Vastus lateralis and rectus femoris echo intensity fail to reflect knee extensor specific tension in middle-school boys

Abstract

The potential dissociation between muscle strength and size has led to interest in the ability to assess muscle quality across the lifespan. Objectives: We examined the association between echo intensity and specific tension in middle-school boys. Approach: Twenty-five boys participated in this study. Sixteen (mean ± SD age = 12 ± 1 years) engaged in a 16-week after-school strength and conditioning program. Nine boys (12 ± 1 years) served as controls. The program involved two 90 min sessions per week of lower-body speed, power, and resistance training. Before and after the intervention, ultrasound imaging was used to quantify vastus lateralis and rectus femoris echo intensity. Main results: Specific tension was calculated as voluntary isometric peak torque divided by dual energy x-ray absorptiometry-derived thigh lean mass (Nm kg−1). The pretest echo intensity and specific tension data were not significantly correlated (r = 0.040, p = 0.850). Training resulted in a small mean increase in specific tension (change = 1.93 Nm kg−1; d = 0.42). The echo intensity values were not affected by training or maturation (training change = −1.13 arbitrary units (A.U.); control = 0.00 A.U.). Both variables showed no interaction and no group or time main effects. The echo intensity and specific tension change scores were not correlated for all subjects (r = −0.080, p = 0.705) or groups (training r = −0.095, p = 0.727; control r = −0.004, p = 0.992). Significance: In middle-school boys, a relationship between echo intensity and the ratio of muscle strength relative to lean mass does not exist.