Abstract and Introduction
Purpose: High-intensity interval training (HIIT) has emerged as a time-efficient strategy to improve children's and adolescents' health-related fitness in comparison to traditional training methods. However, little is known regarding the effects on cognitive function and mental health. Therefore, the aim of this systematic review was to evaluate the effect of HIIT on cognitive function (basic information processing, executive function) and mental health (well-being, ill-being) outcomes for children and adolescents.
Methods: A systematic search was conducted, and studies were eligible if they 1) included a HIIT protocol, 2) examined cognitive function or mental health outcomes, and 3) examined children or adolescents (5–18 yr). Separate meta-analyses were conducted for acute and chronic studies, with potential moderators (i.e., study duration, risk of bias, participant age, cognitive demand, and study population) also explored.
Results: A total of 22 studies were included in the review. In acute studies, small to moderate effects were found for executive function (standardized mean difference [SMD], 0.50, 95% confidence interval [CI], 0.03–0.98; P = 0.038) and affect (SMD, 0.33; 95% CI, 0.05–0.62; P = 0.020), respectively. For chronic studies, small significant effects were found for executive function (SMD, 0.31; 95% CI, 0.15–0.76, P < 0.001), well-being (SMD, 0.22; 95% CI, 0.02–0.41; P = 0.029), and ill-being (SMD, −0.35; 95% CI, −0.68 to −0.03; P = 0.035).
Conclusions: Our review provides preliminary review evidence suggesting that participation in HIIT can improve cognitive function and mental health in children and adolescents. Because of the small number of studies and large heterogeneity, more high-quality research is needed to confirm these findings.
The benefits of physical activity for children's and adolescents' physical health are well established. There is also strong evidence to suggest that regular physical activity can improve a range of mental health outcomes (e.g., self-esteem, anxiety, and depression). In addition to the physical and mental health benefits of physical activity, accumulating evidence suggests that regular engagement in physical activity to improve cardiorespiratory fitness (CRF) may enhance cognitive function in children and adolescents. Of note, the associated benefits of physical activity are largely influenced by the nature of the intervention delivered (i.e., acute and chronic physical activity). Acute interventions involve a single bout of physical activity (between 5 and 60 min) and are typically associated with temporary improvements (i.e., increased affect, release of endorphins, enhanced cerebral blood flow). Conversely chronic interventions typically involve multiple physical activity sessions per week for an extended period of time (e.g., two sessions per week for 10 wk), yielding physiological adaptations (e.g., enhanced brain structure and function). Despite these extensive benefits, 80% of adolescents worldwide are not meeting the international physical activity guideline recommendation of 60 min of daily moderate-to-vigorous physical activity. Furthermore, review-level evidence suggests that physical activity levels decline approximately 7% per year during adolescence.
The decline in physical activity may also contribute to increased prevalence of mental health disorders (e.g., anxiety, depression) that emerge during late adolescence (i.e., 15–19 yr). Worldwide, mental and substance use disorders are the leading cause of disability among youth, accounting for at least a quarter of years lived with disability. Participation in physical activity is important for children's and adolescents' mental health, which includes both positive and negative constructs. In this review, we use the term well-being to describe positive constructs (e.g., psychological well-being, self-esteem, positive affect, life satisfaction, quality of life, and psychological resilience) and ill-being to represent preclinical psychological states and clinically diagnosed mental health disorders (e.g., depression and anxiety).[4,10] As previously mentioned, it seems that physical activity and fitness are important for the development of cognitive function, which may serve as a core foundation upon which mental health is established. Of note, poor cognitive performance during childhood is associated with current and future mental health problems (i.e., generalized anxiety disorder).[11,12]
Cognitive function refers to the set of mental processes that contribute to perception, memory, intellect, and action. Although cognitive function tasks are often dichotomized into two broad categories (basic information processing and executive function), it is important to note that cognitive tasks exist on a continuum, from basic information processing at one end, to tasks requiring high levels of executive function at the other end. Basic information processing requires limited resources and therefore represents a lower level of cognitive function (e.g., simple motor speed/information processing tasks). By contrast, executive functions represent higher-order cognitive processes that contribute toward purposeful, goal-directed behavior. Executive function consists of three core dimensions that are critical for planning, problem solving, and learning. These include inhibition, working memory, and cognitive flexibility. Evidence suggests that executive functions are essential for success in school, vocation, and life. To date, the majority of physical activity research has demonstrated selective and disproportionately greater effects for executive function tasks as opposed to those that are less executive in nature. Recent systematic reviews in school-aged youth and older adults have demonstrated that activity of vigorous intensity improves cognition to a greater extent than activity of moderate and light intensity. One of the clear benefits of engaging in regular physical activity is the development of physical fitness (i.e., CRF, muscular fitness, favorable body composition). There is sufficient evidence to suggest that children and adolescents should participate in vigorous physical activity, as it provides greater health benefits in comparison to light and moderate intensity physical activity.[18,19] A useful approach for accumulating vigorous physical activity is high-intensity interval training (HIIT). HIIT is a form of exercise that typically involves alternating relatively short intervals (from <45 s to 2–4 min) of high-intensity activity (i.e., >85% max heart rate) with periods of active recovery or rest, or reoccurring bouts of maximal sprint efforts, interspersed by a prolonged rest period. HIIT has emerged as a novel and time-efficient strategy for improving children's and adolescents' health-related fitness in comparison to traditional training methods.[20,21] HIIT has gained significant international interest in recent years and was the second highest fitness trend for 2020 (top 5 since 2014). Furthermore, the recent Scientific Report of the 2018 Physical Activity Guidelines Advisory Committee highlighted, for the first time, the need to examine the effects of novel forms of physical activity such as HIIT on health outcomes in youth. Despite this, no previous review has focused on the benefits of HIIT for children's and adolescents' cognitive function and mental health.
Two previously published meta-analyses have explored the effects of HIIT on cognitive and mental health outcomes in a range of populations. However, during childhood and adolescence, the brain undergoes dramatic functional and structural changes. It is therefore difficult to draw firm conclusions regarding the specific effects of HIIT in children and adolescents. Furthermore, these reviews focused solely on the acute effects of HIIT; however, the chronic effects of HIIT are relatively unknown. Therefore, the primary aim of our review was to evaluate the acute and chronic effects of HIIT on cognitive function (basic information processing, executive function) and mental health (well-being, ill-being) in children and adolescents. A secondary aim was to identify potential moderators of effects (i.e., study duration, risk of bias, age of participants, cognitive demand of HIIT, type of comparison group, and study population).
Med Sci Sports Exerc. 2020;52(10):2224-2234. © 2020 American College of Sports Medicine