Reliability of a New Instrument for Measuring Plantarflexor Muscle Strength

Abstract 

Örtqvist M, Gutierrez-Farewik EM, Farewik M, Jansson A, Bartonek Å, Broström E. Reliability of a new instrument for measuring plantarflexor muscle strength.

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°, 30°). 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°. 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.

Key Words: Gastrocnemius muscle, Isometric contraction, Rehabilitation, Reproducibility of results, Soleus muscle