Validity of maximal isometric knee extension strength measurements obtained via belt-stabilized hand-held dynamometry in healthy adults.
Naoko Ushiyama, Yasushi Kurobe, Kimito Momose
PMID 29200641WHAT IT FOUND
Belt-stabilized dynamometry underestimated knee strength by 0.32 Nm/kg but tracked it well enough to replace lab equipment.
Without body straps, it failed completely in stronger patients. You must stabilize the trunk and pelvis to get a usable number.
Key findings
01Belt-stabilized dynamometry with body straps showed a fixed bias, underestimating knee extension torque by 0.32 Nm/kg compared with the gold standard isokinetic dynamometer.
02Belt-stabilized dynamometry without body straps showed proportional bias, meaning the discrepancy grew as the patient's strength increased.
03The study participants were healthy young adults, so these results may not apply to older people or patients with lower baseline strength.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study only included healthy young adults aged 20 to 35, so the findings may not reflect how these devices perform in older patients or people with much lower muscle strength. The belt-stabilized method with body straps still underread strength by 0.32 Nm/kg on average, meaning it is not perfectly equivalent to the gold standard. Only the right leg was tested, and all measurements were performed by a single examiner, so inter-tester variability was not assessed.
Declared interests
No funding sources or conflicts of interest are reported in the supplied text.
The easy way to misread this
Do not assume that belt-stabilized dynamometry without body straps is acceptable for patients who are not severely weak. The lack of correlation with the gold standard and the proportional bias mean that as a patient's strength increases, the device's underreading becomes progressively worse, so a low score may reflect the measurement method rather than the patient's actual capacity.