Investigation of absolute intra-rater and inter-rater reliabilities during the muscle hardness estimation.
Kazunori Morozumi, Katsuyuki Morishita, Masahiro Aoki and 2 others
PMID 35221515WHAT IT FOUND
Muscle hardness readings changed with limb position and rater experience.
Stretched muscle gave larger values than relaxed, but some expert readings were consistently off in one direction. Use the same position and avoid trusting small changes unless they are clearly larger than normal variation.
Key findings
01For repeat measurements by the same rater, no bias that grew with the size of the value was found in either expert or beginner raters, but some measurements were consistently shifted in one direction.
02When different raters were compared, experts showed consistent directional bias in some muscle and device combinations, while beginners showed no consistent directional bias; one beginner comparison had a bias that grew with the value.
03Changing from relaxed to stretched limb position produced differences larger than the smallest change that could be measurement error for all devices and both groups.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study used only healthy adult men with a narrow body size range, so results may not apply to women, older adults, children, or people with movement disorders. Only a small set of muscles and devices was tested, so findings may not apply to other muscles, tissues, or hardness meters. The expert and beginner groups each had very few raters, which limits how much the reliability patterns can be generalized. No rest period was given between measurements of different muscles and positions with the same device, which the authors noted may have affected bias results. For the rectus femoris, the participant moved himself into the stretched position, so instruction and movement speed may have influenced readings. The study reports reliability of measurement, not whether muscle hardness changes improve patient outcomes or treatment decisions.
Declared interests
No funding and no conflicts of interest were declared.
The easy way to misread this
Do not conclude that stretched position is always better or that beginners are more accurate. The study tested healthy men and selected muscles, found some expert readings consistently shifted, and does not show that these hardness measurements improve patient care.