Diagnostic ultrasound: its use in the evaluation of muscle.

We describe a noninvasive quantitative way of measuring muscle with a specially-designed digital ultrasound scanner. Reliability and reproducibility of echo amplitude were determined in 16 normal male volunteers--10 runners and 6 non-runners. Echo amplitudes were recorded from the quadriceps femoris muscle. The muscle was scanned at mid-thigh in a relaxed state with 18 degrees flexion and in an isometrically contracted state with the leg in full extension. Echo amplitudes obtained in the non-runner group were: (1) mean value of the muscle in the relaxed state (174.9 +/- 30.8) and (2) mean value of the muscle in the contracted state (121.8 +/- 31.4). The difference in these values (53.1) was significant at p less than 0.05. Echo amplitudes for runners were: (1) mean value of the muscle in the relaxed state (146.6 +/- 39.2) and (2) mean value of the muscle in the contracted state (107.1 +/- 30.1). The difference in these values (39.5) was significant at p less than -0.01. The data indicate that: values of echo amplitudes are reproducible; there is a statistically significant difference in the mean amplitudes of muscle in a contracted and relaxed state; and while the difference between runner and non-runner muscle is not statistically significant (p greater than 0.1), there is a trend toward significance. Because ultrasound amplitude is a function of tissue structure, this technique may provide a noninvasive method for quantifying muscle collagen and fat.