A Technical Report on Reliability Measurement in Asymmetry Studies
Chris A Bailey1, Kimitake Sato2, Timothy C McInnis3
1Department of Kinesiology, Health Promotion, and Recreation, University of North Texas, Denton, Texas.
Journal of Strength and Conditioning Research
|May 24, 2021
Summary
Reliability in sport asymmetry studies is often overestimated. Evaluating asymmetry as a vector, not just scalar, improves accuracy and avoids biased results in performance assessments.
Area of Science:
- Sport Science
- Biomechanics
- Performance Analysis
Background:
- Current literature on sport performance asymmetry may be unreliable due to flawed reliability testing.
- Evaluating reliability after asymmetry metric production can lead to biased results and misinformed decisions.
Purpose of the Study:
- To evaluate the reliability of asymmetry measurements in countermovement jumps (CMJs).
- To compare reliability before and after producing scalar and vector asymmetry metrics.
- To analyze how quantification methods affect reliability and inform decision-making.
Main Methods:
- Thirteen collegiate baseball players performed bilateral countermovement jumps on two force plates.
- Symmetry index (SI) scores were calculated as scalar (magnitude) and vector (magnitude and direction) quantities.
- Relative and absolute reliability were assessed for peak force (PF), scalar PF SI, and vector PF SI.
Main Results:
- Reliability measures on constituent force-time variables were more favorable (CVs 10.4–15.7%) than on asymmetry measures (CVs 63.2–1,497.1%).
- Reliability differs significantly based on whether asymmetry is quantified as a scalar or vector.
- Vector quantification of asymmetry is recommended for improved reliability due to consideration of both magnitude and direction.
Conclusions:
- Inadequate reliability evaluation in asymmetry studies leads to biased findings.
- Practitioners must exercise caution with asymmetry assessment results, as they may not be as reliable as commonly assumed.
- Quantifying asymmetry as a vector is crucial for accurate and reliable performance analysis in sports.
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