摘要：Co-contraction of abdominal muscles (abdominal bracing) is considered an effective exercise technique for improving spinal stability, and is often recommended and/or included in rehabilitation and/or fitness programs (Maeo et al., 2013b). Abdominal bracing has been shown to induce higher activation in deep abdominal muscles such as transversus abdominis and internal oblique muscles, which are considered to be the key abdominal muscles that contribute to the stability of the spine (Vera-Garcia et al., 2010), even compared to dynamic exercises involving trunk flexion/extension movements (Maeo et al., 2013b). On the other hand, it has also been revealed that none of the abdominal muscles can be fully activated during abdominal bracing, even with maximal effort. For example, muscular activity level during abdominal bracing, expressed as the value relative to its maximum (e.g. % EMGmax), was 18 - 25% for rectus abdominis (RA), 27 - 34% for external oblique (EO), and 52 - 65% for internal oblique (IO) muscles. (Maeo et al., 2013b; Vera-Garcia et al., 2010). To our knowledge, however, no study has focused on its trainability, and whether muscular activity level during the task can be increased remains unclear. To discuss the efficacy of abdominal bracing as a training modality for improving muscle function, this issue should be clarified since exercise intensity, in this case muscular activity level, largely contributes to training outcome (Fry, 2004). Recently, Maeo et al., 2013a demonstrated that bodybuilders, who frequently perform voluntary co-contraction with maximal effort in their training program (Schwarzenegger and Dobbins, 1999), can activate their elbow flexors and extensors simultaneously during maximal voluntary co- contraction task greater than control subjects (non-athletes), which can be attributed to long-term adaptation to the task. In the training routines of bodybuilders, they often perform abdominal bracing with maximal effort as one of their major exercises (Schwarzenegger and Dobbins, 1999). Considering this, it is hypothesized that the activation levels of abdominal muscles during abdominal bracing can also be increased, if the abdominal braining is performed for a long period as an exercise regimen. The present study aimed to clarify this by comparing the data obtained from bodybuilders and non-athletes.
