Measurement of flexibility and hiatus diameters has been suggested as a means to assess the maximal PFM length. The distance between the left and right muscle bellies just below the pubic bone is estimated in centimeters by separating two fingers inserted in the vagina (transverse hiatus diameter) [17]. The distance between the back of the pubic symphysis and the midline raphe of the puborectalis is also measured (anteroposterior diameter). Boyles et al. [17] found a good-to-excellent interrater reliability with correlation coefficients of 0.6–0.8. Likewise, Gentilcore et al. [6] assessed the transverse diameter by grading from 0 (less than one finger insertion) to 4 (two-finger insertions with fingers abducted horizontally ≥2 cm). However, this scale was not studied for its validity and reliability. Maximal muscle length measurement is commonly performed in a general skeletal muscle assessment and is determined by the patient’s tolerance and increases in EMG in order to ensure adequate muscle relaxation during stretching. Because such monitoring is obviously not part of a palpation assessment, these scales are considered as a global measurement of PFM tone without discriminating between active and passive components.

The International Continence Society (ICS) sta dardization group on PFM function and dysfunction recommended assessing the PFM relaxation ability after a contraction [18]. They suggested describing the relaxation as present/absent and partial/complete [18]. Loving et al. [9] studied the test–retest and interrater reliability of this scale in asymptomatic women and found a kappa of 1.0 and 0.60, respectively. Lower test–retest and interrater reliability was observed by Slieker-ten Hove et al. [13], however, with a weighted kappa of 0.76 and 0.17, respectively. In addition to these qualifiers, Reissing et al. [8] suggested documenting the speed of relaxation (slow/fast). Although not studied for its psychometric properties, a scale developed in women with multiple sclerosis was proposed by De Ridder et al. [19] for grading the ability to relax the pelvic floor: 3—active relaxation after active contraction, 2—hypertonic muscle with temporary relaxation after elongation, 1—spastic muscle, unable to relax even after passive elongation. Reissing et al. [8] proposed a scale to grade the relaxation from 0 to 5 (0 returns to resting state; 5 remains fully contracted). Fair interrater reliability was observed only when the assessment was performed using two fingers (r = 0.355–0.400) as opposed to one finger, which yielded unreliable data. Although not studied for reliability, a similar scale was proposed by Gentilcore et al. [6] evaluating the relaxation capacity on a 5-point scale from 0 (which indicated the PFMs were fully able to return to their resting state following a maximal contraction or 100 % relaxation) to 4 (which indicated that the PFMs remained fully contracted after a maximal contraction or 0 % relaxation). One limitation related to these scales is that the scoring refers to the resting state observed before contraction. This is particularly problematic in the case of elevated tone at baseline, whereas a patient would be categorized as having a good relaxation if she returns to the pathological precontraction level.

The myofascial trigger point (TP ) is defined as an identifiable taut band or rope-like indurations palpated in the muscle fiber that can evoke pain both locally (local tenderness) and at distant reference-pain zones specific to each TP [20]. With regard to the muscle physiology [1], TP refers to physiological contracture, one element among the active components of muscle tone. It should be emphasized that TP refers to an endogenous shortening of a specific point in a muscular fiber which is not detectable by global EMG. TP assessment has been deemed important not only because it is associated with pain but it has also been reported that TP can provoke heightened PFM tone (related to electrogenic spasms) [21]. It has been shown that manual therapy for releasing TPs results in PFM relaxation as measured by the reduction in resting EMG activity (i.e., reduction of the electrogenic spasms) [21].

Kavvadias et al. [22] investigated the intensity of pain elicited during palpation of TPs in the anterior levator ani, posterior levator ani, obturator internus and piriformis on both sides using a visual analog scale. They obtained a heterogeneous test–retest and interrater reliability with ICCs of 0.20–0.87 and 0.28–0.87, respectively, in a sample of asymptomatic women. Palpation of the posterior levator ani showed a higher reliability than the anterior portion [22]. Montenegro et al. [23] studied the interrater reliability of the tenderness assessment of the bilateral levator ani, piriformis, and internal obturator muscles in controls and women with chronic pelvic pain. Tenderness was scored according to each subject’s reactions for the six positions as follows: 0, no pain; 1, painful discomfort; 2, intense pain; with a maximum total score of 12. Very good interrater reliability was found with a kappa of 0.91. A systematic review about TP in limbs and trunk muscle pointed out that TP assessment should not be limited to tenderness but should notably include taut bands, patient pain recognition, and pain referral [24]. It should be noted that TPs located in the levator ani have referral zones in the muscle and in both anterior and posterior compartments (rectum, anus, coccyx, urethra, bladder, penis/vulva, buttocks). The obturator internus and piriformis can, in turn, refer to the perineal zone. More information about referred pain patterns in the PFMs and surrounding muscles can be found elsewhere [20, 25, 26]. Hsieh et al. [27] pointed out that the evaluator’s experience might influence the psychometrics of TP assessment. In sum, considering that psychometric studies so far have focused mainly on pain intensity with divergent findings, the assessment of TP using digital palpation warrants further investigation.

Current evidence in patients with heightened PFM tone converges toward the presence of other concomitant alterations in contractile properties. It is generally recognized that the PFMs are difficult to contract correctly. In fact, even among women without urogynecological problems, over 30 % are unable to adequately contract these muscles following verbal instructions and need further teaching such as vaginal palpation [28]. To facilitate PFM contraction, Messelink et al. [18] suggested instructing women to “squeeze and lift as if to prevent the escape of gas or urine.” Crotty et al. [29] demonstrated that verbal cues that included both the anterior and posterior parts of the PFMs yielded stronger contractions: “Squeeze and lift from the front and back together.” Palpation was also suggested to be useful in teaching women to perform adequate PFM contraction avoiding muscle compensation such as buttock, adductor, rectus abdominus contraction as well as perineal inversion (i.e., straining) [30, 31].

Several scales have been proposed to grade the PFM contractile properties including Brinks’ scale [32], Devreese’s scale [14] and Messelink’s scale [13, 18] as well as the Laycock PERFECT assessment scheme, which incorporates the modified Oxford scale [12]. In general, these scales show an acceptable intra-observer and test–retest reliability [9, 13, 14, 32–36]. The modified Oxford scale seems to be the most frequently used in women with chronic pain conditions [6–9, 37]. The Laycock PERFECT assessment scheme, presented in Table 11.3, proposes an assessment of strength and endurance, the number of repetitions and fast contractions. It has been shown that this grading system can be used with different patient positions, lying or upright, with good reliability [34], although it was found that women prefer the supine position for internal examination [38]. Furthermore, the reliability of the modified Oxford scale has also been investigated when a “+” or “−” is added to the original quotation but it was found that the original 6-level quotation (without +/−) yielded better reliability. It was recommended by the ICS standardization group on PFM function and dysfunction to limit the number of levels in a strength-assessing scale to preserve an acceptable interrater reliability [18]. On the other hand, this limitation may interfere with the responsiveness to detect differences between individuals and changes following treatment [31].

Digital palpation assessment of PFMs can be performed by inserting one or more fingers inside the vagina [6–8]. In chronic pain patients, the presence of pain associated with vaginal distention can bias PFM tone assessment by provoking protective-like muscular reactions and thus result in heightened PFM tone and incomplete relaxation [7, 39]. It is also possible that strength reduction is caused by pain inhibition. Despite the influence of pain on muscle assessment, it is already known from studies both of skeletal muscle and of PFMs that muscle lengthening (i.e., by inserting a finger) resulted in higher muscle strength during voluntary contraction as well as superior passive forces recorded at rest [2]. In our population of interest, it is probable that pain and muscle lengthening affect digital palpation scoring .

In sum, although digital palpation is contested for research purposes because of its subjectivity, it is widely used in clinical settings as it is practical, low-cost, and easy to apply. This tool provides important insight into PFM tone including flexibility, relaxation abilities, and TPs as well as PFM contractile properties. Its use for clinical practice is suggested for evaluating PFM dysfunctions, detecting surrounding muscle compensations, identifying tenderness area, and also orienting treatment.

The involvement of the PFMs in dyspareunia, especially in provoked vestibulodynia, has been evaluated using digital palpation. Women with provoked vestibulodynia showed higher tone, as assessed with Reissing’s scale, in comparison with asymptomatic controls [6–8]. Similar findings were also obtained using Lamont’s scale [16]. Lower relaxation capacity and reduced flexibility were also found in women with provoked vestibulodynia [6] as assessed with the aforementioned scales (i.e., relaxation 0 returns to resting state—4 remains fully contracted; flexibility 0 one finger to two fingers abducted more than 2 cm) [6]. Regarding PFM contractile properties, women with provoked vestibulodynia were also found to have lower PFM strength measured with the modified Oxford grading scale [6–8]. Likewise, women with chronic pelvic pain had higher PFM resting tone (Dietz’s scale) and decreased maximal PFM strength (modified Oxford grading scale) and relaxation capacity (absent/complete/partial) compared with pain-free controls [9]. Conversely, Fitzgerald et al. [37] did not find any significant difference regarding muscle strength (modified Oxford grading system) in women with and without chronic pelvic pain in a slightly smaller sample. As mentioned earlier, it is not possible to elucidate with palpation alone whether the reduction of pain results from a true weakness or from pain inhibition.

Studies concurred about the importance of muscle tenderness and TPs in women with chronic pelvic pain. The prevalence of TPs in the PFMs and surrounding muscles (e.g., obturator internus, piriformis) ranged from 63 to 89 % in women with chronic pelvic pain (including interstitial cystitis), which was significantly higher than in asymptomatic controls [23, 26, 37, 41–43]. Interestingly, Montenegro et al. [23] reported that TPs were associated with greater depression symptoms and higher rates of dyspareunia and constipation. Similarly in men, TPs were found in 75–88 % of men with chronic prostatitis/chronic pelvic pain syndrome [44]. Andersson et al. [45] also demonstrated that TP palpation in the PFMs and surrounding muscles reproduced the patient’s symptomatology of pain in the penis, perineum, rectum, testicle, and groin. In fact, TP assessment is part of the UPOINT phenotyping system along with urinary symptoms, psychosocial dysfunction, organ-specific findings, infection and neurologic/systemic domains to classify urologic chronic pelvic pain [46].

EMG measurement is basically the recording of the electrical current travelling along the muscle fibers. During voluntary contraction, motor units, consisting of alpha-motoneurons and the muscle fibers they innervate [47], are recruited resulting in the liberation of acetylcholine (ACh) at the endplate [48]. The binding of ACh at the endplate leads to depolarization of the membrane, which then spreads as an action potential along the muscle fiber allowing liberation of calcium and, thus, the interaction of actin and myosin to produce muscle contraction. Surface EMG assessment will capture this electrical phenomenon and the number of motor units recruited and their frequency of discharge will influence the signal amplitude and, hence, the force output produced. In light of tone physiology, circulating current at rest can only be explained by electrogenic spasms (unintentional muscle contraction) and normal electrogenic contraction (resting activity in normally relaxed muscle, although controversial, and myotatic reflex during stretching). It should be emphasized, however, that neither the passive component (viscoelastic properties) nor the contracture (TP) is captured by EMG.

The literature shows conflicting results when comparing women with and without pelvic /vulvar pain. Some authors have found elevated resting activity [9, 49–51] while others have determined nonsignificant differences between women with pain and controls [7, 52, 53]. This highlights the hypothesis, that, in some women, the involvement of heightened PFM tone is not explained by an electrogenic cause. Various degrees of reliability were also found in the literature when assessing EMG amplitude during maximal contraction as well as resting activity. Such divergences strongly suggest that some confounding factors should be taken into account when interpreting EMG signals. Among other confounding variables, factors related to the detection itself, such as the contact between the electrodes and the mucosa, vaginal lubrication and the thickness of the vaginal tissue, can greatly affect the EMG signal. Moreover, the presence of crosstalk, i.e., contamination from neighboring muscles, should be considered when interpreting the force from the EMG [30]. Chapter 15 is dedicated to EMG and presents thorough discussion of the recommendations and limitations regarding EMG.

Ultrasonography imaging is a technology that has aroused great interest in both clinical and research settings for assessing PFM morphology and function in men and women with various urological and gynecological conditions using transperineal and transabdominal approaches [11, 54–57]. It offers significant advantages over the other methodologies as no vaginal insertion is required and is therefore pain-free. Particularly in a context of chronic pelvic pain, this has the benefit of limiting the bias due to pain and also, presumably, the participant’s fear of pain or penetration. It should be noted that a detailed discussion of the diagnosis of levator ani trauma post childbirth (i.e., avulsion) [58] and pelvic organ prolapse quantification [59] using transperineal ultrasound is beyond the scope of this chapter.

Manometry, also called perineometry or pressure measurement , is commonly used for evaluating PFM tone and contractile properties. It can also be utilized for anorectal investigation (see Chap. 12 ). It basically consists of a balloon—a vaginal pressure probe—connected to a manometer in order to measure the intravaginal pressure coming from the PFMs in millimeters of mercury (mmHg) or centimeters of water (cmH₂O) or other custom units, depending on the brand of manometers. It was in 1948 that Dr. Kegel [86] developed a perineometer to assess PFM strength in postpartum women with sexual dysfunctions. Since then, several types of pressure probes with different shapes and technical properties have been studied [87–90] and marketed under different brand names, for example, Camtech (Norway), Peritron (Australia), Miofeedback perina (Brazil), and Gymna (Belgium).

Vaginal resting pressure as a measure of PFM tone has been studied mainly in asymptomatic women and in women with incontinence. Using the Peritron device, good-to-excellent test–retest (ICC = 0.74–0.77) and interrater (r = 0.78) reliability have been demonstrated [34, 91]. However, resting pressure measurement in the upright position has resulted in poor reliability [38]. It should be pointed out that there are no clear recommendations as to whether the device should be calibrated to zero prior to insertion into the vaginal cavity nor how much the probe should be inflated prior to measurement. The latter would influence the probe size and, consequently, the muscle length and amount of resting pressure recorded. With regard to muscle physiology, intravaginal resting pressure will be influenced by a combination of the active and passive tone components.

Regarding contractile properties, maximal pressure during PFM voluntary contraction has shown excellent test–retest (ICC = 0.88–0.96) and interrater reliability (r = 0.88) [34, 38, 91–94]. These studies were done in a pain-free sample using the Peritron device. It is suggested that the device be recalibrated to zero just before every effort. Maximal strength could be reliably evaluated during a 3-, 5-, or 10-s contraction by considering one trial or the mean of three trials [34, 38, 91–94]. Regarding endurance measurement, Frawley et al. [34] found that endurance assessed during 20 repeated contractions was not reliable. Contrarily, Rahmani et al. [93] demonstrated excellent reliability when assessing endurance during a sustained 60 % maximal contraction (ICC = 0.83).

In support of the validity of manometry, maximal pressure measurement has been found to be correlated with vaginal palpation (modified Oxford scale (r = 0.70–0.81) [33, 95, 96] and Brink’s scale (r = 0.68–0.71) [91, 92]), transabdominal ultrasound (bladder base movement (r = 0.72–0.81) [80, 95]) as well as transperineal ultrasound (bladder neck movement (r = 0.43) [70] and muscle thickness (r = 0.49–0.70)). Resting pressure was correlated with the levator hiatus area assessed by transperineal ultrasound (r = −0.46) [97]. However, it is generally recognized that increases in IAP, occurring if a patient co-contracts the abdominal muscles (rectus abdominis), or strain instead of contracting the PFMs can bias pressure measurements. Bo and Sherburn formulated recommendations to ensure the validity of the measurement [98]: (1) performing vaginal palpation before using the perineometer to make sure the patient is able to correctly contract her PFMs; (2) observing the cranial movement of the vaginal probe during measurement of the muscle contraction and (3) not considering the contractions associated with the Valsalva maneuver or retroversion of the hip [99, 100]. Following the last point, Bo and Constantinou [101] wrote a comment explaining that pressure should not be used to assess the reflex contraction of the PFM during coughing. They argue that pressure measurement is a summation of signals including PFM and IAP caused by the cough itself and that it is unlikely that the PFM reflex can be assessed in isolation. Considering these recommendations, the use of perineometry poses a problem when a patient has a really low PFM strength, because no inward movement of the probe is possible in this case. Furthermore, the size of the probe and the brand of the device have also been shown to influence the measurement [102, 103]. Barbosa et al. [103] compared the Peritron with two Brazilian devices and Bo et al. [102] compared the Peritron to the Camtech. Both studies conclude that measurements of vaginal squeeze pressure differ depending on the probe used. Despite these studies focused on maximal squeeze pressure, the results can be transposed to PFM tone assessment according to findings obtained with other tools [104, 105]. Different devices should therefore not be used interchangeably in clinical settings and results using different probes should not be compared or combined in systematic reviews or meta-analyses. The placement of the probe is another factor reported to be important. It was recommended to position the probe at the level of the PFMs that corresponds to the high-pressure zone inside the vagina [106, 107]. In sum, none of these studies on psychometric properties were undertaken in women with an overactive pelvic floor. Further investigation should be conducted in this population.