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Needle biopsy samples were taken from vastus lateralis muscle (VL) of five male body builders (BB, age 27.4 ± 0.93 years; mean ±s.e.m.), who had being performing hypertrophic heavy resistance exercise (HHRE) for at least 2 years, and from five male active, but untrained control subjects (CTRL, age 29.9 ± 2.01 years). The following determinations were performed: anatomical cross‐sectional area and volume of the quadriceps and VL muscles in vivo by magnetic resonance imaging (MRI); myosin heavy chain isoform (MHC) distribution of the whole biopsy samples by SDS‐PAGE; cross‐sectional area (CSA), force (P_o), specific force (P_o/CSA) and maximum shortening velocity (V_o) of a large population (n= 524) of single skinned muscle fibres classified on the basis of MHC isoform composition by SDS‐PAGE; actin sliding velocity (V_f) on pure myosin isoforms by in vitro motility assays. In BB a preferential …