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Reliability and Validity of Isometric Back Extensor Strength Measurements Using Hand-Held and Isokinetic Dynamometry
Tomohiro Nakatani1, Masakazu Minetama1, Yoshio Yamamoto1
1Spine Care Center, Wakayama Medical University Kihoku Hospital, Wakayama, Japan.
Introduction:
The prone position is generally regarded as the standard posture for back extensor strength testing. However, some older adults may have difficulty assuming this position, making alternative approaches more clinically feasible. It remains unclear whether measurements obtained in the sitting and semi-standing positions demonstrate sufficient validity compared with those in the prone position. This study aimed to evaluate the reliability and validity of isometric back extensor strength measurements using hand-held dynamometry (HHD) in the sitting position and the Biodex system in the semi-standing position. The results were compared with measurements in the prone position.
Methods:
Thirty-four healthy adults (10 males and 24 females; mean age, 23.8 years) participated. Back extensor strength was assessed using three methods: HHD in the prone, HHD in the sitting position, and the Biodex system in the semi-standing position. Test-retest reliability was evaluated using two sessions. Convergent validity of HHD in the sitting position and the Biodex in the semi-standing position was examined and compared with prone HHD, which served as a reference standard.
Results:
The semi-standing Biodex demonstrated excellent reliability and sufficient convergent validity compared with prone HHD, whereas HHD in the sitting position showed acceptable reliability but limited validity. Intraclass correlation coefficients (ICCs) indicated excellent reliability for prone HHD (ICC=0.95) and semi-standing Biodex (ICC=0.92), while sitting HHD showed acceptable reliability (ICC=0.76). Regarding convergent validity, the Biodex in the semi-standing position showed a moderate correlation with prone HHD (r=0.60), whereas sitting HHD showed a weaker correlation (r=0.45).
Conclusions:
The Biodex system in the semi-standing position demonstrated excellent reliability and sufficient validity for assessing back extensor strength. In contrast, HHD in the sitting position showed acceptable reliability but limited validity, which may be influenced by the measurement protocol used. Further studies are needed to improve measurement protocols, particularly for use in older adults and clinical populations.
