Influence of Physical Activity on Radius and Tibia Quantitative Ultrasound Measurements in Peripubertal Girls

The purpose of this study was to investigate the influence of physical activity on radius and tibia quantitative ultrasound measurements in peripubertal girls.

Methods Participants were 174 peri-pubertal girls ages 9.2 to 13.1 yrs, divided into three groups according Tanner stage of puberty, namely, group II (age: 10.8+/-0.9 yrs; bone age: 10.5+/-1.1 yrs; height: 145.5+/-9.5 cm; BMI: 16.4+/-3.1 Kg/m²; fat mass: 18.4+/-6.5%), group III (age: 11.3+/-0.9 yrs; bone age: 11.3+/-1.1 yrs; height: 149.5+/-7.6 cm; BMI: 18.3+/-3.1 Kg/m²; fat mass: 20.5+/-6.3%), and group IV (age: 12.5+/-0.5 yrs; bone age: 13.6+/-1.2 yrs; height: 149.0+/-6.0 cm; BMI:19.0+/-2.0 Kg/m²; fat mass: 20.1+/-5.0%). Evaluation of radius and tibia was conducted with quantitative ultrasound (Sunlight Omnisense) and physical activity (PA) with the Actigraph accelerometer (GT1M) over seven days. The outcome PA variables were the number of minutes the child engaged in activity of different intensities. Cut points of 100 and 1952 counts/min represent sedentary, light, and moderate plus vigorous PA. Pubertal maturation was assessed according secondary sex characteristics (Tanner, 1962). Body composition was estimated through Slaughter et al. (1988) and Lohman (1986) equations. The % body fat was obtained using the mean value of the two equations. Bone age was determined by the Tanner-Whitehouse III Method. Energy and calcium intake were calculated from a semi-quantitative Food Frequency Questionnaire assessing regular intake of a wide set of typical Portuguese foods.

Results ANOVA demonstrated that girls on the group IV have higher radius and tibia speed of sound than girls on the group III and II (radius- IV:3827+/-101 vs. III:3779+/-87 vs. II:3763+/-91 m/s, p=0.004; tibia- IV:3720+/-122 vs. III:3677+/-97 vs. II:3648+/-108 m/s, p=0.008). Inversely, girls on the groups II and III showed higher levels of light and moderate plus vigorous physical activity and lower time spent on sedentary than girls on group IV (light- II:318.3+/-40.1 vs. III:300.3+/-51.0 vs. IV:267.7+/-53.2 min/d, p<0.001; moderate plus vigorous- II:46.2+/-18.5 vs. III:39.8+/-16.4 vs. IV:33.1+/-22.0 min/d, p=0.004; sedentary- II:1003+/-71 vs. III:1038+/-84 vs. IV:1093+/-64 min/d, p=<0.001). Despite chronological and bone age differences between groups (chronological age- II:10.8+/-0.9 vs. III:11.3+/-0.9 vs. IV:12.5+/-0.5 yrs, p<0.001; bone age- II:10.5+/-1.1 vs. III:11.3+/-1.3 vs. IV:13.6+/-1.2 yrs, p<0.001), they were similar in fat mass %, energy and calcium intake. Partial correlation adjusted for bone age and body weight revealed a negative association between tibia speed of sound and moderate plus vigorous PA (r=-0.189, p=0.018).

Conclusion During puberty girls demonstrated higher tibia and radius speed of sound at Tanner stage IV (12.5+/-0.5yrs) than in previous stages in a time period where there is also a significant PA decrease.