Electromyographic analysis of abdominal muscle activity using portable abdominal exercise devices and a traditional crunch

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.     

Electromyographic activity of the rectus abdominis during a traditional crunch and the basic jackknife exercise with the Ab Lounge™

The use of nontraditional exercise devices such as the Ab Lounge? has been promoted as being as effective as the traditional abdominal crunch in strengthening the abdominal musculature. Evidence for this is lacking, however. The purpose of this study was to compare the degree of activation of the upper and lower rectus abdominis using electromyography (EMG) during a traditional crunch with the basic jackknife using the Ab Lounge?. Twenty-two subjects (6 men and 16 women) were randomly selected from the student population at the University of the West Indies (Mona Campus). The mean age of the participants was 20.5 ± 1.5 years, height 166.4 ± 6.2 cm, weight 64 ± 10.3 kg, and waist-hip ratio 0.7 ± 0.1. Surface EMG was used to assess the muscle activity from the upper and lower rectus abdominis while each exercise was performed. The EMG data were full-wave rectified and normalized using a mathematical model that was set up in Microsoft Excel for Windows XP. Statistical analysis was performed on the data using a univariate analysis of variance with gender as a covariate. Significance was determined by p < 0.05. The mean EMG data recorded for the upper rectus abdominis was significantly higher with the traditional crunch when compared with the basic jackknife performed on the Ab Lounge? (F = 4.39, p = 0.04). The traditional crunch produced a higher level of activity in the lower rectus abdominis when compared with the basic jackknife, but this was not statistically significant (F = 0.249, p = 0.62). There was no significant interaction between gender and the effect of the type of exercise on upper and lower rectus abdominis activation. These results suggest that the traditional abdominal crunch is more effective than the basic jackknife is in activating the rectus abdominis musculature.     

Electromyographic comparison of a stability ball crunch with a traditional crunch

The purpose of this study was to compare abdominal muscle activity while performing a crunch on a stability ball with a traditional crunch. Forty-one healthy adults (23 men and 18 women) participated in the study. The subjects performed the crunch with the ball in 2 positions, 1 with the ball at the level of the inferior angles of the scapula (SB-high) and 1 with the ball at the level of the lower lumbar region of the back (SB-low). Surface electromyography was recorded from the upper and lower portions of the rectus abdominis and the external oblique during each repetition. Electromyography values were analyzed using repeated measures analyses of variance and pair-wise comparisons. Muscle activity for the upper and lower portions of the rectus abdominis and external oblique for a traditional crunch was significantly lower than for the crunch performed in the SB-low position but significantly greater than the SB-high position. Our data also showed that, on average, the abdominal muscle activity doubled when the stability ball was moved from the upper to the lower back position. These results support previous findings that a stability ball is not only effective for training the abdominal musculature, but, with the correct placement, it can also significantly increase muscle activity when compared with a traditional crunch. In addition, our results suggest that ball placement is critical for matching the appropriate overload to the condition level of the user.     

An electromyographic analysis of the Ab-Slide exercise, abdominal crunch, supine double leg thrust, and side bridge in healthy young adults: implications for rehabilitation professionals

The purpose of this study was to examine the effectiveness of a commercial abdominal machine (Ab-Slide) and three common abdominal strengthening exercises (abdominal crunch, supine double leg thrust, and side bridge) on activating abdominal and minimizing extraneous (nonabdominal) musculature-namely, the rectus femoris muscle. We recruited 10 males and 12 females whose mean (+/- SD) percent body fat was 10.7 +/- 4 and 20.7% +/- 3.2%, respectively. Electromyographic (EMG) data were recorded using surface electrodes for the rectus abdominis, external oblique, internal oblique, and rectus femoris. We recorded peak EMG activity for each muscle during each of the four exercises and normalized the EMG values by maximum muscle contractions (% MVIC). A two-factor repeated-measures analysis of variance assessed differences in normalized EMG activity among the different exercise variations (p < 0.05). Post hoc analyses were performed using the Bonferroni-adjusted alpha to assess between-exercise pair comparisons (p < 0.002). Gender did not affect performance; hence, data were collapsed across gender. We found a muscle x exercise interaction (F9,189 = 5.2, p < 0.001). Post hoc analyses revealed six pairwise differences. The Ab-Slide elicited the greatest EMG activity for the abdominal muscles and the least for the rectus femoris. The supine double leg thrust could be a problem for patients with low-back pathology due to high rectus femoris muscle activity.     

A comparison of trunk muscle activation: Ab Circle vs. traditional modalities

The purpose of this study was to compare the activation of the rectus abdominis (RA), external oblique abdominis (EO), lower abdominal stabilizers (LASs), and lumbar erector spinae (LES) during performance of 3 traditional trunk exercises vs. exercise on the Ab Circle device. Surface electromyography was used to assess 12 subjects (6 men, 6 women) for 6 exercise conditions, including: abdominal crunch, side bridge, quadruped, and Ab Circle levels 1-3. For the RA, the abdominal crunch elicited significantly greater activity vs. the Ab Circle level 1, and the side bridge elicited significantly greater activity vs. the Ab Circle levels 1 and 2. For the EO, the side bridge elicited significantly greater activity vs. the quadruped. No significant differences were noted between conditions for the LASs. For the LES, the side bridge and quadruped elicited significantly greater activity vs. the abdominal crunch. The results of this study indicate that the anterior, posterior, and lateral trunk musculature can be activated to similar or even greater levels by performing the 3 traditional trunk exercises vs. the Ab Circle. This was particularly evident for the side bridge exercise, which elicited significantly greater activity of the RA vs. the Ab Circle levels 1 and 2, and elicited similar activity of the EO, LASs, and LES at all 3 Ab Circle levels.     

Electromyographic comparison of the ab-slide and crunch exercises

The purpose of this study was to compare the Ab-Slide with crunch abdominal exercises for electromyographic activity for selected muscles. Forty-five subjects who regularly performed abdominal exercises participated. Subjects completed 5 trials for each exercise, with repetition rate controlled by the tester. Electromyographic activity for the external oblique (EO), upper rectus abdominis (URA), and lower rectus abdominis (LRA) was collected. Raw data for each muscle were rectified and integrated over 100-millisecond time intervals. For each muscle, the average concentric and eccentric integrated amplitudes of the middle 3 trials were compared with a dependent t-test. During concentric movement, the EO and LRA had significantly higher integrated activation amplitudes for the crunch exercise. During the eccentric movement, the URA, LRA, and EO had significantly higher average integrated activation amplitudes for the Ab-Slide exercise. The Ab-Slide is a credible abdominal exercise variation, but the crunch should remain the standard abdominal exercise.     

Electromyographic response of the abdominal musculature to varying abdominal exercises

This study examined the electromyographic (EMG) response of the upper rectus abdominis (URA), lower rectus abdominis (LRA), internal obliques (IOs), external obliques (EOs), and the rectus femoris (RF) during various abdominal exercises (crunch, supine V-up, prone V-up on ball, prone V-up on slide board, prone V-up on TRX, and prone V-up on Power Wheel). The subjects (n = 21) performed an isometric contraction of the abdominal musculature while performing these exercises. Testing revealed no statistically significant differences between any of the exercises with respect to the EOs, the URA, or the LRA. However, when examining the IO muscle, the supine V-up exercise displayed significantly greater muscle activity than did the slide exercise. In addition, EMG activity of the RF during the crunch was significantly less than in any of the other 5 exercises. These results indicate that when performing isometric abdominal exercises, non-equipment-based exercises stressed the abdominal muscles similarly to equipment-based exercises. Based on the findings of the current study, the benefit of training the abdominal musculature in an isometric fashion using commercial equipment could be called into question.     

Electromyographic comparison of the upper and lower rectus abdominis during abdominal exercises

The objective of this pilot study was to determine the effect of 6 different abdominal exercises on the electrical activity of the upper rectus abdominis (URA) and lower rectus abdominis (LRA). Eight healthy, adult volunteers completed 6 random abdominal exercises: curl up, Sissel ball curl up, Ab Trainer curl up, leg lowering, Sissel ball roll out, and reverse curl up. Action potentials were recorded and analyzed from the URA and the LRA using surface electromyography (EMG) during a 2-second concentric contraction. The average normalized data were compared between the URA and the LRA in order to determine the behavior of the different muscle sites and between exercises in order to determine which exercises elicited the highest EMG activity. There were no significant differences (p > 0.05) between the EMG activity of the URA and LRA during any exercise. There were no significant interactions between subject and muscle site or between exercise and muscle site. Significant differences were found among the 6 exercises performed, and due to the interaction between subject and exercise performed. Both the URA and the LRA recorded significantly higher mean amplitudes during the Sissel ball curl up than during all other exercises. In addition, the curl up, Sissel ball curl up, and Ab Trainer curl up had significantly higher normalized EMG activity in both muscle sites than the reverse curl up, the leg lowering exercise, and the Sissel ball roll out. The curl up and the Ab Trainer curl up exercises were not significantly different in terms of their normalized EMG activities for both the URA and the LRA.     

Responses of the anterolateral abdominal muscles during cough and expiratory threshold loading in the cat.

The present study was conducted to determine the pattern of activation of the anterolateral abdominal muscles during the cough reflex. Electromyograms (EMGs) of the rectus abdominis, external oblique, internal oblique, transversus abdominis, and parasternal muscles were recorded along with gastric pressure in anesthetized cats. Cough was produced by mechanical stimulation of the lumen of the intrathoracic trachea or larynx. The pattern of EMG activation of these muscles during cough was compared with that during graded expiratory threshold loading (ETL; 1-30 cmH(2)O). ETL elicited differential recruitment of abdominal muscle EMG activity (transversus abdominis > internal oblique > rectus abdominis congruent with external oblique). In contrast, both laryngeal and tracheobronchial cough resulted in simultaneous activation of all four anterolateral abdominal muscles with peak EMG amplitudes 3- to 10-fold greater than those observed during the largest ETL. Gastric pressures during laryngeal and tracheobronchial cough were at least eightfold greater than those produced by the largest ETL. These results suggest that, unlike their behavior during expiratory loading, the anterolateral abdominal muscles act as a unit during cough.     

Abdominal strengthening using the AbVice machine as measured by surface electromyographic activation levels

Twenty-four college students served as subjects in a study that examined the effect of a prototypical abdominal muscle strengthening device (AbVice) compared with other devices currently on the market. The purpose of the present study was to investigate a prototypical device (AbVice) that incorporates contraction of the hamstring and gluteal musculature in conjunction with the abdominals, which may assist in decreasing activation of the hip flexors by allowing greater activity levels of the abdominal musculature via the theory of reflex inhibition, compared with other devices currently available on the market (AbRoller and AbRocker). The repeated-measures study included 17 women and 7 men who ranged in age from 20-23 years (mean +/- SD age, 21.3 +/- 1.5 years). Each subject underwent a single session of data collection during which they completed 10 repetitions of abdominal crunches per device. Subjects completed 4 different crunch sets (AbRocker, AbRoller, standard crunch, AbVice). Counterbalancing of the device was used to negate the effect of fatigue. Speed of repetitions was ensured via use of a metronome set at 40 b.min(-1) to permit similar contraction times and rest periods between repetitions. Rest between conditions was 3 minutes. Mean activation levels of surface electromyography (EMG) were recorded for each condition at the following locations on the right side of the body: rectus abdominis 2.5 cm superior to the umbilicus, rectus abdominis 2.5 cm inferior to the umbilicus, external oblique abdominis 1.0 cm medial to the anterior superior iliac spine, and external oblique abdominis less than 1.0 cm superior to the inguinal ligament. Mean (SD) activation was 1,165.21 mV (634.60 mV) with the AbVice, 242.92 mV (263.03 mV) with the AbRocker, 753.29 mV (514.80 mV) with the standard crunch, and 757.67 mV (542.85 mV) with the AbRoller. Broken down by sex, women had the following mean (SD) EMG values: 1,079.76 mV (705.02 mV) with the AbVice, 680.35 mV (535.35 mV) with the standard crunch, 262.70 mV (305.89 mV) with the AbRocker, and 636.88 mV (502.82 mV) with the AbRoller. Men demonstrated mean (SD) values of 1,372 mV (383.87 mV) with the AbVice, 1,051 mV (560.09 mV) with the AbRoller, 930.43 mV (447.17 mV) with the standard crunch, and 194.86 mV (109.05 mV) with the AbRocker. Two-way analysis of variance with factor 1 (person) and factor 2 (condition) had F values of 11.73 and 36.04, respectively. Post hoc analysis using the Tukey test indicated that all comparisons between conditions were significant at the p = 0.01 level except for the standard crunch vs. the AbRoller. The AbVice activated the selected abdominal musculature more effectively than the other conditions.     

Effect of hypercapnia and PEEP on expiratory muscle EMG and shortening

The present study examined the effects of hypercapnia and positive end-expiratory pressure (PEEP) on the electromyographic (EMG) activity and tidal length changes of the expiratory muscles in 12 anesthetized, spontaneously breathing dogs. The integrated EMG activity of both abdominal (external oblique, internal oblique, rectus abdominis, and transverse abdominis) and thoracic (triangularis sterni, internal intercostal) expiratory muscles increased linearly with increasing PCO2 and PEEP. However, with both hypercapnia and PEEP, the percent increase in abdominal muscle electrical activity exceeded that of thoracic expiratory muscle activity. Both hypercapnia and PEEP increased the tidal shortening of the external oblique and rectus abdominis muscles. Changes in tidal length correlated closely with simultaneous increases in muscle electrical activity. However, during both hypercapnia and PEEP, length changes of the external oblique were significantly greater than those of the rectus abdominis. We conclude that both progressive hypercapnia and PEEP increase the electrical activity of all expiratory muscles and augment their tidal shortening but produce quantitatively different responses in the several expiratory muscles.     

Slow expiration reduces sternocleidomastoid activity and increases transversus abdominis and internal oblique muscle activity during abdominal curl-up

The aim of this study was to investigate the effects of quiet inspiration versus slow expiration on sternocleidomastoid (SCM) and abdominal muscle activity during abdominal curl-up in healthy subjects. Twelve healthy subjects participated in this study. Surface electromyography (EMG) was used to collect activity of bilateral SCM, rectus abdominis (RA), external oblique (EO), and transversus abdominis/internal oblique (TrA/IO) muscles. A paired t-test was used to determine significant differences in the bilateral SCM, RF, EO, and TrA/IO muscles between abdominal curl-up with quiet inspiration and slow expiration. There were significantly lower EMG activity of both SCMs and greater EMG activity of both IOs during abdominal curl-up with slow expiration, compared with the EMG activity of both SCMs and IOs during abdominal curl-up with quiet inspiration (p < .05). The results of this study suggest that slow expiration would be recommended during abdominal curl-up for reduced SCM activation and selective activation of TrA/IO in healthy subjects compared with those in abdominal curl up with quiet inspiration.     

Posture effects on timing of abdominal muscle activity during stimulated ventilation.

In humans during stimulated ventilation, substantial abdominal muscle activity extends into the following inspiration as postexpiratory expiratory activity (PEEA) and commences again during late inspiration as preexpiratory expiratory activity (PREA). We hypothesized that the timing of PEEA and PREA would be changed systematically by posture. Fine-wire electrodes were inserted into the rectus abdominis, external oblique, internal oblique, and transversus abdominis in nine awake subjects. Airflow, end-tidal CO2, and moving average electromyogram (EMG) signals were recorded during resting and CO2-stimulated ventilation in both supine and standing postures. Phasic expiratory EMG activity (tidal EMG) of the four abdominal muscles at any level of CO2 stimulation was greater while standing. Abdominal muscle activities during inspiration, PEEA, and PREA, were observed with CO2 stimulation, both supine and standing. Change in posture had a significant effect on intrabreath timing of expiratory muscle activation at any level of CO2 stimulation. The transversus abdominis showed a significant increase in PEEA and a significant decrease in PREA while subjects were standing; similar changes were seen in the internal oblique. We conclude that changes in posture are associated with significant changes in phasic expiratory activity of the four abdominal muscles, with systematic changes in the timing of abdominal muscle activity during early and late inspiration.     

Transversus abdominis muscle function in humans

We used a high-resolution ultrasound to make electrical recordings from the transversus abdominis muscle in humans. The behavior of this muscle was then compared with that of the external oblique and rectus abdominis in six normal subjects in the seated posture. During voluntary efforts such as expiration from functional residual capacity, speaking, expulsive maneuvers, and isovolume "belly-in" maneuvers, the transversus in general contracted together with the external oblique and the rectus abdominis. In contrast, during hyperoxic hypercapnia, all subjects had phasic expiratory activity in the transversus at ventilations between 10 and 18 l/min, well before activity could be recorded from either the external oblique or the rectus abdominis. Similarly, inspiratory elastic loading evoked transversus expiratory activity in all subjects but external oblique activity in only one subject and rectus abdominis activity in only two subjects. We thus conclude that in humans 1) the transversus abdominis is recruited preferentially to the superficial muscle layer of the abdominal wall during breathing and 2) the threshold for abdominal muscle recruitment during expiration is substantially lower than conventionally thought.     

MVC techniques to normalize trunk muscle EMG in healthy women

Normalization of the surface electromyogram (EMG) addresses some of the inherent inter-subject and inter-muscular variability of this signal to enable comparison between muscles and people. The aim of this study was to evaluate the effectiveness of several maximal voluntary isometric contraction (MVC) strategies, and identify maximum electromyographic reference values used for normalizing trunk muscle activity. Eight healthy women performed 11 MVC techniques, including trials in which thorax motion was resisted, trials in which pelvis motion was resisted, shoulder rotation and adduction, and un-resisted MVC maneuvers (maximal abdominal hollowing and maximal abdominal bracing). EMG signals were bilaterally collected from upper and lower rectus abdominis, lateral and medial aspects of external oblique, internal oblique, latissimus dorsi, and erector spinae at T9 and L5. A 0.5 s moving average window was used to calculate the maximum EMG amplitude of each muscle for each MVC technique. A great inter-subject variability between participants was observed as to which MVC strategy elicited the greatest muscular activity, especially for the oblique abdominals and latissimus dorsi. Since no single test was superior for obtaining maximum electrical activity, it appears that several upper and lower trunk MVC techniques should be performed for EMG normalization in healthy women.     

The external oblique flap for reconstruction of the rectus sheath.

Despite the availability of synthetic materials and distant fascial flaps, primary closure of ventral abdominal defects with contiguous tissues remains the preferred solution. Increased experience with such defects in the lower abdomen, particularly at the time of bilateral rectus muscle transposition, led in 1985 to the investigation of an external oblique abdominis flap for closure of the anterior rectus sheath. From October of 1985 to October of 1990, 33 patients underwent repair of bilateral lower rectus abdominis defects with the help of bilateral external oblique flaps. Each of the patients had undergone synchronous chest or breast reconstruction using a transverse rectus abdominis musculocutaneous flap including bilateral rectus muscle pedicles. Although all patients in this study had undergone double-pedicle rectus muscle procedures, not all patients having had double-pedicle rectus muscle procedures required this maneuver. External oblique flaps were performed at the time of rectus sheath repair only if fascia could not be approximated without tearing. After closure of the bilateral paramedian defect, synthetic mesh overlay was added only if the direct closure still appeared excessively tight. At the time of advancement of the external oblique muscle and fascia, the internal oblique abdominis muscle and lateral cutaneous nerve of the thigh were preserved. Of the 33 patients who underwent this procedure, 7 required the addition of mesh overlay. Thirty-two patients healed uneventfully with a remarkably solid ventral abdominal wall. One patient developed an early postoperative hernia subsequent to a major and prolonged abdominal-wall infection and abscess. Patient follow-up ranged from 1 to 36 months, with a mean of 12 months.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory abdominal muscle recruitment and chest wall motion in myotonic muscular dystrophy.

Abdominal muscles are selectively active in normal subjects during stress and may increase the potential energy for inspiration by reducing the end-expiratory lung volume (EELV). We hypothesized that a similar process would occur in subjects with myotonic muscular dystrophy (MMD), but would be less effective, because of to their weakness and altered chest wall mechanics. Fine-wire electromyography (EMG) of the transversus abdominis (TA), internal oblique (IO), external oblique, and rectus abdominis was recorded in 10 MMD and 10 control subjects. EMG activity, respiratory inductive plethysmography, and gastric pressure were recorded during static pressure measurement and at increasing levels of inspiratory resistance breathing. EELV was reduced and chest wall motion was synchronous only in controls. Although the TA and IO were selectively recruited in both groups, EMG activity of the MMD group was twice that of controls at the same inspiratory pressure. In MMD subjects with mildly reduced forced vital capacity, significant differences can be seen in abdominal muscle recruitment, wall motion, work of breathing, and ventilatory parameters.     

Electromyographic muscle activity in curl-up exercises with different positions of upper and lower extremities

The purpose of the study was to evaluate the electromyographic (EMG) activity of muscles in curl-up exercises depending on the position of the upper and lower extremities. From the perspective of biomechanics, different positions of the extremities result in shifting the center of gravity and changing muscular loads in abdominal strength exercises. The subjects of the research were 3 healthy students (body mass 53-56 kg and height 163-165 cm) with no history of low back pain or abdominal surgery. Subjects completed 18 trials for each of the 9 exercises (static curl-up with 3 positions of the upper and 3 position of the lower extremities). The same experiment with the same subjects was conducted on the next day. The EMG activity of rectus abdominis (RA), erector spinae (ES), and quadriceps femoris-long head (rectus femoris [RF]) was examined during the exercises. The surface electrical activity was recorded for the right and left sides of each muscle. The raw data for each muscle were rectified and integrated. The statistical analysis showed that changing the position of upper extremities in the examined exercises affects the EMG activity of RA and ES but does not significantly affect the EMG activity of RF. Additionally, it was found that curl-up exercises with the upper extremities extended behind the head and the lower extremities flexed at 90° in the hip and knee joints involve RA with the greatest intensity, whereas curl-up exercises with the upper extremities extended along the trunk and the lower extremities flexed at 90° in the hip and knee joints involve RA with the lowest intensity.     

The effect of posture on respiratory activity of the abdominal muscles

The purpose of this study was to determine the influence of posture on the expiratory activity of the abdominal muscles. Fifteen young adult men participated in the study. Activities of the external oblique abdominis, internal oblique abdominis, and rectus abdominis muscles were measured electromyographically in various postures. We used a pressure threshold in order to activate the abdominal muscles as these muscles are silent at rest. A spirometer was used to measure the lung volume in various postures. Subjects were placed in the supine, standing, sitting, and sitting-with-elbow-on-the-knee (SEK) positions. Electromyographic activity and mouth pressure were measured during spontaneous breathing and maximal voluntary ventilation under the respiratory load. We observed that the lung volume changed with posture; however, the breathing pattern under respiratory load did not change. During maximal voluntary ventilation, internal oblique abdominis muscle expiratory activity was lower in the SEK position than in any other position, external oblique abdominis muscle inspiratory activity was lower in the supine position than in any other position, and internal oblique abdominis muscle activity was higher in the standing position than in any other position. During spontaneous breathing, external oblique abdominis muscle activity was higher during expiration and inspiration in the SEK position than in any other position. The internal oblique abdominis muscle activity was higher during both inspiration and expiration in the standing position than in any other position. The rectus abdominis muscle activity did not change with changes in posture during both inspiration and expiration. Increase in the external oblique abdominis activity in the SEK position was due to anatomical muscle arrangement that was consistent with the direction of lower rib movement. On the other hand, increase in the internal oblique abdominis activity in the standing position was due to stretching of the abdominal wall by the viscera. We concluded that differences in activity were due to differences in the anatomy of the abdominal muscles and the influence of gravity.     

Not all instability training devices enhance muscle activation in highly resistance-trained individuals

The objective of this study was to measure the electromyographic (EMG) activity of the soleus, bicep femoris, rectus femoris, lower abdominal, and lumbosacral erector spinae (LSES) muscles with a variety of (a) instability devices, (b) stable and unstable (Dyna Disc) exercises, and (c) a fatiguing exercise in 16 highly conditioned individuals. The device protocol had participants assume standing and squatting postures while balancing on a variety of unstable platforms (Dyna Disc, BOSU ball, wobble board, and a Swiss ball) and a stable floor. The exercise protocol had subjects performing, static front lunges, static side lunges, 1-leg hip extensions, 1-leg reaches, and calf raises on a floor or an unstable Dyna Disc. For the fatigue experiment, a wall sit position was undertaken under stable and unstable (BOSU ball) conditions. Results for the device experiment demonstrated increased activity for all muscles when standing on a Swiss ball and all muscles other than the rectus femoris when standing on a wobble board. Only lower abdominals and soleus EMG activity increased while squatting on a Swiss ball and wobble board. Devices such as the Dyna Disc and BOSU ball did not exhibit significant differences in muscle activation under any conditions, except the LSES in the standing Dyna Disc conditions. During the exercise protocol, there were no significant changes in muscle activity between stable and unstable (Dyna Disc) conditions. With the fatigue protocol, soleus EMG activity was 51% greater with a stable base. These results indicate that the use of moderately unstable training devices (i.e., Dyna Disc, BOSU ball) did not provide sufficient challenges to the neuromuscular system in highly resistance-trained individuals. Since highly trained individuals may already possess enhanced stability from the use of dynamic free weights, a greater degree of instability may be necessary.