Reliability and Validity of a Crane Scale for Isometric Knee and Shoulder Strength Assessment.
Jon Dignazio, Hannah Marchant, Brady Hutchinson and 2 others
PMID 40182915WHAT IT FOUND
A low-cost crane scale produced consistent force readings across repeated trials in the same session for healthy adults.
It read lower than Biodex and hand-held dynamometer, especially at higher knee and shoulder forces.
Key findings
01Repeated crane-scale force readings were very consistent within the same session for the tested knee and shoulder motions.
02Compared with Biodex, the crane scale read lower for all motions, and the underread increased as force increased for knee extension and shoulder abduction.
03Compared with hand-held dynamometry, the crane scale also read lower for all motions, although its readings were very consistent with hand-held dynamometer readings.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Twenty healthy, physically active adults aged 18 to 45 were tested, so the results may not apply to injured populations or people outside this age range. Equipment malfunctions reduced the number analysed for some comparator tests: 19 participants completed Biodex shoulder abduction, 12 completed hand-held dynamometer knee extension, and 11 completed hand-held dynamometer testing for other motions. The study had only one session, so between-session reliability was not shown. The crane scale was not removed and reapplied between trials, so within-session consistency may be optimistic. Interrater reliability was not tested, and the testers were not blinded to device results. Testing was done by three final-year student physical therapists with about two hours of training. Only one side was tested, so limb symmetry index use was not examined. The small sample size reduced precision and limited generalizability, and an a priori power analysis was not performed.
Declared interests
The authors declared nothing to disclose. No funding source is stated in the supplied text.
The easy way to misread this
Do not conclude that a crane scale can replace Biodex or be used to track strength over time. It was tested only within one session in healthy adults, it read lower than Biodex and hand-held dynamometer, and agreement with Biodex was poor to moderate.