**2. Basic effect of altered connective tissues (looseness) on muscle function**

Gordon (1966) studied the relation between muscle force and sarcomere length (figure 1). As a muscle fiber consists of a distinct number of sarcomeres, the determined relation can be leveraged for the full length of the muscle, for which the same relation can be assumed.

This implies that a muscle has a special range of lengths, in which it can perform its peak force. If the muscle is shortened, its force decreases and goes down towards zero. If a muscle is overlengthened, its force goes down, too, sometimes even all the way to zero, at a length half of the one that gives optimal force. This means that a fully innervated muscle with normal morphology can have very low or even no force when it is over-stretched. The same

avulsions have been reported at the pelvic floor (Dietz and Lanzarone 2005, Dietz et al. 2007), but it is more likely that the insertion areas of muscles are dislocated by connective

From a mechanical point of view, the pelvic floor is composed of both muscles and connective tissue. The muscles are the active components that are – through their contractions - responsible for all functions of the pelvic floor. The connective tissues, with their elastic and collagen fibres and their extracellular matrices, provide structural support for the vagina and other organs such as uterus, urethra, bladder and rectum (Abramowitch 2009). It has been shown, that connective tissue changes occur during pregnancy (Rechberger et al. 1988, Harkness 1959). Weakening of collagen cross bonding (Rechberger et al. 1988) added to dilatation of the vaginal canal at childbirth can lead to overdistension or rupture of connective tissue. Extracellular matrix proteases contribute to progression of pelvic organ prolapse in mice and humans (Budatha et al. 2011, Connell 2011). The first vaginal birth is especially associated with the development of a prolapse, whereas additional vaginal births do not show significant increases in the odds of prolapse (Quiroz et al. 2011). Aging is characterized by a loss of collagen, degeneration of the elastic fibre network and a loss of hydration as a result of imbalance between biosynthesis and

In addition to that, there is a significant variability of tissue due to inborn variations (Dietz et al 2004) and collagen-associated disorders (Lammers et al. 2011, Campeau et al. 2011).

Surgical procedures can reduce structural support of the organs, especially those which cut or displace the uterosacral and cardinal ligaments during hysterectomy or which partially

Petros and Ulmsten (1993) stated that looseness or laxity of the vagina and its supporting ligaments can cause stress incontinence as well as urge. Since then the theory has been expanded to include other symptoms such as pelvic pain, voiding dysfunction and more recently, fecal incontinence and constipation (Petros & Swash 2008). In order to fix such loose ligaments Petros et al. (1990) have introduced alloplastic material for planned formation of an artificial neo-ligament. From this rather basic research, new surgical techniques have been developed, such as tapes for midurethral slings (TVT, TOT) and for repair of other pelvic floor ligaments (Petros and Ulmsten 1990, 1993). The new developments and the recent focus on connective tissue are important, not least because

**2. Basic effect of altered connective tissues (looseness) on muscle function**  Gordon (1966) studied the relation between muscle force and sarcomere length (figure 1). As a muscle fiber consists of a distinct number of sarcomeres, the determined relation can be leveraged for the full length of the muscle, for which the same relation can be assumed.

This implies that a muscle has a special range of lengths, in which it can perform its peak force. If the muscle is shortened, its force decreases and goes down towards zero. If a muscle is overlengthened, its force goes down, too, sometimes even all the way to zero, at a length half of the one that gives optimal force. This means that a fully innervated muscle with normal morphology can have very low or even no force when it is over-stretched. The same

tissue alterations than muscle tears (Petros 2008).

degradation (Uitto und Bernstein 1998, Campisi 1998)

resect vaginal tissue or perineal body during colporrhaphy.

looseness of tissues can be repaired surgically..

process occurs in women with descending or prolapsing vaginal wall and pelvic organs. The muscles which attaches directly or indirectly to the vagina or the pelvic organs change their length and their direction of action. This alters muscle force and function according to the relation shown in Figure 1. After re-positioning of the prolapsed organs, the muscle can reach its normal length and function. Hence, atrophy of muscle by immobilization (Hvid et al. 2011) can be avoided at least with some patients.

A prime example of this principle is restoration of urethral closure by a midurethral sling which restores the integrity of the pubourethral ligament. In the original description of the "tension-free" sling (Ulmsten et al 1996), the operation was performed under local anesthesia and the tape was lifted upwards while the patient was coughing, until the urine leakage ceased.

Fig. 1. Relationship of maximal muscle force to muscle (sarcomere)length (modified after Gordon 1966). Maximal muscle strength is exerted over a very short length (between red lines). Contractile strength falls rapidly with muscle lengthening and shortening, for example, due to lax connective tissue attachments.
