Lower Extremity Symmetry and Normative Values During Functional Performance Tests in Entry-Level U.S. Marines.

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.