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The effects of professional tennis participation on dominant and non‐dominant upper extremity muscle volumes, and on fiber types of triceps brachii (lateral head) and vastus lateralis muscles were assessed in 15 professional tennis players. Magnetic resonance imaging (MRI, n=8) examination and dual‐energy x‐ray absorptiometry (DXA, n=7) were used to assess muscle volumes and lean body mass. Muscle fiber‐type distribution assessed by biopsy sampling was similar in both triceps brachii (2/3 were type 2 and 1/3 type 1 fibers). The VL was composed of 1/3 of type 2 and 2/3 of type 1 fibers. The dominant had 12–15% higher lean mass (DXA/MRI) than the non‐dominant (P<0.05). Type 1, 2a and 2x muscle fibers of the dominant were hypertrophied compared with the non‐dominant by 20%, 22% and 34% (all P<0.01), respectively. The deltoid, triceps brachii, arm flexors and forearm superficial flexor muscles of …