Daily 20 minutes of vigorous exercise maximizes cardiorespiratory fitness in teens: AAP

UK: In teens, 20 minutes of vigorous physical activity (VPA) daily may maximize cardiorespiratory fitness (CRF), suggests cross-sectional study data published in the journal Pediatrics. The study provides evidence and highlights the importance of VPA over lesser intensity PA for CRF.

Samuel Joseph, John Radcliffe Hospital, UK, and colleagues directed this study intending to determine the strength of associations between each PA intensity and CRF, independently of other intensities, and the PA duration at each intensity associated with maximal CRF.

CRF is an important marker of youth's physical and mental health and academic achievement. A sedentary lifestyle negatively affects CRF and health. Physical activity (PA) can improve CRF but the intensity and duration of PA  needed for adolescents are not clear. Recently, WHO published updated PA guidelines for all age groups and recommended that children and adolescents should undertake moderate-to-vigorous PA (MVPA) for an average of 60 minutes per day to improve physical, mental, and cognitive health but a maximum number of adolescents failed to achieve these minimum activity levels.

Researchers assessed 339 adolescents aged 13 to 14 years for PA and CRF, by wrist-worn accelerometers and 20-m shuttle runs, respectively. Partial regression modeling was used to construct residualized PA variables at each PA intensity that were uncorrelated with each other. Moving average models were used to determine relationships between residualized PA variables and CRF. Threshold regression models determined the duration of PA above which CRF improvement was minimal.

Data results showed that,

• Greater vigorous PA (VPA) was found to be associated with better CRF until about 20 minutes of daily VPA when the relationship plateaued

• Moderate and light PA and sedentary time was not associated with CRF in partial models.

• Adolescents performing 14 (range 12–17) minutes of daily VPA had median CRF.

• Participants in the upper quartile of VPA had 1.03 z-scores higher CRF than those in the lowest quartile.

• On average, girls exercised less often and had lower CRF than boys.

Researchers concluded that greater vigorous PA per day is associated with better CRF in adolescents, until about 20 minutes after which the relationship plateaued, whereas moderate PA is not, suggesting that this duration of vigorous PA may be enough to gain CRF. Researchers suggest that future guidelines should focus on VPA alone, simplifying public health messaging, as moderate-to-vigorous PA guidelines can be satisfied by only moderate PA, with no evident independent benefit. 

The authors recommend, further research intending to test whether interventions based on the new target set by the present study offer crucial improvements in adolescent cardiometabolic health.

Reference:

Samuel Joseph Burden, BMedSci; Benjamin David Weedon, PhD; Annabelle Turner et al.Pediatrics e2021056003. https://doi.org/10.1542/peds.2021-056003