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PubMed1997

Effects of respiratory muscle training and electrical stimulation of abdominal muscles on respiratory capabilities in tetraplegic patients.

Thirteen tetraplegic patients were included in the study of the effects of respiratory muscle training and of electrical stimulation of the abdominal muscles on their respiratory capabilities. Each patient was subjected for three 1 month lasting periods of the study: for inspiratory muscle training, expiratory muscle training and for a period without training. The sequence of these three periods was random for each patient. Respiratory tests (RT) measuring forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were conducted before and following each monthly period. Measurements were taken under four sets of conditions: the patients' unassisted efforts, their efforts combined with pressure manually applied by a therapist to the upper part of their abdomen, and their efforts accompanied by electrical stimulation (ES) of the abdominal muscles during the early phase of expirium, once triggered by the therapist and once by the patients themselves. RT values were increasing following respiratory muscle training and inspiratory training apparently had a slightly greater effect than its expiratory counterpart. The increments of values of RT were statistically significant (P < 0.05) after the inspiratory muscle training. RT measurements were greater when the patient's voluntary effort was combined with ES of abdominal muscles than when it was not. This study concludes that respiratory muscle training is a potentially effective approach and that ES of the abdominal muscles has potentials to improve coughing in tetraplegic patients.

Abdominal Muscles↗
PubMed2005

Passive mechanics of canine internal abdominal muscles.

The internal abdominal muscles are biaxially loaded in vivo, and therefore length-tension relations along and transverse to the directions of the muscle fibers are important in understanding their mechanical properties. We hypothesized that 1) internal oblique and transversus abdominis form an internal abdominal composite muscle with altered compliance than that of either muscle individually, and 2) anisotropy, different compliances in orthogonal directions, of internal abdominal composite muscle is less pronounced than that of its individual muscles. To test these hypotheses, in vitro mechanical testing was performed on 5 x 5 cm squares of transversus abdominis, internal oblique, and the two muscles together as a composite. These tissues were harvested from the left lateral side of abdominal muscles of eleven mongrel dogs (15-23 kg) and placed in a bath of oxygenated Krebs solution. Each tissue strip was attached to a biaxial mechanical testing device. Each muscle was passively lengthened and shortened along muscle fibers, transverse to fibers, or simultaneously along and transverse to muscle fibers. Both transversus abdominis and internal oblique muscles demonstrated less extensibility in the direction transverse to muscle fibers than along fibers. Biaxial loading caused a stiffening effect that was greater in the direction along the fibers than transverse to the fibers. Furthermore, the abdominal muscle composite was less compliant than either muscle alone in the direction of the muscle fibers. Taken together, our data suggested that the internal abdominal composite tissue has complex mechanical properties that are dependent on the mechanical properties of internal oblique and transversus abdominis muscles.

Abdominal Muscles↗
PubMed1998

Neck and abdominal muscle activity in patients with severe thoracic scoliosis.

Patients with severe chronic obstructive pulmonary disease (COPD) do not use the sternocleidomastoid muscles when breathing at rest, but have a greater than normal neural drive to the rib-cage inspiratory muscles, the abdominal muscles, and the diaphragm. Yet the increased activation of the abdominal muscles and diaphragm in such patients has only limited mechanical effects, and this has led to the suggestion that the overall increase in neural drive is simply an automatic response of the respiratory system to a greater than resting stimulation. To test this hypothesis, we examined the pattern of respiratory-muscle activation in eight patients with severe thoracic scoliosis (Cobb angle between 100 degrees and 136 degrees). We recorded electromyograms of the sternocleidomastoid, scalene, rectus abdominis, external oblique, and transversus abdominis muscles; esophageal (Pes) and gastric (Pga) pressures; and the anteroposterior (AP) diameter of the abdomen during resting breathing in the seated posture. All patients had invariable phasic inspiratory activity in the scalenes; and five patients had invariable phasic expiratory activity in the transversus; intermittent expiratory activity in the transversus was also recorded in three patients. In contrast, only one patient had invariable phasic inspiratory activity in the sternocleidomastoid, and only one patient had invariable phasic expiratory activity in the external oblique. The decrease in abdominal AP diameter during expiration was commonly associated with a rise in Pga. These observations therefore indicate that the pattern of respiratory-muscle activation in patients with severe thoracic scoliosis is essentially similar to that seen in patients with severe COPD. This supports the concept that the order of recruitment of the respiratory muscles during breathing is an automatic response of the central controller.

Abdominal Muscles↗
PubMed1976

Electromyographic evaluation of human detrusor muscle activity in relation to abdominal muscle activity.

Simultaneous electromyographic (EMG) recordings from the bladder detrusor muscle and the inferior rectus abdominis muscle were made in six normal subjects, in four patients with lower motor neuron bladder disease and in two patients with an upper motor neuron type of bladder lesion. Results of the study demonstrate that the bladder electrodes do not record remote muscle activity from the abdominal muscles so that any increased detrusor electrical activity with abdominal contraction must have some other explanation such as a possible abdominal-detrusor reflex or the production of increased intra-abdominal pressure from abdominal contraction. The study also demonstrates that the detrusor EMG is of value in studying the physiology of the bladder in humans, is a safe and simple technique and is of value particularly in assessing neurogenic bladder disorders.

Abdominal Muscles↗
PubMed1989

Abdominal muscle activity and intraabdominal pressure after upper abdominal surgery.

To examine the influence of abdominal muscle activity on intraabdominal pressure, the integrated surface EMG from upper abdominal muscle (EAB) was related to changes in intragastric pressure (PGA) in six patients after upper abdominal surgery. A similar respiratory pattern of EMG activity was observed in all subjects. EAB increased rapidly at the onset of expiration, and thereafter more slowly throughout expiration. At the onset of inspiration EAB decreased abruptly, and was small during inspiration. Changes in intragastric pressures were closely related to changes in EAB. In five patients PGA and EAB waveforms were almost identical over the respiratory cycle. In one subject a biphasic change in PGA during inspiration was observed, suggesting the influence of other respiratory muscles. Abdominal muscle action results in changes in intraabdominal pressure previously attributed to diaphragmatic impairment.

Abdomen↗
PubMed1983

Mechanical role of the abdominal muscles in relation to posture.

Abdominal muscle activity was studied in 10 normal naive subjects during quiet breathing in different body positions. Electromyograms of the upper and lower portions of the external oblique and rectus abdominis were recorded with bipolar needle electrodes and changes in abdominal and rib cage displacements were measured using linearized magnetometers. The abdominal muscles were always silent in the supine posture. In contrast, 8 of the 10 subjects showed tonic abdominal muscle activity in the standing posture and 4 of the subjects did so also in the 45 degrees head-down position; when present, this activity was always greater in the dependent (where the hydrostatic pressure was greater) than in the non-dependent portion of the muscles. Tonic abdominal muscle activity was associated with a reduction of abdominal volume throughout the respiratory cycle and a reduction of the end-expiratory lung volume below the neutral position of the respiratory system. We conclude that (1) tonic activity is present in the abdominal muscles in most standing subjects, (2) this activity is primarily related to the magnitude of hydraulic pressure exerted by the abdominal contents on the abdominal wall, and (3) in most normal individuals standing at rest, the end-expiratory position is at least in part actively determined. Such an abdominal muscle use, although causing quiet breathing to depart from the relaxed abdominothoracic configuration, may be associated with minimum respiratory work.

Abdomen↗
PubMed1981

Load compensating responses of human abdominal muscles.

1. We studied abdominal muscle responses to positive pressure loads applied suddenly to the external airway while subjects held a constant lung volume against steady pressure. The pre-loading holding pressure was 6 cm H(2)O, and the loading pressures were 6 or 12 cm H(2)O lasting for 2 sec.2. Surface electromyograms (e.m.g.) were recorded over the internal oblique, external oblique, and rectus abdominis muscles. The latency and pattern of the e.m.g. reactions were studied by measuring the raw record for each loading trial, and by averaging the rectified e.m.g. for many trials.3. No responses were obtained if subjects were instructed not to respond to the loads. When instructed and trained to maintain their pre-load position in spite of the load, a two-phase compensatory response was found. The initial response (phase I) was 100-300 msec in duration; it was followed by a continuous e.m.g. discharge (phase II) which continued to the offset of the pressure load. Subjects were also trained to make a single respiratory effort as quickly as possible after the load onset or after just an auditory stimulus. These were simple reaction time tasks of a traditional kind and the e.m.g. responses elicited were single, brief bursts.4. For all subjects and experimental conditions the e.m.g. response of the internal oblique occurred first, followed by the external oblique and then the rectus abdominis. For the ;maintain position' task, phase I latencies (internal oblique) averaged 66-90 msec for individual subjects, but for single trials with optimal conditions of practice and preparatory intervals these ranged from 42 to 110 msec with a third of the reactions occurring within 50-60 msec.5. The latencies for reaction time responses to loading were about 6 msec shorter than the phase I latencies. The latency distributions for the two types of responses were similar, and both were affected to the same degree by practice, and changing the length and variability of the preparatory interval. Because of these similarities we suggest that the phase I reaction was a learned response of a ;simple reaction time' type, and not comparable to late stretch reflexes such as the M2 of limb muscles.6. Arm muscle responses to respiratory pressure changes were measured in three subjects under identical conditions used to obtain load reaction times of abdominal muscles. These simple reaction times averaged 61-71 msec, and ranged from 42 to 97 msec. Therefore very short proprioceptive reaction times are not peculiar to the respiratory system, or to load perturbations of the responding muscle.7. Mechanical adjustments of airway pressure and lung volume in response to loading are first expressed at the mouth about 90 msec after abdominal muscle activity begins. In the ;maintain position' task, the accuracy with which pressure and volume adjustments were made during the last 1.5 sec of the loading period approximated that reported in the literature for trained singers holding a tone using constant expiratory pressure.

Abdominal Muscles↗
PubMed1982

The behaviour of the abdominal muscles during inspiratory mechanical loading.

Abdominal muscle activity was studied in eight normal subjects, while seated and supine, during inspiratory resistive and elastic mechanical loading. Electromyograms of the external oblique and rectus abdominis muscle were recorded using unipolar needle electrodes and changes in antero-posterior dimensions of the abdomen (Vab) were measured using linearized magnetometers. Elastic loading evoked abdominal muscle activity during expiration, especially in the rectus abdominis, in seven seated subjects while resistive loading did so in five. In four runs activity was also detectable throughout inspiration. Abdominal muscle activity was associated with a reduction in Vab throughout the respiratory cycle. When the subjects were supine loads did not evoke abdominal muscle activity. We conclude that abdominal muscle recruitment during inspiratory mechanical loading may facilitate inspiration by increasing diaphragmatic length.

Abdominal Muscles↗
PubMed1995

Why leg crossing? The influence of common postures on abdominal muscle activity.

STUDY DESIGN: Abdominal muscle activity is recorded in the supine position, unconstrained standing, and in the sitting position on an office chair with the use of backrest and armrests, with and without crossed legs. OBJECTIVES: To assess the role of oblique abdominal muscles in relation to the stability of lumbar spine and pelvis in commonly adopted unconstrained postures. SUMMARY OF BACKGROUND DATA: Cross-legged sitting is very common for men and women. No solid evidence exists for either a beneficial or a detrimental effect of this posture. No electromyographic study deals with the activity of abdominal muscles in this commonly adopted unconstrained posture. METHODS: In healthy subjects, electromyographic activity of the rectus abdomini and external and internal oblique abdominals was recorded bilaterally during commonly adopted unconstrained postures. RESULTS: The activity of the internal oblique muscle was significantly higher in the sitting position than in supine position. For the external and internal oblique abdominals, the activity was significantly higher in the standing position than in the sitting position. When sitting, the activity of the oblique abdominals is significantly lowered by crossing the legs in the preferred way (either upper legs cross or ankle on knee). In contrast, the activity of the rectus abdominis is not significantly altered by leg crossing. CONCLUSIONS: From these remarkable findings, we conclude that leg crossing is physiologically valuable. It should be studied whether leg crossing can be implemented in the design of the workplace.

Abdominal Muscles↗
PubMed1985

Response of abdominal muscle to graded mechanical loads.

Abdominal muscle electromyograms were monitored in response to graded mechanical loads added to either inspiration or expiration in anesthetized cats. The surgical preparation, the apparatus, and the levels of loads applied (resistive, tracheal occlusion, and continuous positive pressure) were matched with those employed in our previous study on medullary expiratory neurons [Baker et al, 1979]. Although expiratory neuron firing was significantly increased by each of three graded levels of expiratory resistive loads, abdominal muscles were activated in only about 50% of the animals exposed to the highest-level resistive load. The smaller resistive loads failed to elicit any discernible abdominal muscle activity. These findings suggest that the lower motor neurons have a higher threshold for activation than the medullary neurons. Recruitment of medullary expiratory neurons and integration of synaptic input at the spinal level must play important roles in the response to expiratory loading. Abdominal muscles did not respond to mechanical loading during inspiration. Bilateral cervical vagotomy eliminated the abdominal muscle responses to expiratory loads.

Abdominal Muscles↗
PubMed2006

Effects of abdominal muscle fatigue on anticipatory postural adjustments associated with arm raising.

Anticipatory postural adjustments (APAs) are postulated to ameliorate the effects of the disturbance to posture caused by voluntary movement. The primary hypothesis tested in our study was that the magnitude of anticipatory trunk muscle activity is altered by abdominal muscle fatigue. A subsidiary aim of the present study was to examine the directional nature of APAs and use this information to elucidate the central or peripheral nature of changes in postural muscle activity associated with abdominal muscle fatigue. The present study was a within subject design, where abdominal muscle fatigue was induced by a static abdominal curl. Surface EMG was used to assess postural muscle activity in the following trunk muscles; rectus abdominis, erector spinae and internal oblique. Following abdominal muscle fatigue, the magnitude of muscle activity during APAs was significantly reduced by 20% in both the rectus abdominis (fatigued muscle) and the erector spinae (not fatigued) indicating a central rather than peripheral fatigue effect on muscle activity. Abdominal muscle fatigue also induced a 30% increase in the baseline muscle activity of the internal oblique. The changes in magnitude of APA muscle activity may reflect a change in system gain or a change in postural control perhaps related to a change in perceived postural stability. An increase in baseline muscle activity in the internal oblique may compensate partially for the reduction in APAs.

Abdominal Muscles↗
PubMed1994

An electromyographic validation of an abdominal muscle test.

A recently developed abdominal muscle test (AMT), using four levels of difficulty to assess abdominal muscle strength, was validated by examination of the functional interrelationship between the individual muscles during the AMT, and by determining the relationship between the AMT level of difficulty and electromyographical (EMG) activity. EMG data were collected from the upper and lower rectus abdominis, and the external and internal oblique in 22 subjects as they participated in the AMT. Typically, throughout the AMT, lower rectus abdominis was most active, followed by upper rectus abdominis, external oblique, and internal oblique. EMG activity increased significantly (p < .05) for all muscles from Levels 1 to 3. At Level 4, although upper and lower rectus abdominis remained more active than the obliques, the relative contribution from the obliques was increased. The results of this study show that the AMT is a valid indicator of ability to develop voluntary abdominal muscle tension in Levels 1 to 3, although, Level 4 is more indicative of the oblique muscles' functional abilities and therefore may be considered a distinctly different muscle test.

Abdominal Muscles↗
PubMed2006

Exercise-induced abdominal muscle fatigue in healthy humans.

The abdominal muscles have been shown to fatigue in response to voluntary isocapnic hyperpnea using direct nerve stimulation techniques. We investigated whether the abdominal muscles fatigue in response to dynamic lower limb exercise using such techniques. Eleven male subjects [peak oxygen uptake (VO2 peak) = 50.0 +/- 1.9 (SE) ml.kg(-1).min(-1)] cycled at >90% VO2 peak to exhaustion (14.2 +/- 4.2 min). Abdominal muscle function was assessed before and up to 30 min after exercise by measuring the changes in gastric pressure (Pga) after the nerve roots supplying the abdominal muscles were magnetically stimulated at 1-25 Hz. Immediately after exercise there was a decrease in Pga at all stimulation frequencies (mean -25 +/- 4%; P < 0.001) that persisted up to 30 min postexercise (-12 +/- 4%; P = 0.001). These reductions were unlikely due to changes in membrane excitability because amplitude, duration, and area of the rectus abdominis M wave were unaffected. Declines in the Pga response to maximal voluntary expiratory efforts occurred after exercise (158 +/- 13 before vs. 145 +/- 10 cmH2O after exercise; P = 0.005). Voluntary activation, assessed using twitch interpolation, did not change (67 +/- 6 before vs. 64 +/- 2% after exercise; P = 0.20), and electromyographic activity of the rectus abdominis and external oblique increased during these volitional maneuvers. These data provide new evidence that the abdominal muscles fatigue after sustained, high-intensity exercise and that the fatigue is primarily due to peripheral mechanisms.

Abdominal Muscles↗
PubMed1995

The effect of strict muscle stress limits on abdominal muscle force predictions for combined torsion and extension loadings.

The objective of this study was to determine to what extent the central nervous system activates torso muscles so as to equalize the largest muscle stresses. Two optimization models that treat large muscle stresses differently were formulated. One model minimized spinal compression force subject to the lowest possible muscle stress limit, and the other model minimized the sum of cubed muscle stresses. Experimental conditions were determined for which the two models made different muscle force predictions. Specifically, the models predicted different rectus abdominis activity levels for tasks involving torsion and extension moment loadings. Surface electromyography was used to evaluate the model predictions. Applied loads were chosen to assure that the rectus abdominis EMG exceeded 30% MVC. Analysis of variance indicated that rectus abdominis activity was not affected by torsion loading at the p < 0.05 level of significance in a statistical design having 90% power, which was consistent with the predictions of the model that minimized the sum of cubed muscle stresses. Thus, it was concluded that equalization of the largest muscles stress was not the paramount objective of the central nervous system in the tasks studied.

Abdominal Muscles↗
PubMed2005

Postural activity of the abdominal muscles varies between regions of these muscles and between body positions.

The abdominal muscles have an important role in control and movement of the lumbar spine and pelvis. Given there is new evidence of morphological and functional differences between distinct anatomical regions of the abdominal muscles, this study investigated whether there are regional differences in postural activity of these muscles and whether recruitment varies between different body positions. Eleven subjects with no history of low back pain that affected function or for which they sought treatment participated in the study. Electromyographic (EMG) activity of the upper, middle and lower regions of transversus abdominis (TrA), the middle and lower regions of obliquus internus abdominis (OI) and the middle region of obliquus externus abdominis (OE) was recorded using intramuscular electrodes. All subjects performed rapid, unilateral shoulder flexion in standing and six subjects also moved their upper limb in sitting. There were regional differences in the postural responses of TrA with limb movement. Notably, the onset of EMG of the upper region was later than that of the lower and middle regions. There were no differences in the EMG onsets of lower and middle TrA or OI. The postural responses of the abdominal muscles were also found to differ between body positions, with recruitment delayed in sitting compared to standing. This study showed that there is regional differentiation in TrA activity with challenges to postural control and that body position influences the postural responses of the abdominal muscles. These results may reflect variation in the contribution of abdominal muscle regions to stability of the trunk.

Abdominal Muscles↗
PubMed1996

Differential respiratory activity of four abdominal muscles in humans.

Together the abdominal muscles contribute significantly to ventilation under some conditions, but there is little information regarding individual recruitment and timing of activation of the four abdominal muscles in humans. Fine-wire electrodes were inserted under direct vision guided by high-resolution ultra-sound into the rectus abdominis (Rectus), external oblique (Extern), internal oblique (Intern), and transversus abdominis (Transv) in nine awake healthy subjects. Airflow, end-tidal CO2, and moving-average EMG signals were recorded during 1) supine resting and CO2-stimulated ventilation and 2) resting ventilation in the standing position. During resting supine breathing, Transv showed significant phasic EMG activity during expiration. As posture changed from supine to standing, phasic activity during resting ventilation was greatest in Transv, with lesser activity in Intern and Extern, while Rectus remained inactive. As CO2 began to increase, Transv was activated first, followed by Intern, the Extern, and finally Rectus. With moderate CO2 stimulation, Transv and Intern were more active than was Extern and Rectus remained least active. EMG activities in the expiratory muscles after cessation of expiratory flow (postexpiratory expiratory activity) and in expiratory muscle activity preceding expiratory flow were observed consistently during supine stimulated ventilation and standing resting ventilation. These activities before and after expiratory airflow were prominent with stimulated ventilation during a substantial portion of inspiration, suggesting dual control of inspiratory pump action by both inspiratory and expiratory muscles, which provide acceleration and braking actions, respectively. These results suggest that in awake humans 1) during resting ventilation, expiration is an active process; 2) abdominal muscles are activated differentially; 3) Transv is the most active, Intern and Extern are intermediate, and Rectus is the least active expiratory muscle; and 4) during stimulated ventilation, inspiratory and expiratory muscles contribute dually to inspiratory pump action.

Abdominal Muscles↗