Validity and reliability of different kinematics methods used for bike fitting

Area of Science:

• Biomechanics
• Sports Science
• Cycling Performance

Background:

• Bike fitting commonly uses static knee angle at bottom dead centre (BDC) for seat height adjustment.
• Lack of consensus exists regarding the optimal method for measuring knee angle during cycling.
• Accurate measurement is crucial for optimizing cycling biomechanics and preventing injury.

Purpose of the Study:

• Compare the accuracy of three dynamic knee angle measurement methods against a static method.
• Evaluate the intra-session reliability of dynamic knee angle measurements at BDC.
• Determine the most suitable method for knee angle assessment in bike fitting.

Main Methods:

• Eleven cyclists completed cycling trials at various seat heights.
• Knee angle at BDC was measured using 3D kinematics, 2D kinematics, and an electrogoniometer.
• Data were compared against a static measurement for accuracy and reliability.

Main Results:

• All dynamic methods, except 3D kinematics, significantly underestimated knee angle compared to 3D motion capture.
• Dynamic methods showed substantial differences from the static measurement (effect sizes 0.4–0.6).
• All tested dynamic methods demonstrated good intra-session reliability for knee angle measurement.

Conclusions:

• 2D kinematics is a valid and reliable tool for assessing knee angle during bike fitting.
• A correction factor of adding 2.2° to 2D kinematic measurements is recommended for improved precision.
• Standardizing dynamic measurement techniques can enhance the accuracy of bike fitting protocols.