According to the function of the muscle fibers, pelvic floor muscles can be divided into slow muscles (type I muscle fibers) and fast muscles (type Ⅱ muscle fibers). The slow muscle includes the levator ANI muscle group (pubovaginalis, puborectalis, pubococcygeus, iliac coccygeus), which is characterized by a long and lasting contraction time and is not easily fatigued. Fast muscles include the perineal muscle group (superficial transversalis perinealis, deep transversalis perinealis, bulbous cavernosal muscle), and these muscles are characterized by rapid contraction and are easily fatigued [17, 18]. The earliest injury to pelvic floor muscle tension manifests as electromyologic changes, including changes in muscle potential, muscle tension and muscle fatigue, which can be used as indicators for early diagnosis of the injury [19, 20]. The pelvic floor surface EMG assessment refers to the evaluation of the bioelectrical signal sent by recording neuromuscular activity through electrodes on the human surface or cavity, quantitatively reflecting the local fatigue degree of muscle activity, the excitation conduction velocity of the motor unit and the muscle tension level . In this study, the Glazer assessment results were consistent with the results of the clinical pelvic floor muscle tension assessment by vaginal palpation, indicating that it could objectively
on stage was negatively correlated with age and neonatal weight. The EMG values of slow muscle contraction and endurance were negatively correlated with weight gain during pregnancy but positively correlated with age and BMI at delivery. The EMG value of the postresting stage was positively correlated with age, BMI at delivery and neonatal weight (P < 0.05). Multivariate linear analysis showed that weight gain during pregnancy was negatively correlated with the EMG value of slow muscle contraction and slow muscle endurance. BMI at delivery was positively correlated with the EMG value of the slow muscle contraction and postresting stage. There was a positive correlation between age and EMG in the resting stage (P < 0.05). These results mean that the higher the weight gai during pregnancy is, the lower the BMI and lower pelvic floor muscle tension will be. Hola V L et al.  found that pelvic floor tissues would be damaged to varying degrees during pregnancy due to the effect of gravity. During vaginal labor, perineal tearing and lateral resection could lead to extreme stretching and dilation of muscles and nerves around the vagina , as well as damage to the pelvic floor and surrounding urethral tissues and changes in the position and range of activity of the bladder neck. In particular, a prolonged second stage of labor is the main factor associated with pelvic floor tissue injury [24, 25], and forceps-assisted delivery assisted aggravates the pelvic floor muscle injury . Moreover, the higher the number of deliveries, the more serious the pelvic floor tissue damage would be , which is consistent with the results of this study. We found that older age is a high-risk factor for resting-state strength, and the lack of estrogen may damage the vaginal epithelium and lamina propria during smooth muscle contraction, decrease the uterine ligament collagen fiber ratio, reduce vaginal area perfusion, and decrease the resilience of the pelvic floor muscle . QI X et al.  found that an increased BMI during pregnancy is an independent risk factor for postpartum stress urinary incontinence. Urbankova I et al.  also showed that overweight or obese patients have more waist and abdominal adipose tissue, resulting in higher intra-abdominal pressure. Continued abdominal pressure directly acts on the stretching and deformation of the pelvic floor tissue in the direction of stress, weakening the pelvic floor muscle , which is consistent with the results of this study. Excessive fetal weight leads to an increased pelvic floor muscle load and changes in the shape and function of the pelvic floor muscles, leading to PFD . In other studies, the size of the fetal head circumference was considered an independent risk factor. When the fetal head circumference was greater than 35.5 cm, the incidence of levator ANI injury increased by 3.34 times . In a sample of patients with vaginal wall prolapse, Kerkhof M H et al.  found that pelvic floor muscle fibers were sparsely aligned, with a reduced density and decreased number of nerves. The pelvic floor muscles are filled with abundant fibrous connective tissue and infiltrated with inflammatory cells. Lenis et al.  found that the expression of CCL7 and CD195 was upregulated in the urethral epithelium in a vaginal wall traction model of rat stress urinary incontinence and thus affected tissue repair. Due to the small sample size included in this study, only the pelvic floor data of primiparous women who were 6–8 weeks postpartum were collected, and long-term follow-up and basic experiments were not conducted. Multivariate analysis did not confirm relevant conclusions, and further studies are needed in the later stage.
By means of electrical stimulation combined with biofeedback technology in this study, the Kegel exercise intervention dramatically and obviously improved the resting pressure, fast muscle tension, slow muscle tension and endurance in the abnormal pelvic floor muscle group, and these outcomes occurred earlier and were significantly better than those in the control group. This shows that physiological electrical stimulation treatment in the early postpartum period is effective and can maximize pelvic floor muscle flexibility and muscle tension for a quick recovery. This intervention can also improve pelvic floor muscle tension in terms of compressive ability and promote the maternal pelvic floor structure to the maximum extent of recovery. However, Leon-Larios F et al.  proposed that daily perineal massage and pelvic floor exercise from 32 weeks of pregnancy could significantly reduce perineal injury and the lateral resection rate. Additionally, water delivery can reduce the perineal lateral resection rate and reduce damage to pelvic floor muscle .