Estimation of ground reaction force direction in inline speed skating motion

Area of Science:

• Biomechanics
• Sports Science
• Kinetics

Background:

• Accurate estimation of ground reaction forces (GRF) is crucial for analyzing speed skating biomechanics.
• Traditional GRF measurement relies on force plates, which can be limiting in dynamic sports settings.
• Estimating GRF from supporting-leg posture offers a potential non-invasive alternative.

Purpose of the Study:

• To propose and verify a novel method for estimating GRF direction from supporting-leg posture in speed skating.
• To compare the accuracy of two estimation methods (ankle-based vs. knee-based) against force plate measurements.
• To assess the suitability of the validated method for biomechanical calculations.

Main Methods:

• Two methods (Est1 using ankle, Est2 using knee joint center) were developed to estimate GRF direction based on leg posture.
• Three-dimensional kinematic and force plate (FP) data were collected from 16 speed skaters during straight and curved skating.
• Root mean square error (RMSE) and bias were calculated to compare estimated GRF with FP measurements.

Main Results:

• The knee-based method (Est2) demonstrated consistently smaller RMSE compared to the ankle-based method (Est1).
• Estimated GRF errors were generally within 10% of body weight, with biases <8% for most conditions after corrections.
• Intraclass correlation analysis showed good agreement for X' and Z' components, with minimal impact from the Y' component.

Conclusions:

• The developed method (Est2) using knee joint center provides a suitable and accurate estimation of GRF direction in speed skating.
• This posture-based estimation method can be effectively used for biomechanical analyses, such as joint torque and power calculations.
• The findings support the use of non-invasive kinematic data for estimating kinetic variables in sports performance analysis.