The validity and reliability of hand-held dynamometry in assessing isometric external rotator performance

Area of Science:

• Orthopedics
• Sports Medicine
• Biomechanics

Background:

• Assessing shoulder external rotator strength is crucial for diagnosing injuries and guiding rehabilitation.
• Hand-held dynamometry and Cybex dynamometry are common tools for measuring muscle strength.
• Understanding the comparative validity and reliability of these tools is essential for clinical practice.

Purpose of the Study:

• To compare the validity and reliability of hand-held dynamometry versus Cybex dynamometry for measuring maximal isometric shoulder external rotator strength.
• To determine the intrarater reliability of both dynamometry methods.
• To assess the agreement between the two measurement techniques.

Main Methods:

• 14 healthy male subjects performed maximal isometric contractions of the shoulder external rotators.
• Measurements were taken using both a hand-held dynamometer and a Cybex isokinetic dynamometer.
• Testing was conducted across two sessions, approximately one week apart, with three contractions per session.

Main Results:

• No significant differences were found in mean peak torque values between the hand-held and Cybex dynamometers, or between testing days.
• Both instruments demonstrated high intrarater reliability (r = 0.986 for hand-held, r = 0.993 for Cybex).
• Within-day correlations showed moderate agreement (27% on day 1, 60% on day 2), indicating similar strength measurement but different execution.

Conclusions:

• Hand-held and Cybex dynamometry are reliable tools for assessing shoulder external rotator strength.
• While both devices measure peak torque similarly, subtle differences in how they capture strength exist.
• These findings support the use of both dynamometry methods in clinical and research settings for shoulder strength assessment.