High intensity interval training (HIIT) or miss: is HIIT the way forward for obese children?
A lack of time is often cited as a reason for no improvement in physical activity rates. Danielle Lambrick of the University of Southampton, Lee Stoner of Massey University, New Zealand, and James Faulkner of the University of Winchester consider how high intensity interval training (HIIT) may address this problem for children .Globally, there is a continual increase in the prevalence of childhood obesity,[1] placing children at increased risk for premature onset of non communicable diseases (NCDs) including musculoskeletal disorders, some cancers, and cardio metabolic diseases such as type 2 diabetes and cardiovascular diseases (CVD)[1] This rise in obesity and co morbid complications has been strongly linked to lifestyle choices, including physical inactivity.[2] However, despite heightened public awareness of the relationship between physical inactivity and obesity, rates of physical activity are not improving.[3] An often cited barrier to physical activity among both adults and children is a lack of time,[4] which has led to the promotion of high intensity interval training (HIIT) as a more time efficient exercise prescription strategy.A recent meta analysis by Garcia Hermoso et al.[4] has examined the limited number of studies investigating the efficacy of HIIT in overweight and obese youth. HIIT was not reported to be superior to other forms of exercise when examining changes in body composition, but it was suggested to be more effective for improving systolic blood pressure (SBP) and cardio respiratory fitness. These findings indicate that HIIT may be effective for improving cardio metabolic health and thus, decreasing the risk of NCDs. However, these physiological findings need to be considered in the context of clinical inference, implementation science, and the potential for public health outcomes.Clinical InferencePrior to discussing the implementation of HIIT, the potential clinical implications should be contextualised. As a primary outcome, the meta analysis by Garcia Hermoso et al.[4] utilised the gold standard measure of cardio respiratory fitness: maximal oxygen uptake (VO2 max) When compared to other forms of exercise, VO2 max improved, on average, by 1.92 mL kg 1 min 1 While findings in children are inconclusive,[5][6] cardio respiratory fitness has been recognised as a more important correlate of cardio metabolic health than obesity in adults.[7] However, 1.92 mL kg 1 min 1 is greater than the measurement error for VO2 max testing and it is thus unlikely that such a small change is clinically meaningful in terms of risk stratification.Garcia Hermoso et al.[4] also reported that SBP improved, on average, by 3.67 mmHg. High SBP (hypertension) is associated with earlier onset of CVD[8] and, according to the World Health Organization (WHO) is likely the leading risk factor for death worldwide.[9] While child specific data are unavailable, in adults, a 20 mmHg increase in SBP is associated with a two fold increase in risk of death from coronary artery disease or stroke.[10] However, a value of 3.67 mmHg is greater than the measurement error of most blood pressure devices,[11] and it is difficult to discern the clinical importance of such a small change. The authors do also report on several markers of body composition, blood lipids, and insulin resistance, none of which were found to be statistically different or clinically meaningful. Nonetheless, HIIT has been reported to result in clinically meaningful improvements in cardiovascular health among adults,[12] so this form of exercise prescription does hold potential, and discussion is warranted in terms of implementation and public health outcomes.
Perspectives in public health