Abdominal muscle analysis

Electromyographic Analysis of Abdominal Muscle Activity Using Portable Abdominal Exercise Devices and a Traditional Crunch
Eric Sternlicht and Stuart Rugg
Department of Kinesiology, Occidental College, Los Angeles, California 90041

ABSTRACT
The purpose of this study was to compare the abdominal muscle activity elicited while using 4 portable abdominal training devices vs. a traditional crunch. Thirty-three adults participated in this study. The exercise devices tested included the Ab Roller Plus, Torso Track 2, AB-DOer Pro, and the Perfect Abs. All subjects were tested on the Perfect Abs in both a seated and supine position using low-, medium-, and high-resistance bands. The Torso Track 2 was also tested at low- and high-resistance settings. Surface electromyography (EMG) was recorded from the upper and lower portions of the rectus abdominis, external oblique, and the rectus femoris during each repetition. Statistical analyses were performed on the mean EMG values using a repeated analysis of variance (ANOVA) procedure. There was no significant difference in abdominal muscle activity between the Ab Roller Plus, the Torso Track 2 (high resistance), and a traditional crunch. The mean abdominal muscle activity was significantly lower than a normal crunch, however, when using the AB-DOer, Torso Track (low resistance), and the Perfect Abs seated with the low-resistance band. In contrast, the Perfect Abs, when used in the supine position with the medium- and high-resistance bands, elicited significantly greater mean abdominal muscle activity than a crunch. Of the 4 devices tested, only the Perfect Abs when used in the supine position with the medium- and high-resistance bands, elicited more abdominal activity than a crunch. The results suggest that portable abdominal devices are most effective if they not only mimic the mechanics of a traditional crunch, but also provide external resistance to increase the involvement of the abdominal musculature.

Reference Data: Sternlicht, E., and S. Rugg. Electromyographic analysis of abdominal muscle activity using portable abdominal exercise devices and a traditional crunch.
Key Words: crunches, resistance exercise, muscle recruitment, biomechanics. Introduction
Resistance training exercises are designed to overload specific muscles in order to increase muscular strength and/or endurance. Therefore, one of the greatest challenges trainers, therapists, and physicians face is the selection of appropriate exercises and variations in equipment to best isolate a targeted muscle or muscular region. An integral component of most training programs is the use of exercises to increase abdominal strength. For example, crunches (curl-ups), sit-ups, leg raises, and the use of abdominal training devices are all used to increase abdominal strength, enhance performance, and reduce the risk of lower-back injury. In recent years numerous companies have capitalized on this trend by developing portable abdominal exercise devices. Despite manufacturer claims that their abdominal devices are superior to a crunch, published research fails to support these statements .
A common technique for determining a muscle's relative involvement during an exercise is to record its electrical activity using electromyography (EMG). Numerous EMG studies have been performed to assess the involvement of the anterior trunk muscles during various types of abdominal exercises . For example, Sarti et al. reported greater activation of the lower portion of the rectus abdominis when their subjects performed a reverse crunch compared with a traditional crunch. Whiting et al. (19) demonstrated that activation of the upper and lower portions of the rectus abdominis and external oblique were influenced by whether their subjects performed a traditional, oblique, or reverse crunch.
Since the principal reason for performing a crunch, or sit-up, is to train the abdominals and not the hip flexors, the motion should be performed to minimize hip flexor activity. In contrast to a sit-up, a crunch is typically performed by lifting only the head and shoulder blades off the floor. This not only minimizes lumbar motion, but also reduces psoas activation, and therefore reduces the compressive and shear stress on the lumbar vertebra. Research focusing more specifically on the sit-up has shown that although some subjects show iliacus activity throughout the full sit-up, the greatest activity typically occurs after the first 30? (2, 5). According to Travell and Simons , some subjects used the rectus femoris with minimal to no iliacus activity, whereas others used both to initiate the sit-up. Similarly, Juker et al. reported that the sit-up exercises tested activated the psoas between 15 and 35% of its maximal voluntary contraction (MVC), whereas the curl-up (crunch) exercises tested recruited the psoas less than 10% of its MVC. Based on the sit-up? and curl-up?type exercises tested by Juker et al. , the curl-up (or cross-curl) was the best exercise for challenging the abdominal muscles (rectus abdominis, external and internal oblique, and transverse abdominis) and minimizing the compressive and shear stress on the lumbar vertebra induced by psoas activation. Because of the effectiveness of the crunch in recruiting the abdominal muscles, in reducing hip flexor activity and reducing lumbar stress, the crunch has become a popular training exercise and the standard to which portable abdominal devices are compared.
The purpose of this study was to compare the abdominal muscle activity elicited using 4 abdominal exercise devices with the muscle activity recorded during a traditional crunch in order to determine if the claims made by the manufacturers are supported by the current research.

Discussion
This study supports previous findings that there is no significant difference in abdominal muscle recruitment between the Ab Roller Plus and a traditional crunch. Since roller-type devices are designed primarily to facilitate proper form without adding any external resistance, no increase in abdominal muscle activity should be expected when compared with a traditional crunch.
In order for a device to be effective in a seated position, it must provide adequate resistance to counteract the force of gravity eliciting trunk flexion. The principal reason for the significant decrease in abdominal activity when using the AB-DOer is that the vertical support bar does not provide enough resistance to require substantial muscle recruitment. Even with our lighter-weight subjects, flexing their vertebral column enabled the weight of their trunk to bend the vertical support bar. With respect to the AB-DOer, the findings are similar to those reported by Tsai. The minimal abdominal muscle recruitment while performing forward trunk flexion in an upright position has also been confirmed by Bankoff and Furlani and Machado de Sousa and Furlani . In contrast, the Perfect Abs avoided this limitation in the seated position with the medium- and high-resistance bands, because they produced enough load to require comparable abdominal muscle activity as recorded during the crunch.
In order to provide greater overload to the abdominal musculature than a traditional crunch, additional resistance must be provided. In the supine position the Perfect Abs, when using the medium- and high- resistance bands, was significantly more effective than a traditional crunch in recruiting the URA, LRA, and EO. The Torso Track elicited significantly higher EO activity when using the high-tension setting, but no significant difference in URA and LRA activity when using either the low- or high-tension settings.
In summary, all 4 devices elicited abdominal muscle activity when used with proper technique. The Perfect Abs, however, was the only device that not only mimicked a traditional crunch movement, but also provided sufficient external resistance to elicit significantly greater abdominal muscle recruitment than when performing a traditional crunch.
Practical Applications
The data collected in this study verify that portable abdominal devices, when used in a supine position, must provide external resistance to elicit greater abdominal muscle activity than when performing a traditional crunch. Devices used in a seated position provide a viable alternative for performing the crunch motion, particularly for individuals with physical limitations that would prevent them from training in the supine position. These devices, however, must supply adequate external resistance to counteract the force of gravity aiding trunk flexion. A portable abdominal exercise device, which functions with variable resistance, makes it easily accessible and effective for strength and conditioning in the home, gym, on the field, or while traveling. They also enhance the training response because of their ability to provide additional exercise overload.