Masters Thesis

Exploring the Relationship between Lower Extremity Asymmetry and Myosin Heavy Chain Content.

Asymmetries, or the dominant leg favored over the other, can lead to injuries. A clear cause of dominance has not yet been established, in addition no studies have explored the relationship between dominance and myosin heavy chain (MHC) content. The purpose of this study was to explore the relationship between MHC content, leg dominance, and performance. Fourteen resistance-trained men (age = 24.1 ± 2.6 years; height = 181.6 ± 6.6 cm; mass = 87.8 ± 10.9 kg) were recruited for this study. They were asked to answer a dominance questionnaire, perform 30 cm drop-vertical jumps onto two side-by-side force plates, complete a knee extension one-repetition maximum (1RM) test (for each leg), and undergo muscle biopsies of their left and right vastus lateralis muscles. Six participants (age = 23.3 ± 3.3 years) were used for MHC analysis. 134.6 ± 34.4 fibers were isolated per leg of each participant and fiber typed based on MHC isoform composition. For all dominance answers, a higher distribution of MHC IIA fibers was evident for both legs. Landing sagittal knee moment was higher in the non-dominant leg when the leg to “step when catching a fall” was preferred. When “leap” leg was preferred for jumping, lower drop jump vertical ground reaction force (DJVGRF) of both legs corresponded with higher vertical jump height. This study is the first to reveal performance differences from a drop jump based on self-selected dominant leg choice. Further research is needed to explore these relationships to predict dominance and landing injury.

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