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Validity of block start performance without arm forces or by kinematics-only methods.

Mitsuo Otsuka1, Wolfgang Potthast2, Steffen Willwacher2

  • 1a Faculty of Sport and Health Science , Ritsumeikan University , Shiga , Japan.

Sports Biomechanics
|April 17, 2019
PubMed
Summary

Researchers validated methods for calculating reaction time (RT) and normalized power in sprint block starts. The whole force-based method is most valid for RT, while leg force-based methods are better for normalized power.

Keywords:
Agreementhorizontal external powerreaction timesprintersstarting block

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Area of Science:

  • Sports Science
  • Biomechanics
  • Athletic Performance Analysis

Background:

  • Accurate measurement of sprint block start performance is crucial for athlete development.
  • Existing methods for calculating reaction time (RT) and normalized power vary in their reliance on ground reaction forces (GRFs) and kinematics.
  • The validity of kinematics-only methods or methods excluding arm GRFs requires careful examination.

Purpose of the Study:

  • To validate the calculation of RT and normalized power during sprint block starts using different methods.
  • To compare methods that exclude arm GRFs or rely solely on kinematic data against a comprehensive force-based approach.
  • To provide guidance for researchers and practitioners on selecting appropriate analysis techniques for block start performance.

Main Methods:

  • Four methods were employed: whole force-based (GRFs from arms and legs), legs force-based (leg GRFs only), whole position-based (whole-body center of mass kinematics), and partial position-based (subset of segment kinematics).
  • Bland-Altman analysis was used to assess the agreement between the different calculation methods.
  • The whole force-based method using GRFs from arms and legs was considered the criterion standard for validation.

Main Results:

  • The legs force-based method showed significant dissimilarities with the whole force-based method for RT calculation (mean difference 7.4 ms, 95% LoA -45.1 to 59.8 ms), indicating lower validity.
  • Normalized power calculations demonstrated higher validity with the legs force-based method compared to the whole and partial position-based methods.
  • Kinematics-only methods (whole and partial P-based) showed varying degrees of agreement for normalized power but were less valid than force-based methods.

Conclusions:

  • The calculation of reaction time in block starts is most valid when including arm ground reaction forces.
  • For normalized power analysis in block starts, leg force-based methods offer greater validity than kinematics-only approaches.
  • Choosing the appropriate analysis method is critical for accurate assessment of block start performance, impacting training and research outcomes.