Exploring the Adolescent Fall in Physical Activity: A 10-yr Cohort Study (EarlyBird 41).

Area of Science:

• Pediatric Health
• Adolescent Development
• Exercise Science

Background:

• Adolescent physical activity (PA) is often low, particularly in girls, but the drivers—biological maturation, behavioral shifts, or environmental factors—remain unclear.
• Understanding these drivers is crucial for developing effective interventions to promote lifelong activity.
• This study investigates trends in PA from childhood to adolescence in relation to biological and environmental influences.

Purpose of the Study:

• To examine trends in total physical activity (TPA) and intensity-specific PA from age 5 to 15 years.
• To determine the influence of biological factors (biological age, pubertal stage) and environmental factors (socioeconomic status) on PA.
• To assess the relationship between childhood and adolescent PA levels.

Main Methods:

• A cohort of approximately 300 UK children was monitored annually from age 5 to 15 years.
• Physical activity was measured using 7-day Actigraph accelerometry, assessing total PA (TPA) and intensity-specific PA (sedentary, light, moderate-to-vigorous [MVPA]).
• Biological age, pubertal stage (Tanner staging), and socioeconomic status (index of multiple deprivation [IMD]) were also recorded.

Main Results:

• TPA remained stable from ages 5–8 but declined progressively from 9–15 years (approx. 30% in girls, 20% in boys).
• The decline was primarily driven by reduced light-intensity PA, with moderate-to-vigorous PA (MVPA) contributing less.
• PA decline correlated with chronological and biological age, and pubertal stage significantly influenced the steeper decline in girls. Environmental settings and socioeconomic status did not significantly alter PA trends.

Conclusions:

• The significant decline in adolescent physical activity is a consistent trend across various settings.
• Falls in light-intensity, habitual activity, influenced by pubertal development, are key contributors to adolescent inactivity.
• These findings suggest that biological factors, particularly puberty, play a significant role in the reduced physical activity observed during adolescence.