COORDINATED RECRUITMENT of pelvic floor muscles. Contraction of the Pelvic Floor Muscles During Abdominal Maneuvers

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1 1081 Contraction of the Pelvic Floor Muscles During Abdominal Maneuvers Ruth R. Sapsford, DipPhty, Paul W. Hodges, PhD ABSTRACT. Sapsford RR, Hodges PW. Contraction of the pelvic floor muscles during abdominal maneuvers. Arch Phys Med Rehabil 2001;82: From the Department of Physiotherapy, Mater Misericordiae Hospital, Brisbane (Sapsford); and Prince of Wales Medical Research Institute, and the University of New South Wales, Randwick, Sydney (Hodges), Australia. Accepted in revised form September 6, Supported by the National Health and Medical Research Council of Australia. Equipment provided by Arthur Algate, Advantage Health Care, Pty Ltd. The author(s) has/have chosen not to select a disclosure statement. Reprint requests to Ruth R. Sapsford, DipPhty, Dept of Physiotherapy, Mater Misericordiae Hospital, Raymond Ter, South Brisbane, QLD 4101 Australia, rsapsford@oz .com.au /01/ $35.00/0 doi: /apmr Objective: To determine whether voluntary abdominal muscle contraction is associated with pelvic floor muscle activity. Design: Pelvic floor muscle activity was recorded during contractions of the abdominal muscles at 3 different intensities in supine and standing positions. Setting: Research laboratory. Participants: Six women and 1 man with no histories of lower back pain. Interventions: Not applicable. Main Outcome Measures: Electromyographic activity of the pelvic floor muscles was recorded with surface electrodes inserted into the anus and vagina. These recordings were corroborated by measurements of anal and vaginal pressures. Gastric pressure was recorded in 2 subjects. Results: Pelvic floor muscle electromyography increased with contraction of the abdominal muscles. With strong abdominal contraction, pelvic floor muscle activity did not differ from that recorded during a maximal pelvic floor muscle effort. The pressure recordings confirmed these data. The increase in pressure recorded in the anus and vagina preceded the pressure in the abdomen. Conclusions: In healthy subjects, voluntary activity in the abdominal muscles results in increased pelvic floor muscle activity. The increase in pelvic floor pressure before the increase in the abdomen pressure indicates that this response is preprogrammed. Dysfunction of the pelvic floor muscles can result in urinary and fecal incontinence. Abdominal muscle training to rehabilitate those muscles may be useful in treating these conditions. Key Words: Electromyography; Fecal incontinence; Muscle contraction; Pelvic floor; Rehabilitation; Urinary incontinence by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation COORDINATED RECRUITMENT of pelvic floor muscles is a prerequisite for urinary and fecal continence. The pelvic floor forms the base of the abdominal cavity. As such, pelvic floor muscles must contract during tasks that elevate intraabdominal pressure to contribute to the pressure increase and to maintain continence. For instance, pubococcygeus activity is increased during coughing, 1,2 and puborectalis activity is increased during lifting. 3 In cases of dysfunction (eg, stress urinary incontinence), it is generally advised that rehabilitation of the pelvic floor muscles be done in isolation. 4,5 However, it is now known that abdominal muscle activity occurs in association with a pelvic floor muscle contraction, and there is preliminary evidence that the reverse may also occur (ie, pelvic floor muscle activity in response to specific abdominal manuevres). 6 In this study, we wanted to determine whether pelvic floor muscles contract when the muscles of the abdominal wall are contracted and, if so, whether this response depends on the magnitude of the abdominal contraction. We also wanted to determine whether contraction of the pelvic floor muscles precedes the increase in abdominal pressure to enhance the contribution of the striated muscle to continence, in anticipation of the increased demand. METHODS Subjects Electromyographic recordings were made from the muscles of the pelvic floor in 6 women and 1 man. The demographic details are presented in table 1. Subjects were excluded if they had any history of neurologic or respiratory pathology or low back pain that limited function. One woman was nulliparous and the other 5 had had 2 to 4 normal vaginal deliveries. No subject experienced clinical urinary incontinence, although 2 had occasional mild symptoms of incontinence. Written informed consent was obtained from all subjects and all procedures adhered to the Declaration of Helsinki. Electromyography Electromyographic recordings were made from the pubococcygeus (PC) muscle in the women subjects with a Periform Intra-Vaginal Probe electrode. a The shape of these electrodes is such that movement of the electrode relative to the vaginal wall is minimal (fig 1A). In all subjects, electromyographic recordings were also made from a pair of pregelled disposable surface electrodes b that were partially inserted into the anus and attached laterally to opposite sides of the anal canal, up to the level of the dentate line (fig 1B). These electrodes are considered to make recordings primarily from the external anal sphincter (EAS). To record abdominal muscle activity, disposable Ag/AgCl disc electrodes c were fixed to the skin of all subjects over the right lateral abdominal wall, midway between the rib cage and iliac crest in the anterior axillary line. In 2 subjects, pairs of surface electrodes were placed over the hip adductors (3cm from the pubic attachment of adductor longus) and gluteus maximus (parallel to the muscle fibers 10cm inferior and 5cm lateral to the posterior superior iliac spine). These recordings were made to determine whether cross-talk from these muscles contributed to the recordings from the pelvic floor electrodes, which has been suggested as a limitation of the use of surface electrodes such as the ones we used. 7 Example recordings from these muscles along with electromyographic recordings from the anal (EAS) and vaginal

2 1082 PELVIC FLOOR ACTIVITY IN ABDOMINAL MANEUVERS, Sapsford Table 1: Demographics ofstudy Sample Women Man Age (yr) 45.7 (35 63) 30 Height (m) 1.66 ( ) 1.82 Weight (kg) 58.7 (54 61) 85 Maximum birth weight (gm) * Data given as mean (range). (PC) electrodes are shown in figure 1C. Clear differences exist in the activity recorded from each muscle. This figure shows that cross-talk is unlikely, because as the activity recorded by the electrode over the hip adductors decreases, activity from the pelvic floor electrodes increases, and no change is recorded in the gluteal electrode. The data provide evidence that the recordings from the pelvic floor electrodes are valid. In 1 subject, additional recordings were made from the 3 lateral abdominal muscles with bipolar intramuscular fine-wire electrodes to identify the relative activity of each muscle during the abdominal maneuvres. The electrodes were fabricated from 2 Teflon -coated stainless-steel wires d (75 m diameter, 1 mm of Teflon removed) threaded into a mm hypodermic needle. The electrodes were inserted into the transversus abdominis (TrA), the obliquus internus abdominis (OI), and the obliquus externus abdominis (OE) midway between the anterosuperior iliac spine and the rib cage The insertions were guided by ultrasound imaging. Fig 2. Relation between anal and gastric pressures. (A) Maximal pelvic floor contraction. (B) Strong abdominal muscle contraction. Pressures are shown during contractions ofthe abdominal and pelvic floor muscles. The data suggest that the pressure recordings were independent, and thus the pelvic pressure were not simply due to transmitted pressure from the abdominal cavity. Fig 1. (A) Placement ofvaginal and anal electromyographic electrodes. Electrodes were situated on either side ofthe intravaginal probe and anal electrodes were adhered to the right and left anal wall (only the left anal electrode is shown). (B) Placement of vaginal and anal pressure probes. (C) Recordings ofelectromyographic activity ofthe hip adductor and gluteus maximus along with concurrent recordings from the anal and vaginal electrodes. Pressure Recordings Mechanical evidence of contraction of the pelvic floor muscles was obtained by using pressure probes e inserted into the vagina and anus. The probes were covered with a double layer of sterile latex and inserted until the lower margin of the pressure area of the probe was situated at the level of the vaginal introitus and the anal verge. Once the probes were in situ, the balloons of the vaginal and anal probes were inflated with 20 and 5mL of air, respectively. The probes were supported by hand during the trial to prevent them from becoming dislodged. It has been argued that the pressure recorded from probes situated in the anus and vagina may increase as a function of intraabdominal pressure, without contraction of the muscles of the pelvic floor. To confirm that the pressure recordings in this study were due to contraction of the pelvic floor muscles, and not elevated intraabdominal pressure, recordings of gastric pressure (Pga) were made in 2 subjects with a catheter-tip pressure transducer f inserted into stomach through the nose. The relation between Pga and anal pressure is shown in figure 2. In this subject, the anal pressure probe and anal electromyography electrodes were in situ simultaneously. It can be seen that there is a relation between anal and gastric pressures (fig 2B). It is necessary to prevent loss of urine or fecal material as abdominal pressure increases. However, the pressure recordings are independent, as illustrated by the distinct spatial and temporal patterns of pressure change in figure 2A. This finding confirms that the pressure probes used in this experiment measured the mechanical parameters of pelvic floor muscle contraction.

3 PELVIC FLOOR ACTIVITY IN ABDOMINAL MANEUVERS, Sapsford 1083 Ultrasound Measurements The pattern of activity of the abdominal muscles was measured with ultrasound imaging. When a muscle contracts, there is a change in its shape because the muscle fibers shorten. These changes can be seen on ultrasound and have been used to provide a measure of muscle activity. 11,12 Although the nature of the relation between electromyographic amplitude, force, and ultrasound change has not been determined, ultrasound was used in this study to provide an approximation of the change in the relationship between the individual abdominal muscle activity in each of the tasks (see below). The parameter used to measure the change in shape of the muscle with contraction was the change in width of the muscle layers (TrA, OI, OE) with contraction. The ultrasound transducer g (7MHz, linear, 10-cm wide was placed transversely across the abdomen, 10cm to the left of the midline, and midway between the rib cage and iliac crest. The transducer was inserted into a foam block (15 15cm) to ensure that it was maintained perpendicular to the skin. Measurements of the width of the muscle layers were made at a point 3, 5, or 6cm from the medial edge of the ultrasound image (the same position was used for each subject), when the abdominal muscles were relaxed before each contraction and then again during the contraction. All data are expressed as the change in width from baseline and normalized as a percentage of the resting width. Procedure Subjects were placed in supine position, with the hips flexed to approximately 60. The recordings of electromyographic activity from the anal and vaginal electrodes and the pressure recordings were made in separate trials (except for the man, in whom the anal pressure and electromyographic recordings were made concurrently). Ultrasound measurements of abdominal muscle activity were made during the electromyography trials. The procedures for the pressure and electromyography trials were identical. Initially, 2 maximal voluntary contractions (MVCs) of the pelvic floor muscles were performed and all electromyograms and pressure recordings were normalized to this task. Subjects then performed 3 abdominal muscle maneuvres without spinal movement: (1) gentle abdominal hollowing maneuvre this task aimed to activate TrA predominantly and involves gentle inward movement of the lower abdomen 12 ; (2) moderate abdominal contraction this task was performed in a similar manner to the gentle contraction, but with greater effort and was expected to involve contraction of all of the abdominal muscles; and (3) strong abdominal contraction for this maneuvre, subjects were instructed to draw strongly in their abdominal wall, using all of their abdominal muscles. All subjects were given instruction on how to perform the contractions in a separate session at least 7 days before the testing session. After the trials in the supine position, subjects stood with the anal and vaginal electromyographic electrodes in situ and performed 5 additional voluntary tasks: (1) maximal pelvic floor contraction for electromyographic normalization, (2) relaxation of resting tone in the abdominal wall while standing quietly in a relaxed natural position, (3) gentle inward movement of the lower abdomen while standing quietly in a relaxed natural position, (4) relaxation of the abdominal wall while standing with about 15 of trunk flexion, and (5) gentle inward movement of the lower abdomen while standing with about 15 of trunk flexion. Data analysis. Electromyographic data were filtered h between 53Hz and 1kHz and sampled at 2kHz using Spike3. i Anal, vaginal, and gastric pressures were sampled at 200Hz. Ultrasound data were stored on video with a sampling rate of 50Hz. Root mean square amplitude of the electromyographic data was measured for 1 second before the contraction and 1 second during the contraction. At the time of data collection, a marker was recorded along with the electromyographic and pressure data that indicated when subjects were at rest and when they were performing the task. These markers were used to determine the time for amplitude measurement. Electromyographic data were expressed as the increase in amplitude from baseline as a percentage of the electromyographic amplitude recorded during the MVC. Pressure data were averaged for 1 second before and during the contraction, using the markers as was done for the electromyographic data. The change in pressure from baseline pressure was expressed as a percentage of the change recorded during the MVC. Because the responses for the male subject were similar to those of the female subjects, all anal pressure and electromyographic data were combined for analysis. Statistical analysis. The electromyographic, pressure, and ultrasound data were compared between the 3 conditions with 1-way repeated-measures analyses of variance, with post hoc testing (Duncan s multiple range test) using STATISTICA j software. Significance was set at.05. RESULTS Figure 3 presents group and individual data for abdominal muscle activity recorded with surface electrodes and ultrasound imaging in all subjects, and fine-wire electrodes in 1 subject for each of the abdominal maneuvres. The data recorded with the surface electromyographic electrodes (fig 3B) indicate that, although the general activity of the abdominal muscles during the strong contraction was greater than in the gentle or moderate conditions (F 2,10 4.1, p.01), there was no difference between the gentle and moderate contraction levels. The average (fig 3B) and raw data (fig 3C) for each of the abdominal muscles recorded using fine-wire electrodes in 1 subject indicate that activity of all abdominal muscles increased with the abdominal maneuvers. No statistical analysis was used to determine whether the differences were significant between contraction intensities for the subject. The changes in muscle width with the different contraction strengths provide further support (TrA: F 2,8 3.83, p.05; OI: F 2,8 2.44, p.1; OE: F 2,8 0.1, p.9) (fig 3A). However, the change in Pga between contraction strengths (measured in 2 subjects) does suggest an incremental change in effort between the 3 contraction levels. When subjects contracted their abdominal muscles, activity of the muscles of the pelvic floor recorded with both anal and vaginal electrodes was increased above the resting level (figs 4, 5A) (anal: F 2, , p.001; vaginal: F 2,10 7.4, p.01). Although this increase occurred with all contraction levels (ie, gentle, moderate, strong), the increase was greater with the strong contraction level. There was no difference between the gentle and moderate conditions. The increase in electromyographic activity recorded with the vaginal electrode was greater than that recorded with the anal electrode (p.01). Furthermore, the vaginal electromyographic activity recorded during the strong contraction of the abdominal muscles did not differ from that recorded during the maximal contraction of the pelvic floor muscles (p.05). These findings are supported by the changes in vaginal and anal pressure with contraction of the abdominal muscles (figs 5, 6) (anal: F 2, , p.001; vaginal: F 2,10 8.9, p.01). Similar to the electromyographic data, the increase in pressure was greater for the strong contraction level than for the gentle and moderate contraction levels. Again, there was no difference between the gentle and moderate contraction

4 1084 PELVIC FLOOR ACTIVITY IN ABDOMINAL MANEUVERS, Sapsford Fig 3. Abdominal muscle activity during the experimental tasks in supine. Abdominal (Abd) muscle activity with each level ofcontraction are shown as (A) the mean change in width recorded using ultrasound, (B) mean change in electromyographic activity for all subjects recorded with surface electromyography (Abd) and with fine-wire electrodes for 1 subject (TrA, OI, OE), and (C) raw electromyographic data recorded with fine-wire electrodes(n 1).(B)surfaceelectromyographic electrodes, and (C) and fine-wire electromyographic electrodes (n 1) (B & C) are shown. (B) Gastric pressure recorded with each abdominal contraction are also shown (n 2). (A) The inset shows the method for measurement ofmuscle width on the ultrasound image ofthe lateral abdominal wall. Activity was increased in the strong condition, but there was no difference between the gentle and moderate conditions. strengths. Furthermore, the increase in vaginal pressure during the strong contraction was greater than the increase in anal pressure, and the vaginal pressure during the strong contraction of the abdominal muscles did not differ from the pressure recorded during the maximal contraction of the pelvic floor muscles. The latency between the onset of the pressure increase recorded with the vaginal and/or anal pressure probes and that in the abdomen (Pga) was identified in the 2 subjects (1 woman, 1 man) whose abdominal pressures were recorded. Figure 7A shows the raw data from a single strong contraction of the abdominal muscles. The onset of anal pressure (and vaginal pressure in the woman) occurred before the pressure increase in the abdomen. Although these observations were made in a relatively small number of subjects, the results indicated consistently that the pressure response in the pelvic floor preceded the pressure increase in the abdomen (range, ms) (figs 7A B). This finding indicates that the pressures recorded by the anal and vaginal pressure probes did not simply reflect pressure transmitted from the abdominal cavity, (see Methods). The results obtained when the subjects were standing are similar to the supine position data in that contraction of abdominal muscles was associated with an increase in electromyographic activity recorded with the anal and vaginal electrodes (anal: F 3, , p.05; vaginal: F 3, , p.01) (fig 8). This occurred in both the neutral and flexed positions of the trunk. Also, when the subjects voluntarily reduced the resting tone in the abdominal muscles while standing with the spine in a neutral position, there was an associated reduction in activity recorded with the vaginal electrode (fig 8). DISCUSSION This study of healthy subjects shows that vaginal and anal surface electromyographic activity increases with voluntary activation of the abdominal muscles. Furthermore, the extent of increase in pelvic floor muscle activity was related to the extent of the increase in abdominal muscle activity, with greatest pelvic floor muscle activity recorded with the strongest abdominal maneuver. The electromyography findings were supported by similar increases in vaginal and anal pressure measurements when abdominal muscle activity was increased. An important finding was that the increase in vaginal and anal pressure preceded the increase in intraabdominal pressure. This indicates that the mechanical response of the pelvic floor muscles precedes that of the abdominal muscles, and pelvic floor muscle activity is not simply a response to elevated intraabdominal pressure. Methodologic Considerations An increase in abdominal muscle activity was confirmed with electromyography using surface electrodes (intramuscular electrodes in 1 subject), measurement of changes in muscle size with ultrasound imaging, and measurement of intraabdominal pressure. Although electromyographic amplitude (surface and intramuscular) was not different between the gentle and moderate abdominal maneuvers, it increased with the strong contraction. However, a significant difference in contraction strength between the gentle and moderate conditions was identified from the measurement of intraabdominal pressure. Ultrasound imaging was included to confirm the activity of the deep abdominal muscles in the subjects in whom intra-

5 PELVIC FLOOR ACTIVITY IN ABDOMINAL MANEUVERS, Sapsford 1085 Fig 4. Electromyographic activity ofthe pelvic floor and abdominal muscles with abdominal and pelvic floor muscle contractions. The representative raw electromyography shows that activity ofthe pelvic floor muscles accompanied all levels ofabdominal muscle activity. Abbreviation: Abd, abdominal muscle. Fig 6. Pelvic floor pressures and abdominal muscle electromyography with abdominal and pelvic floor muscle contractions. The representative data (same subject as fig 4) shows that activity ofthe pelvic floor muscles accompanied all levels ofabdominal muscle activity. muscular electrodes were not used. Measurement of changes in muscle width and shape, by ultrasound imaging, have been used previously in research 11 and clinical practice 12 to infer changes in activity. Although the relationship between ultrasound changes and muscle activity has not been confirmed, in our experiment, this technique was only used to confirm that activity of the deep muscles was changing with different abdominal maneuvres, and not to infer absolute level of activity. The results confirm that the size (width) of TrA and OI was increased with increasing strength of abdominal contraction. No change in size of OE was recorded with increased contrac- Fig 5. Mean change in pelvic floor response with abdominal muscle contraction. Mean (A) electromyographic and (B) pressure data for the group are shown normalized to the amplitude recorded with the maximal contraction ofthe pelvic floor muscles. Abbreviations: AP, anal pressure; VP, vaginal pressure.

6 1086 PELVIC FLOOR ACTIVITY IN ABDOMINAL MANEUVERS, Sapsford Fig 7. Latency between onsets ofthe increase in gastric and pelvic floor pressures. Representative (A) raw data and (B) data from single subjects are presented. The raw data in A show an increase in anal pressure ofalmost 500ms before an increase in gastric pressure. (B) All onsets ofvaginal and anal pressure are shown relative to the onset of the gastric pressure increase at zero. Fig 8. Mean change in pelvic floor muscle electromyography with abdominal contraction in standing position. Data are presented with subjects standing in (A) neutral and (B) with slight lumbar flexion. tion strength. This is consistent with data that indicate that, for this muscle, there is no consistent change in size on ultrasound imaging with contraction (Hodges et al, unpublished data). This may be because of anatomic factors. Recordings of pelvic floor muscle activity were made with surface electrodes placed in the vagina and anus. Although it is likely that most activity recorded with these electrodes was from the muscles immediately adjacent to the electrode (ie, pubococcygeus and the external anal sphincter for the vaginal and anal electrodes, respectively), activity from neighboring muscles (eg, other muscles of the levator ani group) may have been recorded. In addition, it has been suggested that cross-talk from the adjacent hip muscles (eg, gluteus maximus, hip adductors) may be present in surface electromyographic recordings. 7 However, in the present experiment, activity recorded with electrodes over the hip muscles was found to have a pattern of activity distinct from the pelvic floor muscle recordings (fig 1C), which suggests that cross-talk was minimal. Our results with surface electromyographic recordings agree with the results of a preliminary study in which recordings were made from pubococcygeus using intramuscular electrodes inserted through the vaginal wall in 2 subjects. 6 Finally, the similarity between the electromyography data and the pressure recordings from the transducers placed in the anus and vagina provides further evidence that the electromyographic responses were from the muscles of the pelvic floor. Vaginal pressure is known to increase as a result of transmitted pressure from the abdomen. 13 However, the onset of vaginal and anal pressures before the increase in intraabdominal pressure, and the differences in profile of pelvic and intraabdominal pressures identified in this study, suggest that the pelvic floor pressure recordings were, at least in part, the result of pelvic floor muscle activity. Furthermore, previous studies have identified that pressure in the urethra during a cough is greater in the mid and distal regions, indicating that pressure increases are generated by periurethral structures and not by transmitted intraabdominal pressure. Coactivation of Muscles of the Abdominal Wall and Pelvic Floor The increase in vaginal electromyography with voluntary contraction of the abdominal muscles is consistent with preliminary data from 2 subjects in whom abdominal and PC muscle activity was recorded with intramuscular electrodes during isometric abdominal maneuvres similar to those described here, 6 and in healthy subjects during simple trunk movements. 2 Of note, the increases in vaginal electromyography and pressure recorded in this study during the strong abdominal maneuvre were the same as increases that occurred during a maximal pelvic floor contraction. This finding is consistent with the findings that physically active healthy women who do not do specific pelvic floor exercises have stronger pelvic floor muscles than those with a more sedentary lifestyle. 17 Coactivation of the abdominal and pelvic floor muscles is consistent with the model that predicts that muscles surrounding the abdominal cavity will work together in a coordinated manner to increase pressure in the abdomen and support the pelvic organs. 3,18 Coactivation of these muscles has been reported during lifting, 3 coughing, and forced expiratory efforts, 1,4,19 but, as noted, coactivation during voluntary isometric contraction of one of the muscles is a new observation. The opposite pattern of coordination (ie, abdominal muscle activity during pelvic floor muscle contraction) has recently been reported. 6 Recent studies have shown that the diaphragm, the other major muscular component to the abdominal cavity, coactivates with the abdominal muscles during tasks that challenge the postural stability of the spine Activation of the pelvic floor muscles is essential to maintaining continence when intraabdominal pressure is increased by contraction of the abdominal muscles. The pelvic floor muscles contribute to urinary continence through an increase in urethral closure pressure and maintenance of the bladder neck position. The bladder neck is elevated during voluntary pelvic floor muscle contractions, 23,24 and its position is maintained during coughing (but not in women with urinary stress incontinence 25 ). The timing of the pelvic floor muscle activity is critical in

7 PELVIC FLOOR ACTIVITY IN ABDOMINAL MANEUVERS, Sapsford 1087 maintaining continence in such situations. With a cough, urethral pressure increases before the increase in bladder pressure by 200 to 250ms. This early increase of urethral pressure does not occur in most women with stress incontinence but can be restored after successful surgery. 16 In this study, it was not possible to identify accurately the onset of pelvic floor muscle electromyographic activity due to the high resting activity and the slow rate of increase in electromyography. In 2 subjects, however, recordings were made of intraabdominal pressure in conjunction with the recordings of vaginal and/or anal pressure. These studies confirmed that the mechanical output of contraction of the pelvic floor muscles increased in advance of the increase in intraabdominal pressure. These data suggest that pelvic floor muscle activity occurs in advance of both involuntary (ie, cough) and voluntary contraction of the abdominal muscles. This anticipatory activity cannot be a reflex response to afferent input from muscle stretch as a result of increased intraabdominal pressure, because it precedes such an increase in abdominal pressure. It must be preprogrammed by the central nervous system in preparation for the increase in intraabdominal pressure to maintain continence. Coactivation of the abdominal and pelvic floor muscles was also observed when subjects were standing. In the upright position, there are increased hydrostatic forces on the abdomen and pelvic floor as a result of gravity. Correspondingly, tonic electromyographic activity of the pelvic floor 1,19 and abdominal 8 muscles has been recorded in standing at rest. In standing, a gentle contraction of the abdominal muscles was associated with increased pelvic floor electromyographic activity above the resting tonic level in both neutral and forward lean positions. An important finding was that when subjects relaxed the abdominal wall, there was a decrease in pelvic floor electromyographic activity below the resting level in both positions. Thus, if a person relaxes the abdominal wall while standing, this may result in decreased pelvic support and compromised continence. Consistent with this proposal, patients with urinary incontinence often report sensations of urinary urge or vaginal dragging on leaning forward while standing, and urinary incontinence during a cough in a relaxed sitting position, but not when sitting upright. CONCLUSION The findings of this study indicate that exercise of the abdominal muscles may be beneficial in maintaining pelvic floor muscle coordination, support, endurance, and strength. Similar exercise has the potential to be useful in the rehabilitation of persons with symptoms of dysfunction. For instance, contraction of the abdominal muscles may provide an efficient mechanism with which to initiate and train contraction of the pelvic floor muscles, particularly for patients who have difficulty learning to contract those muscles. However, further research is needed to determine whether pelvic floor muscle function is enhanced by such exercise in cases of dysfunction. Acknowledgments: We thank Elizabeth McDonald and Merryn Hodges for assistance with data collection, Ms. McDonald for subject recruitment, Helen MacDevitt for training the subjects to perform the abdominal maneuvres, and Arthur Algate, Advantage Health Care Pty Ltd, for supplying equipment. References 1. Deindl F, Vodusek D, Hesse U, Schussler B. Activity patterns of pubococcygeal muscles in nulliparous continent women. Br J Urol 1993;72: Bø K, Stien R, Needle EMG registration of striated urethral wall and pelvic floor muscle activity patterns during cough, valsalva, abdominal, hip adductor and gluteal muscle contractions in nulliparous healthy females. Neurourol Urodyn 1994;13: Hemborg B, Moritz U, Löwing H. Intra-abdominal pressure and trunk muscle activity during lifting. IV. The causal factors of the intra-abdominal pressure rise. Scand J Rehabil Med 1985;17: Bø K. Techniques. In: Schussler B, Laycock J, Norton P, Stanton S, editors. Pelvic floor re-education: principles and practice. London: Springer-Verlag; p Bump RC, Mattiasson A, Bo K, Brubaker LP, DeLancey JO, Klarskov P, et al. The standardization of terminology of female pelvic organ prolapse and pelvic floor dysfunction. Am J Obstet Gynecol 1996;175: Sapsford R, Hodges P, Richardson CA, Cooper DH, Markwell SJ, Jull GA. Co-activation of the abdominal and pelvic floor muscles during voluntary exercises. Neurourol Urodyn 2001; 20: Vodusek D. Electrophysiology. In: Schussler B, Laycock J, Norton P, Stanton S, editors. Pelvic floor re-education: principles and practice. London: Springer-Verlag; p DeTroyer A, Estenne M, Ninane V, VanGansbeke D, Gorini M. Transversus abdominis muscle function in humans. J Appl Physiol 1990;68: Cresswell AG, Grundstrom H, Thorstensson A. Observations on intra-abdominal pressure and patterns of abdominal intra-muscular activity in man. Acta Physiol Scand 1992;144: Hodges PW, Richardson CA. Feedforward contraction of transversus abdominis is not influenced by the direction of arm movement. Exp Brain Res 1997;114: Misuri G, Colagrande S, Gorini M, Iandelli I, Mancini M, Duranti R, et al. In vivo ultrasound assessment of respiratory function of abdominal muscles in normal subjects. Eur Respir J 1997;10: Richardson CA, Jull GA, Hodges PW, Hides JA. Therapeutic exercise for spinal segmental stabilisation in low back pain: scientific basis and clinical approach. Edinburgh: Churchill Livingstone; Al-Taher H, Sutherst JR, Richmond DH, Brown MC. Vaginal pressure as an index of intra-abdominal pressure during urodynamic evaluation. Br J Urol 1987;59: Constantinou CE, Govan DE. Spatial distribution and timing of transmitted and reflexly generated urethral pressures in healthy women. J Urol 1982;127: Thind P, Lose G, Jorgensen L, Colstrup H. Variations in urethral and bladder pressure during stress episodes in healthy women. Br J Urol 1990;66: Pieber D, Zivkovic F, Tamussino K. Timing of urethral pressure pulses before and after continence surgery. Neurourol Urodyn 1998;17: Gordon H, Logue M. Perineal muscle function after childbirth. Lancet 1985;2: Hodges PW. Is there a role for transversus abdominis in lumbopelvic stability? [review]. Man Ther 1999;4: Vereeken R, Derluyn J, Verduyn H. Electromyography of the perineal striated muscles during cystometry. Urol Int 1975;30: Hodges PW, Butler JE, McKenzie D, Gandevia SC. Contraction of the human diaphragm during postural adjustments. J Physiol (Lond) 1997;505: Hodges P, Gandevia S. Activation of the human diaphragm during a repetitive postural task. J Physiol (Lond) 2000;522: Hodges P, Gandevia S. Changes in intra-abdominal pressure during postural and respiratory activation of the human diaphragm. J Appl Physiol 2000;89: Christensen L, Djurhuus J, Lewis M, Dev P, Chase RA, Constantinou PS, et al. MRI of voluntary pelvic floor contractions in healthy female volunteers. Int Urogynecol J 1995;6: Bø K, Lilleas F, Talseth T. Dynamic MRI of pelvic floor and coccygeal movement during pelvic floor muscle contraction and straining. Neurourol Urodyn 1997;16:

8 1088 PELVIC FLOOR ACTIVITY IN ABDOMINAL MANEUVERS, Sapsford 25. Wijma J, Tinga DJ, Visser GH. Perineal ultrasonography in women with stress incontinence and controls: the role of the pelvic floor muscles. Gynecol Obstet Invest 1991;32: Suppliers a. NEEN HealthCare, Old Pharmacy Yard, Church St, Dereham, Norfolk, NR19 1DJ, England. b. Medtronic, Tonsbakken 16-18, DK-2740 Skovlunde, Denmark. c. ConMed Corp, 310 Broad St, Utica, NY d. A-M Systems Inc, A Airport Rd, Everett, WA e. Incare Medical Products, 2000 Hollister Dr, Libertyville, IL f. Gaeltec Ltd, Dunvegan, Isle of Skye, Scotland IV55 8GU, UK. g. 128XP/4; Acuson Corp, 1220 Charleston Rd, PO Box 7393, Mountain View, CA h. Digitimer Ltd, 37 Hydeway, Welwyn Garden City, Hertfordshire, AL7 3BE, England. i. Cambridge Electronic Design Ltd, Science Park, Milton Rd, Cambridge CB4 0FE, UK. j. StatSoft Inc, 2300 E 14th St, Tulsa, OK