Muscle strength and electromyogram in boys and girls followed through puberty

The main purpose of this study was to investigate the changes in anthropome tric measures and muscle strength that occur during puberty in children fro m the age of 11 to 16 years. Special attention was paid to possible gender- and muscle action-type-specific alterations in torque/velocity and EMG/vel ocity characteristics. Sixteen children participated in the study (9 boys a nd 7 girls). Eccentric and concentric muscle strength was measured on an is okinetic dynamometer at angular velocities of 45, 90 and 180 degrees . s(-1 ). Simultaneously, a surface electromyogram (EMG) was recorded from the qua driceps muscle. At the age of 11, the boys and girls exhibited equal anthro pometric measures and strength performance. In both genders, body measures and muscle strength increased significantly during the 5-year period, with larger increases being recorded for the boys. In addition, the boys increas ed selectively their eccentric torque per body mass, indicating an action-t ype-specific change in muscle quality. The general shape of the torque/velo city relationship exhibited an adult-like pattern both before and after pub erty, and did not differ between genders. Both pre- and postpuberty, myoele ctric activity was generally lower during eccentric than concentric actions , the highest values occurring for both genders in the concentric 180 degre es . s(-1) test. Ratios of eccentric to concentric torque per EMG, which re flect electromechanical efficiency, showed no significant changes with age. A significant velocity- and gender-specific change in electromechanical ef ficiency was observed at the highest speed at postpuberty, where the ratio for the girls was higher than for the boys.