. Mental toughness has been conceptualized in various ways in the scientific literature [[6]
]. In the present study, we used the 4C(+2) (Challenges, Commitment, Control [emotional and control over life], Confidence [interpersonal and in ability]) model of MT, defined as performing well in challenging situations (“Challenges usually bring out the best in me”), commitment (“I don't usually give up under pressure”), control (emotional control: “Even when under considerable pressure I usually remain calm”; and life control: ”I generally feel in control”), and confidence (interpersonal confidence: ”I usually take charge of a situation when I feel it is appropriate”; and confidence in ability: “I am generally confident in my own abilities”) [[12]
]. In previous studies [9
, 10
, 11
], the authors were able to validate a German version of Mental Toughness Questionnaire–48 (MTQ48) [[12]
] and to show, in a large sample of adolescents and young adults, (1) that the construct of MT is not limited to high-performing elite sportsmen and women [9
, 10
, 11
]; (2) that MT is associated with increased stress resilience [9
, 10
]; and (3) that MT remains stable over time [[11]
], which suggests that MT is related to successful stress management and to psychological well-being.With regard to this last construct, numerous studies have indicated that independent of age, there is a bidirectional relation between psychological well-being and sleep [
[13]
]. For adolescents, sleep and sleep regulation play a crucial role in both well-being and development [14
, 15
, 16
, 17
]. Lemola et al. [18
, 19
] showed that dispositional optimism was associated with better sleep quality and longer sleep duration among children and adults. In contrast, sleep disturbances have been reported in more than 25% of adolescents worldwide; poor sleep in adolescence has become a significant public mental and physical health problem [14
, 20
]. Cross-sectional [21
, 22
] and longitudinal studies [23
, 24
] have shown that acute and chronic sleep loss during development persists over time, with negative effects on adolescents' physical and mental health. At the same time, poor psychological well-being may itself negatively affect adolescents' sleep [25
, 14
].To explain the association between poor sleep and psychological processes, it has been proposed that increased arousal and dysfunctional thoughts are directly involved in psychologically caused sleep disturbances [
26
, 27
, 28
, 29
], whereas, the absence of stress and worries, for instance, are associated with favorable sleep. This research points to interrelations among low stress, favorable personality traits, and restorative sleep. Consequently, it seems possible that high MT and good quality sleep are closely linked.The main goal of the research reported here was to explore the association between MT and objective sleep within a sample of adolescents. The present study may add to the current literature on MT and sleep in an important way by showing a close association between MT (as a marker of psychological well-being) and sleep among non-elite sport adolescents.
The following hypothesis was formulated. Following previous research [
9
, 10
, 11
, 18
, 19
], higher scores for MT would be expected to be associated with improved sleep, as assessed by sleep electroencephalogram (EEG) recordings. More specifically, the researchers expected to find higher sleep efficiency, shorter sleep onset latency, more deep sleep, and less light sleep in adolescents with high MT, with compared to adolescents with low MT. Lower daytime sleepiness (DS) was also expected. Findings that higher scores of MT were associated with subjectively increased improved sleep would confirm the hypothesis.Methods
Participants
A total of 285 adolescents participated in the study (mean age, 18.26 years; standard deviation 4.17 years); preliminary data are presented elsewhere [
[30]
]. All participants completed the MTQ and a questionnaire related to sleep complaints (SC) and daytime sleepiness (DS). To recruit participants, the study was advertised electronically on the homepages of three high schools in the canton of Basel, a district of the German-speaking Northwestern part of Switzerland. Data were collected during spring and summer 2012. Participants were informed about the purpose of the study and about the voluntary basis of their participation. They were also assured of the confidentiality of their responses, and they gave written informed consent. For participants aged <18 years, written informed consent was secured from their parents. The study was approved by the local ethics committee, and the entire study was performed in accordance with the ethical standards in the Declaration of Helsinki.Procedure
After completing the MTQ, a subsample of participants with high MT scores (upper 17% of the total score: ≥141 points) and participants with low MT scores (lower 15.5% of the total score: ≤77 points) were asked to undergo a sleep EEG assessment. Participants undergoing sleep EEG recordings received a voucher of 30 Swiss francs (about $30) for participation.
Materials
Participants completed the MTQ48 [
[12]
] to assess MT, the Insomnia Severity Index [[31]
] to assess SC, and the Epworth Sleepiness Scale [[32]
] to assess DS, and underwent objective sleep EEG monitoring [[33]
].Measurement of MT
Participants (N = 92) were asked to fill out the MTQ48 ([
[12]
]; German version: [9
, 10
, 11
]), which measures overall MT and its six subcomponents: challenge (e.g., “Challenges usually bring out the best in me”), commitment (e.g., I don't usually give up under pressure”), emotional control (e.g., “Even when under considerable pressure I usually remain calm”), life control (e.g., “I generally feel in control”), interpersonal confidence (e.g., “I usually take charge of a situation when I feel it is appropriate”), and confidence in ability (e.g., “I am generally confident in my own abilities”). Answers on the MTQ48 were given on 5-point Likert-type scales ranging from 1 = “strongly disagree” to 5 = “strongly agree”. Items were summed to obtain overall and subscale scores, with higher scores reflecting greater MT (Cronbach α = .89).Assessment of sleep: objective sleep assessment
To assess sleep objectively, sleep EEG recordings were performed at home using a three-channel EEG device (Fp2-A1, C3-A2, and C4-A1; electrooculogram; electromyogram; Somnowatch; Randersacker, Germany). Two experienced raters visually analyzed sleep polygraphs according to the standard procedures described and defined by Rechtschaffen and Kales [
[33]
] (inter-rater reliability: κ = .88). Raters were completely blinded with respect to participants' group assignments. The device provides assessment of total sleep time, sleep efficiency, sleep onset latency, stages 1–4 (minutes and percentage), light sleep (Stages 1 and 2), slow wave sleep (Stages 3 and 4), rapid eye movement (REM) sleep, and number and times of awakenings after sleep onset.Assessment of sleep: SC
The Insomnia Severity Index [
[31]
] is a 7-item self-rating questionnaire to assess SC. The items, answered on 5-point rating scales (0 = “not at all,” 4 = “very much”), refer in part to Diagnostic and Statistical Manual of Mental Disorders, 4th Edition criteria for insomnia [[34]
] by measuring difficulty in falling asleep, difficulties remaining asleep, early morning awakenings, increased DS, impaired daytime performance, low satisfaction with sleep, and worrying about sleep. The higher the overall score, the more the respondent is assumed to experience insomnia (Cronbach α = .92).Measurement of DS
To assess DS, participants completed the Epworth Sleepiness Scale [
[32]
]. Participants were asked about the likelihood of dozing off or falling asleep in specific situations (sitting and reading, watching television, sitting inactive in a public place, being a passenger in a car for an hour without a break, lying down to rest in the afternoon, sitting and talking to someone, and sitting quietly after a lunch). Answers were given on 4-point Likert scales ranging from 0 = “no chance of dozing” to 3 = “high chance of dozing,” with a higher sum score reflecting a greater likelihood of dozing off.Statistical analysis
A series of Student t tests were used to examine difference in target parameters (sleep EEG, SC, and DS) between participants with high MT and those with low MT. Next, Pearson's correlation coefficients were used to calculate the associations between the dimensions of MT and the target parameters across the entire sample.
The level of significance was set at α ≤ .05. All statistical analyses were calculated with SPSS 19.0 for Windows (IBM Company, New York, NY).
Results
All descriptive and inferential statistical information are reported in the tables.
High and low MT, objective sleep parameters, subjective sleep, and DS
Table 1 shows the descriptive and statistical comparisons of sleep parameters, SC, and DS scores between participants with high MT and low MT.
Table 1Descriptive and statistical overview of sleep electroencephalogram data, sleep complaints, and daytime sleepiness separately for participants with high mental toughness (n = 48) and low mental toughness (n = 44)
| Dimension of sleep | Group | t | |
|---|---|---|---|
| High mental toughness | Low mental toughness | ||
| Total sleep duration, hours | 6.85 (1.11) | 6.98 (1.08) | .05 |
| Sleep efficiency, % | 98.04 (.79) | 94.96 (1.92) | 10.19 |
| Sleep onset latency, minutes | 9.54 (7.59) | 11.26 (5.07) | .64 |
| Number of awakenings after sleep onset | 2.33 (1.62) | 6.45 (2.77) | 8.80 |
| Sleep 1 | |||
| Minutes | 8.59 (6.55) | 14.90 (10.53) | 3.49 |
| % | 2.00 (1.30) | 3.63 (2.51) | 3.95 |
| Sleep 2 | |||
| Minutes | 186.38 (53.43) | 200.00 (66.47) | 1.09 |
| % | 43.58 (7.25) | 46.78 (9.01) | 1.88 |
| Sleep 3 | |||
| Minutes | 43.17 (19.41) | 34.14 (11.32) | 2.69 |
| % | 10.17 (4.42) | 8.52 (2.65) | 2.14 |
| Sleep 4 | |||
| Minutes | 95.46 (24.97) | 82.19 (32.77) | 2.20 |
| % | 23.51 (7.54) | 21.61 (9.04) | 1.10 |
| Light sleep | |||
| Minutes | 194.96 (57.61) | 214.91 (69.42) | 1.50 |
| % | 45.57 (7.96) | 51.90 (9.79) | 3.42 |
| Deep sleep | |||
| Minutes | 138.45 (26.97) | 122.38 (34.84) | 2.48 |
| % | 33.68 (7.82) | 30.96 (9.75) | 1.48 |
| Rapid eye movement sleep | |||
| Minutes | 86.54 (27.44) | 70.64 (19.57) | 3.18 |
| % | 20.73 (5.72) | 17.12 (3.09) | 3.71 |
| Sleep complaints | 6.78 (1.04) | 12.01 (2.34) | 9.45 |
| Daytime sleepiness | 2.45 (3.06) | 10.91 (4.43) | 10.42 |
Degrees of freedom = always 90. Sleep complaints were assessed with the Insomnia Severity Index; daytime sleepiness was assessed with the Epworth Sleepiness Scale.
∗ p < .05.
∗∗ p < .01.
∗∗∗ p < .001.
Relative to participants with low MT, participants with high MT had higher sleep efficiency, more deep sleep, more REM sleep, less light sleep, fewer awakenings after sleep onset, and a lower score of subjective SC and DS. No statistically significant differences were found for sleep duration, sleep onset latency, and Stage 2 sleep.
Associations between dimensions of MT and objective sleep dimensions SC and DS
Table 2 shows the correlation matrix and descriptive statistics between the dimensions of MT and objective sleep, SC, and DS across the entire sample (N = 92).
Table 2Correlations (Pearson correlation coefficients) between mental toughness and dimensions of objective sleep, sleep complaints, and daytime sleepiness (N = 92)
| Dimension of sleep | Mental toughness | Descriptive statistics, mean (standard deviation) | ||||||
|---|---|---|---|---|---|---|---|---|
| Challenge | Commitment | Control emotion | Life | Confidence interpersonal | Abilities | Mental toughness total score | ||
| Total sleep duration, hours | .14 | .02 | .10 | –.05 | .09 | .00 | .05 | 6.95 (1.38) |
| Sleep efficiency, % | .75 | .70 | .83 | .63 | .65 | .72 | .74 | 95.04 (2.62) |
| Sleep onset latency, minutes | −.10 | −.08 | −.10 | −.09 | −.13 | −.06 | −.09 | 10.40 (9.78) |
| Number of awakenings after sleep onset | −.57 | −.67 | −.69 | −.70 | −.60 | −.72 | −.69 | 4.30 (3.05) |
| Sleep 1 | ||||||||
| Minutes | −.20 | −.21 | −.27 | −.14 | −.09 | −.23 | −.21 | 11.61 (9.20) |
| % | −.27 | −.22 | −.32 | −.14 | −.12 | −.24 | −.24 | 2.78 (2.12) |
| Sleep 2 | ||||||||
| Minutes | −.04 | −.18 | −.06 | −.19 | −.15 | −.19 | −.14 | 192.89 (60.08) |
| % | −.23 | −.31 | −.22 | −.29 | −.28 | −.29 | −.28 | 45.10 (8.25) |
| Sleep 3 | ||||||||
| Minutes | .13 | .09 | .14 | .09 | .22 | .17 | .14 | 38.85 (16.60) |
| % | −.02 | .03 | .03 | .06 | .10 | .10 | .05 | 9.38 (3.76) |
| Sleep 4 | ||||||||
| Minutes | .27 | .28 | .26 | .11 | .18 | .19 | .24 | 89.11 (29.56) |
| % | .14 | .22 | .19 | .12 | .17 | .19 | .18 | 22.60 (8.30) |
| Light sleep | ||||||||
| Minutes | −.07 | −.20 | −.09 | −.20 | −.15 | −.21 | −.16 | 204.50 (63.96) |
| % | −.30 | −.40 | −.32 | −.33 | −.37 | −.39 | −.37 | 48.60 (9.38) |
| Deep sleep | ||||||||
| Minutes | .33 | .36 | .33 | .22 | .35 | .31 | .34 | 130.77 (31.85) |
| % | .17 | .26 | .18 | .18 | .20 | .22 | .22 | 32.38 (8.85) |
| Rapid eye movement sleep | ||||||||
| Minutes | .31 | .25 | .32 | .23 | .32 | .28 | .29 | 78.94 (25.17) |
| % | .27 | .31 | .30 | .30 | .35 | .35 | .32 | 19.00 (4.97) |
| Sleep complaints | −.78 | −.69 | −.74 | −.87 | −.79 | −.69 | −.73 | 9.92 (1.93) |
| Daytime sleepiness | −.86 | −.90 | −.87 | −.64 | −.81 | −.88 | −.88 | 6.68 (4.69) |
Sleep complaints were assessed with the Insomnia Severity Index; daytime sleepiness was assessed with the Epworth Sleepiness Scale.
∗ p < .05.
∗∗ p < .01.
∗∗∗ p < .001.
The overall pattern of results shows that any dimension of MT was positively and statistically significantly correlated with sleep efficiency, deep sleep, and REM sleep, and negatively and statistically significantly correlated with the number of awakenings after sleep onset, light sleep, SC, and DS. Interestingly, no significant correlations were found for sleep duration and sleep onset latency.
Discussion
The key findings of the present study are that in a sample of adolescents, greater MT was related to better objective and subjective sleep and lower DS.
To perform the study, following previous research [
9
, 10
, 11
, 18
, 19
], the authors expected that higher scores for MT would be associated with improved sleep, as assessed by sleep EEG recordings; data fully confirmed this assumption: Adolescents with high MT, relative to adolescents with low MT, had more favorable sleep dimensions such as an increased sleep efficiency, a lower number of awakenings after sleep onset, or more deep sleep. Subjectively, as in a previous study [[30]
], adolescents reported lower SC and a lower score of DS. The present data agree with the many studies showing an association between restoring sleep and psychological well-being [[25]
]. The present findings mirror previous research in that favorable psychological concepts such as optimism [18
, 19
] were positively related to sleep. The present results expand previous findings in that this was the first study to prove that among non-elite sport adolescents, high scores of MT were associated with improved objective sleep. The authors also think that the present data add to the literature in that the construct of MT is still poorly investigated, but it has the potential to cover a broad variety of favorable motivational, emotional, cognitive, and stress-buffering processes. As this study showed, higher MT scores were related to stress resilience and increased physical activity also over time [9
, 10
, 11
]. Indeed, research has established links between MT and hardiness, which has previously been found to be associated with stress resilience, which is in accord with the idea that resilience does not evolve from avoidance of adversity, but from successful dealing with negative stimuli [[35]
]. Importantly, stress has been proven to increase the risk for maladjustment and psychopathology during adolescence and early adulthood [[5]
]. Although highly speculative and not provable with the present data, the authors assume that MT influences sleep positively via reduced stress [9
, 10
, 11
], reduced hyperarousal [[29]
], and reduced dysfunctional thoughts [26
, 27
, 28
], because it is highly plausible that dysfunctional thoughts and maladaptive behavior are incompatible with the dispositions toward appraisal of high control, challenge, commitment and confidence that characterize an MT person. Here, this overall concept of MT is closely related to objectively and subjectively assessed favorable sleep, and lower DS among a sample of non-elite sport adolescents.Surprisingly, MT was related neither to sleep duration nor sleep onset latency (SOL). Whereas the relative importance of sleep duration as a key factor for psychological well-being is a matter of debate, there is no explanation for why SOL was unrelated to MT.
Difficulty falling asleep is one of the core symptoms of sleep disturbance. It is assumed that dysfunctional thoughts (such as the fear of not being able to fall asleep, fear of not feeling restored the next day; and difficulties with coping with stress) increase psychophysiologic arousal, which in turn hinders falling asleep [
26
, 27
, 28
, 29
]. In this view, it is proven [[29]
] that stress as a dysfunctional concept prolongs SOL. Moreover, MT and stress resilience are closely associated [9
, 10
, 11
]; as a consequence, it would have been expected that MT and shortened SOL were associated; however, the current data did not confirm this expectation.Despite the clarity of the findings, several considerations caution against overgeneralization. First, data were derived from a selected subsample, and participants were recruited only from high schools; therefore, a selection bias cannot be excluded. Second, no thorough psychiatric or medical examination was made; therefore, the pattern of results might result from further latent although unassessed variables such as eating disorders, bipolar disorders, early-stage romantic love, substance abuse, stress at school, and stressful relationships. Third, only participants willing and able complete the questionnaires and to undergo sleep EEG recordings volunteered to take part in the study; therefore, a positive selection bias cannot be ruled out. Finally, in the present model, it was assumed that MT as a mental construct affects objective sleep, although the authors are aware of the bidirectionality between psychological functioning and sleep; that is, favorable or poor sleep also has an impact on cognitive and emotional processing and behavior [
[13]
]. Therefore, it is also conceivable that adolescents sleeping particularly well have developed a particularly high MT.Among a sample of participants in their late adolescence, greater MT was associated with objectively assessed better sleep and low DS. Future research should apply longitudinal and interventional designs to investigate the causal directions between MT and sleep, and to investigate to what extent improving adolescents' MT may improve also adolescents' sleep, and vice versa.
Acknowledgments
The authors thank Nick Emler (Surrey, UK) for proofreading the manuscript. Moreover, they thank Marielle Koenig and Vladimir Djurdjevic from the Sleep Laboratory of the Center for Affective, Stress, and Sleep Disorders, for sleep EEG recordings and analysis.
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Article info
Publication history
Published online: September 03, 2013
Accepted:
July 15,
2013
Received:
April 4,
2013
Identification
Copyright
© 2014 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.
