Application of an Accelerometric System for Determination of Stiffness during a Hopping Task

Area of Science:

• Biomechanics
• Sports Science
• Human Movement Analysis

Background:

• Accurate measurement of limb and joint stiffness is crucial for understanding human locomotion and performance.
• Existing computational methods for stiffness assessment during hopping yield variable results, necessitating validation of simpler equipment.
• The Myotest accelerometer offers a portable alternative for measuring biomechanical parameters, but its accuracy for stiffness quantification requires investigation.

Purpose of the Study:

• To compare vertical stiffness values obtained from a laboratory-based force plate system with those measured using the Myotest accelerometer during a hopping task.
• To assess the validity and potential application of the Myotest accelerometer for monitoring changes in stiffness, such as in response to training.

Main Methods:

• Vertical stiffness was measured in 30 untrained female students using both Kistler force plates and a Myotest accelerometer.
• Participants performed standardized hopping tasks, with stiffness calculated during the countermovement and take-off phases.
• Statistical analysis, including correlation coefficients, was used to compare the stiffness values derived from the two methods.

Main Results:

• The Myotest accelerometer significantly overestimated vertical stiffness compared to force plate measurements (30.7 ± 13.3 kN/m vs. 19.0 ± 9.3 kN/m and 15.1 ± 5.9 kN/m).
• Strong significant correlations were found between Myotest stiffness and force plate stiffness in both countermovement (r = 0.79) and take-off (r = 0.89) phases.
• Potential sources of overestimation include inaccuracies in flight and ground contact time determination and the assumption of harmonic center of mass movement.

Conclusions:

• Despite overestimating absolute stiffness values, the Myotest accelerometer demonstrates strong correlations with force plate measurements during hopping.
• The Myotest accelerometer can be a valuable tool for tracking relative changes or trends in stiffness, particularly in applied settings like monitoring training adaptations.
• Further research may be needed to refine algorithms or account for systematic overestimation when using accelerometers for precise stiffness quantification.