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Reliability of a new instrument for measuring plantarflexor muscle strength
Maria Ortqvist1, Elena M Gutierrez-Farewik, Markus Farewik
1Department of Women & Child Health, Karolinska Institutet, Stockholm, Sweden.
Objectives:
To test the reliability of a new muscle strength testing instrument (the Strength Measuring Chair [SMC]) designed to quantify isometric strength in the lower extremities, and to determine the agreement between the SMC and an isokinetic dynamometer (Biodex).
Design:
Isometric strength tests were performed in plantarflexors with 2 different knee positions (60 degrees, 30 degrees). Measurements were taken at 3 different sessions.
Setting:
Strength testing laboratory.
Participants:
Twenty-three able-bodied adults and 15 able-bodied children.
Interventions:
Not applicable.
Main Outcome Measure:
Isometric plantarflexor strength.
Results:
The reliability of isometric strength measurements of plantarflexors taken in the SMC was excellent for both the adult and children groups (intraclass correlation coefficient range, .84-.87). A Bland-Altman 95% limit of agreement test showed no systematic variation in 3 of the 4 SMC test observations; systematic variation was only observed in the adult group at a knee position of 30 degrees. There was no systematic difference in the adult group between the SMC and the isokinetic dynamometer, but there was a systematic variation in the children's group.
Conclusions:
The SMC reliably measured isometric plantarflexor strength in the tested populations.
