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School-Based Strength Training Helps Kids Become Stronger, Boys Become More Active

Fifth and seventh graders increased strength, but only boys increased physical activity levels outside school

Should strength training become a regular part of physical education in elementary and middle school? A new study published in the journal Pediatrics[1] suggest just that. 

Teenage girl holding dumb bell

Swiss researchers found that substituting 45 minutes of supervised school-based strength training for 2 of 3 regular PE classes significantly increased upper and lower body strength in healthy schoolchildren aged 10 to 14 years, and significantly increased daily spontaneous physical activity outside the training for boys.

"Schools are well suited to introduce children to strength training as they spend most of their time there and such activities are also much more attractive for children if carried out together with classmates [and] the cost of the equipment required for strength training is low," writes lead author Udo Meinhardt, MD, Head of the Center for Pediatric Endocrinology Zurich (PEZZ). 

The study compliments a growing body of evidence links students' physical activity levels to increased academic achievement [2]   and comes in the wake of an earlier 2013 Swedish study[3] finding that an increase in time spent in physical education class helps kids develop stronger muscles, and that increasing weekly physical activity does not increase the risk of bone fractures.   

Study details 

102 healthy fifth- and seventh-graders from a public primary and secondary school near Zurich were randomly assigned by researchers into 2 groups: a control group which continued 3 PE classes per week, and an intervention group which had 2 out of the 3 PE classes replaced by strength-training program supervised by the regular PE teacher.

The program consisted of a 10-minute warm followed by 35 minutes of seven basic multiple-joint exercises performed as a circuit in groups of 2 (barbell back squat, barbell lunge squat, resistive-ball back extension, twisting crunch, barbell bench press, barbell bent over row, and barbell overhead press). 

At the end of the training intervention, which started in August at the beginning of the school year and lasted until June, the researchers found a significant increase of upper and lower body strength in the intervention group in both boys and girls. Boys, but not girls, signficantly increased the amount of spontaneous physical exercise by 10%, which the study said was equivalent to a weekly 2 1/2 hour bike ride for an 88 pound child; the amount of energy needed to burn off 10 kg (22 pounds) of chocolate per year.  Researchers said the reason why strength training induces spontaneous physical activity remains unclear. 

Meinhardt attributed the finding that girls demonstrated no increase in spontaneous PA at the end of the training to maturational differences between boys and girls, as most of the girls studied had entered puberty, while most of the boys had not.  That the onset of puberty may be responsible for changing patterns of PA from a child regulation to an adult one, Meinhardt was supported by a previous study of junior ice hockey players, in whom the positive correlation between training intensity and spontaneous PA was lost with the onset of puberty. 

Declining physical fitness 

The benefits of physical activty are numerous. PA reduces cardiovascular risk, helps protect against type 2 diabetes and some forms of cancer, and is imperative for developing and maintaining muscle strength, joint function, and bone health.  

Despite these benefits:

  • Physical fitness levels in children and adolescents have been declining over the past several decades.  
  • Lack of physical activity (PA) increases the risk for obesity, metabolic and cardiovascular diseases, and orthopedic problems, and may even have a negative impact on PA behavior during adulthood.
  • PA relies on muscle strength, which several studies show has also significantly declined over the past 20 years in children. 
  • A majority of girls and a large proportion of boys fail to meet the minimum target of 60 minutes of at  least moderate intensity PA per day.
  • PA declines as children get older.
  • Individually targeted strength training has been shown to increase spontaneous PA outside of training, both in children with Prader-Willi syndrome (PWS), a complex genetic disorder causing a profound aversion to PA and in healthy junior ice hockey players.

The problem is that a declining number of children and adolescents in the United States get anything close to 60 minutes a day of physical education, much less the 40 minutes a day that is standard in Sweden or the 45 minutes three times a week common in Switzerland.  The adverse health consequences of the decline are enormous.

As a 2009 story published on ESPN Outside the LInes notes, "Put simply, at a time when every penny is being pinched by every school in every district in every county in every state, physical education is taking a beating. The experts and educators say there is no doubt that the erosion of P.E. has been a major contributor to the skyrocketing obesity rates."

As the story goes on to point out, the childhood obesity statistics are numbing:

  • 20 percent of U.S. children will be defined as obese next year, according to the Department of Health and Human Services. That's about four times what the rate was in the 1970s. Using the body mass index (BMI), which is a measure of one's weight in relation to height, obesity is defined as being at or above the 95th percentile based on standards established in the 1970s for kids who are the same age and sex.
  • Between 1971 and 2006, the number of 6-to-11-year-olds considered overweight more than quadrupled -- from 4 percent to 17 percent, according to the Centers for Disease Control and Prevention.
  • There's a 70-80 percent chance that an obese child will become an obese adult.
  • $14 billion is spent annually on child obesity-related health care costs, American Heart Association president Dr. Tim Gardner said during a recent press conference. Overall, annual obesity-related costs total $117 billion.

Equally startling, says ESPN, are the numbers reflecting the state of PE programs in public schools across the country:

  • Only 3.8 percent of elementary schools, 7.9 percent of middle schools and 2.1 percent of high schools provide daily P.E., according to a CDC survey. A study published in a 2007 issue of Health Economics stated that daily P.E. for high school students declined from 41.6 percent in 1991 to 28.4 percent in 2003. (The survey did not have statistics for middle and elementary schools.)
  • 22 percent of schools don't require kids to take any P.E.
  • Nearly half -- 46 percent -- of high school students were not attending any P.E. classes when surveyed by the CDC. 

For more on the US Physical Activity Guidelines, click here 

1. Meinhardt U, Witassek F, Petro R, Fritz C, Eiholzer U. Strength Training and Physical Activity in Boys: a Randomized Trial. Pediatrics 2013;132(6):1-7; doi:10.1542/peds.2013-1343. 

2.  CDC. Physical Inactivity and Unhealthy Dietary Behaviors and Academic achievement; CDC. The association between school based physical activity, including physical education, and academic performance. Atlanta, GA: U.S. DHHS; 2010

3. Löfgren B, Daly R, Nilsson J-A, Denker M, Karlsson Magnus K. An Increase in School-Based Physical Education Increases Muscle Strength in Children. Med Sci Sports Exer 2013;45(5):997-1003. doi: 10.1249/MSS.0b013e31827c0889