Validity Of Equations For Total And Regional Skeletal Muscle Mass By Ultrasound In Japanese Prepubertal-boys

Abstract

At the present time, there are very few effective methods to accurately and non-invasively estimate skeletal muscle (SM) mass in children. Recently, we developed ultrasound-derived prediction equations for estimating total and regional (i.e. arm, trunk and leg) SM mass in adults males and females (Eur J Appl Physiol 96: 24-31, 2006). However, it is unknown whether these equations are a valid method to estimate SM mass in prepubertal children. PURPOSE: To investigate whether ultrasound-derived prediction equations for estimating total and regional SM mass in adults are applicable for prepubertal children. METHODS: Sixty-one healthy Japanese prepubertal boys (mean age 10yr) volunteered for the study. Contiguous MRI images with a 1-cm slice thickness were obtained from the first cervical vertebra to the ankle joints as reference data. The volume of SM was calculated from the summation of digitized cross-sectional area. The volume units were converted into mass by an assumed SM density of 1.041g/cm3. The regional SM mass was determined by anatomical landmarks visible in the scanned images. Muscle thickness was measured by B-mode ultrasound (5 MHz scanning head) at 9 sites on different muscles (lateral forearm, anterior and posterior upper arm, abdomen, subscapular, anterior and posterior thigh, anterior and posterior lower leg). Total and regional SM mass were estimated using prediction equations for adult males, which were developed based on the relationship between ultrasound-measured muscle thickness and MRI-measured SM mass. RESULTS: The measured SM mass by MRI was 11.3±2.8 kg for total, 1.1±0.3 kg for arm, 4.6±1.2 kg for trunk, 4.2±1.2 kg for thigh and 1.4±0.5 kg for lower leg, and were significantly different from the predicted total and regional SM mass by ultrasound (total 8.0±3.6kg, arm 0.9±0.3kg, trunk 5.9±1.1kg and lower leg 0.9±0.4kg, respectively, p<0.01) except for thigh (4.2±1.3kg). CONCLUSIONS: The ultrasound-derived prediction equations for adults are not applicable for prepubertal boys. The specialized equation for estimating total and regional SM mass in prepubertal children is needed.