In a recently released article in Pediatrics, Dr. Solera-Martinez and colleagues have conducted a meta-analysis synthesizing the evidence about the effectiveness of high-intensity interval training (HIIT) on cardiovascular risk factor and cardiorespiratory fitness in children ages 5-12 years (10.1542/peds.2021-050810). HIIT is a now widely popular type of exercise training in which repeated short episodes of maximal or intense exercise alternate with periods of lower intensity recovery. According to the American College of Sports Medicine, “…[HIIT]s can range from 5 seconds to 8 minutes long and are performed at 80% to 95% of a person’s estimated maximal heart rate…” While there is good evidence for the effectiveness of HIIT for cardiorespiratory health among adolescents of any body mass index (BMI)1, evidence for younger children is sparser.
The authors conducted a systematic search and included randomized controlled trials for children ages 5-11 years old of any weight status in which the intervention group received a well-defined high-intensity exercise program with specific intensity and maximal heart rate criteria, and the control group did not receive any physical activity intervention. The main study outcomes had to include body mass index and fat percentage changes, measures of cardiovascular fitness including blood pressure, and lipid profile changes. In total 11 studies with 512 participants were included. The authors walk us through the key steps of the meta-analysis in a clear and informative way, so even those not familiar with meta-analyses can readily understand relevant metrics such as risk of bias assessment and assessment of heterogeneity. A quick review of the abstract tips readers off to the study results revealing the benefits of HIIT in this age group, including its positive effects on both what is usually considered the best measure of cardiovascular fitness, maximal oxygen consumption (VO2max - the maximal amount of oxygen that one can utilize during periods of maximal or intense exercise) and also on lipid profiles.
HIIT replicates the way most children do play, with short intense bursts, followed by periods of lower intensity – tag and hide and seek are obvious examples! What is most interesting to me is the potential implications, as noted by the authors, for gym class for kids. HIIT takes relatively shorter amounts of time, and the advantages for physical education classes, which are always constrained in time, are many. But effective use of HIIT in the classroom is a challenge – calisthenics are not inherently engaging, and physical education experts recommend using games, competitions, “stations” and other strategies to keep students’ interest and enjoyment up. Burpees (a modified squat thrust), jumping squats and lunges, and shuttle runs (back and forth relay races in which the first and third runners race in the opposite direction from the second and fourth runners) are great HIIT exercises, but kids are likely to respond best when these are fun games, not drills. This is a fun article to read! Consider sharing via this blog or our social media sites (Facebook, Twitter, or Instagram) how you might incorporate this physical activity advice into your anticipatory guidance.
References:
- Martin-Smith R, Cox A, Buchan DS, Baker JS, Grace F, Sculthorpe N. High Intensity Interval Training (HIIT) Improves Cardiorespiratory Fitness (CRF) in Healthy, Overweight and Obese Adolescents: A Systematic Review and Meta-Analysis of Controlled Studies. Int J Environ Res Public Health. 2020 Apr 24;17(8):2955. doi: 10.3390/ijerph17082955. PMID: 32344773; PMCID: PMC7215828.
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