Reliability and validity of three isometric back extensor strength assessments with different test postures

Area of Science:

• Biomechanics and Musculoskeletal Health
• Clinical Assessment and Rehabilitation

Background:

• Accurate measurement of back extensor strength (BES) is crucial for clinical assessment and rehabilitation.
• Existing protocols for maximal isometric BES assessment vary in posture, potentially affecting reliability and validity.

Purpose of the Study:

• To compare the test-retest reliability and validity of three maximal isometric BES assessment protocols.
• To identify the optimal clinical protocol for quantifying back extensor strength.

Main Methods:

• Sixty asymptomatic adults over 45 years old performed maximal isometric BES tests in standing, prone, and sitting positions using external fixation dynamometry.
• Test-retest reliability was assessed over a one-week interval.
• Validity was determined by comparing results with isokinetic dynamometer assessments.

Main Results:

• High test-retest reliability (ICC > 0.90) was observed across all three positions (standing, prone, sitting).
• Acceptable convergent validity was found for standing (r=0.50) and prone (r=0.54) positions.
• The sitting position demonstrated lower validity (r=0.32), and the prone position exhibited the lowest measurement error.

Conclusions:

• Maximal isometric back extensor strength assessment in the prone position is the most reliable and valid protocol.
• The prone position protocol is recommended as the preferred method for clinical assessment of BES.