Exercise as it relates to Disease/Effects of school-based physical activity on cardiovascular disease risk factors in children

This is a critique of the journal article titled "Effects of a 2-year school-based physical activity intervention on cardiovascular disease risk factors: the Sogndal school-intervention study" by Resaland GK, Anderssen SA, Holme IM, Mamen A, Andersen LB. Effects of a 2-year school-based daily physical activity intervention on cardiovascular disease risk factors

What is the background to this research?
Cardiovascular disease (CVD) is the main cause of morbidity and premature mortality throughout the world. The underlying pathology is atherosclerosis, which is abnormal narrowing of the lumen. Coronary artery diseases, stroke and heart failure all being types of cardiovascular disease. An association between physical activity and cardiovascular health has been well established in adults. However, this association still remains unclear in children, with adequate data limited. This indistinct association may be due to the fact that cardiovascular disease is usually diagnosed in individuals 50+ years, and as a result, research is heavily focused on this population.

However, children provide a unique tracking device for cardiovascular disease risk factors throughout the lifespan. Thus, data from this population should not be overlooked. Risk factors such as blood pressure, obesity and lipids/lipoproteins are shown to track from childhood to adulthood. For example, research has found that atherosclerosis is evident in childhood and will persist through out the lifespan.

Studies have reported an inverse association between physical activity and CVD risk factors in children. However, this association should be considered with caution as many intervention studies are hampered by several methodological weaknesses including low sample size, inadequate duration and inadequate volume of moderate‐to‐vigorous physical activity (MVPA).

Where is the research from?
This particular research paper was published in the Scandinavian Journal of Medicine & Science in Sports. This is a reputable medical journal that aims to publish high quality and impactful articles in the field of health and disease relating to exercise, among many other areas of medicine and science in sports.

The primary author of this research paper, Geir K. Reasland, has been involved in the production of 11 other research articles which have been published in a variety of other reputable journals. Most of his work focuses on physical activity and cardiovascular disease and health. This can be considered advantageous as it demonstrates a wealth of knowledge in the area of research.

All co-authors, including Reasland, work in the department of sport science across a variety of universities in Norway. Therefore, it can be assumed that knowledge from these authors is reliable and reputable as it is directly related to their field of work.

What kind of research was this?
This research aimed to investigate the effect of a 2 year school-based physical activity intervention in 9 year old children on cardiovascular disease risk factors. The study compared results of the intervention school (completed daily physical activity) to the control school (completed physical activity twice weekly) to determine differences between the baseline and post intervention scores in cardiovascular disease risk factors. However, this physical intervention is not a randomised control trial (RCT). This is recognised as a limitation of the evidence as a RCT is the most appropriate study design for a school intervention study.

What did the research involve?
The study involved one intervention school that included 125 subjects and one control school that included 131 subjects. Children at the intervention school carried out 60 minutes of daily physical activity which was planned, organised and led by expert physical education teachers. Physical activity was instructed to be moderate to vigorous intensity with 15 minutes planned to be at vigorous intensity where children are sweating or out of breath. Some activities included relay racing, obstacle courses and various other active play. The control school was offered the normal curriculum prescribed amount of 45 minutes of physical activity twice weekly. Both schools participated in this study for a total of 2 years. Any child that had an absence of >15% over this time was excluded from the study in attempt to reduce random error in results.

Risk factors including blood pressure, blood lipids and lipoproteins, waist circumference, BMI, insulin resistance and VO2 peak were taken at baseline and post-intervention. All measures were taken at baseline and post-intervention via standardised procedures with the exemption of insulin resistance. Insulin resistance was estimated according to the homeostatic model assessment for insulin resistance. This model is noted as a reliable assessment for insulin resistance, hence no limitation is present. Comparison between baseline and post-intervention scores between the intervention school and control group were observed. This aimed at determining the effect of daily physical activity on cardiovascular disease risk factors in children.

What were the basic results?
The study found the following key results:
 * The school based physical activity intervention resulted in a significantly greater beneficial development of both systolic and diastolic blood pressure, lipid and lipoproteins and VO2 peak in the intervention school children than in the control school children.
 * For both blood pressure and blood lipid and lipoproteins, children in the intervention school that started with lower baseline values showed a greater positive change.
 * No significant differences were observed in changes of waist circumference, BMI and insulin resistance between the two groups.
 * No firm conclusion was possible regarding the effect of PA and insulin resistance in children due to lack of research in this area.

What conclusions can we take from this research?
Overall, this study concludes that physical activity can reduce cardiovascular disease risk factors from a young age. Furthermore, the study provides evidence to suggest that daily physical activity should be taken into consideration for the design of school polices. In particular, this daily physical activity should consist of 60 minutes at moderate to vigorous intensity with activities that are planned, organized, and controlled by expert PE teachers. This conclusion is supported with recent findings from a systemic review which showed that exercise interventions favoured a reduction in cardiovascular disease risk factors, such as waist circumference, in pre-school children.

Although the study is well designed and has many strengths, there are also a number of limitations that must be considered. In particular, the possibility that several confounding factors such as energy intake and pubertal status could partly explain results. Due to age of the subjects and length of the study it must be considered that these confounding factors could influence results, and such significance of them.

Practical advice
Schools provide an optimal setting in which to increase all children’s physical activity levels and acquire a wealth of health benefits. This includes a reduction of cardiovascular risk factors, that will potentially track and persist into adulthood. In order to do so, school based physical activity should be:
 * Daily.
 * 60 minutes in length.
 * Moderate to vigorous intensity. 15 minutes must be at vigorous intensity.

With activities being:
 * Planned, organised and controlled by trained physical education teachers.
 * Varied and fun whilst also being age appropriate to ensure adherence.
 * Examples of activities include: relay races, obstacle courses and high intensity games.

It is recommended that you look at the Australia's Physical Activity and Sedentary Behaviour Guidelines (specifically for children and young people (5-17)) published by The Department of Health prior to taking this practical advice to ensure knowledge of government guidelines are understood and also maintained. Link: [https://www1.health.gov.au/internet/main/publishing.nsf/Content/health-pubhlth-strateg-phys-act-guidelines#:~:text=Be%20active%20on%20most%2C%20preferably,and%20vigorous%20activities%2C%20each%20week. Australia's Physical Activity and Sedentary Behaviour Guidelines ]

Further information/resources
If you are interested in further information please see the links below:
 * Australia's Physical Activity and Sedentary Behaviour Guidelines and the Australian 24-Hour Movement Guidelines: Australia's Physical Activity and Sedentary Behaviour Guidelines
 * World Health Organisation: Prevention of Cardiovascular Disease: World Health Organisation