Pelvic muscle profile types in response to pelvic muscle exercise

Int Urogynecol J (1995) 6:68-72 9 1995 The International Urogynecology Journal

International Urogynecology

Journal

Original Article Pelvic Muscle Profile Types in Response to Pelvic Muscle Exercise A. R. B o y i n g t o n 1, M. C. D o u g h e r t y 2, and C. E. Kasper 2 1College of Nursing, University of Florida, Gainesville; 2School of Nursing, University of California at Los Angeles, Los Angeles, California, USA

Abstract: The purpose of this research was to describe the contractile response of pelvic muscle to exercise (PME). Pelvic muscle pressure curves from ten randomly selected records from a larger study of 65 women with urodynamically demonstrated stress urinary incontinence (SUI) were analyzed. The subjects completed a PME protocol that lasted 16 weeks. Five pressure curves before and after 16 weeks of exercise were analyzed and classified according to pressure-time profile types. Descriptive statistics revealed decreases in urine loss variables and increases in pelvic muscle pressure curve variables. Changes in profile characteristics suggested an increase in type II muscle fiber recruitment; recruitment of type I fibers that appeared less fatigable; and increased contractile force of both type I and type II fibers. Changes were analyzed by descriptive statistics and by reference to putative types. Reference to profile types may be useful to PME prescription to enhance fiber type-specific performance.

Keywords: Exercise training; Muscle fiber type; Pelvic muscles; Stress urinary incontinence

Introduction Current research has increased knowledge of the pelvic muscles during relaxation and contraction; however, the mechanical function of the levator ani remain poorly understood [1]. Previous studies of pelvic muscle contractile function have focused on maximum or sustained pressure attained during voluntary contractions as the primary variables. Similar measurements have been Correspondence and offprint requests to: Alice Boyington, c/o Molly C. Dougherty, College of Nursing, University of Florida, PO Box 100197, Gainesville, FL 32610-0197, USA.

reported with electromyography [2]. Measurement of pelvic muscle function is crucial to the understanding of the alterations in urinary continence that result from behavioral management techniques such as biofeedback and pelvic muscle exercise (PME). Even though PME is often prescribed in the management of stress urinary incontinence (SUI), relatively little attention has been directed to measurement of voluntary pelvic muscle activity. Consideration of the function and contractile properties of pelvic muscles contributes to an understanding of voluntary pelvic muscle activity. Skeletal muscle function and contractile speeds are influenced by the variable populations of fiber types in a muscle, i.e. the percentage population of slow (type I) and fast (type II) twitch fibers [3]. The fiber-type composition of the levator ani has been examined and related to the continence mechanism. Histochemical examination of undamaged levator ani reveals a predominance of type I fibers, which maintain tone over time and support the pelvic viscera [4]. Type II fibers are recruited to increase the force and speed of contraction and are believed to improve urethral closure when there is an increase in intra-abdominal pressure [4]. PME, which has been demonstrated to be effective in the management of SUI, improves pelvic muscle neuromuscular coordination and continence [5,6]. However, measurements of maximum and sustained pressure during voluntary pelvic muscle contractions are not strongly correlated to alleviation of urine loss [6,7]. Therefore, further examination of pelvic muscle training is required to clarify the relationship between pelvic muscle training and continence. The assumptions underlying this study were that (a) in subjects with SUI there is altered pelvic muscle contractile function due to inappropriate reinnervation, partial denervation or a decreased contractile force [1];

Pelvic MuscleProfile TypesAfter Exercise (b) alterations in muscle characteristics alter contractile force during voluntary contractions [8,9]; and (c) the response of fiber types to training will affect contractile characteristics [10,11]. The purpose of this research was to describe the contractile response of pelvic muscles of PME.

Methods

69 1 (before implementation of PME) and Time 2 (following 16 weeks of PME) for 10 subjects, comprised the data set for this analysis. The pelvic muscle contractile pressures and pressure curves were analyzed using the Asystant+ software. The dependent variables were initial pelvic muscle strength (mmHg) and the rate of rise pressure (mmHg/ s). Additional variables used to describe the initial phase of the contraction were initial acceleration phase pressure (IAPP) (mmHg) and maximum acceleration phase pressure (MAPP) (mmHg). IAPP began when the command to contract was given during a period of relaxation (Fig. 1). MAPP was the peak pressure achieved during the initial contractile effort, depicted on the pressure curves as the end of a continual rise in mmHg (Fig. 1). Actual pressure and rate of rise were calculated as follows:

The records of 10 subjects (age X = 51.7 (10.0), parity X = 2.6 (1.0)) who participated in a larger study of 65 women with urodynamically demonstrated SUI [7] were randomly selected for secondary analysis. To obtain a systematic random sample, the random number generating function of a handheld calculator was used to generate a number between one and ten. Subsequently, every fifth subject from a sequential list of the 65 Actual pressure = MAPP - IAPP original subjects was identified for this secondary analyRate of rise = Actual pressure sis. In the original investigation the effect of a 16-week Time to MAPP graded PME protocol on moderate SUI was reported. Prior to implementation of the PME protocol, subjects The values from five pressure curves at Time 1 and Time were assessed for urogynecologic status, general health 2 were averaged respectively to provide IAPP, MAPP, condition and degree of SUI. Women having had prior actual pressure and rate of rise measurements. surgery for incontinence or radiation therapy to the Paired t-tests were computed on the actual pressure pelvis were excluded. Subjects maintained a 24-hour (mmHg), rate of rise (mmHg/s) and urine loss at Time 1 bladder diary to provide information about the fre- and Time 2 measurements. Pearson's correlations were quency of urine loss episodes. The amount of urine loss performed between actual pressure (mmHg), rate of was measured objectively by a 24-hour home pad- rise (mmHg) and urine loss (g). weighing test. A nurse practitioner provided one-to-one To simplify visual inspection of the pressure curve PME instruction and taught subjects to use an audio changes between Time 1 and Time 2 evaluations, digital tape to guide the at-home sessions. Subjects were data stored in Asystant+ were translated into Lotus 1trained using PME three times per week (every other 2-3 version 2.3 (Lotus Development Corporation, day) for 16 weeks. The exercises began with 15 repe- Cambridge, MA). The pressure curves were printed titions of a 10-second pelvic muscle contraction. Ten and independently analyzed by two of the authors. repetitions were added every 4 weeks, resulting in 45 Owing to the preliminary nature of the study, the repetitions at weeks 13-16. The project team made investigators examined the curves simultaneously and weekly telephone calls to subjects to promote protocol adherence and subjects submitted written reports of their at-home exercise sessions. Participants carried out a total of 48 PME sessions. The methods of pelvic muscle assessment and ...... MAPP acquisition of pelvic muscle pressure data using an intravaginal balloon device (IVBD) have been reported previously [7]. Briefly, a vaginal alginate (Healthco International, Boston, MA) impression taken on each subject provided for the subsequent selection of an appropriately sized IVBD. A second balloon device positioned in the posterior fornix of the vagina measured abdominal muscle pressure. Both pressure balloon devices were attached to strain gauge pressure transducers (Bell & Howell, Chicago, IL) and a modified personal computer (Compac Computer Corporation, Dallas, TX) utilizing Asystant+ (MacMillan, New York, NY) data acquisition program. Analog and digital data from the pressure-sensitive balloon devices were collected during voluntary contractions of the TIME pelvic muscles. The pelvic muscle contractions were guided by audio tape commands to contract for 10 Fig. 1. Initial acceleration phase pressure (IAPP) and maximum seconds and relax for 15 seconds. Data collected at Time acceleration phase pressure (MAPP) of voluntary pelvicmuscles.

~----IAPP

70

A . R . Boyington et al. Table 1. Urine loss and pressure curve variables Variable

Baseline X (SD)

Urine loss (g/24 h) Urine loss (episodes/24 h) Actual pressure (mmHg) Rate of rise (mmHg/s) Urine loss (g)/actual pressure

14.1 2.5 18.9 32.9

Baseline correlation

(14.1) (1.5) (10.4) (16.6)

16 weeks X (SD) 2.4 0.4 29.5 49.0

16 weeks correlation

(1.4) (0.7) (12.9) (18.9) -0.25

0.33

---A ---A

.--13

TIME

TIME

TIME

Fig. 2. Pelvic muscle profile types before (B) and after (A) PME. From left, unimodal (40%), bimodal (10%) and unimodal sustained (30%).

defined the profile types represented among the curves. One to three weeks later the investigators independently reviewed the curves and assigned each subject to a profile type. Interrater reliability was verified by 100% concurrence between the investigators on profile type assignment. The curves were classified using Laycock and Jerwood's [12] four types of pressure-time profiles: (a) unimodal (rapid increase in pressure with gradual decline during the 10-second contraction); (b) bimodal (rapid initial increase in pressure followed by a decline, and a second rapid increase in pressure followed by a gradual decline in pressure until end of contraction); (c) amodal (maximum pressure 20 mmHg was achieved with initial effort and maintained until it rapidly declined following the audio command to relax. Each subject's curves from Time 1 and Time 2 evaluations were overlaid to depict changes in pressure curve variables and patterns across the course of the exercise protocol.

Results Five contractions at Time 1 and Time 2 (n = 10) comprised the dataset of 100 pelvic muscle pressure curves. Descriptive statistics show decreases in urine loss variables and increases in pressure curve variables (Table 1). The t-test results showed significant increases in actual pressure (mgHg) (t = 4.86, P =0.0009) and rate of rise (mHg/s) (t = 3.3, P = 0.004) for Time i to Time 2

evaluations. Grams of urine loss revealed a significant decrease (t = -2.51, P = 0.03). Pearson's correlation analysis revealed no significant correlations between the actual pressure and rate of rise and grams of urine loss. When the printed pressure curves were reviewed two of Laycock and Jerwood's [12] types - unimodal and bimodal patterns - were distinctly identified in this dataset. Amodal and multimodal patterns were not identified. Visual analysis revealed an additional distinct pressure curve pattern in one-third (n = 3) of the subjects. Thus, the original classification was modified by adding a unimodal sustained type to accommodate this pattern. Three patterns resulted (Fig. 2). Increases in pressures after PME were noted in unimodal (40% of subjects), bimodal (10% of subjects) and unimodal sustained (30% of subjects) patterns. Two subjects (20%) with unimodal patterns and MAPP less than 20 mmHg did not demonstrate a change over the course of the exercise training.

Discussion The results of this secondary analysis are consistent with the findings of Dougherty et al. [7], who found decreases in urine loss and increases in pelvic muscle pressures (n = 65) over the course of the 16-week PME program. The lack of significant correlations between pelvic muscle variables and urine loss variables reported in this and other studies may result from flaws in the pelvic muscle measurements or the urine loss measures or both. Measurement of pelvic muscle pressures in the original study may have been influenced by selection of the IVBD; placement of the IVBD; stability of the IVBD in the vagina during data collection; adherence to

Pelvic MuscleProfileTypesAfter Exercise equipment calibration procedures; and wide variations in pelvic muscle pressure measurements [13]. It is possible that one or more of these potential sources of error affected the pelvic muscle measurements obtained. Additionally, the measure of urine loss was obtained from a pad test of 24 hours' duration. The high variability found in pad test results and sources of error, such as lack of standardization of subject's activities and fluid intake, pad absorption of perspiration and vaginal secretions [14], may have affected the results obtained. The speed of contraction of the levator ani, which may be altered in women with SUI, influences the periurethral continence mechanism. Alterations in the speed of contraction of an atrophic muscle can be linked to shifts in the regulatory proteins of the muscle. The myosin heads contain ATPase and the actin-binding characteristics of myosin. There is a switch in protein composition during denervation such that the amount of fast myosin isozymes relative to slow myosin increases markedly in slow muscle [9,15], and there is an increase in the slow myosin isozymes in fast muscle. These changes in the myosin heavy chain regulatory proteins result in alteration in the contractile properties of fast and slow fibers. Slow contracting endurance muscles become less able to sustain long-term aerobic activity as inactivity has altered their function to act more like a fast contracting muscle. The fast contracting muscles also change their speed and function to become more like a slow twitch muscle. The result of these shifts in contractile speed is that the original function of the muscle has been altered [3,16]. Additional research on contractile force and speed of contraction in relation to muscle fiber types has been conducted on single fibers [8,9,17,18]. Specifically, it has been previously demonstrated that pressure curve profiles from groups of muscles can be interpreted and related to specific fiber types [10,11,19,20], Thus, the changes in profiles over time in this study may be interpreted similarly to those examined by Laycock and Jerwood [12]. Unimodal profiles suggested increased type II muscle fiber recruitment. Bimodal patterns reflected recruitment of type I fibers that appear less fatigable. The unimodal sustained pattern arose from improved effectiveness of both type I and type II fibers. These patterns concur with the classic shapes of isometric contraction in skeletal muscle [8,9,17,21]. Therefore it is logical that fiber type characteristics may be used to more accurately tailor PME prescription to an individual patient. The effects of training are best described by Astrand and Rodahl [22] as ' . . . exposing the organism to a training load or work stress of sufficient intensity, duration, and frequency to produce a noticeable or measurable training effect' (p. 420). However, the training effect is known to be modified by other factors, such as internal muscle architecture, cross-sectional area of the muscle and intact motor unit innervation. When exercise of a specific intensity and duration is applied to a muscle or group of muscles with a known

71 fiber type population, the response to training is readily predictable. However, with SUI women usually have experienced some form of repeated trauma, i.e. increasing parity, to the pelvic muscles which may have resulted in total or partial denervation of some or all of these motor units. Other forms of trauma, such as tearing during childbirth, may have led to extensive regeneration of the muscles [23,24]. Repeated traumas permanently alter fiber type populations of the involved muscles [15,24-28]. In humans the extent and structural alterations due to trauma vary widely between individuals, and result in large variations in fiber type populations and muscle cross-sectional areas. Therefore, a single training regimen cannot produce a similar training effect in a sample with varied trauma. Two subjects demonstrated no change in pelvic muscle profile characteristics. The exercise protocol employed in this study may not affect the altered muscle group or defect experienced by these women. Based on these findings further research is needed on the link between fiber types and pressure profiles. To better understand these relationships, clinical research on training targeted to a specific fiber type and pressure profile alteration is needed. For example, women who demonstrate recruitment of type II fibers (see Fig. 2) could be taught to carry out endurance exercises, thereby improving the performance of type I fibers and the support of pelvic viscera. Thus, PME could be prescribed for specific neuromuscular or mechanical defects exhibited on pressure curve profiles. To expand our understanding of these preliminary results from a small sample of pelvic muscle pressure curves, a followup study of the total sample with comparisons with a continent sample is planned. This research was supported in part by NR-1115 and NR-3139 from the National Institute of Nursing Research (NINR), National Institutes of Health (NIH) to MCD; and R29 NR-02204 and RO1 NR-02922 from NINR, NIH and NAG-9-323 from the National Aeronautics and Space Administration to CEK.

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EDITORIAL COMMENT: Pelvic floor muscle exercises are now being used more and more as one of the preliminary nonsurgical regimens prior to surgical approach. This is in spite of the fact that we know very little about patient physiological response to these exercises, nor how to grade the enhancement of muscular activity as a result of performing them. This paper points out some of these deficiencies and helps us to understand that this may be due to several different types of muscle fibers that are involved in the contraction of the pelvic floor. Defining different muscle profile types may help physiotherapists to prescribe activities specifically designed to enhance the performance of each group of muscles. Measurement of intraabdominal pressure concurrently with the contraction helps to diminish the contribution of Valsalva to a measured pressure response, and this use of differential pressures is to be encouraged by others who work in this area.