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

The potential dissociation between muscle strength and size has led to interest in the ability to assess muscle quality across the lifespan.

We examined the association between echo intensity and specific tension in middle-school boys.

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.

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).

In middle-school boys, a relationship between echo intensity and the ratio of muscle strength relative to lean mass does not exist.