Ann Rehabil Med.  2017 Oct;41(5):793-800. 10.5535/arm.2017.41.5.793.

Reliability and Validity of a New Method for Isometric Back Extensor Strength Evaluation Using A Hand-Held Dynamometer

• Park HW
• Baek S
• Kim HY
• Park JG
• Kang EK

• KMID: 2440806
• DOI: http://doi.org/10.5535/arm.2017.41.5.793

Abstract

OBJECTIVE
To investigate the reliability and validity of a new method for isometric back extensor strength measurement using a portable dynamometer.
METHODS
A chair equipped with a small portable dynamometer was designed (Power Track II Commander Muscle Tester). A total of 15 men (mean age, 34.8±7.5 years) and 15 women (mean age, 33.1±5.5 years) with no current back problems or previous history of back surgery were recruited. Subjects were asked to push the back of the chair while seated, and their isometric back extensor strength was measured by the portable dynamometer. Test-retest reliability was assessed with intraclass correlation coefficient (ICC). For the validity assessment, isometric back extensor strength of all subjects was measured by a widely used physical performance evaluation instrument, BTE PrimusRS system. The limit of agreement (LoA) from the Bland-Altman plot was evaluated between two methods.
RESULTS
The test-retest reliability was excellent (ICC=0.82; 95% confidence interval, 0.65-0.91). The Bland-Altman plots demonstrated acceptable agreement between the two methods: the lower 95% LoA was −63.1 N and the upper 95% LoA was 61.1 N.
CONCLUSION
This study shows that isometric back extensor strength measurement using a portable dynamometer has good reliability and validity.

Keyword

Back muscles; Isometric contraction; Muscle strength dynamometer; Reproducibility of results

MeSH Terms

Back Muscles
Female
Humans
Isometric Contraction
Loa
Male
Methods*
Muscle Strength Dynamometer
Reproducibility of Results*

Figure

• 

  Fig. 1 Device setting for isometric back extensor strength evaluation with portable dynamometer. (A) Portable dynamometer (Power Track II Commander Muscle Tester; JTECH Medical, Midvale, UT, USA) composed of a compression force sensor (left) and a control/recording unit (right). (B) Square back plate. This wooden plate interface with subjects' back muscle and transmit compression pressure to the attached force sensor unit. (C) Specially designed chair. Vertical linear groove in seatback center is designed for holding a sensor unit with a ruler to set the sensor unit in a specific height. (D) Subject seated in the chair and the pelvis fixed by fastening the seat belt. Square back plate was shown in the red elliptical circle between chair seatback and subjects. The force sensor unit is not visible because it is inserted into the center groove of the chair.

• 

  Fig. 2 Isometric back extensor strength evaluation with isokinetic dynamometer machine (PrimusRS; BTE Technologies Inc., Hanover, MD, USA).

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  Fig. 3 Correlation between PrimusRS and new method (p<0.001).

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  Fig. 4 Bland-Altman plot for muscle strength data. Dotted line indicates 95% limits of agreement ranging from −63.1 to 61.1 N.

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