Bilateral quadriceps and hamstrings muscle volume asymmetries in healthy individuals.

Determining the magnitude of quadriceps and hamstring muscle volume asymmetries in healthy individuals is a critical first step toward interpreting asymmetries as compensatory or abnormal in pathological populations. The purpose of this study was to determine the magnitude of whole and individual muscle volume asymmetries, quantified as right-left volume differences, for the quadriceps and hamstring muscles in a young and healthy population. Twenty-one healthy individuals participated: Eleven females age = 22.6 ± 2.9 years and 10 males age = 23.2 ± 3.4 years. Whole muscle group and individual muscle volume asymmetries were quantified within the context of absolute measurement error using a 95% Limits of Agreement approach. Mean muscle asymmetries ranged from -3.0 to 6.0% for all individual and whole muscle groups. Whole muscle group 95% limits of agreements represented ±11.4% and ±8.8% volume asymmetries for the hamstrings and quadriceps, respectively. Individual muscle asymmetry 95% limits of agreements ranged from ∼ ± 11-13% for the vastii muscles while the biceps femoris short-head (±33.5%), long-head (±20.9%), and the rectus femoris (±21.4%) displayed the highest relative individual asymmetries. Individual muscle asymmetries exceeded absolute measurement error in 70% of all cases, with 26% of all cases exceeding 10% asymmetry. Although whole muscle group asymmetries appear to be near the 10% assumed clinical threshold of normality, the greater magnitude of individual muscle asymmetries highlights the subject- and muscle-specific variability in volume asymmetry. Future research is warranted to determine if volume asymmetry thresholds exist that discriminate between healthy and pathological populations. Statement of Clinical Significance: Muscle volume asymmetries displayed in healthy individuals provide a reference for interpreting asymmetries in pathological populations.