MEASUREMENT OF MUSCLE HARDNESS - A METHODOLOGICAL STUDY

The aim of the present study was to determine the intra- and interobse rver variation during measurement of muscle hardness with a new instru ment, a so-called hardness meter. In addition, we investigated the fac tors which may influence the recording of muscle hardness and whether the hardness differs within the same muscle. Hardness was measured at a standardized Feint on the trapezius muscle in 20 volunteers by 2 obs ervers in random order and again by 1 of the observers after 30 min. M uscle hardness was then measured at 3 different locations on the trape zius muscle. Ln addition, the muscle hardness at the standard point wa s measured in 10 volunteers by both observers at 3 different speeds of the applied pressure. The intraobserver variation was 10% and the int erobserver variation was 12% for recording of muscle hardness. There w as no significant difference in hardness values from time to time with in the same observer (p=0.12), while there was a significant differenc e in hardness measurements between observers (p=0.007). Muscle hardnes s differed significantly among the 3 anatomical locations (p=0.03). Fo r both observers, there was a significant difference among hardness re cordings obtained at 3 different speeds (p=0.01 and p=0.0001). In conc lusion we have shown that the hardness meter can measure muscle hardne ss reliably if the same observer is used throughout a study. The speed factor was a major source of variability In addition, we have demonst rated that muscle hardness differs within the same muscle. We suggest that the muscle hardness meter will be an important tool in future res earch of the mechanisms leading to myofascial pain.