Repeatability of a computerized muscle tonometer and the effect of tissue thickness on the estimation of muscle tone

The aim of the present study was to assess the intrarater repeatability of the computerized muscle tonometer (CMT), which is a computer-driven device designed to measure and register the tone of connective tissues. The second aim was to evaluate the effect of muscle thickness on results and repeatability as well as sensitivity, which was done by comparison to a mechanical hand-held tonometer (HHT). Participants were ten healthy male volunteers. The thickness of soft tissues was measured with ultrasound and the CMT was used to evaluate the muscle tone of thigh muscles 10, 15 and 20 cm and the HHT 15 cm above the patella on both sides. Great individual variability in muscle thickness and tone was noted. Muscle thickness increased proximally on the thigh and thus the mean distance travelled by the indenter of the CMT also increased from distal to proximal from 22 to 26 mm and the work done increased from 116 to 161 mJ. Intraclass correlation (ICC) for travel and work ranged from 0.85 to 0.92 and 0.94 to 0.98, respectively. Repeatability coefficients increased somewhat at proximal measurement sites. ICC for the HHT was 0.78. The CMT also showed a considerably higher range of results, indicating greater resolution power. Despite the twofold pressure used with the HHT the distance measured was on average 60% lower compared to the CMT. In conclusion, the repeatability of the CMT was found to be good. Muscle thickness greatly affected the results and should therefore be taken into consideration when measuring muscle tone. Work was a more reliable unit of measurement than travel, which has been commonly used to describe muscle tone.