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Exercise and Children: Better Brain Health, Less Obesity, Less Stress
By Len Kravitz, PhD

According to the World Health Organization (WHO) (2017), physical activity for children and young people includes sports, play, games, recreation, chores, physical education and planned exercise. Specifically, the WHO recommends youth ages 5-17 to progressively accumulate a target of 60 minutes of moderate- to vigorous-intensity physical activity each day. The WHO also suggests that on at least 3 of the days per week, children include bone-loading activities (i.e., jumping, running and turning) during their physical activity, which will strengthen the muscles and bones. Alas, the WHO concludes that physically active young people may demonstrate higher academic performance at school, self-expression, self-confidence, and social interaction, which leads to two new studies with children.

Study 1. The Effect of Muscular and Aerobic Fitness on Academic Achievement
Kao, S-C., Westfall, D.R., Parks, A.C. et al. (2017). Muscular and aerobic fitness, working memory, and academic achievement in children, Medicine & Science in Sports & Exercise, 49(3), 500-508.

Experimental Approach to the Study
The majority of studies with youth have focused on the cognitive benefits of cardiovascular exercise. Kao et al. (2017) explain that cognitive control refers to a subgroup of mental processes, which manage goal-directed behavior such as working memory. The researchers continue that working memory involves the temporary management and storage of information that is central for academic achievement. Kao and colleagues summarize current findings in research, which demonstrate that cardiorespiratory exercise contributes to working memory in preadolescence boys and girls. The researchers continue that initial evidence is now postulates that muscular fitness may also be beneficial for improving working memory and academic achievement. Thus, the purpose of this study was to determine and compare the effects of muscular fitness and cardiorespiratory exercise on working memory and academic achievement in youth.

A total of 79 children (44 males, 35 females, age 9-11 yrs) completed this study (which followed conventional informed consent procedures). Participants were free of neurological disease and attention deficit disorder. All volunteers did a pre-exercise screening to make sure they could complete the exercise interventions of the study. None of the children were involved in any individualized education program. All participants were administered the Kaufman Brief Intelligence Test (a brief, individually administered measure of verbal and non-verbal intelligence) by a trained academic to gain an estimate of her/his intelligence quotient (IQ).

Aerobic Fitness Assessment
Maximal aerobic fitness was determined by a graded treadmill exercise test. The test maintained a constant speed (3.0 mph) that increased 2.5% in grade every 2 minutes until volitional exhaustion. A 30-minute rest period was provided between the aerobic fitness assessment and the muscular fitness assessment.

Muscular Fitness Assessment
A battery of submaximal muscular fitness exercises were first individually taught to the young participants that included a lunge, front squat, push-up, bent-over row, shoulder press, calf raise and curl-up. All exercises were completed with the person's body weight or a dual grip medicine ball (2.7-8.1 kg). Once the appropriate loading weight was determined and youth were confidently familiarized with all of the exercises, participants completed as many repetitions (with correct exercise form) as possible in 30 seconds. The researchers normalized the results due to differences in body size, which they then calculated muscular fitness indices from the youth performance of the timed exercises.

Cognition and Academic Achievement
For working memory, the researchers used a child-friendly n-back task that has become a standard assessment for measuring working memory. Essentially, this continuous performance task is presented with a sequence of stimuli, and the task consists of indicating when the current stimulus matches the one from steps earlier in the sequence. Academic achievement was determined from standardized mathematics and reading tests.

The study results denote that higher levels of aerobic and muscular fitness are associated with greater task condition performance of working memory. Interestingly, the researchers were able to determine that aerobic fitness has a higher association with algebraic mathematical function and muscular fitness had no association with any area of academic achievement. However, the current study also shows that muscular fitness may have unique contributions to working memory that are independent of aerobic fitness. The researchers hypothesized from recent research showing skeletal muscle releases specialized immune cells (cytokines and peptides) from muscle contractions that may uniquely affect brain metabolism and function.

Take-Home Message
In addition to doing cardiorespiratory and muscular fitness for life-long long health benefits, this new research shows both of these modes of exercise will improve cognitive health in children as well.

Study 2: Fitness, Stress and Body Composition
Gerber, M., Endes, K., Herrman, C. et al. (2017). Fitness, stress, and body composition in primary schoolchildren, Medicine & Science in Sports & Exercise, 49(3), 581-587.

Experimental Approach to the Study
Gerber et al. (2017) recap research demonstrating obese children have an increased risk of developing hypertension, insulin resistance, endothelial dysfunction, nonalcoholic fatty liver disease, orthopedic disorders and chronic pain. Research on the underlying causes of childhood obesity is currently inconclusive. However, Gerber and colleagues summarize that physical inactivity and psychological stress independently (and together) may contribute to the development of childhood overweight and obesity. Thus, the purpose of this study was to determine if physical activity and fitness moderate the relationships between different psychosocial stress indices and obesity-related measures.

A total of 325 first grade children (51% females, 49% males) from public primary schools in Switzerland were recruited for this study (which followed international guidelines of informed consent procedures for children).

Stress (peer, family, life events, and school-related stress) and vigorous physical activity were assessed via parental questionnaires and reports. Physical fitness was assessed with a 20-meter shuttle run maximal aerobic power test. The 20-meter shuttle (a person runs back and forth in the 20-meter course) is a multi-stage, validated run test that estimates maximal aerobic power in children. The tests starts at a running speed of 5 mph, which is increased .3 mph every minute at a constant pace, set by an audio signal. When the child is unable to continue the constant pace, the test is ended and the completed number of stages is used to estimate maximal aerobic consumption. Body mas index (BMI), sum of skinfolds and waist circumference were used to assess obesity-related outcomes.

Young participants with the highest fitness and physical activity levels had lower (and healthier) body mass index, body fat and waist circumference measures. Importantly, Gerber et al. (2017) highlight that current research showing a high correlation with childhood obesity and adult obesity. Thus successful adult obesity may truly need to be started with childhood physical activity programs that continue into a youth's young adult and adult years. As well, the students with the higher fitness levels experienced lower levels of psychological stress. Gerber and colleagues explain that recent research showing that physically active children have a slightly lower stress hormone response (i.e., cortisol, adrenaline, noradrenaline) to psychological stressors.

Take-Home Message
Young children are encouraged to live physical activity lifestyles for the reduction in overweight and obesity, which may help to combat adult obesity, as well as to better manage psychological life stressors.

Side Bar 1. Facts About Childhood Obesity in the United States.
(Data collected by Ogden et al., 2014)
1. In youth 2 to 19 years, obesity is defined as a BMI at or above the 95th percentile of the
Centers for Disease Control sex-specific BMI-for-age growth charts from the year 2000.
2. Overweight is defined as a BMI between the 85th and 95th percentiles.
3. According to the 2011-2012 data, the prevalence of obesity for children is 17% (as compared to 35% for adults &Mac179; 20 years of age).

Len Kravitz, PhD, CSCS is the program coordinator of exercise science and a researcher at the University of New Mexico, where he received the Outstanding Teacher of the Year award. In addition to being a 2016 inductee into the National Fitness Hall of Fame, Len was awarded the 2016 CanFitPro Specialty Presenter Award.

Additional References:
Ogden, C.L., Carroll, M.D., Kit, B.K., and Flegal, K.M. (2014). Prevalence of childhood and adult obesity in the United States, 2011-2012. JAMA. 311(8), pp. 806-814. doi:10.1001/jama.2014.732

WHO (2017). Physical activity and young people.