High-intensity interval training (HIIT) is a form of exercise that involves repeated bouts of near-maximal effort often followed by short (<60 seconds) recovery times (ACSM, 2014). HIIT is popular among adult populations, and studies show health-related benefits (Engel Ackermann, Chtourou, & Sperlich, 2018). Although its wider impact on children is inconclusive (Lambrick, Stoner, & Faulkner, 2016), HIIT has become an online replacement to school physical education (PE) during the Covid-19 pandemic to keep children active (Paul, 2020). However this short-term solution – and a narrowing view of what PE actually is – may be causing more harm than good.

The problem with HIIT for primary-aged children

The World Health Organization suggests that children aged five to seventeen should be undertaking ‘mostly aerobic’ physical activity, with no more than three days per week involving vigorous-intensity aerobic activities. The American College of Sports Medicine even goes so far as to warn against vigorous exercise – such as HIIT – for pre-pubescent children.

There is currently insufficient physiological or practical evidence to recommend HIIT when updating childhood physical activity guidelines (Lambrick et al., 2016). If the argument for HIIT in PE is to improve health, then further evidence is required. HIIT does not significantly improve children’s biomedical markers compared to moderate-intensity activity (Yin, Zhou, & Lan, 2020), but it does carry a higher risk of burnout and injury (McNarry & Jones, 2014). The skeletal system of young children, not yet at full maturity, is not designed to withstand the frequent, high impacts involved in HIIT (ACSM, 2014). Explosive, high-intensity exercises are performed anaerobically since the volume of work is condensed into a short period of time and does not allow for oxygen to reach the relevant muscles. With primary-aged children having a lower anaerobic capacity than adults (McNarry & Jones, 2014) such activities are likely to be a greater challenge for them to perform. Moderate-intensity activity can be taken at a pace and duration determined by the child, matching their maturation, interest and relative health.

‘High-intensity interval training does not significantly improve children’s biomedical markers compared to moderate-intensity activity, but it does carry a higher risk of burnout and injury.’

Medicalising movement

Children have a natural propensity for movement, which should be experienced in its many varied forms. Movement can be as gentle as concentrated breathing through a balancing exercise, or as demanding as pushing the body to its maximum physical and emotional limits. However, the experience of moving for enjoyment, learning, play and curiosity seems to have been lost as society obsesses over the metrics of counting steps, the number of active minutes, and meeting target heart rate zones. Meanwhile, concern continues to grow over children’s sedentary behaviour (Sport England, 2021). With PE in the form of physical fitness being popularised by celebrities throughout the pandemic (see Stirrup et al., 2020), the emphasis on what movement is has become further medicalised. A quality PE programme is much more than a child being shown how to ‘work out’. Such concepts are adult ones, imposed upon children to tick a box. But children are neither adults nor ‘mini-adults’, and therefore it is unlikely that high-intensity ‘training’ (or any form of fitness training) will instil long-term engagement or motivation for a child (McNarry & Jones, 2014).

Conclusion

The suitability of HIIT for young children is questionable. Recent findings from Sport England (2021) showed that 2.3 million children in the UK were ‘inactive’ as a result of the first lockdown in 2020; the need for adequate physical activity is arguably more important than ever. However, HIIT fitness-based programmes, offered to children as part of PE, are at best likely to offer short-term benefits to cardiovascular health, but at worst cause injury or disengagement from movement. The problem with HIIT also extends to the subject of PE, as its value is in danger of being reduced to a series of high-intensity one-dimensional movements void of play, interaction, curiosity and learning. Although it may be argued that ‘something is better than nothing’, the long-term damage of ignoring the meaning and educative purpose of movement may result in poor lifelong physical activity habits and an increase in future health problems for a generation of locked-down children.

References

American College of Sports Medicine [ACSM]. (2014). High intensity interval training [webpage]. https://www.acsm.org/docs/default-source/files-for-resource-library/high-intensity-interval-training.pdf

Engel, F. A., Ackermann, A., Chtourou, H., & Sperlich B. (2018). ‘High intensity interval training performed by young athletes: A systematic review and meta-analysis’ Frontiers in Physiology. https://doi.org/10.3389/fphys.2018.01012

Lambrick, D., Stoner, L., & Faulkner, J. (2016). High-intensity interval training (HIIT) or miss: Is HIIT the way forward for obese children? Perspectives in Public Health, 136(6), 335–336. https://doi.org/10.1177/1757913916663147

McNarry, M., & Jones, A. (2014). The influence of training status on the aerobic and anaerobic responses to exercise in children: A review. European Journal of Sport Science, 14(1), S57–S68. http://doi.org/10.1080/17461391.2011.643316

Paul, A. (2020, May 18). Where to watch Joe Wicks’ HIIT workouts and how often should you do them? Metro. Retrieved from https://metro.co.uk/2020/05/18/where-watch-joe-wicks-workouts-hiit-sessions-totally-shredded-12716219/

Sport England. (2021). Active Lives Children and Young People Survey [webpage]. https://sportengland-production-files.s3.eu-west-2.amazonaws.com/s3fs-public/2021-01/Active%20Lives%20Children%20Survey%20Academic%20Year%2019-20%20report.pdf?4Ti_0V0m9sYy5HwQjSiJN7Xj.VInpjV6

Stirrup, J., Hooper, O., Sandford, R., Harris, J., Casey, R., & Cale, L. (2020, July 20). ‘PE’ with Joe (Bloggs): The rise and risks of celebrity ‘teachers’ [blog post]. BERA Blog. https://www.bera.ac.uk/blog/pe-with-joe-bloggs-the-rise-and-risks-of-celebrity-teachers

World Health Organization [WHO]. (2020). Physical activity [Factsheet]. https://www.who.int/news-room/fact-sheets/detail/physical-activity#:~:text=In%20a%2024-hour%20day,%20children%203-4%20years%20of,activity,%20spread%20throughout%20the%20day;%20more%20is%20better

Yin, J., Zhou, Z., & Lan, T. (2020). High-intensity interval training versus moderate-intensity continuous training on health outcomes for children and adolescents: A meta-analysis of randomized controlled trials [Special issue]. BioMed Research International. https://doi.org/10.1155/2020/9797439