**3. Sleeping habits and health and human performance**

Sleep constitutes a basic need, with durations between 8 and 9 hours depending on the age, that has direct effects on the human health and then on the human performances developed daily [68, 69]. The importance of this behavior is crucial in all the age stages, but with special relevance during childhood and adolescence [70]. The available research has widely investigated this issue under different perspectives such as healthy approaches, healthy programs, physiological needs, social influence, sleep and lifestyle, sleep disorders, sleep deprivation or sleep loss and academic performance [71–75]. The latest area has received greater analysis for children, adolescents, educators, parents and pediatrics due to the important effect on academic performances during the primary and secondary school and the university studies [71, 72, 76, 77]. The next sections of the chapter will try to go in depth about the key aspects that should be known and considered when studying the importance of sleep habits and health, the importance of sleep habits and academic performance in children and adolescents, the relationships between sleep habits and obesity and the importance of healthy programs to educate the children into positive sleep habits.

#### **3.1. Sleep habits and health**

Sleep is an active, repetitive and reversible state that promotes the development of physical, cognitive, affective and behavioral aspects. Sleep is necessary to maintain all the brain functions affecting the good state of human memory, learning/memory capacity, the brain's optimal function or the neurobehavioral function [78–81]. Therefore, sleep habits are one of the most important daily routines that must be correctly done [82]. The absence, loss or deprivation of sleep has a direct effect on health problems [83–85]. However, when these disorders or inadequate sleep habits occur during the childhood or the adolescence, the academic performance and the physical and physiological development are highly compromised [86–88].

Nowadays, sleep loss is one of the problems that the people should face daily. Usually, it is preferable to sacrifice some of the time dedicated to sleep hoping that this time will not have a negative impact during our daily activities such as studying, working, etc. [83]. However, this behavior has a direct and negative effect on physical (fatigue), neurocognitive (impairment in learning and memory) and psychomotor performances (impairment in psychomotor activities) [89].

#### **3.2. Sleep habits and academic performance in children and adolescents**

better attentional control in visual search tasks [63]. The authors argued that those effects can be mediated by changes in brain functioning (i.e., frontal and parietal cortex), although research among children has not been conducted so far. In conclusion, positive relationships and associations between executive functions and physical activity have been found in terms of: (a) moderate-to-vigorous physical activity, (b) aerobic fitness and (c) motor skills [62].

Obesity during school-age period has been proved to have detrimental effects on academic performance [5, 60]. However, high percentage of body fat does not hamper, by itself, the likelihood of academic success. In a recent study over 11,192 kindergartens, achievement scores were significantly lower in overweight children than in no overweight children in standardized tests of mathematics and reading. However, this association was no longer significant after the adjustment to race/ethnicity and socioeconomic status [9]. In another study upon 36,870 adolescents, it has been shown that physical activity can attenuate or even counteract negative association of fatness on academic achievement. In particular, fit adolescents (both high and low fatness) had higher odds for attaining high academic scores (in language and mathematics) than high fatness unfit counterparts. Also, low fatness adolescents were not more likely to reach higher scores in language than their high fatness fit peers [54]. Thus, physical activity seems to strongly mediate between obesity and academic achievement. Although the evidence of this mediator effect is limited, a promising research in this topic is envisaged [60]. Furthermore, as some researchers consider [67] that the association between elevated body mass index and decreased academic achievement was dependent on the extent to which obesity was stigmatized in the school.

Sleep constitutes a basic need, with durations between 8 and 9 hours depending on the age, that has direct effects on the human health and then on the human performances developed daily [68, 69]. The importance of this behavior is crucial in all the age stages, but with special relevance during childhood and adolescence [70]. The available research has widely investigated this issue under different perspectives such as healthy approaches, healthy programs, physiological needs, social influence, sleep and lifestyle, sleep disorders, sleep deprivation or sleep loss and academic performance [71–75]. The latest area has received greater analysis for children, adolescents, educators, parents and pediatrics due to the important effect on academic performances during the primary and secondary school and the university studies [71, 72, 76, 77]. The next sections of the chapter will try to go in depth about the key aspects that should be known and considered when studying the importance of sleep habits and health, the importance of sleep habits and academic performance in children and adolescents, the relationships between sleep habits and obesity and

the importance of healthy programs to educate the children into positive sleep habits.

Sleep is an active, repetitive and reversible state that promotes the development of physical, cognitive, affective and behavioral aspects. Sleep is necessary to maintain all the brain

**3.1. Sleep habits and health**

**3. Sleeping habits and health and human performance**

*2.3.3. Body fat*

220 Health and Academic Achievement

Specifically, the importance of sleep loss increases during the childhood and the adolescence due to the important role that plays in learning capacity, school performance and memory consolidation [72, 73, 81]. During the school and college stages, the students cope with sleep problems, such as sleep deprivation or sleep restriction, which produces a poor sleep quality and then academic problems [73]. The specific literature refers to a mean of 9 hours per night of sleep as a good requirement; however, 45% of the students sleep less than 8 hours per night and around 20–50% considers that they have sleepiness during the day [77, 78, 80]. The reasons of this time sleep reduction can be an interaction of intrinsic (e.g., physical and physiological changes induced by the puberty) or extrinsic (e.g., school schedules, extracurricular activities, family lifestyle, etc.) factors that lead to go late to bed with the daily routines unchanged [90].

The consequence of this sleep loss is the sleepiness that the children and adolescents reflect during the day [68]. This fact reduces some neurobehavioral aspects of learning and memory, such as reduced alertness and decision-making, or difficulties when performing complex tasks (i.e., that require the use of the prefrontal cortex) during planning, integrative processes or abstract thinking [80, 91]. According to this rationale, the sleep loss appears during the stages from school to the university affecting the learning process and the academic performance in the different lessons (i.e., practice, laboratories, theory or exams) received by the students [84, 85, 88].

#### *3.2.1. The importance of sleep-wake cycle and the delayed phase preference*

The physiological explanations of sleep loss are the changes that occur during the sleep-wake cycle caused by going to bed late and waking up early in the morning. The sleep-wake cycle is composed of two opposing processes: the circadian rhythm (described as a natural clock synchronized with the external time and regulates the wakefulness) and the homeostatic drive for sleep (process that increases sleepiness with the accumulated time awake and decreases when sleeping) [79]. The changes of this cycle appear with greater intensity during the adolescence with changes in the students' chronotype due to the delayed phase preference [80]. This delay is not only social, cultural or psychological [79, 81] and is affected by biological processes associated to the puberty (biological factors that slow down the circadian oscillation process and the homeostatic drive for sleep) [81]. The importance of sleep-wake cycle can be associated to the cognitive performance in youth students. Kirby et al. [69] explained that it depends on the time of the day where the accumulation of drive for sleep process increases or decreases the sleep pressure. This mainly occurs during the waking up hours, early in the morning, after eating or with a high sleep debt.

learning, cognitive and neurobehavioral function [65, 68]. Regarding to this relationship, some factors should be controlled for when trying to identify the reasons of this sleep loss and then the poor performance. According to the scientific research [69, 70], some aspects may modify the sleep schedules in both the intrinsic and extrinsic factors. On the one hand, the intrinsic factors can be affected by the students' level of stress due to academic pressure [65, 72, 78] or close schedules [69, 75] that induce to a high-pressure level of tension, anxiety and feelings of stress that disrupt or modify the circadian rhythms [65, 81]. On the other hand, the extrinsic factors can be associated to the high number of hours after the school doing extracurricular activities [72, 73]; the social factors that modify the schedules such as the adolescent life, the campus life or love relationships [74, 76]; the use of afternoon naps [75]; the importance of time watching TV, internet or playing videogames [78]; the influence of the sleep debts during the course (e.g., more fatigue during the second semester) [75] or the weekday or weekend day routines (i.e., the weekend may make up the sleep lost accumulated during the week, but dramatic changes can occur in the sleep-wake cycle if the students increase dramatically the number of hours of sleep) [77]. In addition, the sleep behavior during the childhood and adolescence should maintain an adequate number of hours of sleep and good quality of sleep to avoid a chronic pattern of sleep that would have a negative impact on cognitive, performance, learning, neurobehav-

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The influence of sleep loss and physical/psychomotor performance has been studied in different contexts. When analyzing the psychomotor performance at the school, the studies [83, 84] did not report significant effects of sleep deprivation on motor performances of students. In fact, the only relative significant results were identified with more than 30 hours of sleep deprivation on endurance, agility, balance, strength and speed [83, 84]. However, if we consider the academic activities of physical education subject at the school, the number of hours per week and the intensity of its activities may explain the non-significant results due to the

On the other hand, if we analyze the athletes' context, where they must perform at their highest level, the studies are showing an important effect of sleep loss and physical performance [87]. The athletes can only perform at their optimal level when the sleep habits are hygienic and favorable [87]. It is suggested that the athlete should sleep around 8–9 hours per night to recover and repair their tissues after trainings and competitions. To do so, both sleep phases (REM and NREM) must be covered to have the adequate psychological, hormonal (e.g., growth hormone secretion) and glucose metabolism processes [85]. Additionally, the sleep deprivation in athletes may result in an imbalance of the autonomous nervous system, the immune system and the cognitive function and then simulate the overtraining syndrome symptoms [88, 89]. In fact, sleep deprivation may create a disturbance of the athlete's sleep-wake cycle independent of the fatigue process suffered by trainings and competitions [85], suggesting that the athletes perform better the complex skills early in the day than gross motor skills (better performances late in the day) due to

ioral and mood aspects [73, 76].

*3.2.4. Sleep loss and physical performance*

the circadian rhythm alertness [85, 89].

low impact performance developed during the lessons.

#### *3.2.2. The relationships between sleep and learning-memory processes*

As was previously described, the sleep-wake cycle modifies the cognitive performances according to the sleep loss. This process affects the learning and memory processes during the academic activities. Specifically, the memory can be divided into: (i) the procedural/nondeclarative memory (i.e., knowing how to do a skill or solve a problem) that involves the visual, motor or verbal domains and is gained during the rapid eye movement (REM) sleep and (ii) the declarative memory (i.e., knowing that) that links to the related conscious collection of information and is restored in the no rapid eye movement (NREM) sleep. Both sleep phases (i.e., REM and NREM) are crucial for the learning and memory processes performed during the academic activities. Thus, the sleep deprivation or sleep loss is the great enemy for children and adolescent during the learning stages [65, 68].

In order to summarize the effects of sleep loss and the sleep-wake cycle on the academic performance, we can point out the following key issues [69]: (i) the attention and working memory are more affected by the circadian rhythm (synchronicity effects of optimal performance in specific moments of the day) than the procedural memory [69]; (ii) the optimal performances for executive functions are later in the day [86] and (iii) the sleep debt contributes to learning difficulties on concentration, memory, complex thinking or planning tasks [83]. Accordingly, the schedules established for schools, colleges and universities may impose an early starting time that impairs the students' abilities to perform at their best level due to their sleep loss and the sleep debts accumulated along the week [68].

#### *3.2.3. Sleep loss and academic performance*

The correlations between sleep loss and academic performance have been largely studied using self-reported surveys, grade point average (GPA), parents' or teachers' reports or the analysis of school behaviors [65, 68]. The main conclusion obtained in this research area is that the children's fatigue associated to poor sleep (i.e., quality of sleep) is the best predictor of lower school/college/university performances [70, 71, 73]. Thus, this fact shows a tendency of those students to fall asleep during school time, lose their concentration easily and not focus their attention on the relevant information. More specifically, during the sleep loss, the prefrontal cortex and its neural activity highly affect the divergent thinking, language speech, memory, decision-making, attention, mood, learning processes, critical thinking, creativity or performing complex tasks [66].

The available studies have showed this negative relationship between sleep and academic performance in primary and secondary schools [78] as well as at the university level [76]. The authors referred that the sleepiness produced by the poor quality of sleep impairs the above-mentioned, learning, cognitive and neurobehavioral function [65, 68]. Regarding to this relationship, some factors should be controlled for when trying to identify the reasons of this sleep loss and then the poor performance. According to the scientific research [69, 70], some aspects may modify the sleep schedules in both the intrinsic and extrinsic factors. On the one hand, the intrinsic factors can be affected by the students' level of stress due to academic pressure [65, 72, 78] or close schedules [69, 75] that induce to a high-pressure level of tension, anxiety and feelings of stress that disrupt or modify the circadian rhythms [65, 81]. On the other hand, the extrinsic factors can be associated to the high number of hours after the school doing extracurricular activities [72, 73]; the social factors that modify the schedules such as the adolescent life, the campus life or love relationships [74, 76]; the use of afternoon naps [75]; the importance of time watching TV, internet or playing videogames [78]; the influence of the sleep debts during the course (e.g., more fatigue during the second semester) [75] or the weekday or weekend day routines (i.e., the weekend may make up the sleep lost accumulated during the week, but dramatic changes can occur in the sleep-wake cycle if the students increase dramatically the number of hours of sleep) [77].

In addition, the sleep behavior during the childhood and adolescence should maintain an adequate number of hours of sleep and good quality of sleep to avoid a chronic pattern of sleep that would have a negative impact on cognitive, performance, learning, neurobehavioral and mood aspects [73, 76].

#### *3.2.4. Sleep loss and physical performance*

processes associated to the puberty (biological factors that slow down the circadian oscillation process and the homeostatic drive for sleep) [81]. The importance of sleep-wake cycle can be associated to the cognitive performance in youth students. Kirby et al. [69] explained that it depends on the time of the day where the accumulation of drive for sleep process increases or decreases the sleep pressure. This mainly occurs during the waking up hours, early in the

As was previously described, the sleep-wake cycle modifies the cognitive performances according to the sleep loss. This process affects the learning and memory processes during the academic activities. Specifically, the memory can be divided into: (i) the procedural/nondeclarative memory (i.e., knowing how to do a skill or solve a problem) that involves the visual, motor or verbal domains and is gained during the rapid eye movement (REM) sleep and (ii) the declarative memory (i.e., knowing that) that links to the related conscious collection of information and is restored in the no rapid eye movement (NREM) sleep. Both sleep phases (i.e., REM and NREM) are crucial for the learning and memory processes performed during the academic activities. Thus, the sleep deprivation or sleep loss is the great enemy for

In order to summarize the effects of sleep loss and the sleep-wake cycle on the academic performance, we can point out the following key issues [69]: (i) the attention and working memory are more affected by the circadian rhythm (synchronicity effects of optimal performance in specific moments of the day) than the procedural memory [69]; (ii) the optimal performances for executive functions are later in the day [86] and (iii) the sleep debt contributes to learning difficulties on concentration, memory, complex thinking or planning tasks [83]. Accordingly, the schedules established for schools, colleges and universities may impose an early starting time that impairs the students' abilities to perform at their best level due to their

The correlations between sleep loss and academic performance have been largely studied using self-reported surveys, grade point average (GPA), parents' or teachers' reports or the analysis of school behaviors [65, 68]. The main conclusion obtained in this research area is that the children's fatigue associated to poor sleep (i.e., quality of sleep) is the best predictor of lower school/college/university performances [70, 71, 73]. Thus, this fact shows a tendency of those students to fall asleep during school time, lose their concentration easily and not focus their attention on the relevant information. More specifically, during the sleep loss, the prefrontal cortex and its neural activity highly affect the divergent thinking, language speech, memory, decision-making, attention, mood, learning processes, critical thinking, creativity or performing complex tasks [66].

The available studies have showed this negative relationship between sleep and academic performance in primary and secondary schools [78] as well as at the university level [76]. The authors referred that the sleepiness produced by the poor quality of sleep impairs the above-mentioned,

morning, after eating or with a high sleep debt.

222 Health and Academic Achievement

*3.2.2. The relationships between sleep and learning-memory processes*

children and adolescent during the learning stages [65, 68].

sleep loss and the sleep debts accumulated along the week [68].

*3.2.3. Sleep loss and academic performance*

The influence of sleep loss and physical/psychomotor performance has been studied in different contexts. When analyzing the psychomotor performance at the school, the studies [83, 84] did not report significant effects of sleep deprivation on motor performances of students. In fact, the only relative significant results were identified with more than 30 hours of sleep deprivation on endurance, agility, balance, strength and speed [83, 84]. However, if we consider the academic activities of physical education subject at the school, the number of hours per week and the intensity of its activities may explain the non-significant results due to the low impact performance developed during the lessons.

On the other hand, if we analyze the athletes' context, where they must perform at their highest level, the studies are showing an important effect of sleep loss and physical performance [87]. The athletes can only perform at their optimal level when the sleep habits are hygienic and favorable [87]. It is suggested that the athlete should sleep around 8–9 hours per night to recover and repair their tissues after trainings and competitions. To do so, both sleep phases (REM and NREM) must be covered to have the adequate psychological, hormonal (e.g., growth hormone secretion) and glucose metabolism processes [85]. Additionally, the sleep deprivation in athletes may result in an imbalance of the autonomous nervous system, the immune system and the cognitive function and then simulate the overtraining syndrome symptoms [88, 89]. In fact, sleep deprivation may create a disturbance of the athlete's sleep-wake cycle independent of the fatigue process suffered by trainings and competitions [85], suggesting that the athletes perform better the complex skills early in the day than gross motor skills (better performances late in the day) due to the circadian rhythm alertness [85, 89].

#### **3.3. Sleep habits and obesity**

One of the intriguing relationships of sleep habits and health is the research findings of sleep patterns and obesity. The scientific research has raised the importance of sedentary lifestyle in overweight and obesity. Insufficient sleep plays a critical role in children with overweight and predicts body mass index (BMI) when the students also do sedentary activities [92]. The mechanism associated to the lack of sleep is the level of hormones regulating the body appetite due to a decrease of leptin secretion and an increase of the ghrelin [92]. This mechanism creates an imbalance of both hormones increasing the feelings of hungry and the need to intake foods and then the incidence of overweight and obesity, coronary heart disease, type 2 diabetes or hypertension [73, 78, 92]. Additionally, this relationship appears to have another influence on obese/overweight student's physical growth, the reduction in height [73, 78, 92]. The main body of research of different countries [92] showed negative correlations between sleep deprivation and BMI and positive correlations with height [78, 92]. This result has a gender effect with female students having less sleep deprivation and environmental pressure than their male mates, reflecting a greater prevalence of obesity in male students with less sleep [92].

reducing their performances. Indeed, if sleep is a vital element on the students' health, the regular practice of physical exercise is also a key factor. The scientific research has demonstrated that physical activity improves sleep and then the cardiovascular system, allowing to a better sleep quality. In addition, Flueckiger et al. [27] consider that sleep predicts better achievement than physical activity (i.e., students with higher overall sleep quality had better

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Schools should encourage their students to be active and they should self-promote it for many reasons. Specifically, as has been widely commented, the effect of physical exercise will promote sleep and will have a direct impact on the performance of academic tasks. It is necessary to revitalize and put the Physical Education and Sports subject in the correct place that deserves during the school age [2, 12]. This approach requires that the students can have a minimum of 150 minutes of moderate-to-vigorous exercise per week, as this physical activity will have a direct impact on the performance of schoolchildren and their health. Marshall and Hardman [96] claimed that physical education is in a perilous position in all continental regions of the world. However, the problems of status, curricula, implementation, time allocation, financial support, human resources, teacher preparation and attitude of headteachers,

The key question is to decide: what do we need in the education of children and adolescents. Then, we must decide between two educational options, the first one focused on educational centers where active lifestyles are promoted, and sleep and exercise are present; or the second one focused on active schools in which the general behavior of their members is manifested in healthy behaviors and healthy attitudes, and active school environments, and that favor an

Based on this extensive body of research, some suggestions can be outlined to optimize the effect of physical activity and sleep habits on the academic achievement. Researches findings suggest positive benefits of physical activity throughout a wide range of academic ages, from kindergarten [11] until college [51, 93]. Scientific literature suggests uneven effects as a function of the age, remarking greater effect of physical activity on academic performance in primary school (6–13 years old) in comparison with adolescents (14–18 years old). Thus, students should be encouraged to practice physical activities in early periods of primary school

The meta-analysis done by Fedewa and Ahn [95] examined different interventions on children's cognitive outcomes (mathematics, science, reading, English/language, art achievement, grade point average and intellectual quotient). The results showed that, unlike resistance/circuit training and their combinations, aerobic training, physical education program and perceptual motor training (in that order) significantly affected the academic achievement [46]. Other authors stated that there is still no clear evidence regarding which programs are more effective for cognitive performance. The aerobic and motor skills programs (both combined with cognitive engaging) seem to be the most efficient ones [31]. In the same terms, other studies confirm

parents and other teachers increase the skepticism about its future.

embodied educational work and the performance of the students.

to maximize the potential benefits over the academic achievement [55, 94].

academic achievement).

**5. Concluding remarks**

#### *3.3.1. Sleep breathing disorders*

Some studies also related the students facing with sleep breathing disorders, such as obstructive sleep apnea (OSA) or insomnia, to poor academic performances [65, 68]. These disorders include difficulties to maintain sleep, snoring, insomnia or waking up early in the morning. Then, these students have more problems to perform correctly at the school due to the sleep debt that limits the attention, working memory or learning processes [92]. In fact, these students need to have a nap to adjust their sleep requirements; however, this behavior modifies the sleep-wake cycle and then their neurocognitive and behavioral domains and the increase of BMI [65, 68, 92]. Therefore, from an educational point of view, the students with sleep breathing disorders should be considered when planning specific sleep educational programs.

## **4. Sleep and exercise well during the growing years**

In this chapter, the associations of two health behaviors, such as physical activity and sleep habits with academic achievement of students, have been explored. This analysis allows us to state that there are many more relationships among them than could be thought in a first instance [27].

It should be said that if you want to lead a healthy and satisfying life, you should start sleeping well and practice physical activity. The lack of sleep is related to a whole set of diseases that are not conducive to the health of individuals independently of the age of the student. On the other hand, it has been widely demonstrated that good sleep is a key aspect to personal performance. The scientific research has demonstrated the relationships among sleep loss, academic outcomes and school drop-out in adolescent students. The exams encourage adolescents to significantly reduce sleep, drink energetic drinks [85] and adopt sedentary attitudes that may favor the possibility of higher levels of anxiety and stress on the students reducing their performances. Indeed, if sleep is a vital element on the students' health, the regular practice of physical exercise is also a key factor. The scientific research has demonstrated that physical activity improves sleep and then the cardiovascular system, allowing to a better sleep quality. In addition, Flueckiger et al. [27] consider that sleep predicts better achievement than physical activity (i.e., students with higher overall sleep quality had better academic achievement).

Schools should encourage their students to be active and they should self-promote it for many reasons. Specifically, as has been widely commented, the effect of physical exercise will promote sleep and will have a direct impact on the performance of academic tasks. It is necessary to revitalize and put the Physical Education and Sports subject in the correct place that deserves during the school age [2, 12]. This approach requires that the students can have a minimum of 150 minutes of moderate-to-vigorous exercise per week, as this physical activity will have a direct impact on the performance of schoolchildren and their health. Marshall and Hardman [96] claimed that physical education is in a perilous position in all continental regions of the world. However, the problems of status, curricula, implementation, time allocation, financial support, human resources, teacher preparation and attitude of headteachers, parents and other teachers increase the skepticism about its future.

The key question is to decide: what do we need in the education of children and adolescents. Then, we must decide between two educational options, the first one focused on educational centers where active lifestyles are promoted, and sleep and exercise are present; or the second one focused on active schools in which the general behavior of their members is manifested in healthy behaviors and healthy attitudes, and active school environments, and that favor an embodied educational work and the performance of the students.
