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Lower Extremity Symmetry and Normative Values During Functional Performance Tests in Entry-Level U.S. Marines
Amelia S Bruce Leicht1, Joshua D Winters1, Reiley T Bergin1
1Department of Athletic Training and Clinical Nutrition, Sports Medicine Research Institute, University of Kentucky, Lexington, KY 40506, United States.
Military Medicine
|November 22, 2025
Summary
This study found that sex does not impact limb symmetry index (LSI) performance in healthy Marines during functional tasks, but limb dominance influences loading patterns. Further research may streamline testing by removing redundant exercises.
Area of Science:
- Biomechanics and Functional Performance Assessment
- Sports Medicine and Rehabilitation
Background:
- The Limb Symmetry Index (LSI) is a key metric for evaluating functional performance, with a threshold of ≥90% often used for return-to-activity decisions in injured populations.
- Understanding normative LSI values and the influence of sex and limb dominance in healthy, active individuals is crucial for establishing accurate performance benchmarks.
Purpose of the Study:
- To establish normative Limb Symmetry Index (LSI) characteristics during functional tasks in healthy, entry-level U.S. Marines.
- To evaluate the influence of sex and limb dominance on LSI performance.
- To describe the interrelationships between LSI performance across different functional tasks.
Main Methods:
- A cross-sectional study involving 651 healthy U.S. Marines assessed bilateral force production during bodyweight squats, vertical jumps, and isometric midthigh pulls.
- Force data were collected using dual force plates, normalized to body mass, and used to calculate the Limb Symmetry Index (LSI) as (nondominant limb/dominant limb) * 100%.
- Statistical analyses included independent and paired t-tests to compare LSI values and loading patterns between sexes and limbs, with Pearson correlations examining relationships between tasks.
Main Results:
- No significant differences in Limb Symmetry Index (LSI) values were found between sexes across all tested functional tasks.
- Participants demonstrated a tendency to load their dominant limb more than their nondominant limb, with weak-to-small effect sizes.
- A weak-to-moderate positive correlation was observed between LSI during squat and vertical jump tasks; no other significant relationships were identified.
Conclusions:
- Sex does not appear to influence Limb Symmetry Index (LSI) performance in healthy active-duty Marines during bilateral squat, vertical jump, and isometric midthigh pull tasks.
- Limb dominance may affect loading patterns during these functional assessments, highlighting its importance in performance evaluation.
- The observed similarity in squat and vertical jump performance suggests potential for task redundancy, warranting investigation into optimizing testing battery efficiency.
