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M. Wachi1, T. Jiroumaru1, R. Fujitani1, S. Noguchi1,2, N. Kanazawa1,3, N. Kida2, T. Nomura2
1Biwako Professional University of Rehabilitation, Physical Therapy, Higashiomi, Japan, 2Kyoto Institute of Technology, Kyoto, Japan, 3Kanazawa Orthopedic & Sports Medicine Clinic, Ritto Coty, Japan
Background: Large trunk muscles contribute to successful performance in various sports (Kubo et al., 2011; Tachibana et al., 2007). Therefore, previous studies have reported specific asymmetry in trunk muscles (Hides et al., 2008; Sanchis-Moysi et al., 2010, 2013). In baseball, the trunk muscles are engaged to transmit energy from the lower extremities to the upper extremities during swinging and throwing (Braatz, & Gogia, 1987; Shaffer et al., 1993).Trunk rotation strength is associated with the bat speed and ball velocity of baseball players (Szymanski et al., 2007, 2010). Thus, the trunk muscles in baseball players may become asymmetrical due to batting or throwing. However, it is unclearthat suchasymmetry is associated with either swinging or throwing.
Purpose: This study aimed to clarify the effects of swinging and throwing on the asymmetry of the trunk muscles in baseball players.
Methods: Fifty collegiate baseball players (age: 19.8 ± 1.1 years, height: 174.3 ± 4.1 cm, weight: 73.2 ± 6.4 kg) participated in this study. Twenty-five players had the same dominant side for swinging and throwing, whereas twenty-five players had different dominant sides. The thicknesses of the rectus abdominis, external abdominal oblique, internal abdominal oblique (IO), transversus abdominis(TrA), and multifidus lumborum (MF) muscles were measured using B-mode ultrasonography. The asymmetry of each muscle was evaluated as asymmetry = dominant side/non-dominant side × 100, and expressed as a percentage.
Results: Based on swinging, significant differences in muscle thicknesses between the dominant and non-dominant sides in baseball players with the same dominant side were observed for the IO (92.0±16.5%), TrA (88.5±17.0%), and MF (97.6±7.5%) (P < 0.05), respectively. Similarly, significant differences in muscle thicknesses between the dominant and non-dominant sides in baseball players with different dominant sides were observed for the IO (93.1±11.5%) and TrA (86.4±18.6%) (P < 0.01), respectively, but not for the MF (99.2±3.5%).
Conclusion(s): We observed that baseball players with the same dominant side displayed asymmetries of the IO, TrA, and MF. Similarly, in baseball players with different dominant sides, we observed asymmetries of the IO and TrA, but not of the MF.These results suggest that asymmetries of the IO and TrA are not affected by throwing. On the other hand, asymmetry of the MF is affected by throwing. Thus, trunk rotation during throwing compared with that during swinging might inhibit a difference in the thickness of the MF.
Implications: Previous studies have demonstrated that asymmetry in the thickness of the MF may be associated with low back pain (Hides et al., 2008). Because the progression of asymmetry in the thickness of the MF may potentially lead to low back pain, using different dominant sides for swinging and throwing may be useful to prevent low back pain.
Funding, acknowledgements: None
Keywords: Multifidus, Ultrasonography, Injury prevention
Topic: Musculoskeletal
Did this work require ethics approval? Yes
Institution: Ritsumeikan University
Committee: Institutional Review Board of Ritsumeikan University
Ethics number: (BKC-IRB-2015-027)
All authors, affiliations and abstracts have been published as submitted.
