Biological maturity, physical fitness, and body composition of boys and girls in a South African Quintile 2 (no-fee) school: A cross-sectional exploratory study

Despite its importance as a health indicator, there is limited recent data available on the physical fitness of South African adolescents. Few studies have described physical fitness and body composition alongside skeletal maturity. Using a cross-sectional exploratory design, we included 97 participants (55 girls and 42 boys; age 10–15 years) from a no-fee school in the Western Cape, South Africa. Tests included a skeletal age (SA) estimation (BAUSport ultrasound) and anthropometry, body composition (bioelectrical impedance) and physical fitness (handgrip strength, sit-and-reach flexibility, broad jump, and 20 m shuttle run) assessments. Pearson's correlation coefficient (r) was used to assess linear relationships between variables, with 95% confidence intervals (CI) and p-values adjusted for multiple comparisons. On average, boys were 1.3 years (SD 1.1) delayed in SA compared to chronological age (CA), whilst girls were 0.4 years (1.3) delayed. For boys, large correlations (r ≥0.50) were seen for SA against height (r = 0.95, 95% CI: 0.91–0.98), muscle mass (r = 0.94, 0.89–0.97), handgrip strength (r = 0.81, 0.66–0.90) and body mass (r = 0.68, 0.45–0.83). Large correlations were observed for CA against height (r = 0.73, 0.54–0.84), handgrip strength (r = 0.65, 0.42–0.80) and muscle mass (r = 0.64, 0.42–0.80). For girls, we found large correlations against SA for muscle mass (r = 0.84, 0.74–0.91), height (r = 0.83, 0.73–0.90), body mass (r = 0.75, 0.60–0.85), handgrip strength (r = 0.74, 0.59–0.84), and against CA for height (r = 0.54, 0.32–0.71). The observations in this study must be interpreted in light of its exploratory nature and research using more sophisticated designs is required to confirm these. Additional validation studies for the ultrasound device in different populations are recommended.