Influence of number of records on reliability of myotonometric measurements of muscle stiffness at rest and contraction.

Purpose: The aim of this study was to determine an effect of myotonometric records' number on stiffness measurements' reliability in muscles at rest and contraction. Methods: Muscle stiffness was measured using Myoton-3 device. Twenty records were taken for: (i) biceps (BB) and triceps brachii (TB) at rest and for BB at 10% of maximal voluntary contraction (MVC) in healthy elderlies (HE) and in Parkinson's disease patients (PD); and (ii) brachioradialis (BR) at rest and at 25, 50 and 80% MVC in healthy young (HY) subjects. Also, in HY group, the 3-records mode was used for BR's measurements at maximal contraction. Each measurement taken with 20-records was classed into five records groups: the whole 20- and the first 15-, 10-, 5- and 3-records. Test-retest reliability for these records groups was analyzed. Results: In HE and PD group measurements' reliability was excellent for all groups of records (20-3 records). In HY group, for the five groups of records taken at rest and submaximal levels of contraction (25, 50 and 80% MVC) the measurements reliability: (i) was mostly excellent or rarely average; and (ii) only in one per three 50% MVC conditions was unacceptable, i.e., for the 3-records group. The reliability of 3-records mode measurements at maximal contraction were unacceptable. Conclusions: Reliable myotonometric stiffness measurements in muscles at rest and during submaximal contractions can be achieved with less than 20 records (15, 10, 5 records) and even for the most of measurements with 3 records in HY and HE as well as in the PD patients. Myotonometric stiffness measurements with 3-records mode during maximal contraction were not reliable. [ABSTRACT FROM AUTHOR]