Is muscular activity level during abdominal bracing trainable? A comparison study between bodybuilders and non-athletes.

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 (VeraGarcia 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 cocontraction task greater than control subjects (nonathletes), 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 nonathletes. Ten male bodybuilders and twelve male nonathletes participated in this study. The means and SDs of age, body height, and body mass in the subjects were 38.8 ± 7.8 yrs, 1.67 ± 0.04 m, and 68.7 ± 6.0 kg for bodybuilders, and 20.2 ± 1.1 yrs, 1.69 ± 0.04 m, and 63.1 ± 5.7 kg for non-athletes, respectively. The experience of bodybuilding in the bodybuilders was 16.5 ± 8.4 yrs. All bodybuilders were ranked at the elite level by their successful performance in domestic competitions. Firstly, the participants performed a static maximal voluntary contraction (MVC) task for each muscle for normalization. After a process of sufficient warming-up and a rest period, the subjects were encouraged to exert maximal force against manual resistance for 5 s two times with at least 3 min between trials. The positions and tasks for MVC were adopted on the basis of a previous report (Maeo et al., 2013b) and the criteria for success in the MVC trial were the same as described elsewhere (Maeo et al., 2013a). In brief, the subjects performed MVC trunk flexion and trunk lateral flexion (bending right). After the completion of MVC tasks, the subjects performed abdominal bracing task with maximal effort for 5 s two times with at least a 3-min interval (Maeo et al., 2013b).