Bilateral Fiber Type And Performance Differences In The Leg Muscles Of Resistance Trained Men

Abstract

Structural and functional asymmetries exist between limbs. Previous research on cadavers and sedentary individuals indicates a possible link between these asymmetries and muscle fiber type composition. However, no study has utilized the highly accurate method of single fiber sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), nor addressed the question in exercise-trained humans. PURPOSE: Investigate differences in leg dominance and fiber type composition of the left and right vastus lateralis (VL) of resistance-trained men. METHODS: Five resistance-trained men (age=23.5±3.4yrs; height=180.2±8.7cm; mass=82.9±12.2kg) volunteered to undergo whole-muscle performance testing and muscle biopsies (at the identical location) of their left and right VL. Myosin heavy chain (MHC) isoform composition (MHC I, I/IIA, IIA, IIA/IIX, IIX, I/IIA/IIX) of 141.9±36.2 isolated muscle fibers (per leg) was determined via SDS-PAGE. RESULTS: Paired sample T-tests revealed a significantly higher percentage of MHC I fibers in the right leg compared to the left leg (right=33.4±9.7% vs. left=25.0±14.3%). Four participants displayed no difference in MHC IIA distribution between the left and right VL. However, two participants showed a ≥13% difference in MHC I distribution, with one of the two also showing a 12% difference in MHC IIA/IIX (hybrid) fibers. Split file paired sample T-test revealed a significantly higher percentage of MHC I fibers in the dominant leg when dominance was identified as “Which leg do you prefer to kick a ball with?” All participants identified as right leg dominant while kicking. CONCLUSION: These observations indicate some individuals possess substantial differences in muscle fiber type composition between their left and right VL, yet others do not. This could be related to the amount of time each participant spends performing unilateral or bilateral physical activities. It is difficult to interpret the relationship between MHC I percentage and dominant kicking leg as all participants answered the question uniformly (right leg). Our findings may have important bearing on studies that use biopsies from the left and right VL interchangeably.