Validity and Reliability of Two Field-Based Leg Stiffness Devices: Implications for Practical Use.

Area of Science:

• Biomechanics
• Sports Science
• Human Movement Analysis

Background:

• Leg stiffness is a critical factor influencing athletic performance in various sports.
• Accurate measurement of leg stiffness is essential for training and performance optimization.

Purpose of the Study:

• To evaluate the criterion-related validity and reliability of two field-based leg stiffness devices: Optojump NextR (Optojump) and Myotest ProR (Myotest).
• To compare different testing approaches for assessing leg stiffness using these devices.

Main Methods:

• Thirty-four male participants performed maximal hop trials.
• Leg stiffness was measured using Optojump, Myotest, and a force platform (FP) synchronously.
• Validity and reliability were assessed using correlation coefficients, bias, limits of agreement, coefficient of variation, intraclass correlation coefficient, and standard error of measurement across different trial methods.

Main Results:

• Optojump demonstrated high correlation (r = .98-.99) and low bias compared to the force platform.
• Myotest showed high correlation (r = .81-.86) but with significantly larger bias.
• Optojump exhibited superior reliability with lower coefficient of variation and higher intraclass correlation coefficients compared to Myotest.

Conclusions:

• Optojump is a valid and reliable device for field-based leg stiffness assessment.
• The findings support the use of a single hop trial for time-efficient and accurate leg stiffness measurement.
• Athletes and coaches can confidently use Optojump for performance monitoring and training adjustments.