Reliability of a new, hand-held device for assessing skeletal muscle stiffness

Objective. The aim of the study was to examine the test–retest reliability of the Myoton-2 myometer for measuring skeletal muscle viscoelastic stiffness. Methods. Ten healthy volunteers took part. On day 1, the viscoelastic stiffness of the rectus femoris, vastus lateralis, biceps femoris, and gastrocnemius muscle (lateral and medial heads) was measured at rest using the Myoton-2 myometer. On day 2, the tests were repeated, and the rectus femoris was also examined during the maintenance of submaximal contractions of the quadriceps, and at a different resting muscle length. Results. The myometer showed good to excellent test–retest reliability for all muscles (ICCs 0.80-0.93), except for the vastus lateralis (ICC 0.40). Viscoelastic stiffness showed a linear increase with increasing quadriceps’ force output, and was higher in stretched than in shortened resting muscle. Conclusion. The Myoton-2 myometer is a reliable device for measuring the viscoelastic stiffness of resting muscle. Furthermore, viscoelastic stiffness showed the expected changes in response to increases in force output and muscle length, suggesting that the measurements were also valid.