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.     

Differential respiratory muscle recruitment induced by clonidine in awake goats

The purpose of this study was to test thehypothesis that dysrhythmic breathing induced by the₂-agonist clonidine isaccompanied by differential recruitment of respiratory muscles. Inadult goats (n = 14) electromyographic(EMG) measurements were made from inspiratory muscles (diaphragm andparasternal intercostal) and expiratory muscles [triangularissterni (TS) and transversus abdominis (Abd)]. EMG of thethyroarytenoid (TA) muscle was used as an index of upper airway(glottal) patency. Peak EMG activities of all spinal inspiratory andexpiratory muscles were augmented by central and peripheralchemoreceptor stimuli. Phasic TA was apparent in the postinspiratoryphase of the breathing cycle under normoxic conditions. Duringdysrhythmic breathing episodes induced by clonidine, TS and Abdactivities were attenuated or abolished, whereas diaphragm andparasternal intercostal activities were unchanged. There was no tonicactivation of TS or Abd EMG during apneas; however, TA activity becametonic throughout the apnea. We conclude that1) ₂-adrenoceptor stimulationresults in differential recruitment of respiratory muscles duringrespiratory dysrhythmias and 2) apneas are accompanied by active glottic closure in the awake goat.

     

Triangularis sterni muscle use in supine humans

The electrical activity of the triangularis sterni (transversus thoracis) muscle was studied in supine humans during resting breathing and a variety of respiratory and nonrespiratory maneuvers known to bring the abdominal muscles into action. Twelve normal subjects, of whom seven were uninformed and untrained, were investigated. The electromyogram of the triangularis sterni was recorded using a concentric needle electrode, and it was compared with the electromyograms of the abdominal (external oblique and rectus abdominis) muscles. The triangularis sterni was usually silent during resting breathing. In contrast, the muscle was invariably activated during expiration from functional residual capacity, expulsive maneuvers, "belly-in" isovolume maneuvers, static head flexion and trunk rotation, and spontaneous events such as speech, coughing, and laughter. When three trained subjects expired voluntarily with considerable recruitment of the triangularis sterni and no abdominal muscle activity, rib cage volume decreased and abdominal volume increased. These results indicate that unlike in the dog, spontaneous quiet expiration in supine humans is essentially a passive process; the human triangularis sterni, however, is a primary muscle of expiration; and its neural activation is largely coupled with that of the abdominals. The triangularis sterni probably contributes to the deflation of the rib cage during active expiration.     

Mechanical role of expiratory muscles during breathing in prone anesthetized dogs

The purpose of the present study was to assess the mechanical role of the expiratory muscles during spontaneous breathing in prone animals. The electromyographic (EMG) activity of the triangularis sterni, the rectus abdominis, the external oblique, and the transversus abdominis was studied in 10 dogs light anesthetized with pentobarbital sodium. EMGs were recorded during spontaneous steady-state breathing in supine and prone suspended animals both before and after cervical vagotomy. We also measured the end-expiratory lung volume [functional residual capacity (FRC)] in supine and prone positions to assess the mechanical role of expiratory muscle activation in prone dogs. Spontaneous breathing in the prone posture elicited a significant recruitment of the triangularis sterni, the external oblique, and the transversus abdominis (P less than 0.05). Bilateral cervical vagotomy eliminated the postural activation of the external oblique and the transversus abdominis but not the triangularis sterni. Changes in posture during control and after cervical vagotomy were associated with an increase in FRC. However, changes in FRC, on average, were 132.3 +/- 33.8 (SE) ml larger (P less than 0.01) postvagotomy. We conclude that spontaneous breathing in prone anesthetized dogs is associated with a marked phasic expiratory recruitment of rib cage and abdominal muscles. The present data also indicate that by relaxing at end expiration the expiratory muscles of the abdominal region are directly responsible for generating roughly 40% of the tidal volume.     

A new method for the noninvasive determination of abdominal muscle feedforward activity based on tissue velocity information from tissue Doppler imaging.

Rapid arm movements elicit anticipatory activation of the deep-lying abdominal muscles; this appears modified in back pain, but the invasive technique used for its assessment [fine-wire electromyography (EMG)] has precluded its widespread investigation. We examined whether tissue-velocity changes recorded with ultrasound (M-mode) tissue Doppler imaging (TDI) provided a viable noninvasive alternative. Fourteen healthy subjects rapidly flexed, extended, and abducted the shoulder; recordings were made of medial deltoid (MD) surface EMG and of fine-wire EMG and TDI tissue-velocity changes of the contralateral transversus abdominis, obliquus internus, and obliquus externus. Muscle onsets were determined by blinded visual analysis of EMG and TDI data. TDI could not distinguish between the relative activation of the three muscles, so in subsequent analyses only the onset of the earliest abdominal muscle activity was used. The latter occurred <50 ms after the onset of medial deltoid EMG (i.e., was feedforward) and correlated with the corresponding EMG onsets (r = 0.47, P < 0.0001). The mean difference between methods was 20 ms and was likely explained by electromechanical delay; limits of agreement were wide (-40 to +80 ms) but no greater than those typical of repeated measurements using either technique. The between-day standard error of measurement of the TDI onsets (examined in 16 further subjects) was 16 ms. TDI yielded reliable and valid measures of the earliest onset of feedforward activity within the anterolateral abdominal muscle group. The method can be used to assess muscle dysfunction in large groups of back-pain patients and may also be suitable for the noninvasive analysis of other deep-lying or small/thin muscles.     

Onset in abdominal muscles recorded simultaneously by ultrasound imaging and intramuscular electromyography

Delayed onset of muscle activity in abdominal muscles has been related to low back pain. To investigate this in larger clinical trials it would be beneficial if non-invasive and less cumbersome alternatives to intramuscular electromyography (EMG) were available. This study was designed to compare onset of muscle activity recorded by intramuscular EMG to onset of muscle deformations by ultrasound imaging. Muscle deformations were recorded by two ultrasound imaging modes at high time resolution (m-mode and tissue velocity) in separate sessions and compared to simultaneously recorded intramuscular EMG in three abdominal muscles. Tissue velocity imaging was converted to strain rate which measures deformation velocity gradients within small regions, giving information about the rate of local tissue shortening or lengthening along the beam axis. Onsets in transversus abdominis (TrA), obliquus internus abdominis (OI) and obliquus externus abdominis (OE) were recorded during rapid arm flexions in ten healthy subjects. During ultrasound m-mode recordings, the results showed that mean onsets by EMG were detected 7 ms (95% CI of mean difference; ±4 ms) and 2 ms (95% CI of mean difference; ±6 ms) before concurrent ultrasound m-mode detected onsets in TrA and OI, respectively. In contrast, OE onset was recorded 54 ms (95% CI of bias; ±16 ms) later by EMG compared to ultrasound m-mode. The discrepancy of ultrasound m-mode to accurately record onset in OE was practically corrected in the ultrasound-based strain rate recordings. However, this could only be applied on half of the subjects due to the angle dependency between the ultrasound beam and the direction of the contraction in strain rate recordings. The angle dependency needs to be further explored.     

Differential activation of psoas major and rectus femoris during active straight leg raise to end range

The purpose of this study was to investigate the activation of the hip flexor and abdominal muscles during an active straight leg raise (ASLR) to end range of hip flexion. Data were recorded from nine healthy men. Fine-wire electromyography (EMG) electrodes were inserted into psoas major (PM), and surface electrodes were placed over rectus femoris (RF), rectus abdominis, obliquus externus abdominis (OE), and obliquus internus abdominis/transversus abdominis (OI/TrA). EMG and kinematic data were obtained during concentric, hold (at end range) and eccentric phases of an ASLR. Concentric and eccentric movements were divided into three phases (early, mid, and late). Onsets of EMG relative to the onset of the ALSR movement and EMG amplitudes in each phase were compared between muscles. Onsets of the PM (–33 ± 245 ms) and RF (-3 ± 119 ms) EMG prior to leg elevation were significantly earlier than those of the OE and OI/TrA. PM EMG showed highest activation in the late concentric, hold, early eccentric phase, and was significantly higher than RF EMG. OI/TrA EMG was significantly greater in mid and late concentric, hold, and early eccentric phase than other phases. During the ASLR, unlike RF, PM EMG continues to increase towards the end range of hip flexion. Activation of OI/TrA muscle may be involved in control trunk and pelvic movement.     

Effects of midline laparotomy on expiratory muscle activation in anesthetized dogs

Abdominal surgery has a marked inhibitory influence on the diaphragm, but its effect on the expiratory muscles is not known. Therefore, we have recorded the electromyograms of the triangularis sterni, abdominal external oblique, and transversus abdominis before and after a midline laparotomy in 10 anesthetized, spontaneously breathing dogs. Measurements were obtained during quiet breathing in the supine posture, during breathing against expiratory threshold loads, during head-up tilting, and during hyperoxic hypercapnia. Expiratory activation of the transversus abdominis in all conditions was considerably reduced after laparotomy. This reduction was real, as no change in the compound muscle action potential during single pulse stimulation was observed. In contrast, expiratory recruitment of either the triangularis sterni or the abdominal external oblique was maintained or increased. We therefore conclude that laparotomy inhibits not only activation of the diaphragm during inspiration but also activation of the transversus abdominis during expiration. Visceral afferents thus affect in concert the two respiratory muscles lining the peritoneum. The present findings also emphasize the important fact that the pattern of activation of a particular abdominal muscle is not necessarily representative of the entire abdominal musculature.     

Inspiratory and expiratory patterns of the pectoralis major muscle during pulmonary defensive reflexes

Experiments wereconducted to determine the discharge pattern of the pectoralis majormuscle during pulmonary defensive reflexes in anesthetized cats(n = 15). Coughs andexpiration reflexes were elicited by mechanical stimulation of theintrathoracic trachea or larynx. Augmented breaths occurredspontaneously or were evoked by the same mechanical stimuli.Electromyograms (EMGs) were recorded from the diaphragm, rectusabdominis, and pectoralis major muscles. During augmented breaths, thepectoralis major had inspiratory EMG activity similar to that of thediaphragm, but during expiration reflexes the pectoralis major also hadpurely expiratory EMG activity similar to the rectus abdominis. Duringtracheobronchial cough, the pectoralis major had an inspiratory patternsimilar to that of the diaphragm in 10 animals, an expiratory patternsimilar to that of the rectus abdominis in 3 animals, and a biphasicpattern in 2 animals. The pectoralis major was active during both the inspiratory and expiratory phases during laryngeal cough. We conclude that, in contrast to the diaphragm or rectus abdominis muscles, thepectoralis major is active during both inspiratory and expiratory pulmonary defensive reflexes.

     

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.     

Laryngeal and abdominal muscle electrical activity during periodic breathing in nonsedated lambs

Kianicka, Irenej, Véronique Diaz, Sylvain Renolleau,Emmanuel Canet, and Jean-Paul Praud. Laryngeal and abdominal muscle electrical activity during periodic breathing in nonsedated lambs. J. Appl. Physiol. 84(2):669-675, 1998.We recently reported that glottic closure waspresent throughout central apneas in awake lambs. The present studytested whether glottic closure was also observed during periodicbreathing (PB). We attempted to induce PB in 21 nonsedated lambs onreturn from hypocapnic hypoxia to room air. Airflow and thyroarytenoid(a laryngeal constrictor, n = 16),cricothyroid (a laryngeal dilator, n = 10), and abdominal (n = 9) muscleelectrical activity (EMG) were monitored continuously. PB was observedin 16 lambs, with apneic phases in 8 lambs. Thyroarytenoid muscle EMGwas observed at the nadir of PB, either throughout apnea or withprolonged expiration during the lowest respiratory efforts. Phasicinspiratory cricothyroid muscle EMG and phasic expiratory abdominal EMGdisappeared at the nadir of PB. Active glottic closure at the nadir ofPB, without abdominal muscle contraction, could be a beneficialmechanism, preserving alveolar gas stores for continuing gas exchangeduring the apneic/hypopneic phase of PB. However, consequences ofactive glottic closure on ventilatory instability, either enhancing orreducing, are unknown.

     

Anticipatory postural adjustments to arm movement reveal complex control of paraspinal muscles in the thorax

Anatomical and empirical data suggest that deep and superficial muscles may have different functions for thoracic spine control. This study investigated thoracic paraspinal muscle activity during anticipatory postural adjustments associated with arm movement. Electromyographic (EMG) recordings were made from the right deep (multifidus/rotatores) and superficial (longissimus) muscles at T5, T8, and T11 levels using fine-wire electrodes. Ten healthy participants performed fast unilateral and bilateral flexion and extension arm movements in response to a light. EMG amplitude was measured during 25 ms epochs for 150 ms before and 400 ms after deltoid EMG onset. During arm flexion movements, multifidus and longissimus had two bursts of activity, one burst prior to deltoid and a late burst. With arm extension both muscles were active in a single burst after deltoid onset. There was differential activity with respect to direction of trunk rotation induced by arm movement. Right longissimus was most active with left arm movements and right multifidus was most active with right arm movements. All levels of the thorax responded similarly. We suggest that although thoracic multifidus and longissimus function similarly to control sagittal plane perturbations, these muscles are differentially active with rotational forces on the trunk.     

Feedforward activation of the quadratus lumborum during rapid shoulder joint abduction

This study aimed to clarify the difference in the onset of EMG activity between eight trunk muscles, including the anterior (QL-a) and posterior (QL-p) layers of the quadratus lumborum during rapid shoulder joint abduction. Thirteen healthy men participated in this study. Electromyography of the QL-a, QL-p, transversus abdominis (TrA), internal oblique (IO), external oblique (EO), rectus abdominis (RA), lumbar multifidus (LMF), lumbar erector spinae (LES) on non-movement side, and middle deltoid (MD) on the movement side were measured. Subjects who were standing in a relaxed position performed rapid shoulder abduction with the dominant hand after light stimulus with or without a 3 kg wrist weight. Two-way ANOVA (muscles × weight conditions) was used to compare the onset of trunk muscles relative to that of MD. There was a significant main effect of the muscles. The onset of the QL-a, QL-p, and TrA was significantly earlier than that of the IO, EO, LMF, and LES (P < 0.01). This result suggests that the activities of the QL-a, QL-p, and TrA have a crucial role in controlling the center of mass within the base of support and stabilizing the lumbar spine in the coronal plane during shoulder abduction.     

Rib cage mechanics during quiet breathing and exercise in humans

Kenyon, C. M., S. J. Cala, S. Yan, A. Aliverti, G. Scano, R. Duranti, A. Pedotti, and Peter T. Macklem. Rib cage mechanics during quiet breathing and exercise in humans. J. Appl. Physiol. 83(4): 1242-1255, 1997.Duringexercise, large pleural, abdominal, and transdiaphragmatic pressureswings might produce substantial rib cage (RC) distortions. We used athree-compartment chest wall model (J. Appl.Physiol. 72: 1338-1347, 1992) to measuredistortions of lung- and diaphragm-apposed RC compartments (RCp andRCa) along with pleural and abdominal pressures in five normal men. RCpand RCa volumes were calculated from three-dimensional locations of 86 markers on the chest wall, and the undistorted (relaxation) RCconfiguration was measured. Compliances of RCp and RCa measured duringphrenic stimulation against a closed airway were 20 and 0%,respectively, of their values during relaxation. There was marked RCdistortion. Thus nonuniform distribution of pressures distorts the RCand markedly stiffens it. However, during steady-state ergometerexercise at 0, 30, 50, and 70% of maximum workload, RC distortionswere small because of a coordinated action of respiratory muscles, sothat net pressures acting on RCp and RCa were nearly the samethroughout the respiratory cycle. This maximizes RC compliance andminimizes the work of RC displacement. During quiet breathing, plots ofRCa volume vs. abdominal pressure were to the right of the relaxationcurve, indicating an expiratory action on RCa. We attribute this topassive stretching of abdominal muscles, which more thancounterbalances the insertional component of transdiaphragmatic pressure.

     

Abdominal muscle use during breathing in unanesthetized dogs

The pattern of abdominal muscle use during breathing in unanesthetized dogs is unknown. Therefore, we have recorded the electromyograms of the rectus abdominis, external oblique, and transversus abdominis in eight conscious animals breathing quietly in the sitting, standing, and prone postures. During quiet breathing in the sitting posture, all animals invariably had a large amount of phasic expiratory activity in the transversus abdominis. In contrast, only four animals showed some expiratory activity in the external oblique, and only one animal had expiratory activity in the rectus abdominis. A similar pattern was observed when the animals were standing or lying prone, although the amount of expiratory activity was less in this posture. Bilateral cervical vagotomy in four animals did not affect the degree of transversus abdominis expiratory activation or the influence of posture. We conclude that in conscious dogs 1) the abdominal muscles play an important role during breathing and make spontaneous quiet expiration a very active process, 2) the transversus abdominis is the primary respiratory muscle of the abdomen, and 3) unlike in anesthetized animals, extrapulmonary receptors play a major role in promoting abdominal expiratory contraction.     

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.     

Functional role and structure of the scalene: an accessory inspiratory muscle in hamster

Fournier, Mario, and Michael I. Lewis. Functional roleand structure of the scalene: an accessory inspiratory muscle inhamster. J. Appl. Physiol. 81(6):2436-2444, 1996.Although the scalene muscle (Sca) is a primaryinspiratory muscle in humans, its respiratory function in other speciesis less clear. The electromyographic (EMG) activity of the Sca wasstudied during resting ventilation (eupnea) in both the awake andanesthetized hamster and after a variety of respiratory challenges inthe anesthetized animal. The EMG activities of the medial Sca and thecostal diaphragm were compared. The medial Sca, the major component ofthe Sca, originates from cervical transverse processes 2 to 5 andinserts primarily onto rib 4, with a small segment onto rib 3. In both the anesthetized and awake animal, the Sca was always silent during quiet breathing. WithCO₂-stimulated hyperpnea, the Scawas always recruited during inspiration in phase with the diaphragm.Active recruitment of the Sca was also observed after resistive loading and total airway occlusion. After ipsilateral phrenicotomy, the Sca waspersistently recruited during eupnea. The specificity of the EMGsignals was tested both by excluding cross contamination from other ribcage muscles and by selective denervation studies. Muscle spindles wereidentified in the medial Sca histochemically, suggesting that therespiratory activity of the Sca can also be modulated by changes inmuscle length and/or load. These results indicate that the Scafunctions as an accessory inspiratory muscle in the hamster and mayplay an important role in conditions of chronic load.

     

Persistence of improvements in postural strategies following motor control training in people with recurrent low back pain.

This study investigated long-term effects of training on postural control using the model of deficits in activation of transversus abdominis (TrA) in people with recurrent low back pain (LBP). Nine volunteers with LBP attended four sessions for assessment and/or training (initial, two weeks, four weeks and six months). Training of repeated isolated voluntary TrA contractions were performed at the initial and two-week session with feedback from real-time ultrasound imaging. Home program involved training twice daily for four weeks. Electromyographic activity (EMG) of trunk and deltoid muscles was recorded with surface and fine-wire electrodes. Rapid arm movement and walking were performed at each session, and immediately after training on the first two sessions. Onset of trunk muscle activation relative to prime mover deltoid during arm movements, and the coefficient of variation (CV) of EMG during averaged gait cycle were calculated. Over four weeks of training, onset of TrA EMG was earlier during arm movements and CV of TrA EMG was reduced (consistent with more sustained EMG activity). Changes were retained at six months follow-up (p<0.05). These results show persistence of motor control changes following training and demonstrate that this training approach leads to motor learning of automatic postural control strategies.     

Location and sequence of muscle onset in deep abdominal muscles measured by different modes of ultrasound imaging

Various modes of ultrasound (US) imaging have been introduced as an alternative to electromyography for determining muscle onset. The purpose of this study was to compare the agreement between US motion-mode (US_m-mode) and US strain rate (US_SR) derived from tissue velocity imaging in determining latency time, location and sequence of muscle onset in abdominal muscles using the same data set (contractions). Twenty-four subjects performed four rapid arm flexions in response to a light signal while US recordings were made from the abdominal muscles on the contralateral side. The examined muscles were transversus abdominis (TrA), superficial and deep obliquus internus abdominis (OI_deep and OI_sup), and obliquus externus abdominis (OE). The results showed that the two methods detected the first muscle onset on average within 0.1 ms (95% CI; ±1.4 ms) of each other. US_SR detected the second muscle onset on average 27 ms after US_m-mode. While US_SR and US_m-mode can be used interchangeably to detect the first muscle onset, the location of both first onset and subsequent muscle onsets can be reliably detected by US_SR only. Furthermore, this study indicates that OI may be functionally subdivided into a superficial and deep region, with onset in OI_deep occurring on average 53 ms before OI_sup. First onset was detected more frequently in OI than in TrA (65% versus 25% of detected onsets, 10% were equal).     

Quantification of abdominal and pelvic floor muscle synergies in response to voluntary pelvic floor muscle contractions

The relative levels of pelvic floor muscle (PFM) activation and pressure generated by maximum voluntary PFM contractions were investigated in healthy continent women. The normal sequence of abdominal and PFM activation was determined.Fifteen women performed single and repeated maximum voluntary PFM contractions in supine, sitting and standing. PFM electromyographic (EMG) signals and associated intra-vaginal pressure data were recorded simultaneously. Surface EMG data were recorded from rectus abdominus (RA), external obliques (EO), internal obliques (IO) and transversus abdominus (TA).Abdominal and PFM EMG and intra-vaginal pressure amplitudes generated during voluntary PFM contractions were not different among the positions. Muscle activation sequence differed by position. In supine, EO activation preceded all other muscles by 27 ms (p = 0.043). In sitting, all of the muscles were activated simultaneously. In standing, RA and EO were activated 11 and 17 ms, respectively, prior to the PFMs and TA and IO were activated 10 and 12 ms, respectively, after the PFMs (p ≪ 0.001).The results suggest that women are able to perform equally strong PFM contractions in supine, sitting and standing, however the pattern of abdominal and PFM activation varies by position. These differences may be related to position-dependent urine leakage in women with stress incontinence.